Spectroscopic investigations of aerosol graphitic carbon

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SPECTROSCOPIC INVESTIGATIONS OF

AEROSOL GRAPHITIC CARBON

by

Charles Raymond McLaine

A Thesis: Submitted to the Faculty of the

DEPARTMENT OF CHEMISTRY

In Partial Fulfillment o f the Requirements For the. Degree of

MASTER OF SCIENCE

In the Graduate Col 1ege

THE UNIVERSITY OF ARIZONA

1 9 8 0

STATEMENT BY AUTHOR

This thesis has been submitted in partial fu lf i l lm en t of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In a ll other instances, however, permission must be obtained from the author.

SIGNED: Q .

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

1 y * T * """ . . S. V ? ' I f ' , f ■ 'Jarvis L. Mayer.s, Director, Analytical Center

Chemistry

ACKNOWLEDGMENTS.

I am indebted to Dr. Jarvis L. Moyers for the use of the

University Analytical Center fa c ilit ie s , project support, and his

expediency in reading and suggesting minor modifications to the

manuscript.

As a; representative of The Arizona Carbon Film Company,

Dr. John 0. Stoner, Jr. provided the carbon film standards used in

calibrating the transmittance and photoacoustic spectrometers'.

Michael R. Jacobson provided the use of an integrating

Spheres reflectance: spectrometer and was qui te helpful in the

interpretation o f optical phenomena for diffusely reflecting

materials..

My deepest gratitude extends to my typist, illu s tra to r,

and wife, Joan. Her encouragement, and artis tic ab ilities are

greatly appreciated.

TABLE OF CONTENTS

LIST OF- ILLUSTRATIONS «.. . . . . . .. ... . .. . ... ... . . . ... . vi;

LIST OE TABLES ... . .. . . ... ... . « . . .- .- . . . . . . . © ... « .. ®. vt "i "i

ABSTRACT ... . . .. ... ... ..... . . . «=. *... ... ... . . ... ... ... ... ... ©. ... .. .. ©. . i

I '.. INTRODUGTION. ..... . . *. ..... *. .... «... .... ... ... .... .. .. «. . .. ... ©. .. © ... .. T

1.1. Graphi tic: AerasoT Cycle .- . . . . . . ... ., .. . . 2

T. ©-I ■..T.... Sources . . *.. ». .. * » . ... .' 1.. ... . ... ... *. . . 2̂

T..T.2L Sooty Aerosol Influences .. . . ̂ ̂ . . . . . 5'

T.T.Tl AerosoT Sinks . .. ... . . . . .. . . . .. .: .* . .. g

, T.2. Chemical and Physical Properties of Soot . . . . . . . I T

2T SPECTROSCOPIC TECHNIQUES;; . . . . . . .. . . .. . ... . . .. . 16 T

2.1. Evaluation of Sel ected Techniques . . ̂ ̂ . T6i

2 .2 .: Characteristics of Photoacoustic. Spectroscop f̂ .. ...... .. ... .. ... . ... . ... ... ... .. .... «.. ....... * .. . ig■

3v INSTRUMENTATION . . ; . .. .v.. :.v .. 24 .:

3 . 1 AerosoT Collection and Sample Preparation .. . . . . .. . 24

3.2. Transmittance Instrumentation: . . . . . .. .. . . .. ... . 25

3.3. Ref 1 ectance Instrumentation . ... ... . . ... . . . . . . . . . . 32

3.4. Photoacoustic Spectrometer . . . . . . . . . . .. . ... ... 32

3.4oTi SignaT Trocessingi CircuTts ; . . ; .. .. . . . 32

; 3.4.2, Sampler Cell . ̂ . > v TV.;-.. .. ... .. 41

3.4.3. In itia l Calibrations and DeviceLi mi ta 110ns ..... . .. ....... © « .. « . .. . . «... .' . . 41

3.5. Standard Calibrations . . . . . . . . . . . . . . . 5T ; r;

TABLE OF CONTENTS—Conti nued

Page:

4, EXPERIMENTS WITH FILTER SAMPLES: . . .. ... . .. .. .. 56:

4.1. Evaluation of Reference F ilte r Properties^ . . . . . . . §§

■ 4.2. Spectroscopic Sample Studies . .. . . . .. ... ... . . ... . . gT

4i.2;lv Optimum Wavelength Range for Analysis . . . . . 68

4.2.2:. Gbmparisons; of Techniques .. . . . . . . . . . . .. ... 68

4.3. Correlations of PAS and Absorbance withTotal . Carbon ... ... .... . .. .. ... .. .. .....©. ..... ... . ... . . ... .. . .. T3

4.4.. Additional CorreTations for MissouTa Samples ̂ . .. . .. ̂ 80

5v CONCLUSIONS AND SUGGESTIONS: . . ... ... .. . . .. ... . .. . . . . .. 86

5:.T. Summary of Conclusions „ ̂ . .. . .. .. .: ., ,, . . ... 86

.5..2-.... . Suggestins^".. ...... ... ■ . ... — .. ...—.—-■........— . .... ... .. . —........ . . . . .

APPENDIX A: METHODS FOR CALCULATIONS ; .: . .1 . . . 89

Ail ., Single Point Calculations . .. .. . .. . .. . . . . . . . .. . 89

A.2.. Curve Fitting Calculations . . . . . . . . . . . . . . . 90

REFERENCES. . . . ... @i -..... •., .... ... .. «... .. . .....«...'- . . « . ». ... .... ... ... ... 91

LIST OF ILLUSTRATIONS'

Figure Page

3.1. Cross Section of Sample, Chamber for Gilford 240 ... r - ... .. 26r

3.2. Comparison of F ilter Cuvettes . ... . . . . . . . . . . . . ... 28

3.3. Cuvette Orientations ... . . . . . .. . . . . ... . . ... . ► 29

3.4. Block Diagram of the Constructed Single-BeamPhotoacoustic: Spectrometer System . . . .. . . . .. ̂ ... .. ... 31

3.5. Reference Detector and Associated Waveforms . „ ... . . . . . 34

3.6. Phase Adjustment Device .. . . . . . . ̂ . .:. . — . .. . . 35

317. Voltage-tb-Frequency-Transducer Circuit . . . ., .. . . . . 36

3.8. Gated Frequency Counter . . . . . . .. . .. . .. .. . .. . . .. 38

3.9. Timing Diagram for Frequency Counter . . . . . .. . . . 39

3.10. Frequency Multiplier . . . . . . . . . ... . . ., . . ... . . 40

3.11. Cutaway View of Photoacoustic Cell. . . . . . . . ... .. . ., 42

3.12. Reference Frequency Generator and Associated’Waveforms... *. ... . . . ... . ... . ... . . ... . .. ... « ... . * . . . 44. ■

3.13. Precision Full-Wave: Rectifier . . .. . . ., . .. . . . . . . 45

3..14. PAS Response as a Function of Sample Cell Volume ... .... ... 47

3.15. PAS’ Response as a Function of Source Voltage >' . .. . . 48

3.16. PAS Response as a Function of Chopping Frequency . . . . 50

3.17. Calibration Curves for PAS and Gilford 240 . . . . . .. . 54

4.1. Experimental Configurations for ISR Study o fQuartz Blanks ... ... . . * ». . .. . ... . . . .. -... .. . .= ». . . « . 57.

4.2. Absorbance. Spectra for Dl -UAC-61 Samples 1. . / . .: .. . . 69

4.3v Reflectance Spectra for D1-UAC--61 Sampl es . . .. . . . > 70

list: of ILLUSTRATIONS—Continued:

Figure

4.4.. Photoacoustic Signal Versus Absorbance(Missoula Samples*) .. «. . ... . . * . .. .. .. .. .. . .... .

4.5.. Estimate; of Total Carbon as a Function of PASRes po ns e.* . . .. . . . . . ... .. . . .. . . . «...

4.6. Estimate of Total Carbon as a Function Of Absorbance ,

4 . 7 Estimate of Total Sulfate as a Function of PASResponse. .. .- . .. .. .. • . .. . . .. ... .. .. ■.. . .. .. ... .... ...

4.8.. Estimate of Total Sulfate as a Function of Absorbance

4.9. Estimate-of TbtaT Ni trate: as a Function of PASResponse .. .. .. . . .. .. ... .. ... ... . ». . ., ... .. ... . . .. .. «.

4.10. Estimate of Total Ni trate; as a Function of Absorbance

vii.

