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This article was downloaded by: [Van Pelt and Opie Library]On: 21 October 2014, At: 20:32Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK
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Air Quality at Night Markets in TaiwanPing Zhao a & Chi-Chi Lin ba Department of Marine Environmental Engineering , National Marine University ,Kaohsiung , Taiwan , Republic of Chinab Department of Civil and Environmental Engineering , National University ofKaohsiung , Kaohsiung , Taiwan , Republic of ChinaPublished online: 24 Jan 2012.
To cite this article: Ping Zhao & Chi-Chi Lin (2010) Air Quality at Night Markets in Taiwan, Journal of the Air & WasteManagement Association, 60:3, 369-377, DOI: 10.3155/1047-3289.60.3.369
To link to this article: http://dx.doi.org/10.3155/1047-3289.60.3.369
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Air Quality at Night Markets in Taiwan
Ping ZhaoDepartment of Marine Environmental Engineering, National Marine University, Kaohsiung, Taiwan,Republic of China
Chi-Chi LinDepartment of Civil and Environmental Engineering, National University of Kaohsiung, Kaohsiung,Taiwan, Republic of China
ABSTRACTIn Taiwan, there are more than 300 night markets andthey have attracted more and more visitors in recentyears. Air quality in night markets has become a publicconcern. To characterize the current air quality in nightmarkets, four major night markets in Kaohsiung wereselected for this study. The results of this study showedthat the mean carbon dioxide (CO2) concentrations atfixed and moving sites in night markets ranged from 326to 427 parts per million (ppm) during non-open hoursand from 433 to 916 ppm during open hours. The averagecarbon monoxide (CO) concentrations at fixed and mov-ing sites in night markets ranged from 0.2 to 2.8 ppmduring non-open hours and from 2.1 to 14.1 ppm duringopen hours. The average 1-hr levels of particulate matterwith aerodynamic diameters less than 10 �m (PM10) andless than 2.5 �m (PM2.5) at fixed and moving sites in nightmarkets were high, ranging from 186 to 451 �g/m3 andfrom 175 to 418 �g/m3, respectively. The levels of PM2.5
accounted for 80–97% of their respective PM10 concen-trations. The average formaldehyde (HCHO) concentra-tions at fixed and moving sites in night markets rangedfrom 0 to 0.05 ppm during non-open hours and from 0.02to 0.27 ppm during open hours. The average concentra-tion of individual polycyclic aromatic hydrocarbons(PAHs) was found in the range of 0.09 � 104 to 1.8 � 104
ng/m3. The total identified PAHs (TIPs) ranged from 7.8 �101 to 20 � 101 ng/m3 during non-open hours and from1.5 � 104 to 4.0 � 104 ng/m3 during open hours. Of thetotal analyzed PAHs, the low-molecular-weight PAHs (twoto three rings) were the dominant species, correspondingto an average of 97% during non-open hours and 88%during open hours, whereas high-molecular-weight PAHs(four to six rings) represented 3 and 12% of the total
detected PAHs in the gas phase during non-open andopen hours, respectively.
INTRODUCTIONAccording to the air quality monitor of the Environ-mental Protection Agency in Taiwan, the ratio of un-satisfactory air quality days to the total number ofmonitored days in Kaohsiung has been by far the high-est in Taiwan. In the densely populated city of Kaohsi-ung, some of the heaviest population densities are lo-cated in the various night markets. Meanwhile, thenumber of night markets has increased dramaticallyand attracted more and more visitors in recent years.The night market is an especially dense outdoor cook-ing environment where many locals and foreignersspend a lot of time. In fact, the night market is afundamental element of Taiwan society and a uniquelocation that Taiwan citizens they are proud of. How-ever, food stalls in night markets usually use fans orexhaust hoods to vent their cooking fumes that spreadthe exhaust into nearby occupied spaces or right abovemarket streets. Good air quality at night markets notonly enhances the enjoyment of the market visitors,but also protects the health of market workers andcustomers from exposure to harmful air pollutants.
Cooking methods have a strong impact on theamount of emitted air pollutants. Barbecued food hasbecome very popular in night markets. Researchersfound indoor levels of respirable suspended particulates(RSPs) and carbon monoxide (CO) were elevated inbarbecue-cooking restaurants.1 The use of charcoalburners degraded indoor air quality and elevated aver-age indoor levels of RSPs and CO in these restaurants.RSPs, CO, and volatile organic compounds are commonair contaminants emitted from frying food on a hotsteel pan and broiling food on steel bars above a char-coal burner.1–4 Chinese cooking methods involve theuse of many different cooking oils. However, it wasdocumented that heated cooking oils emit various haz-ardous airborne agents, some of which are proved to bepotential human or laboratory animal carcinogens,such as formaldehyde (HCHO).3,5 It was found that theLPG (liquified petroleum gas) stoves, which are com-monly used in night markets, usually generate moreHCHO than natural gas and kerosene gas stoves.6 Total
IMPLICATIONSCooking activities in night markets can cause serious airpollution so that people who visit or work at night marketsare probably exposed to a higher health risk than others.Vehicles and motorcycles should be prohibited to enternight markets. Environmental policy-makers in Taiwan aresuggested to make regulations related to cooking styles innight markets for better air quality.
