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APPROVED: Kuruvilla John, Committee Chair and Chair of
the Department of Mechanical and Energy Engineering
Weihuan Zhao, Committee Member Sheldon Shi, Committee Member Costas Tsatsoulis, Dean of the College of
Engineering Victor Prybutok, Vice Provost of the Toulouse
Graduate School
CONCEPTUAL FRAMEWORK FOR THE DEVELOPMENT OF AN AIR QUALITY
MONITORING STATION IN DENTON, TEXAS
Robyn Boling, B.S.
Thesis Prepared for the Degree of
MASTER OF SCIENCE
UNIVERSITY OF NORTH TEXAS
August 2016
Boling, Robyn. Conceptual Framework for the Development of an Air Quality Monitoring
Station in Denton, Texas. Master of Science (Mechanical and Energy Engineering), August 2016,
89 pp., 2 tables, 40 illustrations, references, 34 titles.
Denton, Texas consistently reaches ozone nonattainment levels. This has led to a large
focus of air pollution monitoring efforts in the region, with long-range transport being explored
as a key contributor. For this study, the University of North Texas Discovery Park campus was
chosen as a prospective location for an extensive air quality monitoring station. Sixteen years
of ozone and meteorological data for five state-run monitoring sites within a 25 mile radius,
including the nearest Denton Airport site, was gathered from TCEQ online database for the
month of April for the years 2000 to 2015. The data was analyzed to show a historical, regional
perspective of ozone near the proposed site. The maximum ozone concentration measured at
the Denton Airport location over the 16 year period was measured at 96 ppb in 2001.
Experimental ozone and meteorological measurements were collected at the Discovery Park
location from March 26 to April 3 and April 8 to April 25, 2016 and compared to the Denton
Airport monitoring site. A time lag in ozone trends and an increase in peak ozone
concentrations at the proposed location were observed at the proposed site in comparison to
the Denton Airport site. Historical and experimental meteorological data agreed in indicating
that southern winds that rarely exceed 20 miles per hour are the predominant wind pattern.
Back trajectories, wind roses, pollution roses, and bivariate plots created for peak ozone days
during experimental periods support long range transport as a considerable cause of high ozone
levels in Denton. Furthermore, a study of the precursor characteristics at the Denton Airport
site indicated the site was being affected by a local source of nitrogen dioxide that was not
affecting the proposed location. The differences in the Denton Airport site and the proposed
site indicate that further monitoring at Discovery Park would be insightful. An outline of an
expansive mobile monitoring station and suggestions for effective utilization are provided to
guide future studies in Denton and the surrounding North Texas region.
ii
Copyright 2016
by
Robyn Boling
iii
ACKNOWLEDGEMENTS
I would like to recognize those who have helped me to learn and develop the technical
skills necessary to complete this work, or who have contributed in discussions that have helped
to advance this work, in no particular order: Sauritha Karnae, Maleeha Matin, Mahdi Amahdi,
Guo Quan Lim, Andy Dean, Richard Roberts, Alex Reese, and most importantly, my parents. I
would like to especially thank, and express my sincerest gratitude to Dr. Kyle Horne for his
instruction in programming and simulation in addition to his unwavering encouragement during
my graduate career, Dr. Weihuan Zhao and Dr. Sheldon Shi for providing their feedback and
support as committee members, and Dr. Kuruvilla John for his guidance and leadership as my
thesis committee chair.
iv
TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS ................................................................................................................... iii LIST OF TABLES ................................................................................................................................ vi LIST OF FIGURES ............................................................................................................................. vii CHAPTER 1 INTRODUCTION ............................................................................................................ 1
1.1 Thesis Objective ...................................................................................................... 2
1.2 Organization of Thesis ............................................................................................ 2 CHAPTER 2 BACKGROUND .............................................................................................................. 4
2.1 Air Pollution ............................................................................................................ 4
2.2 Long Range Ozone Transport .................................................................................. 6
2.3 Air Quality Standards .............................................................................................. 8
2.4 Monitoring Methods and Devices ........................................................................ 10
2.4.1 Passive Ozone Monitoring Network in Dallas, Texas ................................ 11
2.4.2 Ozone Monitoring at Remote Sites .......................................................... 12
2.4.3 Wireless Sensor Networks ........................................................................ 13 CHAPTER 3 STUDY AREA AND METHODOLOGY ............................................................................ 16
3.1 Proposed Location ................................................................................................ 17
3.2 Data ....................................................................................................................... 21
3.2.1 Ozone ........................................................................................................ 21
3.2.2 Meteorological Parameters ...................................................................... 22
3.3 Ground Based Monitoring .................................................................................... 22
3.3.1 Compliance Grade Monitoring ................................................................. 23
3.3.2 Portable/Compact Ozone Monitor ........................................................... 27
3.3.3 Ultra-portable, Low-cost Sensors ............................................................. 28
3.3.4 Comparison of Monitoring Devices .......................................................... 30
3.4 Aerial Monitoring .................................................................................................. 31
3.5 Statistical Analysis ................................................................................................. 33
v
CHAPTER 4 RESULTS AND DISCUSSION......................................................................................... 35
4.1 Historical Data ....................................................................................................... 35
4.1.1 Meteorological Influence .......................................................................... 35
4.1.2 Historical Ozone Data ............................................................................... 38
4.2 Monitoring Results ................................................................................................ 42
4.3 Precursor Characteristics ...................................................................................... 55 CHAPTER 5 DESIGN SPECIFICATIONS ............................................................................................ 63
5.1 Foundation for the Discovery Park Mobile Monitoring Station ........................... 63
5.2 Mobile Monitoring Platform ................................................................................. 67
5.2.1 Platform Specifications ............................................................................. 67
5.2.2. Monitoring Equipment Specifications ...................................................... 69
5.3 Aerial Monitoring Platform ................................................................................... 71
5.3.1 Platform Specifications ............................................................................. 72
5.3.2 Aerial Monitoring Equipment Specifications ............................................ 72
5.4 Future Station Utilization ...................................................................................... 73 CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS ................................................................ 75
6.1 Conclusions ........................................................................................................... 75
6.2 Future Directions .................................................................................................. 78 APPENDIX: ADDITIONAL TRAJECTORY ANALYSES ......................................................................... 79 REFERENCES .................................................................................................................................. 87
vi
LIST OF TABLES
Page
Table 1. Continuous Ambient Monitoring Stations (CAMS) within 25 miles of the proposed Discovery Park location ................................................................................................................. 20
Table 2. Technical specifications of monitoring devices/sensors ................................................. 31
vii
LIST OF FIGURES
Page
Figure 1. Nonattainment counties in the central North Texas region showing Denton County (red) and surrounding counties (green) ....................................................................................... 18
Figure 2. Map of Continuous Ambient Monitoring Station (CAMS) locations within 25 miles of the proposed monitoring location at Discovery Park ................................................................... 19
Figure 3. Stationary monitoring shelter setup with meteorological tower at Discovery Park ..... 23
Figure 4. Image of Teledyne T400 EPA compliance grade UV absorption ozone analyzer from manufacturer website www.teledyne-api.com ............................................................................ 24
Figure 5. Detection mechanism in compliance grade ozone monitors including Teledyne T400 25
Figure 6. Image of Teledyne T430 compact UV absorption ozone analyzer from manufacturer website www.teledyne-api.com ................................................................................................... 27
Figure 7. Libelium Waspmote Gas Board equipped with temperature, humidity, ozone, nitrogen dioxide, methane, and carbon dioxide sensors ............................................................................ 28
Figure 8. Calibration curve for Gas Board ozone sensor provided by Libelium ........................... 29
Figure 9. Calibration curve for Gas Board ozone sensor .............................................................. 30
Figure 10. Aerial monitoring platform developed by University of North Texas Mechanical and Energy Engineering students ........................................................................................................ 32
Figure 11. Wind Roses for specified North Texas CAMS sites ...................................................... 37
Figure 12. Box and whisker plot showing the minimum to maximum ozone levels at CAMS 56 for the month of April for 2000 through 2015. ............................................................................ 38
Figure 13. Bivariate polar plots of mean daily maximum ozone concentration in Denton Airport and Pilot Point for the month of April during the years 2000 to 2015......................................... 40
Figure 14. Bivariate polar plots of mean daily maximum ozone concentration in Grapevine, Frisco, and Keller for the month of April during the years 2000 to 2015 ..................................... 41
Figure 15. Comparison of ozone concentrations by date from Discovery Park and CAMS 56 from March 26, 2016 to April 3, 2016 ................................................................................................... 43
Figure 16. Comparison of ozone concentrations by date at Discovery Park and CAMS 56 from April 8, 2016 to April 25, 2016 ...................................................................................................... 44
viii
Figure 17. Hourly ozone concentrations on March 26, 2016, the peak ozone day during the second monitoring period, at Discovery Park and CAMS 56 ........................................................ 44
Figure 18. Hourly ozone concentrations April 23, 2016, the peak ozone day during the second monitoring period, at Discovery Park and CAMS 56 .................................................................... 45
Figure 19. Wind roses for the Denton Airport site and the Discovery Park site during the experimental monitoring period .................................................................................................. 46
Figure 20. Pollution roses for CAMS 56 (left) and Discovery Park (right) for combined dates of March 26, 2016 to April 3, 2016 and April 8, 2016 to April 25, 2016 ........................................... 48
Figure 21. Bivariate polar plots of mean daily maximum ozone concentrations at the CAMS 56 (left) and Discovery Park (right) sites for combined dates of March 26, 2016 to April 3, 2016 and April 8, 2016 to April 25, 2016 ...................................................................................................... 49
Figure 22. Backwards trajectory from Denton on March 26, 2016 at 14:00 showing the path of particles (left) and the altitude of particles during the 24 hours (right) with initial altitudes of 500 meters (top) and 10 meters (bottom) ................................................................................... 50
Figure 23. Backwards trajectory from Denton on April 23, 2016 at 14:00 showing the path of particles (left) and the altitude of particles during the 24 hours (right) with initial altitudes of 500 meters (top) and 10 meters (bottom) ................................................................................... 51
Figure 24. 24-hour back trajectories for low ozone days during the monitoring periods ........... 52
Figure 25. Discovery Park diurnal plot with wind vectors for March 26, 2016 ............................ 53
Figure 26. Denton Airport diurnal plot with wind vectors for March 26, 2016 ........................... 53
Figure 27. Discovery Park diurnal plot with wind vectors for April 23, 2016 ............................... 54
Figure 28. Denton Airport diurnal plot with wind vectors for April 23, 2016 .............................. 54
Figure 29. NO, NO2, and NOx concentrations by hour for March 26, 2016. ............................... 55
Figure 30. Concentrations of nitrogen dioxide, nitrous oxide, and nitrogen oxides at the Denton Airport monitoring station from April 8, 2016 to April 25, 2016 .................................................. 56
Figure 31. Comparison of ozone and oxides of nitrogen during nitrogen dioxide peaks in the first monitoring period ......................................................................................................................... 57
Figure 32. Hourly O3/NOx comparison for March 26, 2016 at C56 ............................................... 58
Figure 33. Hourly O3/NOx comparison for April 23, 2016 at C56 ................................................. 59
ix
Figure 34. Bivariate plot of mean NOx concentrations from March 26 to April 3 and April 8 to April 25, 2016 ................................................................................................................................ 60
Figure 35.Concentrations of fine particulate matter (PM2.5) at the Denton Airport monitoring station from March 26, 2016 to April 3, 2016 .............................................................................. 61
Figure 36. Concentrations of fine particulate matter (PM2.5) at the Denton Airport monitoring station from April 8, 2016 to April 25, 2016 ................................................................................. 62
Figure 37. Photograph of the Continuous Ambient Monitoring Station (C56) located at the Denton Airport (“Denton Airport South C56/A163/X157,” 2013)................................................ 65
Figure 38. Aerial map of Denton, Texas with the proposed monitoring location at Discovery Park marked by a green star and the current Denton Airport site marked with a red circle .............. 65
Figure 39. Aerial view of the entire property of the proposed monitoring location with red circle marking the general location of the air monitoring site on the premises ................................... 66
Figure 40. Aerial view of the precise location of the proposed monitoring site on the property with red circle marking the exact location of the air monitoring station .................................... 67
1
CHAPTER 1
INTRODUCTION
The Texas Commission on Environmental Quality developed the Continuous Ambient
Monitoring Station (CAMS) for the purpose of monitoring and analyzing air quality across the
state of Texas. Currently, many CAMS sites exist across the state, including over 50 monitoring
ozone, 46 monitoring NO2, 13 monitoring CO, 27 monitoring PM10, 25 monitoring PM2.5, and
several other pollutants of various numbers (Texas Commission on Environmental Quality,
2016). Many of these monitoring stations are located in the larger metropolis areas such as
Dallas and Houston. This study focuses on the Dallas-Fort Worth region, specifically Denton,
Texas located approximately 40 miles from the center of Dallas. Denton County is one of ten
counties in the Dallas-Fort Worth region that is an ozone nonattainment area.