Page;

, . 72-

. 75

, .. 76

„ . 82

^ 83

, ..' 84

i- « 85

LIST OF TABLES

TabT& Page;

3.1. Absorbance as a Function of Orientation ofStraight-Channeled CeTT and Sample; . . . „ . .. . . . . . . 30

3.2. Absorbance as a Function of Orientation ofAnnular-Channeled Cell and Sample . . . . . . . . . 30

3.3. Voltage-to-Frequency- Transducer Responsê ► . . .. . . . ... ... 46

3.4. Carbon Film Measurements and. Calculated: Responses . . . 52!

4.1. Reflectance Measurements on a Quartz Blank . . . 58!

4.2. Comparison of Reference Blanks- ... .. ... . ... . . . . .. .. . . ... GO

4v3. Comparison of Absorbance and Reflectance Values ... . . . .. 62

4-.4".. Missoula.; Sample Data «. «. . . ®. . . . . . •. . ... « , «. .. 63

4.5. Research Triangle Park Sample Data . . , .. .. . . • - • • - 65

4.6. Tucson Sample Responses . . . . ... .. . ... .. . .. . . . ... . . 65

4.7. Betatakin Sample Responses; .. . .. . . . . .. . . . . ... .. ... .. 66!

4.8. Black Mesa Sample- Responses . . . . . ... . . . . . . . . ... . 67!

4.9. Estimate of Graphitic. Carbon Contents . . . . . . . . . . . 78

4.10. Correlations for Missoula Samples . ... . ... ... . . . ... . . 81

ABSTRACT'

Spectroscopic determinations of aerosol sooty carbon concentra

tions on diffusely reflecting filte rs are described. Since graphitic

species possess larger imaginary indices of refraction, they are

expected to dominate:observed absorbances for collected aerosols unless

less absorbing species;, are present in high; concentrations. Transmit

tance,. refTectance, and: photoacoustic spectroscopy (PAS) techniques

provide absorbance data, but only PAS is exclusively responsive; to

sample; absorbance; Therefore, PAS is: proposed as a viable, and

superior, technique for the quantitation of graphitic aerosol species..

Photoacoustic, determinations of the percentage of graphitic ,

aerosols; with respect toe total carbon generally agreed wi th publ ished;

results which required solvent: extractions. Approximately 20 to 100

percent of the collected carbon: appeared; to be graphitic. Visible

light transmittance spectroscopy overestimated thespercentage of

graphitic: aerosols, and results indicated an apparent 60 to 240 percent

of the carbonaceous fraction-was graphitic.

The construction, calibration, and limitations of a simple

photoacoustic spectrometer is also discussed..

CHAPTER 1

INTRODUCTION:

Atmospheric; particulates; are: often physically and chemicaTfy

complex and result from a wide variety; of sources. Oceanic aerosols are;

rich in salts and; Nemeriuk (1970) found; that transpiration: also intro

duces; salt; particles into the atmosphere, Curtin, King, and Hosier (1974)

found; that conifer trees can emit at least 27 trace metals probably in

the form of metal -rr-complexes with terpenes:. Linton et aT. (1976) found

that fossil fuel emissions contain several trace metals, and Pierson and

RusselT (1979) correlated:: lead: with;carbon and suggested that burning

leaded:fuels provided a probable common source, Rasmussen and Went

(1965) and Went, STemmons,; and; Moringo: (1967) found: that plant emissions;

such as aromatic and terpene compounds; are likely to oxidize and form

aerosol particles, and olefin vapors in general are expected to condense

into nuclei mode aerosols (approximately 0,005 to 0,05 ym) or onto

existing particl es (Wi 11 eke and; Whitby; 1975% Schnel 1 and Vali (1972,

1973) found that decomposing vegetation apparently produces atmospheric

ice nuclei, and Rosen and Novakov (1978) noted that vehicular exhausts

contain large quantities of nuclei mode: particles.

Several types of carbonaceous aerosols have been determined.

Gundel et a l . (1978), Appel et a l , (1979) and Pierson and Russell (1979)

separated organic and elemental species, but the elemental determinations

1

included carbonates which could not be extracted, by the employed solvent.

Rosen and Novakov (1978) and? Rosen et a l. (1980) identified soot as the

optically absorbing, component of urban aerosols, and Ember (1979) stated

that graphitic species are highly absorbing with ligh t. Went: et a l .

(1967) noted, that carbon black could be collected in remote areas where

vegetation, activity dominates over human contributions.. Atmospheric:

elemental carbon,, graphitic aerosols, or sooty aerosols appear ubiqui

tous, and determinations o f their properties and quantitation could

provi de information on such topics as: the formation of sol fates, and

nitrates in urban atmospheres and the long range v is ib ility o f various

regions..

1.1. Graphitic Aerosol Cycle

L .T .I. Sources'

Authorities generally agree on the. origins of graphitic aerosols.

Anthropogenic and much of the naturally produced soot originates from:

incomplete combustion of hydrocarbons ranging in complexity from methane

to long-chained hydrocarbons. Rosen, Hansen, and Novakov (1977) stated

that primary emission sources produce large quantities of graphitic

particles, and the typical particle size is indicative of the source.

Several laboratory studies o f soot production exist. Turk et

al. (1974) cite the familiar luminous flame associated with burning

paraffin, gasoline, and paper as evidence of graphitic particle forma

tion. The flame heats the freshly formed carbon particulates which

causes the characteristic yellow luminescence of most flames. Wersburg,

Fox5- and: Howard (1975) studied soot formation in a fuel-rich flame and

found, large hydrocarbon molecules ranging in weight from a few hundred

to a few thousand amu. In a, study of a ir-acetylene flame products,,

Toossi (1978) found a bimodel distribution o f particle* sizes, with the

greatest: numbers at 80 A and 500 and Dalzell and Sarofim (1969) found

particles, from 50: A to 800 A are readily produced by flames. Evidently,,

soot production is a natural consequence: o f fuel-rich combustion mixtures

im both laboratory and environmental situations.

Fuller (1974) estimated:: one-third of to ta l anthropogenic particu

lates, by mass originated: from power generating plants,, and ninety-six

percent of. the; T970 energy consumption* in power production- came from

burning; fossil fuels. Particulate matter produced in this operation is:

parti al ly preci pi tated, by use o f cyclone separa tors , wet scrubbers,

electrostatic precipitators,, and. f i lte rs . These devices: reduce emis

sions of particles larger than 0.1 micron but are ineffective in

removal of smaller particles, and the estimated contribution by parti

cles less than 0.1 micron amounts to 0.3 percent by weight and 88 per

cent by number of the; total particul ates produced in this process.

Open burning o f municipal refuse and vegetated areas provides

obvious particulate pollution. Gerstle and Kemnitz: (1967) listed

municipal refuse incineration as the source of about 16 pounds of particu

late matter per ton of material burned. Burning piles of leaves and .

twigs in many communities contributes about 17 pounds o f particles for

each tor burned. Additionally, the burning of automobile components'

such as: tires contributes an estimated 100 pounds of particulates per

ton, which translates to about 5 percent conversion of the original

materials to emitted: atmospheric particulates by weight. Since: the

burning fuel is high in carbon content, graphitic particulates are.

expected as products. Because of high local concentrations of these

emissions, many communities have outlawed the once common practice of

refuse burning.

Feldstein et a!. (1963) stated that grass and stubble fires

contribute to particulate; pollution. The forest service and some farm

ing communities of the western. United: States periodicalTy burn over

grown and: harvested areas. Through the confTagratiom o f underbrush and

fallen tree: matter, the forest service: actively controTs, the risk: of

extensive forest fires . Farmers of the Great Valley near Sacramento

and: those in the- drier parts of Oregon burn harvested fields to; rid:

their lands of the remaining:straw. Unfortunately, these practices add

large, localized quantities' of sooty particulates to the a ir .

Automobiles: emit large quantities of sooty aerosols. Fuller

(1974); estimated 108 particles are emi tted per second of vehicle opera

tion. Rosen and Novakov (1978) investigated;the particular emissions of

gasoline-powered automobiles and diesel-powered vehicles- Sooty aero

sols were found at the exhaust port as the major particulate:product

and ranged in size from about 50 A at the exhaust to typically 100 A

a short distance from this orfice. Fuel evaporation from the gas tank

or carburetor and untuned or decelerating vehicles unload uhburned■■■. ■ -■/ ■ ■ ■ ■ ■ ■■ ■■■ - ■

hydrocarbons into the atmosphere (Johnston et a l. 1973). These vapors

may then condense on existing graphitic; particulates, as Well as other

species, or they may photochenicany a ite r and form particulates

(Willeke and Whitby 1975).