TECHNICAL PAPER ISSN:1047-3289 J. Air & Waste Manage. Assoc. 60:369–377DOI:10.3155/1047-3289.60.3.369Copyright 2010 Air & Waste Management Association
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suspended particulate (TSP), CO, and HCHO were dis-covered to be major air pollutants emitted from burn-ing LPG in stoves.7,8
Earlier studies found that restaurant cooks had anincreased risk of lung cancer because they were con-stantly exposed to cooking stove smoke in kitchens.9.10
Polycyclic aromatic hydrocarbons (PAHs) were found tobe generated during food processing or cooking stepssuch as roasting, grilling, barbecuing, and smoking.11
The PAHs are semi-volatile substances at atmosphericconditions and frequently occur in the gas phase andattached to particles depending on the vapor pressureof each PAH.12–14 Lighter PAHs are found predomi-nantly in the gas phase, whereas those with four ormore rings are mainly found adsorbed in particulatematerial.15–17 PAHs are considered highly toxic for hu-man beings and several of these compounds are carci-nogenic, mutagenic, or teratogenic.18–20 For example,some PAHs such as benzo[a]pyrene (BaP), benz[a]an-thracene (BaA), and dibenz[a,h]anthracene (DBA) havebeen classified into Group 2A by the InternationalAgency for Research on Cancer.21
Air quality in night markets has become a source ofpublic concern. Unfortunately, few data are available onthe air quality found at night markets. Therefore, thepurpose of this study is to determine concentrations ofselected air pollutants in four major night markets inKaohsiung and to compare the results with indoor andoutdoor air quality objectives in Taiwan and the UnitedStates. The results of this study are of particular value inurban areas such as Kaohsiung, where the high density ofnight markets is likely to magnify the effect of air pollu-tion on workers and customers. This study may also bevaluable for supporting the inclusion of pollution emis-sion guidelines in future regulations dealing with nightmarkets.
METHODSField Study Design
A study of four major night markets in Kaohsiung withhigh visitor densities was conducted from August 2008to November 2008. Each night market was an outdoorenvironment and labeled as N1, N2, N3, and N4. Onefood stall was chosen in each night market as thesampling site. These food stalls were labeled as F1, F2,F3, and F4. No vehicles or motorcycles are allowedinside of the night markets except for N4. The charac-teristics of the four food sites are described in Table 1.All four food stalls are not air-conditioned (e.g., nomechanical ventilation is used). The stalls are small andopen-courted. They all use a movable kitchen with noexhaust fume extractor above stoves. Customer seatsand tables are facing or are near the kitchen; thus, theyexperience almost natural ventilation. The selectednight markets have land areas of 6000–30,000 m2 with500-2000 cooks and service workers, as well as thou-sands to tens of thousands of visitors depending onseasons and holidays. At N1, the food stall distributionwas 30% hot-pot, 20% barbecue, 20% grilling, 10%deep fry, 10% stir fry, and 10% were considered
“other.” They all use LPG, except that half of the hot-pots use alcohol. At N2, the distribution was 20% hot-pot, 25% barbecue, 20% grilling, 15% deep fry, 10% stirfry, and 10% other. They all use LPG. At N3, the distri-bution was 25% hot-pot, 25% barbecue, 20% grilling,15% deep fry, 10% stir fry, and 5% others. They all useLPG, except that approximately one-third of the hot-pots use alcohol. The distribution at N4 was 30% hot-pot, 25% barbecue, 20% grilling, 10% deep fry, 15% stirfry, and 10% others. They all use LPG, except thattwo-thirds of hot-pots use alcohol.
In this study, the carbon dioxide (CO2), CO, HCHO,PAHs, and levels of particulate matter (PM) with aerody-namic diameters less than 10 �m (PM10) and less than 2.5�m (PM2.5) at night markets were measured simulta-neously by a researcher carrying all portable monitors inone bag. The outdoor hourly PM10 and CO levels mea-sured by ambient air quality monitoring stations nearselected night markets are considered the correspondingpollutant levels in the urban atmospheric environment inKaohsiung. As shown in Figure 1, their relative distancesaway from corresponding night markets are 1.9, 2.9, 2.7,and 1.7 km.