National Ambient Air Quality Standards (NAAQS) provide regulatory levels for ozone and
other pollutants. In 2008, the EPA set the ozone standard at 75 ppb. In 2015, the EPA reduced
this to 70 ppb (EPA, 2015).
Historically, Denton County has experienced high ozone levels. This is due in-part to the
pollution in other surrounding areas, in particular, air flow from Dallas seems to be a large
contributor. Dallas has significantly larger in situ ozone formation than Denton, which means
that much of the ozone measured at the Denton CAMS site is ozone that has been transported
into the area from the surrounding regions.
2
The goal of this study is to construct a framework for expanding Denton, Texas air
pollution monitoring by determining the possible impact of long range transport and
introducing the means to address it.
1.1 Thesis Objective
The main objective of this project was to develop a pollution monitoring station and
operations protocol for air quality monitoring at the University of North Texas (UNT) Discovery
Park campus that houses the College of Engineering, College of Information, and the university
Computing and Information Technology Center. The monitoring station and protocol then can
be used to determine the viability of further development of a monitoring site at the Discovery
Park campus, or the potential for an alternative approach. The objective was achieved through
addressing the following statements:
1. Spatio-temporal variability of air pollutants observed over North Texas is
a result of the influence of local and regional sources of pollution.
2. Long-range pollution transport across the North Texas region is
significant enough to affect the local and regional air quality.
1.2 Organization of Thesis
Chapter 2 presents information obtained through literature survey and review of
relevant scientific investigations and air quality reports. The development of ambient air
monitoring in the United States is examined and a focus on Texas, the Dallas metropolis, and
3
specifically, Denton County as one of the ten nonattainment counties in the region is
presented.
Chapter 3 discusses the geographic area studied as well as the methods of data
collection and data analysis. The chapter exhibits the location of data collection and proposed
development of the project. A contextual preface to the experimental objectives constructs a
foundation for the following chapter.
Chapter 4 introduces data analysis of publicly available data provided by state run
pollutant monitoring stations and experimental data at the study locations. The processes and
equipment used for experimental testing for a localized representation of pollution levels are
presented. The information obtained from publicly available databases takes into account a
historical perspective of the air pollution problem. The experimental data obtained during the
study provides an understanding of the monitoring situation and goals.
Chapter 5 discusses the implications of the results in the previous chapter and offers a
proposal for the furtherance of the study. The concept and design of the air monitoring station
explains the details for the continuance of this project. The monitoring platform and the
monitoring equipment are detailed with high level specifications.
4
CHAPTER 2
BACKGROUND
Denton County has consistently been classified as an ozone nonattainment county.
Ozone is a pollutant that causes concerns, however it is not a pollutant that is anthropologically
created. Ozone is created when nitrogen dioxide and volatile organic compounds react in
sunlight (EEA, 2010). Since ozone is not a directly emitted pollutant, attempts to reduce the
levels require significant monitoring and analysis. Currently, one continuous ambient
monitoring station exists within the large county municipality of Denton, Texas. Previous
studies have shown that significant portions of the Denton ozone levels can be attributed to
polluted air that has been transported into the region from more pollution producing areas.
2.1 Air Pollution
Air pollution has been a concern for many years. Increasing concern in the past century
has heightened the focus on pollutant levels and sources across the United States. There are six
criteria pollutants that are of concern: carbon monoxide (CO), nitrogen dioxide (NO2), ozone
(O3), sulfur dioxide (SO2), particulate matter (PM), and lead (Pb). Several other pollutants are
being monitored as well, and various methods of monitoring and modeling of air pollutants are
continuously being developed as pollution concerns spread and change.
Cardelino and Chameides (1995) presented an observation based model for analyzing
hydrocarbon, NO, and ozone measurements. The model they presented provided the
5
framework for establishing monitoring and emission reduction programs by determining which
hydrocarbons most greatly impacted ozone levels. Since ozone is a secondary pollutant, it is
necessary to monitor the precursor pollutants, that is, in order to adjust tropospheric ozone
levels, the precursors that create them must be managed. And while volatile organic
compounds (VOC), methane (CH4), oxides of nitrogen (NOx), and carbon monoxide (CO) are all
ozone precursors that should be monitored (EEA, 2010), a study in the Colombian Andes
concluded that the best way to reduce regional ozone levels was to focus on the reduction of
the NOx emissions in that region (Toro et al., 2006). They discovered that an increase in NOx
resulted in a more noticeable overall increase in ozone than an increase in VOCs. Additionally, it
was noted that a lower VOC/NOx ratio resulted in larger formation of ozone whereas when
VOC/NOx ratios were greater than 1.0 the ozone formation in the air was decreased.
Background surface ozone, or the ozone that is naturally formed due to continental
biogenic, fire, and lightning sources, was monitored across the United States, and analyzed by
Lefohn et al.(2014). Emissions influenced background ozone (EIB) levels and chemical
interactions with anthropogenic emissions were analyzed in the study to reflect the current
state of naturally occurring ozone. As well, the authors of this study investigated global
background ozone and found that higher levels of EIB ozone in the spring were generally
followed by lower levels during the summer which they attributed to the increased chemical
interactions with anthropogenic sources in that season. Furthermore, global background ozone
6
that occurred in spring, fall, and winter months was associated with meteorological events that
increased stratospheric to tropospheric transport (Lefohn et al., 2014).
2.2 Long Range Ozone Transport
Managing ozone precursors within a region is decidedly imperative to addressing local
pollution concerns, however, the cause of the concerns may not be limited to the region alone.
Although high ozone regions may be able to decrease their emissions, and subsequently local
pollutant levels, pollution transport into the region cannot be corrected by a nonattainment
area. Pollution transported into a region can originate not only from local or immediately
adjacent regions, but can originate from distant regions as well. One particular study addressed
the notion that “increasing baseline ozone flowing into the western U.S. is counteracting ozone
reductions due to domestic emission reductions” (Cooper et al., 2012). In general, the transport
of air pollutants across regional boundaries can be difficult to address. Decreasing pollution in a
region may not influence the overall pollution levels if pollution transport into the region is a
significant influence.
Many studies have verified that long distance pollution transport is affecting areas to a
statistically significant degree (Chin et al., 2007; Kemball-Cook et al., 2009; Xue et al., 2014). It
has even been shown that these transport trends can have an impact at distances far greater
than just the local geographic region. Lin et al. (Lin et al., 2012) showed that pollution
originating in Asia can reach the western United States. Their study examined the transport
7
mechanisms that resulted in trans-oceanic pollution transport by utilizing a model that
compared wind patterns and ozone events. A reanalysis of historical wind patterns resulted in
the observed incidence of Asian pollution over the western US proving the accuracy of their
model. Results revealed that approximately 20% of the maximum 8-hour average ozone
exceedances of 60 ppbv and 53% of the exceedances of 75 ppbv would not have occurred in
the western United States without the addition of ozone transported into the region from Asia.
In addition to trans-atlantic pollution originating in Asia, long range transport across North
America affects other areas as well. Wang et al. (2009) quantified the effects of anthropogenic
emissions from Canada and Mexico on daily maximum 8-hour average ozone concentrations in
the United States. The model showed that US background levels alone never exceeded 60 ppb.
The average increase of pollution levels was 3 ± 4 ppb with a maximum effect of 33 ppb.
Significant pollution transport at the national and regional levels has also been shown by
Langford et al. (2010); their study investigated the lifting of surface ozone to the free
troposphere in the Los Angeles Basin due to the physical characteristics of the region. Using
trajectory calculations, they determined that the ozone that left the surface of the Basin was
potentially transported over 1000 km reaching as far as Colorado. Overall, transboundary
pollution transport at continental, national, and regional levels all affect local ozone
concentrations substantially and must be considered when addressing ozone concerns.
8
Analyzing pollution levels at specific areas has resulted in further proof that
transboundary pollution transference results in a significant misrepresentation of local
pollution formation and the established regulations to address the local pollution problems.
One particular analysis of the ozone levels in Dallas showed that on one exceedance day the
ozone transported into the area totaled 72% of the measured ozone concentration (Kemball-
Cook et al., 2009). The study strongly suggested that local control strategies would not
sufficiently address nonattainment and that regional control strategies were necessary.
Pollutants transported into the municipal area could mostly be contributed to regional and
even national sources, none of which the local area would have the ability to monitor or
restrict.
Further studies analyzed the greater DFW area to determine whether the predominant
source of ozone formation could be classified as point sources such as power plants or mobile
sources (Luria et al., 2008). It was concluded that mobile sources contributed to the total ozone
levels more than large point sources. The researchers determined this by concurrently
measuring SO2 and CO as point and mobile source tracers, respectively. The levels of the tracers
were then compared to O3 and NOx levels.
2.3 Air Quality Standards
In 1955, the United States Congress passed the first air quality related legislation called
the Air Pollution Control Act. In 1963, the Clean Air Act (CAA) was passed. In 1970 a revision of
9
the CAA established the Environmental Protection Agency (EPA) and gave the agency the task
of developing national ambient air quality standards (NAAQS).
Legislation regarding air pollution in the United States was examined at length in a
paper discussing the historical events that occurred throughout the country from the beginning
of air pollution concerns through 1977 (Stern, 1982). Legislation related to air pollution control
began at the municipal level in the 1890s followed by county and state legislation in the 1910s
and 1950s respectively. Smoke abatement was the predominant concern in the early
environmental regulatory era. In the 1940s, Los Angeles smog was a pressing issue that
advanced the cause of air pollution legislation. On June 14, 1955, the Air Pollution Control Act
was signed into action.
Texas government agencies conducted the first air study in the state in 1952 followed by
the establishment of its first air quality initiative in 1956 (“History of TCEQ and Its Predecessor
Agencies,” 2016). The state of Texas considers the health of its citizens a priority, and in order
to address the issue of air toxicity due to pollutants, an independent series of state based
programs were developed to monitor and reduce air pollution levels. The three programs
developed were the air permitting, air monitoring, and the air pollution watch list (APWL)
programs (Capobianco et al., 2013). The air permitting program involves reviewing new and
modified facilities in order to monitor and verify that adverse health effects will not result from
the increase in emissions. The air monitoring program is an extensive program that involves
10
fixed-site and mobile monitoring. The monitoring occurs predominantly in industrialized regions
and provides data on pollutants and their concentrations. The APWL program allows the state
to concentrate its efforts on the areas of most concern. Areas that have continually seen
pollution measurements that exceed levels of potential health concern (LOCs) are subject to
increased monitoring and additional inspection for air permitting. Although the three programs
are independent, they rely on each other to effectively address Texas’ air pollution concerns.
Naturally, legislative changes in air quality and environmental regulations have had a
direct impact on industrial entities, as they are direct contributors to pollution. A study
conducted by a researcher working with the United States Census Bureau’s Center for
Economic Studies estimated the outcomes that environmental regulations had on industrial
activity (Greenstone, 2001). He revealed that environmental regulations resulted in greater
regulatory oversight in nonattainment areas as opposed to attainment areas. Approximately
590,000 jobs were lost in nonattainment counties in relation to attainment areas. Additionally,
capital stock decreased by $37 billion, and the output in industries with excessive pollution
decreased by $75 billion. While these declines can be severe for nonattainment counties, the
overall effect on the all-inclusive manufacturing sector is modest.