Anpthe ̂ source: of graphitic aerosol s is the mechanical intro

duction) of sooty particles into; the a ir. Moyers (1979) listed; coal dust,

as: the contributor of 15 percent of the total suspended particulates

monitored; at; Black Mesa, Arizona. This; type of action normally results

in production of larger particulates, a few micrometers; in- diameter..

Although: this type of activity may be of l i t t l e significance on a^global

scale, ground; and suspended coal dust may be of high local significance.

1.J.21 Sooty Aerosol Influences:

Graphitic aerosols exert a wide range of influences. Particu

lates; alter weathen, long-range v is ib ility , population heal th,, and*

property . Additionally,, graphitic aerosols may catalytically convert

sulfur dioxide te sulfate products in the presence o f water and oxygen,

and:they may produce nitrates and:organic nitrogen products a ll of which

probably contribute to productibn of acid rain. Needless to say, none

o f these affects are desirable,, and? addi tional studies; in a ll o f the

cited areas are required fo r a more; thorough understanding of particulate

' influences.

Ember (1979) stated that carbonaceous soot absofbs:light very

eff iciently and an increase in hydrocarbon* emissions contributed to a

decrease in v is ib ility for the Southwest. Trijbnis and Yuan?(1977)

believed that aerosol scattering: dominated; Rayleigh scattering,, aerosol

absorption, and gas absorption terms, in scattering calculatibns for the

Southwest. Studies of Maricopa;County, Afi zona showed a O.81 correla

tion coefficient for scattering versus aerosol sulfate concentrations

and 0.71 for Scattering versus aerosol nitrate-concentrations.; About

' ■ ’ ■ ■ ’ : '■■ ■ ' ' ■ ■ ’ W; -8 percent of the Tight: scattering in Maricopa County and 10 percent: o f

the Tight scattering in Phoenix remained unexplained, by these authors;.

Light scattering and graphitic species would: have undoubtedly shown high

correlations and probably contributed to some of the: unaccounted: scat

tering, Perhaps, the association of sulfates and nitrates with sooty

aerosols. (Chang, and Novakov 1977; Brodzinsky et al . 1978) incorporated:

some of the graphitic aerosol contribution into the stated correlations;.

Those; particulates; which affect long-range; v is ib ility alsd:

influence meteorological phenomena, Moore and Moore (1976) declared

that: localized urban centers have: become heat islands with denser cloud

cover and more: rain,, snow, and fog than nearby nonurban regions, Chjflek

and Coakley (1974) found urban centers typical Ty possess: about three

times: the aerosol concentration as; nonurban centers. Corresponding:

urban light levels are lower, and precipitation and: fog markedly increase'

with higher particulate: concentrations. Particles with diameters from

about 0,1 to 1 ]M are efficient condensation sites and cause local

weather alterations, Changnon (1968) studied 1951 to 1965 regional

precipitation data and discovered 3.1 percent more precipitation,, 38 per

cent more thunderstorms and a 246 percent increase of hail incidents for

La Pbrte, Indiana: compared to neighboring rural areas, Robinson (1976)

pointed out that Changnon's paper met with great controversy, but

simi 1ar trends with other urban centers were reported. The particulates

in the urban and industrial areas may have; contributed to the reportedly

heightened, local condensations o f water, Additionally, Reck (1974)'

stated that the overall effect o f global heating or codling depends on

the extent which aerosols scatter light versus absorb 1i ght, However ,1

. . .. . ■ ; . .

at: this? time many authorities are uncertain of future trends; for the;

heat balance.

Catalytic phenomena are; associated: with graphitic: aerosols.

Chang and Novakov (1977) performed Raman studies for determination of

nitrogen species cataTytically produced by soot and found a wide variety

of inorganic and organic compounds in chemical forms; such as nitrates s,

cyanides, and; amines. Novakov et a l. (1974) in another study used

Nuchar, a commercial brand of activated.-' charcoal, to simulate1 atmo

spheric soot under laboratory conditions. They found; the rate of

sulfur dioxide conversion to sulfuric acid and; sulfates was proportional

to the amount of soot: present: when water, sulfur dioxide, and oxygen

are- not: limiting factors.. Although catalytic sulfur dioxide conversion

proceeds, about one: hundred times more rapidly with manganese(II); and.: ..

i r o n ( I I I ) , their atmospheric concentrations are several times less than

soot. Therefore, Novakov et a l. fe l t soot contributions to sulfate

production in the presence of water were more; significant than inorganic

ion contributions. Both studies determined: diminished catalytic

activity for soot as the pore sites became- plugged with sulfates and

nitrogenous products..

Brodzinsky et a l. (1978) performed a similar experiment with;

Nuchar and showed that the production rate of sulfate was independent of

pH from 1.45 to 7.5 pH units. They also tested the possibility o f

metallic; impurities of Nuchar contributing to the reaction rate and: the

possibility that environmental species inhibit the ra te anct found no

such reTationships exist. The cohelusibns derived from this experiment

appear reasonable although laboratory conditions, notably sulfurous acid*

concentrations, of 1.5 x 10" ̂ to 1.0 x lo"3 probably do not approximate

environmental- conditions;.

Graphitic: aerosols affect health. Particles, of the correct

dimensions9, regardless of species, may cause bronchial irritation,; or

they may plug the alveoli and render labored breathing. Foord, Black,,

and Walsh (1977) labeled polystyrene particles: with " mTc, and nonsmokers

breathed in these particles at a rate of ten breaths per minute. Nasal

passages effectively stopped most particles greater than 5 pm in

diameter, but. passed at least 84 percent of 2.,5; pm particles into the:

pulmonary regioni. Moore and Moore (1976) stated that particles smaller

than 0 .1 pm have only a- 50 percent chance of being deposited, and

Hoiland (1972) stated that human lungs effic ien tly trap particles less

than 5 pm in: diameter. Therefore, the range of particulate; sizes: most

likely to be trapped in human lungs, i f inhaled, is approximately 0.1 pm;

to 5 pm.

Holland (1972) cited several studies that: linked particulates

with Tung disorders. Graphitic particulates may load the lungs, render

breathing d if f ic u lt , and heighten respiratory d ifficu lties by providing

sorption sites for infectious agents and irritan ts . However, Coffin

and: Stokinger (1976) believed elemental carbon is; relatively innocuous.

Exposure?to the polycyclic aromatic hydrocarbons (PAH) associated

with combustion-produced soot could produce cancer. Mori in, Kertesz,

and Kiss (1978) and Wersburg, Fox, and; Howard (1975) found that PAH

species consistently associate with fossil fuel combustion-generated.

soot. Many of these species are carcinogenic and are associated with

automotive exhausts and urban soot (Marikawa 1979; Handa et a !. 1980).

Johnston et: aT. (1973) cited a 1775 study of English chimney sweeps in

which workers showed a higher than typical rate of Skin cancer, and in

1933 benzo(a)pyrene was isolated from coal soot and proved to be highly

carcinogenic. Thus, the species associated with and absorbed on graphit

ic aerosols may significantly influence.' general health..

I# addi tion to heal th damage, particulates of various types; can?

cause' extensi ve damage to various substances., Hon and: (1972 ) descri bed

a& T66T study on London smoke in? which- Evelyn noted: building? damage,, crop

faiiurey and? fabric; deterioration. Johnston et a l . (1973) stated* that

particulates grind: exposed materials, cause electrical? contact faiiurey

andr render paint: deterioration by channeling? water to? exposed, surfaces:

beneath the paint. Yocum and Upham. (1976) found that particulates may

enhance metal corrosion, cracking rubbery and? bullding erosion. Aerosol

particulates: cause various damages,, and their disposal is a subject of

obvious concern.

1.1.3. Aerosol Sinks

Removal of atmospheric particulates generally requires physical,

rather than chemical ,, means. Direct gravitational, settling efficiently

removes the larger and heavier species from the atmosphere. Smaller

species require condensation or aggregation to enlarge size? and mass for

effective removal by settling. Thus, coprecipitation of small particu

lates with rain or snow, rids the atmosphere o f much of the visible lig h t-

interfering graphitic carbon species. When industries are involved with

particulate removal from combustion stacks, several physical removal

methods may be employed with various degrees of efficiency.