Sampling and Analytical MethodsAll air samples were collected from approximately 1 to1.5 m above the ground. At each night market, a re-searcher carrying monitors was seated at a fixed stall for2 hr and then walked in the streets of the night marketfor 2 hr. The night markets are open for 9 hr, and thefixed sites were measured 2 hr after the opening andmoving sites approximately 3 hr before the closing.Thus, the 2-hr data for fixed sites and 2-hr data formoving sites should presumably represent the generalcondition in night markets. Four moving sites werelabeled as M1, M2, M3, and M4 and consisted of aresearcher walking in the streets of the night market for2 hr. All of the pollutants levels were measured duringopen- and non-open hour periods on weekends. Theweekend open-hour period is 5:00 p.m. to 2:00 a.m. Theweekend non-open hour period is 2:00 a.m. to 5:00p.m. During the open-hour sampling period, outdoortemperature was 27–31 °C (mean � 29 °C), relative hu-midity (RH) was 60–80% (mean � 69%), and windspeed was 0.2–0.8 m sec�1 (mean � 0.4 m sec�1). Dur-ing the non-open hour sampling period, outdoor tem-perature was 31–34 °C (mean � 33 °C), RH was 51–76%
Table 1. Features of four food stalls.
FixedSites Types
CookingFuel Kitchen Description
F1 Hot-pot LPG Kitchen counter, one stove,no fume extractor
F2 Burger LPG Kitchen counter, two stove,no fume extractor
F3 Barbecue LPG Kitchen counter, two stove,no fume extractor
F4 Hot pot Alcohol Kitchen counter, one stove,no fume extractor
Notes: F � fixed sites (stalls) at selected night markets.
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(mean � 60%), and wind speed was 0.4–1 m sec�1
(mean � 0.7 m sec�1). During the whole samplingperiod, there was no cigarette smoking found nearby.
At each night market, the researcher carrying thesamplers was seated at a fixed stall for 2 hr. A TSIportable Q-trak (model 7565, TSI, Inc.) was used tomonitor CO2 and CO concentrations. A Dust-Trak airmonitor (model 8520, TSI, Inc.) was used to measurePM10 and PM2.5 concentrations. Pre- and post-zerochecking of the Dust-Trak monitor was conducted.HCHO concentrations were measured by a HCHO sen-sor (model htV, PPM Technology, Inc.). Before sam-pling, the Q-trak, Dust-Trak, and HCHO sensor detectorwere all calibrated by the manufacturers. The detectablemechanisms, ranges, and minimum detection limits ofall device analytical methods are summarized in Table2. These data stem from the manufacturers’ specifica-tions. It should be noticed that mobile measurementscan only be performed with these small, mobile de-vices. Also, these kinds of measurements had their ownlimits. The European legislation requires a so-calledexpanded uncertainty for the gravimetric referencemethod of 25% for a single value, which is a 24-hraverage.22 Broad investigations show that the lowestuncertainties for these gravimetric methods are in therange of 10–15%. For advanced automated methods,uncertainties are in the range of 15–25% or evenhigher. High values occur, especially for the opticalmethod using light scattering. In addition, all measur-ing values presented in this study are short time aver-ages over 1 hr or some hours. As a consequence, it canbe suggested that the uncertainty of the concentrationspresented are approximately 25% or even higher.
As for PAHs, each researcher carried a pump aroundtheir waist that was connected via a silicon tube to theair sampling device. The device was attached to theclothing on the shoulder within 30 cm of the nose andmouth. Small battery-powered pumps (Gilian 5000)were used to pump air through the sampling tube con-taining XAD-2 adsorbent. Air samples were collectedwith a flow rate of 3 L/min for 2 hr (360 L/sample)during the open time period from 8:00 to 10:00 p.m.and during the non-open time period from 1:00 to 3:00p.m. Sampling devices were protected against light dur-ing and after sampling by wrapping them in aluminumfoil. The samples were stored at 0 °C before the analy-ses. Each sample was Soxhelt extracted in a mixed sol-vent (n-hexane and dicholoromethane vol:vol � 1:1)for 24 hr. The extract was concentrated by purging withultrapure nitrogen to 2 mL. The collected eluate wasfurther concentrated to 1 mL with ultrapure nitrogen.PAH content was determined using a gas chromato-graph (GC; Agilent 6890) with a mass selective detector(MSD; Agilent 5973). This GC/mass spectrometer (MS)was equipped with a DB-5MS capillary column (30 m �0.25 mm; 0.25-�m film thickness). The running condi-tion were as follows: splitless injection of 2 �L, splitopening after 30 sec, and injector temperature at280 °C; the oven temperature program was 50 °C (hold2 min), 50–200 °C at 10 °C/min (hold 1 min), and200–300 °C at 5 °C/min (hold 8 min). The detector wasrun in electron impact mode with electron energy of 70eV and ion source temperature of 230 °C. Helium at aconstant flow rate of 1 mL/min was used as carrier gas.PAHs were monitored using selected ion monitoring(SIM) mode. The standard of the 16 PAHs was pur-chased as a mixture of solution (mix 610-M) from Su-pelco, USA. The mass of PAHs was quantified using aminimum six-point external calibration curve withminimum correlation coefficients of more than 0.995over the course of experiments. The remarks givenabove for uncertainty hold also true for PAH measure-ments.