2.4 Monitoring Methods and Devices
Areas that do not have monitoring technologies are subject to models and estimations
in order to determine air pollution levels. While models are generally capable of providing
11
reliable information, these models must still be created and verified, and they must be
provided with pollutant monitoring data to be analyzed. Different monitoring methods can be
applied to different situations in order to obtain the necessary information on existing pollution
and meteorological characteristics. Technological advancements continue to occur in the air
pollution monitoring industry which leads to improvements in the ways that air pollution levels
are measured and analyzed. Analyzing and monitoring devices exist for all relevant pollutants,
and monitoring instruments can vary according to accuracy, mobility, simplicity, cost, and
several other parameters. As the focus of this study primarily addresses ozone, these
monitoring methods and devices will be the focus of discussion in this section.
2.4.1 Passive Ozone Monitoring Network in Dallas, Texas
Concerned citizens have been the instigators of widespread pollution monitoring. One
instance of this was presented in a study that covered the establishment of a passive ozone
monitoring network in Dallas, Texas. This study addressed the idea of widespread passive ozone
monitoring by concerned citizens and concluded that regional ozone monitoring can indeed be
conducted by trained public. Citizens were trained to handle and mail samples that were
collected at each site. A cost analysis prepared by the author of the study concluded that the
passive ozone monitoring publically operated could monitor four to five geographical regions,
whereas the continuous monitors would be capable of monitoring only one region (Sather et
al., 2001).
12
2.4.2 Ozone Monitoring at Remote Sites
Pollution is not limited to populated, easily accessible areas, which means monitoring
levels across the land involves actively travelling to and analyzing the ambient air in distant and
remote locations. The Rocky Mountain Research Station prepared a research note that
discussed the application of a low-power ozone monitoring device developed by 2B
Technologies, Inc., Boulder, Colorado that would allow monitoring in areas where monitoring
would be difficult to sustain (Korfmacher and Musselman, 2014). The group developed three
monitoring installations that encompassed all required aspects of ground-level ozone
monitoring and was capable of being deployed in remote areas. They were deploying the
automated, stand-alone system in areas that was infeasible to deploy heavier, bulkier ozone
analyzers that required high-power consumption. The research group created the smallest,
simplest, and least expensive setup they could for the circumstances that the installations were
deployed in, given the equipment and components that they had access to. The deployment
locations were generally remote areas where grid-electricity was inaccessible and access was
limited by terrain. The solution that the group selected was to place solar panels at the sites.
The approximate cost of the installation was $13,770. Further developments of the original
system included cold-weather adaptions that somewhat increased the cost, but provided a
heater, greater battery power, and increased solar panel capacity. The deployment of these
13
ozone monitoring installations were conducted for six years prior the completion of this
research note and several failures and improvements were acknowledged.
2.4.3 Wireless Sensor Networks
Wireless monitoring has become one of the methods used to observe pollution levels
across a more vast area. Researchers have investigated these methods, including one of
investigation in which three categories of wireless, sensor based pollution monitoring networks
were discussed and compared (Yi et al., 2015). The Static Sensor Network (SSN), Community
Sensor Network, and Vehicle Sensor Network (VSN) are the categories which are determined by
the carrier of the sensor. The author compared the sensor networks based on six properties:
mobility/geographic coverage, temporal resolution, cost efficiency, endurance, maintenance,
and data quality. The SSN achieved the highest ranking among these properties. There are still
many challenges to overcome including increasing the spatio-temporal resolution, addressing
the limits to passive monitoring, and expanding the mobility of the sensor carriers.
There are several different types of ozone sensors and analyzers, each with their
respective attributes and purposes. Selection of the right monitoring device for a specific
project depends on all of the project parameters, and sometimes can depend on external
environmental factors and accessibility for regular maintenance.
Ultraviolet absorbance ozone monitors (UV) and nitric oxide chemiluminescence ozone
instruments (CL) were compared by E.J. Williams et al. (2006) in order to address the concern
14
that UV absorbance ozone monitors can be affected by volatile organic compound (VOC)
species. The UV and CL instruments were then compared to Differential Optical Absorption
Spectrometer (DOAS). After comparing the data, the authors concluded the commonly used UV
absorption monitor is an accurate instrument as long as it is well-maintained.
UV and CL instruments are considered highly accurate, yet, their pitfalls include their
cumbersome size with combined dimensions exceeding one meter and weighing over 12 kg.
Developments in the monitoring equipment have resulted in analytical devices of significantly
smaller size. Due to these developments, low-cost instrumentation for ozone monitoring now
comes in several forms, including, but not limited to: sensors, filters, and chemical detection
papers (Koutrakis et al., 1993; Miwa et al., 2009; Williams et al., 2013).
Decreases in size, and overall cost of analyzers typically introduces concerns regarding
precision, efficiency, and accuracy of the miniaturized devices. These concerns can be examined
while exploring the different detection methods of the smaller monitoring technologies. A
commonly contested sensor type is that of a resistance based sensor, such as the one created
by Williams et al. (2013) that can detect conductivity changes of heated tungsten oxide. These
sensors are often criticized and considered insufficient due to the frequent occurrence in which
readings of zero are measured and calibration slope drifts as well as cross sensitivities to other
gases. The research group defends their sensor system by supplying the necessary calibration
procedures and providing data that verifies the accuracy and stability of the instrument.
15
Koutrakis et al. presented a study that pointed out the problems with the typical large,
heavy, and expensive monitoring instruments that are used for active monitoring and aimed to
develop and verify a passive sampling device that could monitor ozone levels at a greater
spatial resolution (1993). Their passive sampling method utilized a nitrate-based oxidation
reaction. The filter medium was coated with nitrite which was oxidized to a nitrate ion when
exposed to ozone. The filters were extracted after the sampling and were analyzed using ion
chromatography. Another passive monitoring sampler was developed Monn and Hangartner
(1990) based on an ozone reaction with 1, 2-di-(3-pyridyl)-ethylene.
In 2009, a group of researchers developed an improved colorimetric ozone detection
paper that could be used for outdoor ozone monitoring (Miwa et al., 2009). The colorimetric
detection paper used indigo carmine which, when exposed to ozone, changes color. Indigo
carmine is significantly affected by UV light which made the original paper unsuitable for
outdoor sampling. The group improved the detection paper by incorporating UV absorbers. The
resulting paper was significantly more resistant to UV light making them suitable for outdoor
ozone monitoring.
16
CHAPTER 3
STUDY AREA AND METHODOLOGY
This chapter provides a discussion about the selected study area (Denton, Texas and the
University of North Texas Discovery Park campus), the types of data acquired, analysis
methods, and various air quality monitoring systems. Before extensive pollution monitoring can
be introduced, a preliminary study should be done. This study analyzes the ozone monitoring
stations located within a 25 mile radius of the proposed Discovery Park location. Data for ozone
and meteorological parameters was retrieved from the TCEQ online database.
Analyzing the pollution levels across the North Texas region aims to show the regional
and long distance transport that occurs in relation to ozone concentrations. A combination of
techniques were used to examine the data. The open source programming software “R” (R Core
Team, 2015) was used to develop detailed mapping of pollution concentrations, as well as a
package called Openair (Ropkins, 2012) that was specifically designed to examine and interpret
air pollution data.
Meteorological data can be analyzed to determine the direction from which pollutants
are entering the vicinity of the monitoring station and by combining the meteorological data
with pollutant data such as concentration, a fully developed profile of pollution concentration
densities and transport directions can be created. The first analysis which focused on
directional transport required collections of wind speed, wind direction, and specific pollutant
17
concentration data. The data was also instrumental for the second analysis which focused on
developing bivariate plots that were capable of estimating potential pollution sources.
3.1 Proposed Location
This study aims to verify the necessity of a continuous air monitoring station in the
North Denton area, specifically, the Discovery Park campus of the University of North Texas.
The foundation of the study begins with the classification of Denton County and 9 other North
Texas counties as ozone nonattainment counties. Figure 1 shows the location of these ten
counties in the North Texas region. Denton County is situated in the top, center of the
nonattainment region.
The physical address of this campus is 3940 N Elm Street, Denton, TX, 76207. This
campus is located approximately 4 miles northeast of the existing CAMS site located at Denton
Airport. The Discovery Park location lies between the Denton Airport site (CAMS 56) and the
Pilot Point monitoring location (CAMS 1032). CAMS 56 is located approximately 20 miles
southwest of CAMS 1032. Precisely, the Denton Airport site is 19.6623 miles from the Pilot
Point location at a bearing of 227.67 degrees.
18
Figure 1. Nonattainment counties in the central North Texas region showing Denton County
(red) and surrounding counties (green)
Several factors make Denton a desirable location to further study and monitor pollution
levels in the region, including developments in the oil and gas industry to the west and the
continuously expanding and developing cityscape to the south and southeast. Ozone is one of
the key focuses in this air monitoring initiative. Therefore, it is necessary to look at the
monitoring locations that already exist and the extent of their contributions to air monitoring
plans. Figure 2 shows a 25 mile radius around the proposed location. Each ozone monitoring
site in or near the radius is marked. Furthermore, figure 2 shows CAMS sites within the region
that are not limited to ozone monitoring alone.
19
Figure 2. Map of Continuous Ambient Monitoring Station (CAMS) locations within 25 miles of the proposed monitoring location at Discovery Park
Two sites (C1064 and C31 in Figure 2), both east of the proposed location, only monitor
ozone. These are the Pilot Point and Frisco locations. Four sites (C88, C1007, C1013, C1064)
south and southwest of the proposed location monitor only volatile organic compounds (VOCs).
These are the Flower Mound, Rhome Seven Hills Road, Decatur, and Dish Airfield. The Denton
Airport, Keller, and Grapevine locations located in the southern direction monitor ozone, VOCs,
and NO2.
C88
C1064
C56
C31
C17
C1013
C1007
C70
C1064
20
Table 1. Continuous Ambient Monitoring Stations (CAMS) within 25 miles of the proposed Discovery Park location
CAMS Number
Location Name Location Coordinates Species*
Monitored Activation Date
C17 Keller Lat: +32.922474° Long: -97.282088°
O3, NO2,
TNMOC February 11, 1981
C31 Frisco Lat: +33.132400° Long: -96.786419° O3 May 7, 1992
C56 Denton Airport South
Lat: +33.219069° Long: -97.196284°
O3, NOx, NOy,
TNMOC, PM2.5
February 16, 1998
C70 Grapevine Fairway
Lat: +32.984260° Long: -97.063721°
O3, NO2,
TNMOC August 4, 2000
C88 Decatur Lat: +33.221721° Long: -97.584445° VOC October 6, 2010
C1007 Flower Mound Shiloh
Lat: +33.045862° Long: -97.130002° VOC October 27, 2010
C1013 Dish Airfield Lat: +33.130930° Long: -97.297650°) VOC March 31, 2010
C1032 Pilot Point Lat: +33.410648° Long: -96.944590° O3 April 4, 2006
C1064 Rhome Seven Hills Road
Lat: 33.0440280° Long: -97.486618° VOC November 12, 2012
* Species include ozone(O3), nitrogen dioxide (NO2), total non-methane organic compounds (TNMOC), volatile organic compounds (VOC), fine particulate matter (PM2.5)
21
3.2 Data
Texas Commission on Environmental Quality (TCEQ) conducts extensive air monitoring
and the majority of the information used in this study was provided by them. Monitoring sites
managed by TCEQ measure most parameters at a rate of once per hour. Additional data for this
study was obtained through local monitoring systems at the proposed Discovery Park location
and funded by the Department of Mechanical and Energy Engineering, University of North
Texas.
3.2.1 Ozone
Ozone is considered a critical pollutant which has caused it to be one of the most
monitored pollutants by TCEQ. Government standards have gradually decreased the acceptable
ground-level ozone levels making compliance more difficult for flourishing metropolitan areas.