Industrial particulate removal involves several methods. Fuller’

(1974) stated; that combustion-generated: particuTates greater than O J urn

contributed; about:99i7' percent of total particulate mass but only 12:

percent of the: total number of particles.. Johnston et a l. (1973) cited:

filtra tion ,, centrifugation,, water sprays, ultrasonic vibration, and;

electrostatic precipitation as effective: removal means, for most; larger

particulates. Fuller (1974) state# that coal-fired generators; commonly-

used cloth bags, cyclone: separatorsand wet scrubbers: to remove dust

sized species. Electrostatic precipitators coupled:with periodic

vibrations were? the most efficiently: employed: means o f removal for most

particles greater than 0.1: pm: but remained" inefficient in the collection

Of the majority o f smaller particlesL

Moor#and? Moore: (1976) predicted;; particulate: precipitation: rates; ?

by applying; Stokesf Law-which; states:

vo ^ gd2 (p2; - pi )/18h (1.1).

where v is:the termi nal particles velocity; 9, gravitational accelera-

tion constant; d;,. particles diameter; pi and pz, a ir and particle

densi ties:,, respectively;; nt system viscosity. Thi s mathematical; re lar

tionship does not account for aspherical particles, turbulent a ir flow,

random or Brownian motion,, and? nonideal weather conditions. Thus, only

under ideal conditions: 0.1 pm particles? should descehd; about 1 pm each

second: or about:32 meters every year;?. Obviously, 0.1 pm and smaller

particles must aggregate, or otherwise acquire greater size and; mass,

to assure efficient gravitational settling? Since particles between Oil

and 10 pm act as nucleatibn sites for rainand snow, the size increases

due to water condensation provider favorable condi tions: for removal of

vi si b ierli ght-i nterferi ng particulates.

1.2. Chemical and Physical Properties of Soot

DaTzell and Sarofim (1969) described a sooty aerosol as a:

collection of randomly oriented; graphi te microcrystals: wi thin am

amorphous carbon matrix ., X-ray investigations showed that: soot consists

of separaterand: irregularly located crystallites of approximately paral

lel graphite layers: (Tesner 1973). These: studies also indicated: that

layers off graphitic sheets bend tor form a shell for the particle. When

minute soot particles were cross^sectioned andf analyzed:, concentric

spherical layers of bent graphite were identified. To elucidate more

properties: o f this; environmental particulate species than merely physical

structure,, one: must begin with: studies o f previously characterized,

similar model materials.

Although graphite, coal, and graphitic aerosols are not

identical, many sim ilarities exist. Rosen and Novakov (1978) showed the

Raman signal a t about 1350 cm-1 and 1600 cm-1 for activated charcoal,

polycrystalline graphite, auto and diesel exhausts, and ambient sooty

aerosol s were: a ll coincident to wi thin 10 cm"1. McCartney and Ergun

(1967) used graphite as a model compound clbsely resembling high grade

coal in reflectance and transmittance properties. All Of these studies

allude to the close chemical similari ties: among coal, graphite,: and soot.

However, according to Dalzeli and Sarofim (1969), the molecular struc

ture is only a minor determiner of Optical properties; several compli

cated factors are: involved in determinations of exact optical properties.

Whenever h igh ly o p tic a lly absorbing m ateria ls are comprehensiveTy

NussbaumranldrphiET-ipsi(1976) detailed the total index of refractionn,»

as the sum of a constant term,. nr indicative of the velocity of

light propagation within the material, and a variable term, k, descrip

tive of an exponential Tight amplitude decrease as a function? of the

distance light travels through the substance. This may be stated as;

where i =•- AT. . McCartney and Ergun (1967) and Toon,. Pollack, and Khave

(1976) used a, detailed form of the imaginary refractive; index term,.

where X fsr the Tight:_wavelength> Ig is incident lig h t intensity , I is

Tight intensity a fte r the material absorbs a portion of Tgand t is

sample thickness. A comprehensive, complex analysi s shouTd also include

the Born and Wolf (1959) expansion of I/Tg as given by McCartney and

Ergun (1967) in their study of coal sections as follows:

analyzed, complex mathematics must be used to describe ̂the system.

(1 .2)

k = XTnClg/1)/4ft

T6nsnm(n2+k2)/ [((n s+n)2+k2) (n+nm) 2+k2)](1.4a)

exp (47rkt/X )+p|p|exp (-4irkt/X J+ZpgP̂ cos (

. 13

where: the subscript s indicates substrate,, m indicates the specimen—

and: substrate-covering medium,, and no subscript indicates specimen.

The term,, p_, represents: a: Tight: amplitude: change:as the photons pass. V''-, ■ ' , - ' • , .

from substrate: to sample:; p_ is the Tight amplitude change from sampleHI -

to medium; corresponding phase changes are expressed by ^ and This

theoretical treatment works weTT with simple systems- such as thin coaT .

sections fixed upon transparent substrate and covered by an a ir medium,

but becomes immensely more complicated with aerosol samples.

Since aerosols are conectedi on glass, quartz, or po.ly-

perfTuoroethylene polymer f i lte rs , each particle acts 11ke a separate

system similar to the thim coal sections studied by McCartney and Ergun

(1967) .. However,, sooty aerosols are not evenly cut plates; mounted:

firmly on transparent substrates;. Instead, particles are several sizes:

and shapes, and the substrate is, fibrous and diffusely reflective.

Thus,,, complicated interactions between̂ lig h t and: substrate: and sample

will occur maki ng any exhausti ve: theoretical treatment of this

phenomena d iff ic u lt. Consequently,, general bulk properties are commonly

studied to characterize; aerosol prbperties instead; of complex individuaT

particle or particle system analyses.

Generally, carbonaceous materials are believed to be highly

aromatic i f they are low in H/C: ratio , Friedel, Retcofskyand Queiser

(1967) found evidence of polynuclear aromatic compounds in coal through

the use of infrared and; ultraviolet, spectroscopic techniques. Broado

band reflectance shoulders near 2650 A are typical of chars and coal,

and this is similar to the position-of maximum reflectance for graphite

at 2600 A calculated by Reynolds (1968) for the: ir -f -rr* transition of

wA ■ -" ' - .

aromatic, electrons. McCartney and Ergun (1967) found increasing the

average number of conjugated rings, in coal-Tike structures: shifts the?O

absorption maximum to waveTengths progressively greater than 2600: A-

The. H/C value for as given: sample also greatly influences its,

reflectance and: transmittance qualities. Chippett and Gray (1978)

stated that a decreasing H/C should yield; a higher concentration; of

free electrons. These authors found: an increase:in free electron con

centration produces a general increase in; scattering and: absorbing)

abilities, due to slowly decreasing real indices of refraction and more:

rapidly increasing imaginary indices of refraction.. To? verify their

poi nts the?authors cited values obtained from flame-generated soot with

decreasing H/C [actual range not given]» and found values for real

indices of refraction ranged; from: 1.613 to 1.54: and) corresponding values,

of 0 . # to 1.1 were found for k. McCartney and: Ergun (1967) determined;

that: reflectance for coals with H/C from about 0.2 to 0:9 followed the

expression

Ft - R_ exp[;-3.6(H/C) J: (1.6)■ ' .. ' -

where? R is the sample reflectance, Rn is the reflectance for graphite^

and H/C is the ratio of hydrogen atoms to carbon atoms for the; sample..

Particle sizes also determine general optical properties. Moore

and Moore ( 1 9 7 6 ) Lin (1976), and Ember (1979) contended:that particles

from about 0.1 pm to 1 pm interact most efficiently with visible light

since they approximate the wavelengths of visible l i g h t . T w i t t y and

Weinman (1971) asserted that a value; o f T.5: for the ratio of particTe

circumference to wavelength implies that efficient scattering and

; . 15

reflectance: interactions* between Tight and particle are probable, and

particles; of lesser ratios have rapidly decreasing influences on these

parameters.