Quality AssuranceThe XAD-2 adsorbents, after being successively dried inan oven at 350 °C and in a desiccator for 48 hr, weresubjected to the sequential processing steps of extract-ing, concentrating, further concentrating, and analyz-ing. These sequential processing steps were also appliedto the used (sampled) adsorbents to measure the back-ground content of native PAHs in adsorbents. All of the
Table 2. Instruments used in the study and their characteristics.
ParametersDetection
Mechanism Range
MinimumDetection
Limit
CO2 NDIR �0–5000 ppm 1 ppmCO Electrochemical �0–500 ppm 0.1 ppmHCHO Electrochemical �0–10 ppm 0.01 ppmPM10 Light scatterring �0.001–100 mg/m3 1 �g/m3
PM2.5 Light scatterring �0.001–100 mg/m3 1 �g/m3
Notes: NDIR � nondispersive infrared sensor.
Figure 1. Sampling night markets and corresponding monitoringstations.
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background PAH concentrations in the blank tests werebelow the detection limit and deemed as zero. To ob-tain a general idea of the extent of PAH loss during theprocessing steps, an aliquot of a l-mL PAH standardmixture was spiked into the Soxhelt extractor, pro-cessed, and analyzed. The standard mixture containedthree components as follows: naphthalene (Nap; tworings), acenaphthene (Ace; three rings), and pyrene(Pyr; four rings). The average recovery percentages, ob-tained in triplicate, were 82 � 4%, 89 � 3%, and 95 �2% for Nap, Ace, and Pyr, respectively.
RESULTS AND DISCUSSIONConcentrations of CO2, CO, HCHO, and PM
The statistical summaries for the concentrations of thestudied air pollutants in night markets are shown inTable 3. Table 4 shows the outdoor and indoor airquality objectives currently used in Taiwan and theUnited States. Statistical results generally demonstratethat the concentrations of all measured air pollutantswith the exception of HCHO were significantly greaterduring open hours than those during the non-openhour period at fixed and moving sites (all P � 0.001).The average HCHO concentrations at fixed and movingsites in night markets ranged from nondetectable (ND)to 0.05 parts per million (ppm) during non-open hoursand from 0.02 to 0.27 ppm during open hours. Theaverage HCHO levels at hot-pot stall F1, barbecue stall
F3, and hot-pot stall F4 were above Taiwan (TW) andU.S. Environmental Protection Agency (EPA) 1-hr aver-age indoor standards of 0.1 ppm and 20 �g/m3, respec-tively. Again, it was shown that the mean HCHO levelsat all of the surveyed fixed and moving sites in nightmarkets were greater during open hours than thoseduring non-open hours.
The average CO2 concentrations at fixed and mov-ing sites ranged from 326 to 427 ppm during non-openhours and from 433 to 916 ppm during open hours. Thereported lowest concentrations of CO2 (320 and 326ppm) are approximately 8% below that expected for thebackground atmospheric concentrations in the Pacificatmosphere (347 ppm currently, plus or minus a couplefor seasonal changes), and even corrections for RHwould only account for a 3% difference. These lowestvalues seem too low. The reason might come from thefact that Q-trak may underestimate the real CO2 con-centrations. In addition, the mean CO2 levels duringopen hours were lower than what were measured insideof restaurants.4 In addition to the uncertainty fromQ-trak, another reason is probably that most stalls atnight markets are open-courted with natural ventila-tion. Among all fixed and moving sites, the mean CO2
level at barbecue stall F3 was the highest at 916 ppm,which was above the EPA 8-hr average indoor standardof 800 ppm. This shows that inadequate ventilation canoccur in occupied stalls at night markets, althoughmost stalls are open-courted, and that customers and
Table 3. Statistical summary of target air pollutants identified in different types of restaurants.