Ozone is a secondary pollutant which means that it is not emitted directly from sources.
Instead, ozone is created through interactions between nitrogen dioxide and volatile organic
compounds when they are exposed to sunlight (“Ozone Pollution,” 2016). Pollution control
measures cannot be structured around ozone alone, and must include the precursors as well.
Since ozone is not a pollutant directly emitted from sources, it is essential to monitor the local
concentrations to determine when ozone episodes occur and compare and address precursor
concentrations to moderate the levels.
22
3.2.2 Meteorological Parameters
A key component of determining the validity of establishing an air monitoring station at
the Discovery Park location lies in the analysis of the meteorological factors that affect the
region. Wind speed, wind direction, maximum wind gust, temperature, relative humidity, solar
radiation, and precipitation are all meteorological parameters that are measured at the Denton
Airport site. Of these parameters, wind speed and wind direction were selected as a primary
data for analysis due to their correlation to long-range transport of pollutants and they provide
the greatest influence on the justification of developing an air monitoring site at the proposed
location.
3.3 Ground Based Monitoring
As air pollution concerns have increased over the decades and likewise pollution
monitoring has increased, following these trends, ground based monitoring stations have been
seen significant development and improvement. Measuring air pollutants at ground level
provides a more accurate understanding of exposure to humans, and possibly health risk
associations. Figure 3 shows a typical setup for ground based monitoring of ambient air
pollutants. The ambient air monitoring station consists of an air conditioned shelter and a
meteorological tower.
23
Figure 3. Stationary monitoring shelter setup with meteorological tower at Discovery Park
The stationary monitoring site shown in figure 3 is the Discovery Park monitoring shelter
and meteorological tower. The campus can be seen in the distance to the let of the students
and shelter.
3.3.1 Compliance Grade Monitoring
Government air pollution monitoring requires standards and more precise
measurements than general community environmental testing. Teledyne T400 is a UV
Absorption O3 Analyzer used for precise monitoring and has a full scale operational
concentration detection range from 0 to 100 ppb (0-10ppm). The weight of this monitor is 30.6
lbs.
24
Figure 4. Image of Teledyne T400 EPA compliance grade UV absorption ozone analyzer (www.teledyne-api.com)
Ozone analyzers can observe ozone concentrations using various scientific principles.
The Teledyne T400, shown in figure 4 determines the concentration of ozone with the principle
of Beer-Lambert Law as follows:
𝐶𝐶 = ln𝐼𝐼0𝐼𝐼∗
10−9
∝ 𝐿𝐿∗ �
𝑇𝑇273𝐾𝐾
∗29.92 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖
𝑃𝑃�
Where,
C = concentration of species (ppb)
I0 = intensity of the light with no absorption
I = intensity of light with absorption
L = absorption path, or distance the light travels as it is being absorbed
T = sample temperature in Kelvin
P = sample pressure in inches of mercury
25
Compliance grade monitors are the largest of the possible instruments due to the mechanism
of which ozone concentration is analyzed. The absorption path length of the sample gas, which
in general would be ambient air containing ozone, is 42 inches. The instrument has an internal
pump that brings in air flow at a constant 8 L/min where the sample will either pass through a
scrubber in order to remove ozone and be analyzed as a reference or will be directly routed to
the absorption tube for the ozone concentration (McElroy et al., 1997). Figure 5 shows the
basic design of the instrument in relation to how the concentration is determined.
Figure 5. Detection mechanism in compliance grade ozone monitors including Teledyne T400
Compliance grade ozone analyzers, including the Teledyne T400 mentioned above,
require periodic calibration. The calibration procedure involves the use of a verified dilution gas
calibrator which generates ozone at specific, or known concentrations. First, the ozone monitor
and the dilution calibrator must be placed in a laboratory fume hood system to prevent ozone
from being leaked into the lab and exposing occupants to dangerous gas levels. The dilution
calibrator has two output ports. Teflon tubes are affixed to these ports, where one of the tubes
26
is rerouted back into the dilution calibrator to measure and verify the generated ozone levels,
and the other tube connects to the ozone monitor that is being calibrated. The ozone generator
has three switches, the “T/P” and the “Valve” switches must be in the on position during
calibration procedures. The ozone generator has a bi-directional manual revolution counter for
inputting the ozone concentration. Initially, the calibrator mode must be set to “Manual” and
the concentration counter must be positioned at “000”ppb. The calibrator and ozone monitor
must then be turned on and let run for 30 minutes for the machines to warm up. After 30
minutes, the ozone monitor can be evaluated. If the ozone monitor reads “0 ppb” or is within
the allowed error range of 3%, then the next calibration level can be checked. If the ozone
monitor is reading a value that exceeds the allotted error amount, the monitor must be
adjusted. On the main screen of the ozone monitor, the “CalZ” option is used to select and
adjust the “zero” to reset the “0 ppb” value of the monitor. After adjusting the device, the
monitor takes approximately 20 minutes to equilibrate and settle to the new values before
continuing onto the next concentration. When it is time to continue on to the next ozone
concentration, the dilution calibrator unit can be switched from “Manual” mode to “Auto”
mode. Through this investigation, the manual counter was set to “400” ppb for the start of
calibration procedures. After allowing the devices to stabilize for approximately 30 minutes the
ozone monitor can be checked; if the difference between the ozone monitor and the value on
the dilution calibrator exceeds 3% then the monitor must be adjusted again, similar to the
“zero” procedure. Adjustments that are not made at the zero level, must be calibrated by
selecting the “CalS” option on the screen of the monitor. For instance, in calibrating at a
concentration level of 400 ppb the gas concentration of 400 ppb would be entered at this point.
27
When the device adjusts, a “SPAN” option will appear. The option must be selected and 20
minutes must be allowed for the equipment to complete adjustment and stabilize. This
calibration process was repeated for verification and adjustment of the monitor with
concentration levels of 400 ppb, 300 ppb, 200 ppb, and 100 ppb. In general, after all
concentrations have been checked and adjusted as needed, the ozone monitor should be ready
to be used.
3.3.2 Portable/Compact Ozone Monitor
A portable version of the compliance grade monitor, Teledyne T430 shown in figure 6,
was also used in order to determine the possible setup for the proposed Discovery Park
ambient air monitoring location. The portable monitor functions with the same UV absorption
mechanism as the compliance monitor, however, this compact analyzer is a fraction of the full-
sized analyzers weight at 5.2 lbs.
Figure 6. Image of Teledyne T430 compact UV absorption ozone analyzer from manufacturer website www.teledyne-api.com
28
3.3.3 Ultra-portable, Low-cost Sensors
The Libelium Waspmote is a sensor board that can be outfitted with air monitoring
sensors. The Waspmote is commercially available and is a generalized board that can work with
air monitoring sensors as well as an extensive number of other setups. The Libelium Waspmote
Gas Board (shown in figure 7) utilized in this study was equipped with ozone, temperature, and
relative humidity sensors.
Figure 7. Libelium Waspmote Gas Board equipped with temperature, humidity, ozone, nitrogen dioxide, methane, and carbon dioxide sensors
The Gas Board is not a calibrated line, however, for future work, calibrated sensor lines
are available. Due to the lack of calibration and standards, the gas sensor board requires
significantly more analysis and benchmarking than that of the high-end monitors, making them
viable for more basic studies, but not long-term in depth investigations.
The ozone detection sensor, MiCS-2614, is a silicon gas sensor which consists of a
sensing layer on top and a micro-machined diaphragm with an imbedded heating resistor
29
beneath. In principle, the resistor cannot be calibrated in such a manner that the output can be
adjusted, however, benchmarking can be done and a calibration curve can be created to
determine concentrations. The drift for the sensor significantly exceeds that of the precision
instruments and the calibration must be conducted more frequently. An example calibration
curve is depicted in figure 8.
Figure 8. Calibration curve for Gas Board ozone sensor provided by Libelium
The process of developing a calibration curve for the sensor involves a lengthy process
of comparing actual values to read values. The resulting curve of the testing is found in figure 9.
While calibration is generally considered a term in which a system is compared and adjusted,
the sensor system tested does not have the ability to be adjusted, thus the calibration curve
concept is a general solution to that limitation. When using the sensor for in-field monitoring,
the results can be compared to the curve to provide the coinciding concentration of the
monitored pollutant in parts per billion.
30
Figure 9. Calibration curve for Gas Board ozone sensor
After a working code was created, the calibration curve had to be created, however,
there are variables related to each sensor that affect the output. The ozone sensor included
resistance and gain variables which were input to the code and affected the results. The
resistance and gain of the sensor system became the most notable problem while the system
was being developed and tested. The calibration curve in Figure 9 was created with a gain of 1
and a resistance of 20. Developing a curve with more confident characteristics would require an
extensive comparison against different resistance and gain values.
The assessment of the Libelium Waspmote was performed to test the validity of the
sensor system as a monitoring device for an aerial monitoring platform. Choosing an aerial
monitoring apparatus and verifying its ability to effectively observe air pollution concentration
levels was essential for this study.
3.3.4 Comparison of Monitoring Devices
The T400 compliance grade analyzer, the T430 compact analyzer, and the Libelium
Waspmote sensor board have areas of extreme benefit such as the precision and reliability of
y = 7E-10x4 - 6E-07x3 + 0.0001x2 + 0.0183x + 23.137
2021222324252627282930
10 100 1000
Resis
tanc
e (K
Ω)
ozone concentration (ppb)
Ozone Sensor Calibration Curve
31
the compliance monitor, the reliability and mobility of the portable monitor, and the ultra-low-
cost and extreme portability of the sensor board. There are however significant concerns which
includes the high cost and bulkiness of the compliance monitor, the lack of certified EPA
compliance of the portable monitor, and the instability of sensors. Table 2 shows the
specifications for the compliance grade monitor, portable ozone monitor, and monitoring
sensor.
Table 2. Technical specifications of monitoring devices/sensors
Teledyne T400 Teledyne T430 Libelium Waspmote
Type UV Absorption UV Absorption Resistive Sensor Range 0 - 100 ppb 0 - 100 ppb 10 - 1000 ppb
Measurement Units
ppb, ppb, µg/m3, mg/m3 (selectable)
ppb, ppm (selectable) kΩ
Dimensions 7" x 17" x 23.5" 4.2" x 7.1" x 10.2" 73.5 x 51 x 1.3 mm Weight 30.6 lbs 5.2 lbs 20 grams
Operating Temperature 5 - 40⁰C 5 - 40⁰C -30 - +85⁰C
Humidity Range 0 - 95% 5 - 95%
Power Requirements
100V - 120V 220V - 240V
50/60 Hz 12VDC, 9W Board: 5V
Sensor: 1.95 ~ 5V DC
Certifications EQQA-0992-087 Sira MC 050070/04 EQQA-1015-229 None
3.4 Aerial Monitoring
Pollutants that are measured at ground level are generally not created at the monitoring
site. Long range transport is the phenomenon in which pollutants are moved into an area from
distant sources (Morris et al., 2006). Examining the tropospheric ozone at several levels will
32
allow further analysis and understanding of the Denton ozone profile. Aerial monitoring can be
conducted by placing an ultra-portable sensor as mentioned above onto an unmanned aerial
vehicle (UAV). Figure 10 shows a possible setup for a UAV platform for air pollution monitoring.
The device in the image is a quadrotor designed and built by students in the Department of
Mechanical and Energy Engineering at the University of North Texas.
Figure 10. Aerial monitoring platform developed by University of North Texas
Utilizing an UAV comes under some governmental restrictions. The Federal Aviation
Administration (FAA) labels UAVs as Unmanned Aerial Systems or UAS (“Unmanned Aerial
Systems Civil Operations (Non-Governmental),” 2015). There are three classifications of UAS,
which include public operations, civil operations, and model aircraft. Public operations are
government projects and are subject to the least restriction. Civil operation are projects that
are not explicitly government operated, but are not recreational in nature. This type of UAS
classification is not limited by the recreational regulations. The aerial monitoring system
presented in this study would ideally fall under this classification, provided the proper
documentation and processes are completed.