CHAPTER: 2

SPECTROSCOPIC TECHNIQUES

Results of several spectroscopic: methods for analyzing; graphitic

aerosol s and graphi tic model materials have; been published . McCartney

and Ergun (1967) used: ultraviolet: and visible light: transmittance*and

reflectance spectroscopy on thin coaT sections,mounted on clear, color

less substrates.. FriedeT efcal.. (1967): employed ultraviolet and infrared:

transmittance: and reflectance-spectroscopy measurements to characterize

various classes of coal. Novakov e t a l. (1974) evaluated sulfate pro

duction: on graphitic surfaces with electron^ spectroscopy for chemical

analysis: (ESCA):.. Rosen andv Novakov* (1977,, 1978), and Rosen e t al . (1978)

used: integrated Taser Raman scattering; fo r studies of urban sooty aero

sols.. In a recent, artic le Yasa et al . (1979) used photoacoustic spectro

scopy (PAS) to evaluate optical attenuation; methods. Although; many

spectroscopic techniques are available,, only a few are suitable for

rapid, low-cost aerosol determinations.

2.1. Evaluation of Selected Techniques

Transmittance spectroscopy is relatively easy to use, and.

reproducibility of measurements is generally good. For performance

evaluations one may use Beer's Law and; the;absorbance-transmittance

relationship:

A = ebc ' (2,1)

A = log(Tg/T) (2.2)

where A represents absorbance;: e is the molecular absorbance3 coefficient;/

b is the ligh t path length; and c is the moTecular concentration; Tg is

the transmittance of a reference or blank; T is sample transmittance,

Willards Merritt and Dean (1974) stated: that a one: percent transmittance

error yields less than 8 percent concentration errpr when the: absorbancê

reading ranges: between approximately 0.T and ILA absorbance; units: in

electronically noi se-1imi ted;instruments. When the shot effect presented

by* the: photomultiplier tube: (detector) limi ts precisions, the same uncer

tainty occurs from about 0.1 to 3.2. absorbance units;.. Am additional:

desirable quality is, the ab ility for the? instrument tov accommodate: small

f i l ter sections. However, when quartz or glass f i l t e r sections: are

analyzedy relatively: wide s l i t widths; are needed tm allow sufficient

l ight throughout for absorbance readings; to range: within the low error

region.. Wider s l i t widths resu lt im a wider spectral bandpass and

correspondingly lower resolution. In: the case of analysis of graphitic:

speciess resolution is not especially important at longer visible wave

lengths because the spectra are nearly f la t with a shallow slope from

about: 500 nm to beyond 625 nm.

KefVecl^m^i^dnni^BS-- such a t integrating sphere reflectance

spectrophotometry require l i t t le user s k ill but possess: many Intrinsic

drawbacks, Willard, M erritt, and Dean (1974): stated that when light

repeatedly encounters grai ns and fibers,, such as the case where aerosols

are embedded in quartz or glass fibers, specular reflections, occur.

When: several light and specimen interactions occur for each incident

photon, the surface appears uniformly or diffusely reflective. Reflec

tance: increases as particles approach the size of one-half the incident

light wavelength and decreases as particle diameters fa ll below about

one-fourth the incident light, wavelength due to increased scattering;.

Specular reflectance depends upon the angle made by source,, sample, and

detector. lhus,:exact interpretations of particulate reflectance data,

are complicated.

Hercules (1978) evaluated ESCA data acquisition as slow but

useful in determining oxidation states of surface species. ESCA systems

encounter limitations from shot noise; originating; in the electron

multipl iers, and vacuum pumps often contaminate the sample- chamber-. This

method requires more expertise in positioning the sample,, operating; the?

instrument, and interpreting data than conventional transmittance and:

reflectance techniques.

Raman techniques: rely on the ab ility of the sample to exhibit

mol ecular polarizations under the influence of the incident light.. Blah a

and: Rosasco (1978) stated that Raman spectroscopy is sensitive to the

chemical units present in the sample, and energy losses found in scat

tered lig h t from the sample surface relate: to vibrational and rotational

relaxations. Because: the scattering from aerosols is pronounced,, a

double or trip le monochromator system is required to distinguish between

Rayleigh' scattering and Raman signal., Additionally, a bright mpnochro-

matic source such as a laser is required to assure sufficient light

throughput and precision. This implies that a relatively elaborate:

19

instrumental set-up is necessary and: should, include a device to rotate

highly absorbing samples so that extensive: surface damage is avoided

(Andrews and Hart 1977).

Each of these techniques possesses desirable- attributes and,

several drawbacks. ESCA and Raman may yield multielement- valence state

information, but equipment: is relatively expensive and requires rela

tively high operator sk ills . Transmittance and reflectance methods are

relatively inexpensive and require lit t le ; operator s k ill. However, only

general molecular information, such as,the presence of aromaticity, is:

available with uTtraviolet and: visible sourcesgreater molecular detail

may? be possible with infrared; sources, but the? quartz and glass filte rs

used to collect aerosols absorb in this spectral region. Transmittance,.

reflectance,, and Raman techniques depend on photon detection: by devices

such as; photomultiplier tubes,, which typically respond nonlinearly wi th

respect to varying wavelengths. This lim its the useful response range.

Photoacoustic spectroscopy (PAS) is unresponsive to scattered:

light,, does not depend upon photon detection,, and the equipment is rela^

tively inexpensive- and relatively easy to operate. PAS, therefore,

merits consideration as a possible technique for aerosol analysis.

2.2. Characteristics of Photoacoustic Spectroscopy

In 1881 several articles: on the; photoacoustic effect appeared.

Bell (1881) discovered that a r interrupted beam of sunlight produces

sound when directed onto an absorbing substance within a Sealed container.

He developed instrumentation which included single beam and double: beam

spectrometers fitted with earphones: and telephpne receivers. Liquids,

20

vapors , gases , and sol ids produced sounds , but TampbTack and; charred,

cotton produced the strongest observed responses.. BeTT observed,; "The

loudest, sounds are produced from substances in a. loose,- porous, spongy

condition, and from those that have the darkest or most absorbent

colours." Mercadi er (1881) observed that the photoacoustic phenomenon

is surface-related for opaque-substances. He found photoacoustic

responses with;luminous platinum: wirev Bunsen burners, and electric

lamps fo r opaque materials. Preece; (1881) credited Professor Stokes

with proposing; that alternating)expansion and contraction of a ir molecules

covering an opaque materia! actually produces; the noted sounds. Rontgen

(1881) experimented with this; effect and found; the signal intensi ty is

inversely related; te chopping) speedi. However,/be expressed skepticism

regarding; i ts use& as; an analytical techni que, and) other authorities of

his; era; apparently concurred.

. According to King and; Kirkbright (1976) no; further photoacoustic

phenomenon publications: were produced until Veingerov (1938)V Luft (1943),

and; Gorelik (1946) issued their results of PAS: gas; analyses.. After 1964'

numerous articles on the photoacoustic effect for solids appeared. Many

authorities such as Aamodt, Murphy, and: Parker (1977), Adams, King, and

Kirkbright (1976), Gray,, Fishman, and, Bard (1977), McClelland and:

Kniseley (1976) and Yasa e t al .. (1979) claimed PAS superiority fo r

solids and powders over conventional techniques. Typical applications,

such as those reported by Karasek (1977), range from spectra, of inorganic

sal ts such as potassium diChromate and potassium permanganate to; analysis

of bio1ogical substances such as leaf sections and human blbod. PAS

theory for solids also was developed a t this time.

' 21Several empirical and theoretical relationships for solid PAS

parameters: are listed, in the-literature-. Adams, et al . (1976) used

carbon black to study several PAS signal dependencies. They found,

linear relationships between signal and the lamp current,, the quantity

of sample loading; on the target within a limited range, and the inverse

of chopping; frequency. Aamodt et a l. (1977) found g for carbon black

is approximately 10s cm-1 ,, and Rosencwaig and Gersho (1976) established;

that; PAS' signal depends on the backing; used and; is; independent, o f g

with highly absorbi ng; substances. Yasa et al . (1979) produced a rela

tionship specifically for graphitic aerosols collected on fibrous

substrates:

f: - [ i - exp(-0i ) I . (2 .8)2v*/ bT0Vkb

where n is heat conversion efficiency;, y is C./C for the gas withinp vthe c e ll; Pq is cell pressure;: Iq is input photon power; p represents

thermal diffusion length; G(w) is microphone response: a t a given

frequency; b is efficiency o f heat, transfer from sample to; backing; Tq

is cell temperature; V is cell volume; k is thermal conductivity; g is

the absorption coefficient; I is the effective path length for light;

and the subscripts b and g represent backing and gas, respectively.