TargetPollutanta
Fixed Moving
Open Non-OpenTwo-Tailed
Test P-Value
Open Non-OpenTwo-Tailed
Test P-ValueMeanb SD Range Mean SD Range Mean SD Range Mean SD Range
Night market 1CO2 480 38 599–412 347 6 361–336 �0.001 439 40 560–362 326 4 346–320 �0.001CO 3.6 2.2 10–0.9 0.3 0.2 1.2–0.1 �0.001 2.6 2.3 9.6–0.2 0.2 0.1 0.5–0.1 �0.001PM10 227 58 428–176 133 15 146–98 �0.001 273 64.6 516–172 111 5.35 133–105 �0.001PM2.5 214 43 414–168 108 13 159–107 �0.001 252 30.0 280–180 89.0 4.94 119–99.0 �0.001HCHO 0.12 0.07 0.19–0.04 ND ND ND NA 0.07 0.08 0.20–0.02 ND ND ND NA
Night market 2CO2 479 32 630–450 365 21 433–336 �0.001 464 25 558–429 427 96 734–352 �0.001CO 3.9 4.0 31–1.5 0.8 0.9 6.4–0.2 �0.001 3.3 4.1 32–1.1 1.0 2.4 18–0.1 �0.001PM10 211 67 483–156 143 12 155–119 �0.001 186 16 230–158 125 12 150–101 �0.001PM2.5 202 40 299–127 117 19 185–118 �0.001 175 33 270–143 100 13 148–94 �0.001HCHO 0.04 0.02 0.08–0.02 0.02 0.01 0.03–0.01 0.105 0.04 0.03 0.10–0.02 0.03 0.02 0.04–0.01 0.277
Night market 3CO2 916 92 1205–758 375 10 430–365 �0.001 433 26 559–398 383 17 437–359 �0.001CO 14.1 7.9 52–3.6 1.1 0.4 2.3–0.6 �0.001 2.1 2.0 7.5–0.1 0.6 0.2 1.3–0.2 �0.001PM10 451 200 1030–225 231 17.0 278–208 �0.001 224 124 824–142 157 16.0 200–142 �0.001PM2.5 418 170 920–222 190 11.2 225–189 �0.001 206 33.4 316–125 129 5.27 153–131 �0.001HCHO 0.27 0.17 0.56–0.16 ND ND ND NA 0.02 0.01 0.04–0 ND ND 0–0.1 NA
Night market 4CO2 484 24 557–440 397 15 440–369 �0.001 555 92 929–461 423 91 734–360 �0.001CO 10.6 4.3 26.6–4.4 3.5 1.9 9.8–1.2 �0.001 6.0 3.8 19–2.1 2.8 1.7 8.7–0.5 �0.001PM10 309 191 1177–168 210 18 274–190 �0.001 304 63 530–225 171 33 247–119 �0.001PM2.5 284 198 1055–150 177 34 254–130 �0.001 275 47 422–202 138 28 217–94 �0.001HCHO 0.12 0.05 0.18–0.06 0.05 0.03 0.08–0.02 0.035 0.13 0.07 0.21–0.05 0.02 0.01 0.03–0.01 0.021
Notes: aUnits: CO2 � ppm, CO � ppm, PM10 and PM2.5 � �g/m3, HCHO � ppm. bMean � average concentrations over 1-hr sampling period. NA � not available.
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workers can sometimes be exposed to an insufficientsupply of fresh air.
The average CO concentrations at fixed and mov-ing sites ranged from 0.2 to 2.8 ppm during non-openhours and from 2.1 to 14.1 ppm during open hours. Theaverage CO levels at barbecue stall F3 and hot-pot stallF4 were above the TW and EPA 8-hr average indoor andoutdoor standard of 9 ppm. There were a few minuteswhen the CO level was even at 52 ppm in barbecue stallF3. This high level of CO was above the TW 1-hr aver-age outdoor standard of 35 ppm. This result shows thatthe CO levels at all of the surveyed fixed and movingsites were significantly higher during open hours thanthose during non-open hours (P � 0.001). In addition,the mean CO concentrations at moving sites duringopen hours were 4–8 times greater than those measuredat the corresponding ambient monitoring stations (Fig-ure 2). This indicates that cooking can be a dominantCO source at night markets. It was noted that in Figure2 the mean CO concentrations at moving sites duringnon-open hours was up to 3.5 times greater than thosemeasured at corresponding monitoring stations exceptfor the concentration at M1. It seems that the air pol-lutants at night markets were so concentrated duringopen-hour periods that they did not decrease to ambi-ent levels during non-open time.
Airborne particulate is one of the major pollutantsgenerated by cooking. In this study, mass concentra-tions of PM10 and PM2.5 were measured at fixed andmoving sites in night markets during open and non-open time periods. The average 1-hr levels of PM10 atfixed and moving sites in night markets ranged from111 to 231 �g/m3 during non-open hours and from 186to 451 �g/m3 during open hours. The average 1-hrlevels of PM2.5 at fixed and moving sites in night mar-kets ranged from 89 to 190 �g/m3 during non-openhours and from 175 to 418 �g/m3 during open hours.The highest levels of PM10 and PM2.5 during open hourswere observed at barbecue stall F3. The levels of PM10
and PM2.5 were TW and EPA indoor and outdoor stan-dards. Levels of PM10 and PM2.5 at all of the surveyedfixed and moving sites in night markets were signifi-cantly higher during open hours than those duringnon-open hours (all P � 0.001). Table 5 illustrates thatthe mean concentration ratio of PM2.5 to PM10 at fixedand moving sites in night markets ranged from 80 to84% during non-open hours and from 90 to 96% duringopen hours. In addition, the mean PM10 concentrationsat moving sites during open and non-open hours weregreater than those measured at the corresponding am-bient monitoring stations (Figure 3). A study on PM2.5
and PM10 ambient levels was conducted in urban areasof Taiwan.23 Their results demonstrated that the PM10
and PM2.5 mass concentrations in Kaohsiung were77.10 and 48.47 �g/m3, respectively, similar to thevalues reported at ambient monitoring stations, whichwere lower than those measured at night markets inthis study. They also found that the PM2.5 fraction ofPM10 accounted for only 67% of the total PM10, muchlower than the PM2.5 fraction of PM10 in this study.Therefore, cooking was most likely the dominantPM source in night markets because no cigarette smok-ing was found and no vehicle was allowed inside ofall of the night markets except N4. Thus, the meanPM10 emissions at night markets were much higherthan ambient and largely composed of PM2.5, whichwas presumably generated by cooking activities at nightmarkets. Researchers found that each 10-�g/m3 in-crease in PM2.5 air pollution was associated with an
Table 4. Outdoor and indoor air quality objectives currently used in Taiwan and the United States.