33
3.5 Statistical Analysis
Data analyzed in this section includes data obtained from the TCEQ website (
http://www.tceq.state.tx.us/agency/air_main.html) that holds publicly available pollution
concentrations at the various CAMS sites. In addition, data gathered at the Discovery Park
location utilizing the currently available ozone monitors was archived at UNT and also used in
this study.. A brief discussion is presented on how the data should be interpreted for the
purpose of this experiment that is to determine the viability of a monitoring system for UNT’s
Discovery Park campus, and the surrounding area.
The R software tool is an open source program that provides extensive statistical
analysis (R Core Team, 2015). The R software tool with the Openair package has many more
aspects that should be utilized in order to aid in monitoring air pollution levels (R Core Team,
2015; Ropkins, 2012).
The tools used in this study were the wind rose, pollution rose, and bivariate polar plot.
The wind and pollution roses indicate the frequency of which wind or pollution reaches a
specific location from each direction. The bivariate polar plots were created for this study by
applying a mean statistic to the data. The pollutant concentration, wind speed, and wind
directions are utilized in a manner such that the mean pollutant concentration can be
calculated at different combinations of wind speed and wind direction. Bivariate plots do not
directly indicate concentration, but instead, are a visual aid to assist in interpreting the data.
The Openair package includes many interesting tools that extend far beyond the scope
of this project. Pollution monitoring in the Denton area could benefit greatly from statistical
analysis using this tool. The analysis conducted for this study involved only ozone, however NOx
34
and NO2 can be measured and the Openair tool “CalcFno2” can be used to estimate NOx and
NO2 ratios. Time series analysis, trend analysis, and cluster analysis can all be conducted using
the Openair package with the “R” software.
The features of the Openair package that include meteorological data and ozone data
provide an informative tool for pollution analysis with respect to Denton, Texas. The following
chapter utilizes the wind rose and pollution rose tools to show the meteorological influences in
the region and the directional pollution patterns. Additionally, bivariate plots are used to show
the spatial extent of the observed ozone concentration by coupling with the wind data.
35
CHAPTER 4
RESULTS AND DISCUSSION
4.1 Historical Data
The basis for introducing a fully equipped air monitoring system at Discovery Park
begins with a historical analysis of pollution monitoring in the North Texas region. Sixteen
years, 2000 to 2015, of data was collected from the Texas Commission on Environmental
Quality (TCEQ) online database. Since the monitored focus of the study highlights ozone
concentrations during the month of April, the historical data analyzed was also limited to April.
The ozone monitoring sites in the 25 mile study radius were used to demonstrate the emphasis
on an expanded Denton air monitoring program. The Denton Airport, Grapevine, Frisco, and
Keller monitoring locations were active for the entire sixteen year study period. The Pilot Point
monitoring site was established on April 4, 2006, therefore 2007 to 2015 were the only years
with complete data for the month of April. Each site collected at the very least, wind speed,
wind direction, and ozone concentration data, which were used to develop the following
historical perspective.
4.1.1 Meteorological Influence
Different aspects of pollution monitoring influence the need for air pollution monitoring
sites, including meteorological data. While temperature, humidity, and barometric pressure can
influence pollution concentrations, the focus for this study is pollution transport which is largely
affected by wind direction and wind speed as opposed to other weather related parameters.
Wind speed can be collected in the form of meters per second or miles per hour. Wind
direction measurements are typically based on a 360 degree plot. The direction due north
36
coincides with 0 degree, such that east is 90 degrees, south is 180 degrees, and west is 270
degrees.
The ozone monitoring sites within the defined study radius have also provided
meteorological data that is shown in figure 11. These wind roses display wind direction and
speeds for the month of April from the years 2000 to 2015. The wind roses show a strong wind
pattern coming from the southern direction which affects all North Texas air monitoring sites.
The highest wind speeds exceed 20 miles per hour which are indicated by the blue sections of
the wind roses. Wind speeds that exceed 20 miles per hour are not frequent in the area, but
each of the sites indicates that the largest percentage of high wind speeds comes from the
southern direction. The Denton Airport site did show some additional higher speed winds-
coming from the north-north west direction, however other sites do not display the same
pattern.
The radial scale of the wind roses created from the historical data at the five sites was
able to be standardized for four of the five locations. The Denton, Pilot Point, Grapevine, and
Frisco locations maintained a distribution of wind patterns that limited the radial limit to 30%.
The Keller location, which lays south of the other four sites, experienced a slighter distribution
which led to the conglomeration of winds coming from the southern direction. While all sites
had a predominant southern wind, almost 40% of the wind reaching the Keller site came from
within 15 degrees of due south, as depicted in figure 11.
37
Figure 11. Wind Roses for specified North Texas CAMS sites
Keller C17
Denton C56
Pilot Point C1032
Grapevine C70
Frisco C31
38
4.1.2 Historical Ozone Data
The ozone nonattainment status of Denton has persisted since ozone monitoring
became a focus for air pollution monitoring. While ozone action months, or months that exhibit
significantly higher ozone concentrations than compared to the rest of the year, are considered
to be the months spanning from May through October, in future long-term studies, every
month should be analyzed to determine important patterns in pollution levels.
Over the course of this study period, ozone concentrations at the Denton Airport
location have shown a slight increase over the 16 year period. Figure 12 is a box and whisker
plot displaying the distribution of the measured ozone concentrations at CAMS 56 for the
month of April for the years of the study.
0
20
40
60
80
100
120
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Ozo
ne C
once
ntra
tion
(ppb
)
Year
Distribution of Historic April Ozone Levels
Interquartile Range (Q1-Q3) Yearly Mean
Figure 12. Box and whisker plot showing the minimum to maximum ozone levels at CAMS 56 for the month of April for 2000 through 2015.
39
Over the 16 year study, the maximum ozone value of 96 ppb was measured on April 26,
2001; the largest mean occurred in 2005 at 37.15 ppb. Since 2001, the mean concentrations
and the maximum measured values have experienced oscillations, the largest increase in the
mean value was 32.1% over five years from 2000 to 2005. Since 2005 the mean has decreased
only 15.94% and the yearly mean continues to maintain values larger than observed in April of
2000.
Extending the analysis to the entire study area provides a more in depth look at ozone
levels across the region and the historical activity that ozone has shown. The Denton, Pilot
Point, Grapevine, Frisco, and Keller sites that monitored ozone concentration vary in location
around the proposed site at Discovery Park. Figure 13 shows the bivariate plots for CAMS 56,
70, 31, and 17 for the month of April during the years 2000 to 2015 and CAMS 1032 for the
month of April during the years of 2007 to 2015.
These bivariate plots evaluate three parameters in order to develop a visualization of
the locations and transport directions of ozone. Ozone concentration, wind direction, and wind
speed together can indicate the general direction of the source location. This spatial
visualization can be interpreted to determine where the greatest source areas of ozone are
located in relation to a specific area.
The plots presented in figure 13 were created with the data corresponding to the daily
maximums of ozone measured during the investigation period. The mean statistic was applied
to the values to generate a visualization of ozone concentrations. Ozone concentrations that
are slightly high were noticed around the entire Denton site with a greater concentration
approaching from the south and southwest directions. Grapevine, located south of Denton,
40
displayed high ozone values south and southwest but at a higher density and nearer to the
origin of the plot, or the site location. Keller, located southeast of all other sites observed high
ozone concentrations in the southwestern quadrant. Ozone concentrations around Frisco had a
high concentration density in the south west, and ozone concentrations relatively spread out
among the western reaches. Pilot Point showed the greatest difference in concentration
patterns across the area, and was seemingly linearly divided into ozone concentration regions.
While little ozone was found in most of the northeastern direction, there was a linear expanse
of mid-level ozone slightly northeast of the monitoring site, and high ozone expanded from the
mid-level ozone boundary to the entire western side of Pilot Point.
Figure 13. Bivariate polar plots of mean daily maximum ozone concentration in Denton Airport and Pilot Point for the month of April during the years 2000 to 2015
41
Figure 14. Bivariate polar plots of mean daily maximum ozone concentration in Grapevine, Frisco, and Keller for the month of April during the years 2000 to 2015
42
4.2 Monitoring Results
Although the Discovery Park location is geographically very near the current Denton
airport monitoring site, experimental results show that a noticeable difference exists in the
ozone concentrations, wind speeds, and wind directions. The ozone monitor at Discovery Park
was in operation for a total of 28 days during the months of March and April in 2016. The ozone
concentrations measured during these days are shown in figures 15 and 16, respectively.
The concentrations presented were split into two periods during this study. Figure 15
shows the first segment of the monitoring span which occurred from March 26, 2016 to April 3,
2016. Figure 16 shows the ozone measurements observed during the second ozone monitoring
period which occurred from April 8, 2016 to April 25, 2016. Furthermore, the highest ozone
days in each period are observed by the peaks which occur on March 26, 2016 and April 23,
2016. The hourly ozone concentrations observed during the highest concentration days in each
period are shown in figures 17 and 18.
A visual inspection of the daily graphs indicate with no uncertainty that Discovery Park
ozone concentrations are predominantly higher than that observed at Denton Airport site. The
ten day span from March 25, 2016 to April 3, 2016 easily shows a strong correlation between
the Denton Airport site and the Discovery Park location, albeit with a consistent offset.
The peak ozone values at Discovery Park occur slightly later than those at the Denton
Airport site the meteorological analysis in previous sections can explain this, as the
predominant wind direction is from the south, which means ozone transport from the south is
observed at the Denton Airport site first.
43
Figure 15. Comparison of ozone concentrations by date from Discovery Park and CAMS 56 from March 26, 2016 to April 3, 2016
The peak ozone concentration found in figure 15 occurs on March 26, 2016. The hourly
ozone concentrations observed at each site for that day are shown in figure 17. The hourly
ozone levels further expand on the observation of ozone transport from the south. The peak
ozone level on March 26, 2016 at Discovery Park occurred at approximately 17:00, whereas the
peak at CAMS 56 occurred at 16:00.
0
10
20
30
40
50
60
70
80
90
Ozo
ne C
once
ntra
tion
(ppb
)Ozone Comparison between Denton Airport and Discovery Park
Discovery Park Ozone Concentration CAMS 56 Ozone Concentration
44
Figure 16. Comparison of ozone concentrations by date at Discovery Park and CAMS 56 from April 8, 2016 to April 25, 2016
Figure 17. Hourly ozone concentrations on March 26, 2016, the peak ozone day during the
second monitoring period, at Discovery Park and CAMS 56
0
10
20
30
40
50
60
70
80
90
Ozo
ne C
once
ntra
tion
(ppb
)Ozone Comparison between Denton Airport and Discovery Park
Discovery Park Ozone Concentration CAMS 56 Ozone Concentration
0102030405060708090
Ozo
ne C
once
ntra
tion
(ppb
)
Ozone Concentration ComparisonMarch 26, 2016
Discovery Park Concentration CAMS 56 Concentration
45
Looking at the display of ozone concentrations at Discovery Park and CAMS 56 for
certain days during the months of March and April of 2016 as shown in figures 15 and 16 clearly
highlights a time delay and concentration variances between the two locations. It can be seen
that the Discovery Park location registers ozone levels higher than that of the Airport site
consistently. These concentrations are also measured consistently later than at the Denton
Airport site.
It can be ascertained that the ozone transport is a large contributor to high ozone levels
in the Denton area due to the observations made previously. The Discovery Park site measured
an increase of approximately 12 parts per billion higher than the Denton Airport site on March
26th and approximately 16 parts per billion higher on April 23rd.
Figure 18. Hourly ozone concentrations April 23, 2016, the peak ozone day during the second
monitoring period, at Discovery Park and CAMS 56
0102030405060708090
Ozo
ne C
oncn
etra
tion
(ppb
)
Ozone Concentration Comparison April 23, 2016
DP Conc Denton Conc
46
Weather parameters were also gathered at Denton Airport and Discovery Park. Several
parameters were measured at each site, however the only parameters of concern for pollution
analysis during this study were wind speed and wind direction, as previously mentioned.