[Note that the Rosencwaig convention fo r PAS terms is applied wherever

possible.] Since g is large for carbon black and £ is: believed large

for fibrous f ilte rs , exp(-g£) is approximately zero for determinations

of sample signal, Q, with sooty aerosols. These authors also noted

that response from 5 to 100 Hz chopping frequency remained constant for

• 22

each f i l ter sample" analyzed" due: to compensating changes in b, and the

addition of a boundary layer provided: by pores, in the substrate. How

ever,. actual data was not presented, and the trend: is: contrary to

evidence’ presented; by- other authors such as Rosencwaig and Gersho: (1976)

and Adams et at. (1976) ..

Rosencwaig (1976) and-McClelland and KniseTey (1976) described:

a thermoviscous dampening: factpr. As distance from the sample surface;

increases:,, the thermal oscillations: experienced, by the. overlying,

boundary layer of gas decrease. The?equations;

L - 2-rr/ag, (2v3):

a*. ~ (^f/d )?/2 (2.4)

a; ^ k/pC_ (2;.5)

describe the; limi ting: distance for the observed phenomenon; L is the

active: distance for thermal oscillations (m) ;, f is: chopping; frequency

(Hz); k is thermal conductivity (Jsrim"1K"1);! p is density (kgm"3);; C-.■ ■ ' ■ ■ ' '. "• ' . , ; ' - . ; - ■ • ' p: -

represents specific: heat (Jkg""1̂ "1) ̂ subscript g represents gas. The

thermal amp! itude. A,, a t distance x from the sample surface is given bŷ

A - exp(-xag) (2 .6 )

where subscript.s denotes: sample. Rosencwaig (1977) defined thermo

viscous dampening, e, by

e = (neM/2p0) L /2(dv)'"1 (2 .7 )

where;nQ represents the effective viscosity and depends upon gas

viscosity and thermal conductivity;: w is chopping frequency; pQ is. gas

density; d represents the closest distance between ce ll boundaries; and

23

v is, the: veloci ty of sound. At: room temperature: and pressure* i f d: is

greater than 0.T mm and chopping: frequency is: 100 Hz: or greater, the;

thermoviscous, signal: dampening: is negligible. This is fortunate since

a: very smal l sample cell may be designed; to maximize the sample signal

without introducing, fluctuations from the thermoviscous dampening when;

the stated conditions: are; observed.

The incident photons, are readily converted to heat in 10"8‘

second or less (Adams: e t a l. 1976) ,. and sample; signal is, independent: of

optical diffusion lengths and depends upon the characteristics of the:

substrate material such as thermal conductivity and thickness

(Rosencwaig and Gersho5 1976) . Adams and Kirkbright (1976:, 1977) noted

time lags: (At) for plastic: films on copper and: black, enamel paint on

glass:,: and? deri ved: t h a t - ... - - - - - - - - -r — ; : — -

(2,3)

where d represents substrate thickness (m); w is chopping frequency

(rad s~ l); a is thermal conductivity o f the substrate (m2s“i ); and 6

represents instrumental 'contributions to the time lag (s). Through the

use o f this type of experiment one could observe differences, in effec

tive: f i l t e r thicknesses and one could find effective a values for

various: filte rs i f standard; materials are employed as references.

CHAPTER' 3

INSTRUMENTATION

Several techniques are suited to aerosol analyses, but few are

rapid,, inexpensive, and: nondestructive.. Transmittance, reflectance,,

and: photoacoustic techniques possess these attributes:, and transmittance

and: reflectance, instruments* were readily available for this study

although instrumental modif ications were necessary to accommodates the:

sample f ilte rs . Obtaining- PAS data*required:the construction andvcali

bration of a custom: uni t.. General descriptions of the instrumentation

used and:: calibration: resul ts: are: discussed wi thin: this chapter.

'■31T... Aerosol Collection and Sample Preparation

Two types of collection systems were used to fix particulates

on quartz and glass:fiber f i lte rs . Bendix 550 high volume systems with

model 310 flow controllers pull a ir through Gelman Type A 8x10 inch

glass fiber f ilte rs or Pall flex QAST 8x10 inch quartz fiber f ilte rs .

Since a single f i l t e r is used to collect a l l aerosols smaller than about

20 to 60 pm, precise size discrimination, available in multipie-stage

samplers, is not possible. Another system. Sierra:Instruments 240

Dichotomoiis Sampler, distinguishes between particles from approximately

15 pm to 3.5 pm (coarse cut) and those smaller than about 3.5 pm in

diameter (fine cut). This system uses circular f i lte rs , 3.2 cm in

diameter, which may be sections o f the glass or quartz material

previously cited.

Three styles of f i l t e r shapes were required for the experiments.

Transmi ttance cuvettes- use 0.6x3.8: cm rectangular strips and; 0.9 cm

diameter circuTar sections:. The circular sections are- al so used in the

PAS: unit. A square f i l ter of at: least- 4x4 cm is required:for the

integrating sphere refTectometer. Cutting templates reduced sample

preparati om effort and time, and: on% the 4x4 cm fiTters; were prepared

w it^ or singie-edged, razors . ATI prepared fi1 ter sections-,

were handTed:with:stainTess: steeT tweezers and stored: in acid-washed

vials or plastic petri dishes.

3„2. Transmittance Instrumentation

A: Gi l ford 240: Spectrophotometer measured: aerosol f iTter trans-

mfttances^ and as Gilford: 410:Absorbance: Meter provided direct digital

readings qf absorbance:values., Since no provisions for automatic scan

ning exist,, al 1 studies of absorbances versus:wavelength are performed: ;

: manually on a point-by-point basis. The observed: usable wavelength

range extends from about 350 nm to beyond 750 nm for quartz and glass:

V f i l ters. i

: Modifications to the sample chamber were necessary to;optimize

responses for f i l t e r samples (Figure 3 .1 ). Fibrous materials yield

large light reflectance values; therefore, ligh t transmitted; directly

through these materials is relatively low. A Tens added in front of

the cuvette collimates the diverging:light from monochrqmator; thus,

higher incident light power is provided to the sample. FolTowing thee :

cu vette th e baffle blocks much" of the scattered ligh t from the

detector and reduces unwanted contributions to readings.

26

Figure 3.1. Cross Section of Sample Chamber for Gilford 240.

LEGEND

A. Entrance S l i t for Monochromatized Light

B. Collimating Lens

C. F i l te r Cuvette

D. Light Baffle

E. Exit S l i t

27

An exact set of replacements for standard quartz cuvettes

assured reproducible positioning of f i l t e r samples. Two styles were

machined from aluminum bar stock (Figure 3.2); one was given a rectan

gular, straight channel and the other was given two annular channels.

Samples were placed within the cuvettes and four orientations were

tested for responses. (See Figure 3.3 and. Tables 3.1 and 3.2,) The

rectangular, straight-channeled cuvettes showed pronounced differences

between orientations I and I I and orientations I I I and IV and small

differences between orientations I and I I I and orientations I I and IV.

This indicates that placing either the loaded side of the f i l t e r or

blank face of the substrate toward the source produces no appreciable

change in response. The larger responses achieved in orientations I

and I I I imply that the light beam probably diverges as: i t passes

through the f i l te r toward the detector. This is expected since fibrous

substrates tend to diffuse light in all directions. The annular-

channeled cuvette was designed to collimate the diverging light over

the distance through which the cuvette interacts with the beam.

Observed responses showed that this probably occurred since, changing

sample orientations produced no observable changes in reSponsev

Positioning either the larger or smaller annular channel in front of

the detector produced no noticeable changes in responses. This implies

that the detector was receiving virtually the same amount of incident

photons in both cases, and the larger channel probably illuminates

more of the baffle. This baffle only blocks light from the detector

and cannot contribute to the observed signal.

End Views

StraightChannel

AnnularChannels

Front Views

Mask

Figure 3.2. Comparison of F i l te r Cuvettes.

tww

ww

ww

wi

Particulates

I II III

Figure 3.3. Cuvette Orientations.

The collimating lens is located to the le f t side of the cuvette as il lu stra ted .