Pollutants
Outdoor Indoor
TW EPA TW EPA
CO2 NA NA NA NA 8-hr 600 ppm �800 ppmNA NA NA NA 1000 ppm –
CO 8-hr 9 ppm 8-hr 9 ppm 8-hr 2 ppm �9 ppm1-hr 35 ppm 1-hr 35 ppm 9 ppm –
PM10 Daily 125 �g/m3 24-hr 150 �g/m3 24-hr 60 �g/m3 �20 �g/m3
Annual 65 �g/m3 150 �g/m3 –PM2.5 NA NA Annual 15.0 �g/m3 24-hr 100 �g/m3 –
NA NA 24-h 35 �g/m3
HCHO NA NA NA NA 1-hr 0.1 ppm �20 �g/m3
NA NA NA NATVOC NA NA NA NA 1-hr 3 ppm �200 �g/m3
NA NA NA NA
0
2
4
6
8
10
12
1 2 3 4
CO
Con
cent
ratio
ns (p
pm).
Moving Sites
Open
Non-open
Monitoring Station
Figure 2. Comparison of CO concentrations between moving sitesof the four night markets during open and non-open hour periods andthe corresponding monitoring stations.
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approximately 4, 6, and 8% increased risk of all-cause,cardiopulmonary, and lung cancer mortality, respec-tively.24 This indicates that people who work atnight markets may be exposed to a higher level ofhealth risk if this pollution condition is a long-termphenomenon.
Concentrations and Sources of PAHsThe quality of air at night markets was partially charac-terized by measuring concentrations of PAHs in the gasphase. Sixteen PAHs were detected in all of the samples inthe gas phase for two- to six-ring PAHs (Table 6). Theconcentration of individual compounds was found in therange of 0.09 � 104 to 1.8 � 104 ng/m3. The total iden-tified PAHs (TIPs) ranged from 7.8 � 101 to 20 � 101
ng/m3 during the non-open hour period and from 1.5 �104 to 4.0 �104 ng/m3 during the open period. High PAHconcentrations in night markets could be caused by cook-ing operations, vehicle emissions, traffic flow, and mete-orological factors such as lower mixing layer height, lowwind speed, scant rainfall, and so on. However, except forthe night market N4, no vehicles were allowed inside ofall of the night markets, and there was no obvious changein meteorology between the time period of open-hoursampling and the period of non-open-hour sampling ateach night market. Therefore it seems likely that combus-tion due to cooking is the main cause for the largeamount of PAHs. As mentioned above, the wind speedduring the non-cooking hours was larger than that duringthe cooking hours. In addition, researchers reported thatmixing height usually rises from 200 m at 2:00 a.m. to
Table 5. Average concentrations of PM2.5/PM10 ratio at fixed and movingsites for open and non-open periods.
PM2.5/PM10
Fixed Moving
Open Non-Open Open Non-Open
N1 0.94 0.81 0.92 0.80N2 0.96 0.82 0.94 0.80N3 0.93 0.82 0.92 0.82N4 0.92 0.84 0.90 0.81
Tabl
e6.
Conc
entr
atio
nsof
16ga
s-ph
ase
PAHs
atfo
urni
ght
mar
kets
inKa
ohsi
ung.
PAHs
(ng/
m3 )
FB1
FB2
FB3
FB4
F1F2
F3F4
MB1
MB2
MB3
MB4
M1
M2
M3
M4
Nap
6251
5659
4.5
�10
34.
7�
103
4.6
�10
34.
6�
103
3839
2149
4.6
�10
38.
0�
103
4.7
�10
34.
2�
103
Acy
6449
3449
3.8
�10
32.
6�
103
3.2
�10
32.
2�
103
4733
2753
3.5
�10
32.
9�
103
2.6
�10
32.
3�
103
Ace
3430
3233
2.1
�10
31.
7�
103
1.9
�10
31.
4�
103
2118
1126
1.1
�10
39.
9�
102
1.7
�10
31.
6�
103
Flu
6.1
5.0
5.6
4.9
1.1
�10
36.
8�
102
9.1
�10
28.