Significant changes in weather patterns between two close-proximity locations are not
generally considered a frequent occurrence. This would lead to the assumption the locations
located near each other would not experience noticeably varied wind directions and wind
speeds. The meteorological data for the Denton Airport and Discovery Park are shown in figure
19. The data is presented in the form of wind roses. The frequency of wind speeds by direction
are displayed in a radial fashion about the monitoring sites.
Figure 19. Wind roses for the Denton Airport site and the Discovery Park site during the experimental monitoring period
The wind roses obtained from the wind speed and wind direction data at Denton Airport
and Discovery Park have expectedly similar wind patterns over the span of the study, however
the Denton Airport observed higher maximum wind speeds than the Discovery Park location
experienced. The variation here can be assumed to be related to the equipment at each
Denton Airport C56 Discovery Park
47
location. The primary difference was the height of the monitoring equipment. The Denton
Airport meteorological tower reaches the typical 10 meters, however the Discovery Park
meteorological tower utilized for this study was a 3 meter tower.
While the Denton Airport site shows a very small percentage of higher speed winds
coming from the north west quadrant, the majority of the winds exceeding 15 miles per hour
and virtually all wind speeds exceeding 20 miles per hour approach the Denton Airport site
from the south to the east. The Discovery Park location did not experience winds that exceeded
20 miles per hour, which is likely due to the equipment height, and the maximum wind speeds
approached from the general south and southeast directions.
The pollution transport directly correlates to the wind speed and wind direction as
shown in the pollution roses in figure 20. These indicate that the Discovery Park site observes
the largest ozone concentrations when the wind direction comes from the south east. Another
observation in these figures is the maximum ozone levels at each site over the study period.
The Denton Airport observed a maximum of 67 parts per billion and the Discovery Park site
observed a maximum of 83.2 parts per billion.
Interestingly, ozone at Discovery Park can be seen coming from several directions,
whereas the Denton Airport site is predominantly coming only from the southeastern direction.
Additionally, there appears to be a greater pollution influence from the northwest direction at
the Discovery Park site. This is an interesting observation as it indicates that ozone is entering
the Discovery Park area differently than the ozone that is being observed at the Denton Airport
site. Another interesting note is the lack of ozone coming from the southwestern direction at
Discovery Park. This is noteworthy due to the fact that the Denton Airport is southwest of the
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Discovery Park location. This further suggests that ozone measurements at Discovery Park have
a perceptible difference than ozone measurements at Denton Airport.
Figure 20. Pollution roses for CAMS 56 (left) and Discovery Park (right) for combined dates of March 26, 2016 to April 3, 2016 and April 8, 2016 to April 25, 2016
Combining the data used in the wind roses and pollution roses provides a spatial
representation of the ozone concentrations in the form of bivariate polar plots. The polar plots
shown in figure 21 were created by applying the mean statistic as explained in the previous
chapter. The mean ozone concentrations at CAMS 56 and Discovery Park, during the combined
monitoring periods, respectively, was 30.3 ppb and 39.5 ppb.
Discovery Park Denton Airport C56
49
Figure 21. Bivariate polar plots of mean daily maximum ozone concentrations at the CAMS 56
(left) and Discovery Park (right) sites for combined dates of March 26, 2016 to April 3, 2016 and April 8, 2016 to April 25, 2016
The Denton Airport sites is located directly south east of the Discovery Park location.
The bivariate plot of the Discovery Park site shows that some of the ozone can be attributed to
transport from the southeast, however the greatest source of ozone at that location is coming
from the region southwest of Discovery Park. This indicates that the increase in the ozone
concentration at Discovery Park in relation to Denton Airport can be partly attributed to
sources south east of Discovery Park that are not directly in line with the Denton Airport site.
The wind roses, pollution roses, and bivariate plots provide some indication of local
pollution concentrations and transfer, however a more expansive look at the region can deliver
a more complete picture of where the pollutants are coming from. Figure 22 shows a 24 hour
backwards trajectory at Denton, Texas from March 26, 2015 at 15:00 which coincides with the
50
highest ozone concentration during the first experimental monitoring period. Figure 23 shows
the 24 hour backward trajectory from the same location on April 23, 2016 at 15:00 which
coincides with the peak ozone level measured during the second monitoring period. These
backward trajectories are created using the Hybrid Single Particle Lagrangian Integrated
Trajectory Model (HYSPLIT), a government run program available to the public.
Figures 22 and 23 each show where the air parcels that were being analyzed in the
Denton area were 24 hours prior. Each map marks metropolitan areas in Texas including
Dallas/Fort Worth, Houston/Beaumont, San Antonio, Austin, El Paso, Lubbock, and Abilene. The
graphical representations on the right side of each trajectory map show the altitude changes of
particles from their origination altitude of either 10 meters or 500 meters above ground level.
Figure 22. Backwards trajectory from Denton on March 26, 2016 at 14:00 showing the path of particles (left) and the altitude of particles during the 24 hours (right) with initial altitudes of
500 meters (top) and 10 meters (bottom)
51
An important observation that can be made with the March 26 trajectory shown in
figure 22 are wind patterns that originated from the southeastern direction. Approximately 500
kilometers south-southeast of Denton, the Houston metropolitan is situated. Both trajectories
of 10 meter and 500 meter altitude origins displayed air transport from that region which is
known to have high ozone levels (Byun, 2003). The region surrounding Houston and along the
gulf have experienced excessive pollution levels similarly to the Dallas area. The trajectory
reinforces that the influence of long-range pollution transport is measureable and pertinent.
Figure 23. Backwards trajectory from Denton on April 23, 2016 at 14:00 showing the path of particles (left) and the altitude of particles during the 24 hours (right) with initial altitudes of
500 meters (top) and 10 meters (bottom)
The trajectory shown in figure 23 showed an interesting wind pattern in which the air
monitored on April 23 was in the DFW for the 24-hours prior. The air parcels looped around and
through the Dallas/Fort Worth metropolitan area. With both high ozone days, the air was
located in or near a large metropolitan area 24 hours before it was measured in Denton.
52
Figure 24. 24-hour back trajectories for low ozone days during the monitoring periods
The backward trajectories in figure 24 showed the origination of the air that was
measured in Denton on the lowest ozone days during the monitoring periods. These dates were
March 30 and April 23. It should be noted that these were not the precise minimum days, an
adjustment for precipitation was made while choosing appropriate dates. March and April are
notorious for significant rainfall events which can often result in artificial low ozone
measurements. The dates with the lowest ozone measurements and the lowest precipitation
resulted in these two dates.
The March 30 trajectory in figure 24 (right), appears to have a similar path to the high
ozone day that occurred four days prior. The primary difference between the high and low
ozone day trajectories is their origin. The high ozone day was located in Houston, Texas 24
hours before it reached Denton, whereas the low ozone day originated south east of Houston
and did not travel through significant metropolitan areas. The April 13 trajectory (left) shows a
wind pattern that varies significantly from both high ozone days. The wind that reached Denton
53
on April 13 did not enter Denton from the south and did not originate in or near a metropolitan
area. Further inspection of the wind trajectories during the monitoring period may reinforce
the patterns that occur on high and low ozone days in Denton, Texas. The backward trajectories
for all days during the monitoring periods can be found in Appendix A.
As it was noted in the wind trajectories, the high ozone days experience south-southeast
wind patterns. Figures 25 and 26 show the ozone levels at Denton Airport and Discovery Park
on March 26 in addition to the wind vectors at each hour. The wind directions at Denton
Airport and Discovery Park are similar, and the slight difference in the magnitude of the vectors
can once again be attributed to the height of the equipment located at Discovery Park.
Figure 26. Discovery Park diurnal plot with wind vectors for March 26, 2016
Figure 25. Denton Airport diurnal plot with wind vectors for March 26, 2016
54
Figures 27 and 28 show the diurnal plots with the hourly wind vectors for the high ozone day in
the second monitoring period, April 23, 2016. The Discovery Park and Denton Airport plots
show a large difference of ozone concentration and a noticeable difference of wind speed and
wind direction near the early morning hours. There are strong implications that come from the
variations in this circumstance. The wind patterns indicate calm, nearly unmoving winds which
indicates that different local events are affecting ozone levels near Discovery Park and Denton
Airport. The near zero ozone levels and winds in the early morning hours at Denton Airport
indicates that a specific event is reducing ozone levels in that area, and more specifically, the
event is local and may be a result of local emissions of oxides of nitrogen, the ozone precursor.
Figure 27. Discovery Park diurnal plot with wind vectors for April 23, 2016
Figure 28. Denton Airport diurnal plot with wind vectors for April 23, 2016
55
4.3 Precursor Characteristics
Ozone is not the only pollutant that is of concern. Since the reaction of nitrogen dioxide and
volatile organic compounds in sunlight results in ozone, it is important to consider these
precursors as well. While the Discovery Park location held only an ozone analyzer, the Denton
Airport location is equipped with a NOx analyzer. The difference in ozone levels between the
two sites draws attention to the prospect of other intriguing monitoring insights with regards to
other pollutants.
While ozone was the focus of this study, other pollutants are equally important and
should be considered, particularly NOx as it accounts for NO2 which is a primary ozone
Figure 29. NO, NO2, and NOx concentrations by hour for March 26, 2016.
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precursor. The Denton Airport pollution monitoring site measures several different pollutants
and other parameters as described in Chapter 3. Pollution measurements include oxides of
nitrogen, nitrogen dioxide, nitric oxide, total non-methane organic compounds, fine particulate
matter, and non-continuous canister sampling for VOCs, in addition to the ozone considered in
this study. Figures 29 and 30 show the NOx concentrations observed at the Denton Airport site
during the monitoring periods. As expected, the nitrogen dioxide levels on the peak ozone day
was very low. Since ozone is created by a reaction with oxides of nitrogen and volatile organic
compounds in the presence of sunlight, an inverse relationship such that when nitrogen dioxide
is decreasing, ozone generally increases can be explained (“Ozone Pollution,” 2016).
Figure 30. Concentrations of nitrogen dioxide, nitrous oxide, and nitrogen oxides at the Denton Airport monitoring station from April 8, 2016 to April 25, 2016
57
Figure 31 shows a comparison of ozone and oxides of nitrogen over a several day period
in order to ascertain the relationship to a fuller extent. The lowest ozone drops occurred on
March 27 and another drop occurred on March 30. The figure shows an increase in NO2 at those
times. While NO2 peaks are seen during the morning hours and after sundown, O3 peaks are
found in the afternoon. These observations align with the ozone formation mechanism where
sunlight catalyzes the interaction between precursors to create ozone. During analysis, only
74% of the observed NO2 concentrations were numerical, non-zero, non-negative values. This
means that over one quarter of the NO2 data at the Denton Airport site does not properly
represent the actual concentrations, furthering the notion that an extensive, fully operational
monitoring site at Discovery Park would be further beneficial.
Figure 31. Comparison of ozone and oxides of nitrogen during nitrogen dioxide peaks in the first monitoring period
0
10
20
30
40
50
60
70
Conc
entr
atio
n (p
pb)
Ozone/NOx Comparison at Denton Airport Monitoring Site (CAMS 56)
NOx Ozone
58
An hourly comparison of the oxides of nitrogen and ozone measurements for the high
ozone days are shown in figures 32 and 33. As figures 29 and 30 show, the predominant
content of the NOx measurements are due to NO2 which validates the comparison. The figure
indicating the measurements on March 26 shows a typical relationship between ozone and the
oxides of nitrogen. A slight increase in ozone at 4:00 directly correlated with a slight drop in the
oxides of nitrogen concentrations. Additionally, the typical rise in ozone during the peak of the
day matches zero and near zero measurements in NOx.