Table 3.1, Absorbance as a Function of Orientation of Straight-Channeled Cell and Sample,

Sample Absorbance3Designation Orientation I Orientation I I Orientation I I I Orientation IV

UA-84 0.238 ± 0.001 0.354 ± 0.001 0.242 ± 0.001 0,352 ± 0.002

UA-105 0.430 ± 0.004 0.744 ± 0.004 0.441 ± 0.001 0,744 ± 0.003

RR-105 0.110 ± 0.002 0.142 ± 0.002 0.107 ± 0.002 0.148 ± 0.002

100I I 0.076 ± 0.001 0,096 ± 0,003 0.067 ± Q.002 0.098 ± 0.002

^Average of 2 repetitions op each sample for each orientation at 625 m. An unloaded f i l te r section is referenced as zero absorbance,

Table 3.2. Absorbance as a Function of Orientation pf Annular-Channeled pell pnd Sample.

SampleDesignation

Absorbance3

Orientation I Orientation I I Orientation i l l Orientation IV

UA-84 0,390 ±0.001 0,396 ± 0.005 0.388 ± 0.006 0.392 ± 0.003

UA-105 0.975 ±0.002 0.988 ± 0.003 0.966 ± 0.005 0.988 ± 0,004

RR-105 0.156 ± 0.004 0.159 ± 0.002 0.146 ± 0.006 0,158 ± 0,002

10011 0.104 ± 0.002 0.103 ± 0,001 0.088 ± 0.006 0.106 ± 0,002

-Average of 2 repetitions on each sample for each orientation at 625 nm. An unloaded f i l te r section is referenced as zero absorbance,

31

Phase Control

ChopperVoltage

PhaseSensitiveDetectorChopper

Four Digit Display

FrequencyMultiplier

PhototransistorDetector

Voltage-to-FrequencyConverter

PhotoacousticCell

Microphone

Postamplifier

Preamplifier

FrequencyCounter

ReferenceSource

PrimarySource

Figure 3.4. Block Diagram of the Constructed Single-Beam Photoacoustic Spectrometer System.

3.3. Reflectance Instrumentation

The integrating sphere reflectance spectrometer described by' ■ • . . , .

Jacobson e t aT. (19.78) was employed in aerosol f i l t e r studies. The

sphere walls are coated with finely powdered barium sulfate> which

diffusely reflects incident radiation provided by the quartz-halogen

source. A' Tight baffle prohibits direct sample illumination by the

sources, and two sets of monochromators and detectors monitor sample and

reference'reflectance intensities. A Motorola 6800 microprocessor

system controls the monochromators and s l i t widths, digitizes detector

responses:,, outputs the ratio of sample reflectance to reference- reflec

tance, and controls signal lock-in amplification. Each sample- scan

requires about 17 minutes.

3.4. Photoacoustic Spectrometer

A sample, photoacoustic: spectrometer (PAS) was, constructed

primarily from standard: CMOS and operational amplifier integrated

circuits. Interfacing the various general circuits illustrated in■ , "

Figure 3.4 required careful design and construction techniques becauseW ' '

of the ease in which CMOS circuitry is; destroyed i f voltages and cur

rents are not regulated within specifications (Lancaster 1978). The

omission of a monochromator in the in it ia l set up allows more photons

to reach the sample; consequently, responses from very low sample load

ings are more easily detected and processed.

3.4.1. Signal Processing Circuits

Direct reading of the chopping:frequency and the provision of

the reference signal for the phase sensitive detector (PSD), Evans model

- 33

number 41 TO, were accompTished by- ai single c ircu it (Figure 3.5), A Tow-

current Tight buTb output: is directed toward a photo transistor (FPT TOO)

detector. When the chopper blocks the ligh t, the phototransistor

circuit outputs a 14 volt: signaT which shuts the PSD off and sends a

high logic signaT to the frequency counter. When the chopper slots

permit Tight to reach the phototransistor, a* 2 volt signal is output.

This: turns on the PSD and drives the logic signal Tow. Thus, the PSD is

only when the. chopper slots are. in a favorable position,, and the fre

quency counter alternately: receives high and; Tow logic signals in

sympathy with chopping frequency.

Since sample signals are not generally in exact phase with

reference signals, a phase: adjustment device (Figure 3.6) is required to

provide the:needed:change: in reference timing. The reference source and

phototransistor detector are aligned and mounted, on an aluminum bar, and:

these components: staddle the chopper wheel.. By rotating the position

adjustment screw, one;moves the two circuits simultaneously to another

position. This allows the reference: signal to Tag, lead, or match the

sample signaT timing.

After the sample signal is rectified, amplified, and smoothed,

a precision voltage-to-frequency c ircu it (VFC) transduces the DC output

of the PSD to a proportional frequency (Figure, 3.7). The final adjust

ment produced output frequencies (in Hz) equal to the input voltage

times ten thousand. This:allows a frequency counter with a 0.1 second

timing gate to provide a display of "1.000" for a T.000 volt input

signaT. The 741 voltage follower provides voltage inputs with Very Tow

33 <

ro V

Point Waveforms

V \ _ _ / \ __ / V

c ______ ______ ____

Figure 3.5. Reference Detector and Associated Waveforms.

a0utput is chopper frequency

35

Cross Brace

Figure 3.6. Phase Adjustment Device.

36

BB VFC 32KP

- 15'

♦ 15 V

Figure 3.7. Voltage-to-Frequency Transducer C ircu it .

^Voltage input

^Frequency output

resistances so that the circuit w ill not draw sufficient current, to

power the VFC and: thereby drop the input voltage.

A frequency counter enables the user to read chopping frequen

cies, directly or voltages that are: transduced to frequencies (see

Figure 3.8). A 555 is.wired as ah astable vibrator9 and this integrated

circuit alternately produces a 0.1 second high logic signal and a 0.02

low logic signal. While the 555 outputs high logic,, the seven-segment

displays are held to the last count value, and the four cascaded decade

counters register the number of pulses from the frequency of interest

that accrue during the: present 0.1 second counting interval.. One 4013

gate is wired as a monostable and: triggers as the 555 output goes from

high to low logic levels. A: 44 microsecond pulse updates the display

and triggers the other 4013 monostable: gate. A 44 microsecond pulse

from the second monbstable resets the counters.. The system then waits

for the astable vibrator output to reach high logic level which restarts

the-counting process (Figure: 3.9).

A frequency multiplier circuit enables frequencies as low as

0.1 Hz to register on the displays (Figure: 3.10) . A 4046 phase-locked

loop with a dual decade counter fixed in the divide-by-n position

multiplies the input frequency by 100. This, circuit was designed

specifically to multiply the typically low chopping frequencies so that

±0.1 Hz precision is possible in 0.1 second. Without this circuit the

frequency counter gate (555) must be extended to 10 seconds for the

same precision.

Figure 3.8 Gated Frequency Counter.

Component Value

Ri ~ Has 330' - . •

R 2 9 and R31 3.3K

Rao and R32 book

R33 and R34 100K

Component Value

Ci and C2

C ,

C4

Diodes

0.01 yF

0.001 yF

0.1 yF

1N914

4511451145114511ZTST

45184518CL

555>«

CLl

C4-

Figure 3.8. Gated Frequency Counter.

555 Output

FrequencyInput

4081 Input to 4518 LSD

4013 Qi to 4511 Store

4013 Q 2 to 4518 Reset

Figure 3.9. Timing Diagrams for Frequency Counter.CO10

INKAA/V

rSquareWave

Outputs

Figure 3.10. Frequency M u ltip lie r .

a Input frequency x 1

bInput frequency x 100

|A1 leoK— •— /V/\y—

4046 l»*X

TTPVo\|

4518

2 .1 k f

o

' 41

3.4.2. Sample Cell

A 5x5x6.5 cm aluminum block was machined as illustrated in

Figure 3.11. Aluminum provides a rigid, sample chamber, is. easily

machined and polished, and rapidly dissipates sample-generated heat.

The sample platform fits snuggly into the 0.95 cm diameter hole. The

sample chamber is a ir-tight,, and the microphone detector is recessed

perpendicular to the chamber so that ligh t w ill not impinge upon the

microphone surface and create a- background signal.

A Radio Shack, model 270-092, electret microphone monitors the

photoacoustic: response of sample materials. Sessler and West (1966)

studied: similar microphone systems and found, that: sensitivity is

typically constant for a: period of years, and humidity has a negligible

influence: on response: sensitivity. They calculated; that the probable

useful lifetime of an electret microphone is from about 30 to 1000

years. Radio Shack specifications show a virtually constant response

for frequencies between 30 and 1000 Hz, and this imp!ies that a change

in chopping frequency requires no correction for microphone sensitivity

throughout this wide range.