0�
102
3.7
3.9
2.5
5.1
1.0
�10
32.
6�
102
8.6
�10
29.
3�
102
Phe
7.0
6.3
3.9
5.5
7.4
�10
29.
5�
102
8.4
�10
29.
0�
102
4.4
3.2
2.1
4.8
4.0
�10
26.
6�
102
9.9
�10
25.
0�
102
Ant
3.9
3.4
3.7
3.8
4.6
�10
28.
0�
102
6.3
�10
27.
2�
102
2.4
2.5
2.8
3.9
8.4
�10
21.
5�
103
7.8
�10
24.
1�
102
Flt
2020
1618
9.6
�10
28.
0�
102
5.8
�10
39.
5�
103
1312
9.5
175.
3�
102
9.9
�10
29.
5�
102
1.3
�10
4
Pyr
1.5
1.1
0.97
1.2
6.9
�10
36.
8�
103
1.8
�10
42.
7�
103
0.87
0.47
0.78
1.06
3.4
�10
32.
3�
103
2.8
�10
31.
6�
104
BaA
0.58
0.49
0.54
0.56
1713
1514
0.36
0.33
0.27
0.48
1413
1411
Chr
0.70
0.52
0.38
0.54
1614
1514
0.41
0.36
0.21
0.49
1414
1414
BaF
0.60
0.28
0.44
0.52
1813
1514
0.29
0.35
0.24
0.44
1414
1413
BaF
0.71
0.43
0.16
0.44
9.1
6.6
6.4
7.3
0.38
0.29
0.38
0.52
6.7
6.5
6.9
9.2
BaP
0.73
0.39
0.46
0.59
5.3
2.5
1.3
3.6
0.31
0.40
0.25
0.48
2.5
1.9
3.1
2.7
DBA
0.63
0.46
0.54
0.59
147.
68.
710
0.36
0.39
0.20
0.48
8.9
8.2
8.9
9.9
Bghi
P0.
470.
350.
230.
3512
9.9
10.4
910
0.27
0.24
0.14
0.32
1010
1012
Ind
0.26
0.24
0.25
0.26
1711
1313
0.21
0.17
0.09
0.23
1312
1211
TIPs
2.0
�10
21.
7�
102
1.6
�10
21.
8�
102
2.1
�10
41.
9�
104
3.6
�10
42.
3�
104
1.3
�10
21.
2�
102
7.8
�10
11.
6�
102
1.5
�10
41.
8�
104
1.5
�10
44.
0�
104
Not
es:
FB�
fixed
site
back
grou
nd,
MB
�m
ovin
gsi
teba
ckgr
ound
durin
gno
n-op
entim
epe
riod,
Acy
�ac
enap
hthy
lene
,Fl
u�
fluor
ene,
BaF
�be
nzo�
aflu
oran
then
e,Bk
F�
benz
o�k
fluor
anth
ene.
Figure 3. Comparison of PM10 concentrations between movingsites of the four night markets during open and non-open hourperiods and the corresponding monitoring stations.
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1400 m at 7:00 p.m., then starts to decrease after 8:00p.m.25 Thus, low wind speed and mixing height may alsocontribute to the high PAH concentrations during cook-ing hours.
In this study of night markets, total PAH levels wereespecially high at barbecue stall F3 compared with theother three fixed sites during the open time period, sim-ilar to what was observed previously in terms of CO, PM,and HCHO concentrations. Thus, barbecue operationscaused the most air pollution among all cooking methodsin night markets. The total PAH concentrations weregreater at fixed sites than at moving sites during theopen-hour period except for the M4 site, which allowsvehicles to enter. Alcohol was the cooking fuel at the F3fixed site, which led to a low emission of pollutants,including PAHs. The fact that the PAH concentrations atF4 were lower than those at M4 was probably because ofthe low-pollution fuel that was used in the fixed site of F4rather than vehicle emissions.
Table 7 provides information on diagnostic ratios forPAHs, including phenanthracene (Phe)/Phe anthracene(Ant), fluoranthene (Flt)/Flt Pyr, BaA/BaA chrysene(Chr), and indeno[1,2,3-cd]pyrene (Ind)/Ind benzo-[g,h,i]perylene (BghiP), which can be used to investigatetheir origin or the age of the air samples.26,27 These datacan help to fully estimate the contribution of anthropo-genic emissions. All of the diagnostic ratios fall within therange of those found in other studies,28,29 confirming thatthe PAHs measured in the night markets originated fromcombustion due to cooking.
Although the PAH concentrations are reported asgas phase, the XAD-2 filters would efficiently collect gasand aerosol components.30 A comparison of the PAHconcentrations (totaling 20–40 �g/m3) with the PM2.5
concentrations (175–275 �g/m3) when the markets areopen indicates that the PM2.5 is highly enriched inPAHs. However, this may be an artifact of the measure-ment method of the PM2.5—optical scattering, whichfavors white solids and liquid phases over black partic-ulate or soot components. The portable Dust-Trak airmonitors are probably underestimating the PM concen-trations as a result of this bias.