Figure 32. Hourly O3/NOx comparison for March 26, 2016 at C56
The comparison between ozone and NOx for April 23, shown in figure 33, shows entirely
different characteristics than the March 26 comparison. The early morning hours of April 23
witnesses NOx levels that exceed the ozone levels. In conjunction with the observations of wind
speed mentioned in the previous section, this occurrence is curious. Typically, high
0
10
20
30
40
50
60
70
Conc
entr
atio
n (p
pb)
Ozone/NOx Comparison at Denton Airport Monitoring Site (CAMS 56) - March 26, 2016
NOx
59
concentrations of nitrogen dioxide and other oxides of nitrogen in urban areas can be
attributed to mobile sources. These high NOx levels would generally occur during peak travel
hours, 6:00 am to 9:00 am and 3:00 pm to 6:00 pm. This pollution characteristic can be noticed
in both comparison figures. The morning travel peak observes a small rise in NOx levels. The
observation is not necessarily seen in the afternoon hours due to the reactions that result in
ozone. While there is a rise in NOx levels as shown in figure 33 during the morning travel hours,
the concentrations measured prior to that were already high.
Figure 33. Hourly O3/NOx comparison for April 23, 2016 at C56
Although the fluctuations in the oxides of nitrogen should be explored more, the initial
assumption would be a local source of nitrogen dioxide. Taking into consideration the low
ozone levels, the high NOx levels, and the stagnant winds that were observed in analyses in the
previous section, suggesting the possibility of the existence of a local nitrogen dioxide emission
source. In order to further verify this assumption, a bivariate plot was created as shown in
0
10
20
30
40
50
60
70
Conc
entr
atio
n (p
pb)
Ozone/NOx Comparison at Denton Airport Monitoring Site (CAMS 56) - April 23, 2016
NOx
60
figure 34. A mean statistic was applied to NO2 concentrations along with wind speed and wind
direction measurements at Denton Airport during the monitoring period. The largest
concentration of nitrogen dioxide was located during very low wind speeds which further
indicates that a local emission source is affecting the Denton Airport measurements.
Monitoring outside of the area that is directly affected by this source would be valuable when
understanding the regional pollution levels. This furthers the prospect that monitoring at
Discovery Park would be a solution to address gaps in the air quality monitoring data.
Figure 34. Bivariate plot of mean NOx concentrations from March 26 to April 3 and April 8 to April 25, 2016 at Denton Airport
61
In addition to direct precursors, analysis of other pollutants at the Denton Airport site
can show a need for monitoring at Discovery Park. Fine particulate matter, with diameter not
exceeding 2.5 microns (PM2.5), is monitored at the Denton Airport site and the observations
from that device for during the monitoring period can be found in figures 35 and 36. The
observations of the fine particulate matter aligned closely with the ozone measurements. The
lowest measurements can be seen on March 27 and March 30, 2016. The concern with ozone
concentrations merits another look at other pollutants that could also be introduced to the
area through long range transport. The fluctuations of PM2.5 that align with ozone draws
attention to the extensive monitoring that should be conducted at a location other than Denton
Airport and the scope of the air quality analyses that should be conducted.
Figure 35.Concentrations of fine particulate matter (PM2.5) at the Denton Airport monitoring station from March 26, 2016 to April 3, 2016
02468
10121416
PM2.
5M
easu
rem
ent
Concentrations of Fine Particulate Matter at Denton Airport
PM2.5
62
Figure 36. Concentrations of fine particulate matter (PM2.5) at the Denton Airport monitoring station from April 8, 2016 to April 25, 2016
Overall, Denton Airport has observed interesting characteristics of precursors, some of
which appear to be highly localized. While measurements of ozone and wind parameters at
Denton Airport and Discovery Park showed similarities in trends, there are obvious differences
in local influences that will likely result in significant variations in air quality analysis between
the two locations. Standardizing the meteorological equipment heights and establishing an
equivalently equipped monitoring station for data collection could provide insightful spatio-
temporal characteristics of air pollution in the Denton region.
0
2
4
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8
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16O
zone
Con
cent
ratio
n (p
pb)
Concentrations of Fine Particulate Matter at Denton Airport
PM2.5
63
CHAPTER 5
DESIGN SPECIFICATIONS
As variations in pollution concentrations across Denton continued to be highlighted
throughout the historical and monitored analyses, exploring alternate monitoring methods and
locations including Discovery Park could result in a more efficient and informative air quality
monitoring endeavor. Challenges faced by the stationary monitoring shelter used for the
experimental data collection in this study verified that improvements in air pollution
monitoring could be made at that location. Based on the analysis from the historical pollution
and meteorological data from Denton and the four surrounding sites in addition to the
experimental data at Discovery Park, the necessity for a platform with improved monitoring
capabilities was made abundantly clear. In addition to the potential improvements that would
be introduced by a new state of the art monitoring station, the focus on long-range pollution
transport introduces the potential need for mobile and aerial monitoring systems at this
proposed location. The solution to these concerns is a mobile monitoring trailer equipped with
an aerial monitoring platform, as suggested in chapter 3 and depicted in figure 10.
5.1 Foundation for the Discovery Park Mobile Monitoring Station
The stationary air monitoring at Discovery Park faced many challenges, most of which
would have been relatively easy to overcome. Initial improvements to the shelter involved
increasing insulation and creating weatherproof seals. Extreme bouts of thunderstorms allowed
water to leak in. Fortunately, the equipment was not on the floor of the shelter and was not
under the leaking portion of the shelter roof. Extreme wind eventually resulted in the
detachment of the sampling manifold.
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Along with all of the potential benefits provided by developing a modern state of the art
monitoring system at the proposed location, there is an additional benefit provided by the
existence of the University of North Texas Net Zero Energy Lab which is capable of self-
sustained energy. The monitoring platform placed in this location would be able to utilize the
electricity generated by the net zero energy lab, and thus would essentially, have a zero-
pollution footprint.
The initial shelter for this study was limited to its predetermined location and the
meteorological tower was not operated by the same team that operated the shelter. Figure 24
shows the monitoring site at Denton Airport. While the structure housing the equipment is
larger and more inclusive, the site is still stationary. The meteorological tower is stabilized with
wires which increases the permanence of the monitoring location. A mobile monitoring station
would have the ability to measure meteorological parameters, while simultaneously
maintaining its overall mobility.
The development and utilization of a modernized pollution monitoring system with
both mobile and aerial monitoring platforms should be the primary goal for studying and
understanding of the pollution transport issues faced by the region. Figure 37 shows an image
of the current monitoring station at Denton Airport. The monitoring initiative at Discovery Park
should exceed the capabilities of the Denton Airport monitoring station for the enterprise to be
exceptionally beneficial.
The proposed mobile monitoring station would be housed on the Discovery Park
premises owned and operated by the University of North Texas. The site is located on the
northern edge of Denton, Texas. Figure 38 is an aerial view of the Denton, Texas highlighting
65
the locations of the current monitoring site at Denton Airport and the proposed location at
Discovery Park.
Figure 37. Photograph of the Continuous Ambient Monitoring Station (C56) located at the Denton Airport (“Denton Airport South C56/A163/X157,” 2013)
Figure 38. Aerial map of Denton, Texas with the proposed monitoring location at Discovery Park marked by a green star and the current Denton Airport site marked with a red circle
66
Figure 39. Aerial view of the entire property of the proposed monitoring location at Discovery Park with red circle marking the general location of the air monitoring site on the premises
The proposed mobile monitoring trailer will be located near the net zero energy lab,
shown in figure 39. The specific location would be on a concrete pad site on the south side of
the building as shown in figure 40. It was decided that the close proximity to the building would
not be an impedance to air pollution monitoring when the trailer is located at its home site.
This conclusion came after the original review of the location occurred. The initial blueprint
placed the monitoring trailer on the gravel drive on the north side of the building. Additionally,
the area to the south of the building includes a small fenced area with previously established
power access. The originally planned area for such a monitoring system did not have a
foundation on which a mobile platform system or trailer could rest. A concrete pad site has
thus been suggested as a solution.
67
Figure 40. Aerial view of the precise location of the proposed monitoring site on the property with red circle marking the exact location of the air monitoring station
5.2 Mobile Monitoring Platform
A mobile monitoring platform capable of ambient air-monitoring is currently being
designed to meet the needs proposed for mobile monitoring in future studies. The historical
analysis and the experimental data reinforce the necessity of addressing the issue of long range
transport of pollutants. A result of this study was a concept trailer designed to address future
ambient air monitoring goals. Specifications for the system and monitoring devices are
discussed in the next sections.
5.2.1 Platform Specifications
The design for the monitoring station addresses several issues. The current air
monitoring goals must be achievable with the setup, and future goals must be attainable by
allowing ample opportunity for potential expansion and modification.
A tandem axle, enclosed cargo trailer with dimensions that meet or exceed 16’ length, 7’
height, and 6.5’ width allows for the ideal setup in current and future fashion. In addition to the
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physical proportions of the monitoring trailer, other features must be addressed. A fully
equipped trailer can run a multitude of analyzers, all of which require the proper power supply.
A 100A electrical capability with full power distribution to all analyzer equipment, lights, and
workbench outlets is essential. Occupant safety is paramount, therefore in addition to the
interior overhead lights and the exterior side panel lights, there must be safety lights. The
monitoring station requires work stations for computers and workbench space for equipment
upkeep and manipulation. Each workbench area requires a double duplex outlet receptacle.
The equipment in the station, including analyzers, computers, data loggers, and lighting
all release heat, and the environment in which the station would be located has a severe heat
climate, thus necessitating the use of an air conditioning system. An appropriately sized HVAC
system would need to exceed 24k Btu, to sufficiently cool the interior while all equipment was
functioning and the area occupied. Two possibilities were presented with respect to the HVAC
system, one of which would be a single unit at 24k Btu or above, or a twinned system which
would possibly include 2 – 13.5k BTU roof mounted air conditioners.
Other features required in the monitoring trailer include a cylinder rack for gases
required for equipment functionality or calibration. A minimum of 3 cylinders must be able to
fit within the rack, and be mounted according to safety guidelines and procedures. In the case
of a tandem axle trailer, the equipment and cylinders can cause an imbalance in the load. In
order to counter this, the location of the cylinder rack would logically be placed over or near
the axle and opposite of equipment or other equally weighted stationary objects in the trailer.
A monitoring trailer would be able to keep equipment protected and accessible,
however sampling must still come from the ambient atmosphere outside of the trailer.
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Addressing this requirement involves creating a sampling manifold that is routed from
equipment to the outside. Studies have shown that the sampling manifold can affect the results
of the analysis if certain materials are used, if the manifold is not designed properly, or if the
interior gas pathway is exposed to sunlight (Teitz and Mustafa, 2009). Managing these
requirements and limitations is not difficult and specifying a glass manifold, exterior protection
(including shielding, rain protection, and a bug screen), and necessary mounting hardware
ensures that the sampling manifold performs effectively. The base stipulation of the sampling
manifold is that it can provide ambient air samples to all equipment that requires it inside the
trailer. A minimum of six ports is specified in order to guarantee full operation.
The monitoring trailer would not be confined to the location at Discovery Park and
mobile monitoring is a large part of the design specifications. In order to ensure that mobile
monitoring is possible, and barring the lack of a power source at the remote monitoring site, a
generator is essential.
5.2.2. Monitoring Equipment Specifications
A meteorological tower should reach a height of ten meters and should contain
equipment that monitors wind speed, wind direction, temperature, barometric pressure,
relative humidity, and solar radiation.
Oxides of nitrogen and specifically nitrogen dioxide are important pollution parameters
to consider, especially when ozone is a focus. As mentioned in the previous chapter, due to NO2
being a precursor to ozone, the two pollutants should have an inverse relationship such that as
NO2 decreases, the ozone concentrations in the same area should increase. This relationship
necessitates the monitoring of this parameter. The monitoring equipment for nitrogen dioxide
70
would ideally have a lower detection limit of 0.4 ppb and would be able to monitor the
pollutant in the 0 to 20 ppm range.
Carbon dioxide and carbon monoxide analyzers with ranges and limits noted below.
Analyzers should have internal memory/data storage and data acquisition capabilities.
Independent analyzers or a combined system would both be feasible if the minimum
capabilities are reached. Carbon monoxide should be able to monitored in the 0 to 200 ppm
range with a lower detection limit of 0.4 ppb and the carbon dioxide range should be able to be
read from 0 to 2000 ppm with a +/- 2% error allowance.