PAH contents were further sorted into five catego-ries according to the number of rings that they have:two-, three-, four-, five-, and six-ringed PAHs. Theirdistributions are shown in Figure 4. Of the total ana-lyzed PAHs, the low-molecular-weight PAHs (two tothree rings) were the dominant species, correspondingto an average of 97% during the non-open period and
88% during the open period, whereas high-molecular-weight PAHs (four to six rings) represented 3 and 12%of the total detected PAHs in the gas phase during thenon-open and open period, respectively. Low-molecu-lar-weight PAHs tend to stay in the gas phase relative tothe high-molecular-weight PAHs, which contain fourrings or more. This finding is significant because theselighter gas-phase PAHs, the most abundant type in theatmosphere at night markets, can react with other pol-lutants to form more toxic derivatives although theyhave weaker carcinogenic/mutagenic properties.16,31 Itis well known that most of the heavier PAHs, which hadlower levels than the lighter PAHs in the gas phase,tend to stay in the particulate phase. During openhours, total PAHs increased and the contribution offour-ringed PAHs increased dramatically relative toother PAHs. This phenomenon was observed at fixedand moving sites in all night markets. The reason is notquite clear; however, it was suspected that the increasein contribution from four-ringed PAHs might comefrom more generation by cooking operations, frommore partition in the gas phase than the particulatephase, or both.
CONCLUSIONSIn conclusion, the highest concentrations of air pollut-ants were found near barbecue stalls in night markets.Results showed that the CO2 levels in night marketswere lower than what were measured inside of restau-rants and did not exceed limit values. The levels of COand HCHO exceeded TW and EPA standards at someselected stalls in night markets. In the studied nightmarkets, the PM10 and PM2.5 exceeded all TW and EPArecommended limit values and are likely to cause ad-verse health effects. In addition, the results showed thatover 80% of the PM10 measured in night markets werePM2.5. The average concentration of individual PAHswas found in the range of 0.09 � 104 to 1.8 � 104
ng/m3. TIPs ranged from 7.8 � 101 to 20 � 101 ng/m3
during non-open hours and from 1.5 � 104 to 4.0 � 104
ng/m3 during open hours. Of the total analyzed PAHs,the low-molecular-weight PAHs (two to three rings)were the dominant species, corresponding to an aver-age of 97% during non-open hours and 88% duringopen hours. High-molecular-weight PAHs (four to sixrings) represented 3 and 12% of the total detected PAHsin the gas phase during non-open and open hours,respectively. More research efforts are thus needed tofurther characterize the PAHs in the particulate phase,as well as better pinpoint the major emission sources of
Table 7. Molecular diagnostic ratios of gas-phase PAHs.
Diagnostic Ratios F1 F2 F3 F4 M1 M2 M3 M4
Phe/Phe Ant 0.62 0.54 0.57 0.56 0.32 0.31 0.56 0.55Flt/Flt Pyr 0.12 0.11 0.24 0.78 0.14 0.31 0.25 0.45BaA/BaA Chr 0.51 0.49 0.50 0.50 0.50 0.46 0.50 0.45Ind/Ind BghiP 0.37 0.28 0.17 0.33 0.27 0.23 0.31 0.23
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the PM and the PAHs to facilitate formulation of acontrol strategy and regulations for night markets inTaiwan.
ACKNOWLEDGMENTSThis study was funded by the National Science Council(NSC) of the Republic of China, Taiwan, under contractNSC 96-2218-E-390-003. The authors are grateful to NSCfor the financial support provided for the pursuit of thisproject.
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Figure 4. PAH distributions for samples collected at night markets in Kaohsiung. PAH distributions at fixed sites during (a) non-open and (b)open hours. PAH distributions at moving sites during (c) non-open and (d) open hours.
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26. Cotham, W.E.; Bidleman, T.F. Polycyclic Aromatic Hydrocarbonsand Polychlorinated Biphenyls in Air at an Urban and a Rural Sitenear Lake Michigan; Environ. Sci. Technol. 1995, 29, 2782-2789.
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Gas-Phase Polycyclic Aromatic Hydrocarbons to the Front Filter; En-viron. Sci. Technol. 1994, 28, 655-661.
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About the AuthorsPing Zhao is a postdoctoral fellow in the Department ofMarine Environmental Engineering at National KaohsiungMarine University. Chi-Chi Lin is an assistant professor inthe Department of Civil and Environmental Engineering atthe National University of Kaohsiung. Please address cor-respondence to: Chi-Chi Lin, Department of Civil and En-vironmental Engineering, National University of Kaohsiung,No. 700, Kaohsiung University Road, Kaohsiung, Taiwan;phone: 886-7-591-9718; fax: 886-7-591-9376; e-mail:[email protected].
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