Sulfur dioxide and hydrogen sulfide are pollutants that should also be monitored. Some
equipment types are capable of monitoring both. Sulfur dioxide should be able to be observed
at levels that range from 0 to 20 ppm and hydrogen sulfide should be able to be detected when
ambient concentrations are within 0 to 2 ppm. Hydrogen sulfide should have a lower detection
limit that does not exceed 0.3 ppb.
Equipment capable of measuring methane and non-methane hydrocarbons has become
increasingly relevant and necessary with the rise in natural gas activity in the North Texas area.
The equipment necessary for this project will utilize a flame ionization detector (FID). The FID
requires a gaseous fuel either in the form of a hydrogen molecule (H2) or in the form of a
hydrogen/helium blend (H2He). The volumetric flow of the gas must be 50 cc/min if the fuel is
hydrogen alone and 100 cc/min if the fuel is the hydrogen/helium blend.
Particulate matter is another pollution concern. Particles less than 2.5 microns (PM2.5)
and less than 10 microns (PM10) are the focus when monitoring for fine particles. These
pollutants can include dust, soot, and other industry or transportation released pollutants
71
Ideally, the system chosen for PM2.5 and PM10 monitoring will be capable of continuous,
simultaneous measurement and sampling. Either a separate system, in which each particle size
is measured using its individual device, or a combined system in which both particles can be
measuring with the same equipment are allowable.
Calibration equipment is required for an effective pollution monitoring station. If the
station attempts to be classified under state or national monitoring programs, certain
requirements must be met and equipment must be maintained under certain standards. A zero
air generator is a piece of equipment that provides a self-contained source of contaminant-free
air for calibrating equipment. This system requires air scrubbers for SO2, H2S, NOx, CO,
hydrocarbons. The measured output of the gas must measure 20 standard liters per minute.
Data acquisition systems provide a comprehensive location for data to be maintained.
Most modern monitors and analyzers have the feature of internal memory, however, some
types of equipment, and older versions of some monitors, do not have this capability.
If internal memory and data storage is not possible for all equipment in the monitoring
station, an external data logger capable of functioning on a windows-based PC, must be
obtained also, with sufficient external data storage.
5.3 Aerial Monitoring Platform
In order to effectively monitor height-resolved pollution levels, a device capable of
steadily hovering at specific altitudes must be used. The design must not impede the air flow of
the pollution sensors, therefore, avoiding significant fluctuations in the airflow around the
sensors and preventing airflow impedance are two primary constraints.
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5.3.1 Platform Specifications
Several possible system arrangements exist. The key objective of this device is to
provide a steady hovering platform for an air monitoring sensor. The unmanned aerial vehicle
discussed in previous chapters is a quadrotor design with a sufficient thrust force to carry a
reasonable payload. There are four equally-spaced arms that are mounted with alternating
motors in order to maintain stabilization.
5.3.2 Aerial Monitoring Equipment Specifications
Several constraints affect air pollution analysis when using a portable, airborne
monitoring platform. As previously described, pollutant monitoring equipment that meets EPA
standards remains cumbersome, heavy, and expensive. The first constraint in order to achieve
aerial monitoring is to overcome flight limitations. The weight of the monitoring equipment
must not exceed the available thrust of the monitoring platform.
The aerial monitoring concept originated with the combination of the Libelium
Waspmote gas board and an unmanned aerial vehicle. The intended platform was a quadcopter
developed by undergraduate students at the University of North Texas in the Mechanical and
Energy Engineering program. The design was capable of holding the Libelium Waspmote and
the proposal was to place the sensors on that specific drone or any other quadcopter capable
of steady, incremental flight to investigate the possibility of more extensive aerial monitoring.
The current Libelium Waspmote Gas Board setup available at the University of North
Texas is an uncalibrated line of sensors which includes temperature, relative humidity, ozone,
nitrogen dioxide, carbon dioxide, and methane. The line of pollution sensors distributed by
Libelium includes pressure, CO, NO, SO2, NH3, H2S, and particulate matter. The pollution line is
73
not limited to these sensors and any other sensors available from Libelium should be studied to
determine the validity and reliability of their measurements. Libelium sensors that are studied
and are found to exceed monitoring expectations are the ideal components of the aerial
monitoring system.
5.4 Future Station Utilization
While the primary location has been covered in detail, the prospect of mobile
monitoring could result in vast amounts of understanding of pollution in the North Texas
region. Maintaining a permanent monitoring station as Discovery Park would provide valuable
insight into the pollution concentrations across the Denton municipality. The ability to deploy
the station would provide even more understanding. The mobile monitoring station would
ideally be utilized for mobile monitoring during peak pollution events. Interesting possibilities
for in depth analysis could include holiday travel weekends in which roadside monitoring would
have significant impacts on local pollution levels, wildfires and other natural or manmade
events that result in catastrophic pollution concentrations, and monitoring near pollutant
sources such as nuclear power plants, industrial areas, or oil and gas production wells.
Stationary and mobile monitoring could provide a new understanding of transported and locally
created pollution.
With respect to the aerial monitoring setup, monitoring sensors should continue to be
studied. Examining the various monitoring sensors available is an essential next step for the
aerial monitoring initiative. The ability to develop a three-dimensional visual of pollution
concentration could contain valuable insight, particularly if emission sources are being
analyzed. The ability to measure pollutants in a vertical manner and across a distance would
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provide more information than current measurement techniques. Combining ground
monitoring and aerial monitoring through the use of the mobile monitoring platform and aerial
monitoring platform could allow the attainment an encompassing understanding of transport
and source pollution that could potentially result in significant advancements in managing local
pollution concentrations.
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CHAPTER 6
CONCLUSIONS AND RECOMMENDATIONS
6.1 Conclusions
The primary goal of this study was to construct a framework for future ambient air
monitoring in and around Denton, Texas that would address pollution concerns. The region has
already been a focus of ambient air monitoring by the Texas Commission on Environmental
Quality (TCEQ) due to the high ozone concentrations measured in the region which designated
Denton and other surrounding counties as nonattainment areas. Denton County is not in the
center of highly dense population region of the Dallas metropolis which has led to some focus
on long range transport as a culprit for the regions high ozone levels observed. Currently, one
air pollution monitoring site is located at Denton Airport. Four monitoring sites were chosen for
historical analysis based on their proximity (within 25 miles) to a proposed monitoring location
at the Discovery Park campus of the University of North Texas. Historical data collected from
the TCEQ website for the month of April for sixteen years from 2000 to 2015 provided pollutant
information from the four monitoring sites and the Denton Airport site. The parameters at
every site included ozone and meteorological data. Ozone data at the Denton Airport location
did show a steady decrease in maximum ozone concentration since a measured concentration
of 96 ppb in April 2011, however the Denton region continues to surpass the ozone
nonattainment threshold. The weather data which included wind direction and wind speed
showed that the typical wind patterns for the region initiate from the south with wind speeds
that rarely exceeded 20 miles per hour.
76
In addition to the analysis of the historical meteorological and concentration data,
experimental data was collected at the proposed location. An ozone analyzer was placed in a
preexisting shelter on the premises and was set to monitor ozone levels every five minutes, 24
hours a day throughout the investigation period. The shelter in which the ozone monitor was
placed was located next to a meteorological tower that was equipped with wind speed and
direction sensors, however these were not operational. A different nearby meteorological
tower operated by another research group provided wind speed and wind direction data to use
in conjunction with the ozone data collected. The measurements collected at Discovery Park
were compared by coinciding measurements of the same parameters at the Denton Airport
site. The results of this comparison showed a time lag and a concentration increase between
the Denton Airport site and Discovery Park. The existing monitoring site located at Denton
Airport is approximately 4 miles southwest of Discovery Park. Although this site already exists in
the Denton area a mobile air monitoring trailer for ambient pollution monitoring in the region
would allow for more expansive monitoring to address pollution transport. Based on
meteorological data and measured ozone levels, the slight geographical position difference is
sufficient to introduce large enough variances in ozone levels to substantiate the need for
additional and more extensive air monitoring in North Denton.
Further air pollution data was collected from the Denton Airport site to study the
characteristics of ozone precursors in the region. Concentrations of oxides of nitrogen at the
Denton Airport site were analyzed. Fluctuations in the nitrogen dioxide concentrations during
nonpeak hours suggest a local source of nitrogen dioxide that was affecting the Denton Airport
site. Bivariate plots coupling the meteorological data with oxides of nitrogen measurements
77
further confirmed the conclusion. The activity of ozone precursors near the Denton Airport
could not be translated or compared to the Discovery Park site. Evidence indicates that the two
sites experience noticeably different precursor activity which could be demonstrated with
further monitoring at both sites.
The design work for the mobile and aerial monitoring platforms lays a foundation for
the development of the systems. After the systems are manufactured further experimental
analysis can be conducted at the Discovery Park location. In accordance with the statistical
analysis already conducted, the “R” software Openair package should be used to examine
further experimental data. The data collection should be expanded beyond wind direction,
wind speed, and ozone. The new mobile monitoring trailer has specifications that exceed the
current Denton Airport site and also includes the aerial monitoring platform with ultra-portable
sensors that are capable of measuring pollution at different altitudes. The aerial platform used
in conjunction with the ground based trailer station has the prospect of providing a fully
developed understanding of pollution transport. The ground level pollution concentrations and
the vertical profile of pollutant concentrations developed by the aerial platform can provide a
three dimensional account of pollution movement across the region. Since the abilities of the
monitoring trailer would exceed all other monitoring stations within the 25 mile radius, mobile
monitoring should be extensively conducted in order to develop a broader understanding of
pollution levels in the region.
78
6.2 Future Directions
Spatio-temporal variations seen in the ozone levels across the Denton municipality
indicate that the extensive monitoring proposal would provide interesting and new insight into
the local and regional pollution that affect the area.
Utilizing the proposed system to its fullest extent would involve semi-permanent
deployment at the Discovery Park location with mobile monitoring during peak events or near
point sources that have garnered the attention of those concerned about local pollution levels.
Continuing to pursue information on aerial monitoring as described in the previous chapter
should be the focus in the near future so that the monitoring initiative can support the
collection of data over varying space and time scales.
79
APPENDIX
ADDITIONAL TRAJECTORY ANALYSES
80
Figure A 1. 24-hour backward trajectories from 15:00 at a height of 500 meters for Denton, Texas (33.20 W, 97.20 N) on March 26 (top left), March 27 (top right), March 28 (bottom left),
and March 29 (bottom right) of 2016
81
Figure A 2. 24-hour backward trajectories from 15:00 at a height of 500 meters for Denton, Texas (33.20 W, 97.20 N) on March 30 (top left), March 31 (top right), April 1 (bottom left), and
April 2 (bottom right) of 2016
82
Figure A 3. 24-hour backward trajectories from 15:00 at a height of 500 meters for Denton, Texas (33.20 W, 97.20 N) on April 3 (top left), April 8 (top right), April 9 (bottom left), and April
10 (bottom right) of 2016
83
Figure A 4. 24-hour backward trajectories from 15:00 at a height of 500 meters for Denton, Texas (33.20 W, 97.20 N) on April 11 (top left), April 12 (top right), April 13 (bottom left), and
April 14 (bottom right) of 2016
84
Figure A 5. 24-hour backward trajectories from 15:00 at a height of 500 meters for Denton, Texas (33.20 W, 97.20 N) on April 15 (top left), April 16 (top right), April 17 (bottom left), and
April 18 (bottom right) of 2016
85
Figure A 6. 24-hour backward trajectories from 15:00 at a height of 500 meters for Denton, Texas (33.20 W, 97.20 N) on April 19 (top left), April 20 (top right), April 21 (bottom left), and
April 22 (bottom right) of 2016
86
Figure A 7. 24-hour backward trajectories from 15:00 at a height of 500 meters for Denton, Texas (33.20 W, 97.20 N) on April 23(top left), April 24 (top right), April 25 (bottom) of 2016
87
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