3.4.3.; In it ia l Calibrations and Device Limitations

Before any sample readings were made on the PAS, the instrument

was calibrated. An exact: frequency reference set the chopper frequency

output, and the frequency multiplier circuit produced square wave

signals one hundred times greater than the input frequency. For this

system to perform properly the sine or square wave input must range

between 5 and 15 volts in amplitude and 0.1 and 170 Hz. The circuit in

Sample Platform

Neoprene O-ring

Glass Window

Microphone Cable

Electret Microphone

Plexiglass Plate

Figure 3.11. Cutaway View of Photoacoustic Cell.

(All aluminum construction except where noted.) Approximate to scale.

■ 43

Figure 3.12 locks onto alternating line current (60.0 Hz) and provides

various sine wave amplitudes. After the output of this circuit was

processed by the frequency multiplier, the frequency counter timing gate

(555) was carefully adjusted to provide "060.0" on the display.

The reference frequency generator also provided several sine

wave amplitudes through the adjustment of a variable AC transformer.

The precision full-wave re c tifie r (Figure 3.13) transduced the AC signals

to a proportional DC output for use with the VFC (Figure 3.7). The

correlation coefficient for the 16 points listed in Table 3.3 was in

excess of 0.999; therefore, the linearity of the VFC is nearly ideal

between nearly 0 volt and ±14 volts DC.

Additional instrumental evaluations of the PAS were made employ

ing a moderately loaded sample, number Dl-271f. In one experiment the

position of the sample platform was adjusted to vary the volume of the

sample chamber, and PAS responses for 8 chamber volumes were observed.

(See Figure 3.14.) In another experiment PAS response was observed as a

function of the source Tamp voltage. (See Figure 3.15.) Responses agreed

with Equation 2.8 and trends illustrated by Adams et a l . (1976).

Each sample placed in the sample chamber of the PAS yielded a

time lag between the moment light strikes the sample and the time the

maximum signal was produced. In each case the adjustment of the phase

control (Figure 3.6) showed that an offset of about 24° above the cell

window was required to produce the maximum signal value. Since a chop

ping wheel with 6 slots was used, each cycle represents 60°, and at 80.5

Hz chopping frequency the observed signal lag represents about 5 ms of

44

H O VAC

Point

A

B

C

Figure 3.1

33 K AAA-

u o Va c

Waveforms

/ W V A

n n n .

• Reference Frequency Generator and Associated Waveforms.

1 » K

ACInput

DCOutput

Point Waveform

C

Figure 3.13. Precision Full-Wave Rectif ie r.

46

Table 3.3. Voltage-to-Frequency Transducer Response.

Input Voltage (volts)3

Output Frequency (kHz)

Input Voltage (volts)3

Output Frequency (kHz)

0.00 0.00 8.24: 28.85

1.36 V 4.82: 10.6: 36.87

f T.89* 6.66 10.8 38.50

3 .-75- 13.23 11.1 39.65

; 4:. 53 16.11 12.3 43.48

: 5.15 18.02 12.7 44.72

7.50 26.68: 13.0 46.43

7.89 28.21 14.0 49.56

aThis represents the output of a precision AC re c tifie r.

VOLT

S

47

oo

PAS

(VOL

TS)

.72

48

CN

00

O480 24 72 96 120

SOURCE (VOLTS)

Figure 3.15. PAS Response as a Function of Source Voltage.

' 49

time lag. Once the maximum signal for one sample was produced, no

additional phase adjustments were required to maintain the apparent

maximum sample response for other samples, and sample loading had no

apparent influence on the time delay.

The constant lag probably occurs because the parameters listed

in Equation 2.9 are apparently constant for the analyzed samples on

quartz f ilte rs . The substitution of glass filte rs for quartz produced

no appreciable change in phase angle beyond a typical ±2° uncertainty

in angle measurement. This is fortunate in one respect because informa

tion from quartz and glass samples may be related without the use of a

correction factor, but i t is unfortunate that the instrument is unable

to distinguish subtle differences between f i l te r thicknesses and thermal

conductivities.

Three samples of various loadings illustrate sample response as

a function of chopping frequency, and instrumental responses followed

the family of curves illustrated in Figure 3.16.1 Yasa et a l . (1979)

stated in a footnote that the presence of the pore volume in the f i l t e r

steadies the f i l te r responses over a range of 5 to 100 Hz. Whereas

relatively lightly loaded samples such as D1-271c appear to yield steady

signals from about 35 to TOO Hz, moderately loaded samples such as

Dl-271f and BT-105 do not exhibit the same f la t response. These data

suggest that the explanations and observations offered by Yasa et a l.

^It should be noted that a ll PAS measurements listed in this work were made on the xlO setting unless specifically noted to the contrary.

PAS

RESP

ONSE

(V

OLTS

o -i

00 -

oI—I X

vO -

. . .. , 51

may be valid for Tightly loaded samples but do not adequately describe

the situations observed in this experiment for more heavily loaded

samples. ■

3.5. Standard Calibrations

Blank filte rs set the reference values for the three spectro

scopic techniques employed. Adjustment of the s l i t width for the Gilford

240 Spectrophotometer provided zero absorbance readings; a microprocessor

provided corrections for the ISR so that blanks yielded TOO percent

reflectance; no provision exists for adjusting the PAS readings, and

corrections for blank absorbances must be made mathematically. Whenever

a series of blanks did not match the in itia l choice, the average of all

blank values were subtracted from the sample responses.

A series of black standards also served to calibrate instrumental

responses, A black plate rated as 3 percent reflecting set the lower

lim it for the ISR. A set of carbon films, supplied by the Arizona

Carbon Film Company, calibrated the Gilford 240 Spectrophotometer and

the PAS unit. These films ranged from 3.1 to 32 pm/cm2 with a density

of 1.8 g/cm3, and the index of refraction was determined as 2.75±0.25 -

0.72i±0.02i (Stoner 1969). While the carbon standards were s t i l l on

glass substrates, the transmittance spectrophotometer showed absorbances

which closely agreed with the calculated values from Equation 1.4. (See

Table 3 .4 .)

Linear least squares f its for data obtained while standards

were on glass plate substrates yielded

ABS = 1.05 x NOM - 0.036 (r = 0.995), (3.1)

Table 3,4- Carbon Film Measurements and Calculated Responses.

Surface Density (yg/cm )

Absorbance at 550 nm . PAS

Plate Glass Substrates Quartz Fiber Substrates

ObservedResponse

Calculated ResponsesObserved Response

ObservedResponse*

Nominal Range

0 .000 .000 .000 T.032 ± .016 .000 ± .000

3.1 .226 ± .018 .242 .203 - .249 ,112 ± .013 .673 ± .015

4.5 .327 ± ,010 .294 ,245 - .323 .190 ± ,010 .790 ± .008

8.1 .517 ± .009 .437' .393 - .481 ,335 ± .013 .958 + .011

16.9 .846 ± .008 .801 ,720 - ,881 .662b 1.854 ± .058

32. 1.344 ± ,063 1.426 1.283 -1.569 1,116b 1.285 ± .008

aVolts on the xlO scale.

bSingle measurements; all others are averages of 4 repetitions.

mro

53

ABS = 0.0412 x C + 0.100 (r = 0.989), (3.2)

and NON = 0.0427 xC + 0.073 (r = 0.997), (3.3)

where ABS represents the Gilford: 240 Spectrophotometer absorbance, NOM

is the nominal Calculated response; and C is surface, density of the

standards in ug/cm2.

The standards were transferred to quartz fiber f i l ters by flo a t

ing film segments; on water and collecting them oh freshly cut blank

material. The standards were cut and dried, and responses showed

ABS - 0.872: x NOM - 0.077 (r = 0.997)„ : (3.4)

VOLTS =- 2:. 19 x NOM;+ 0.088 (r = 0.994), (3.5)

VOLTS: = Z M x ABS + 0.228 (r = 0,980) , (3.6)

and: VOLTS = .QV10.0." x G: + 8,203 (r = 0 .974) , (S. 7 )

where VOLTS represents PAS response and other terms are as previously

stated-

Comparisons of data show that standard absorbances are: lower on

quartz substrates; (n = 1.45) than; on glass plate substrates (n = 1.51) .

However, Equation 1.4 predicts, absorbanc-s on quartz: substrates should

be slightly larger than with glass. Although this discrepancy is odd:

i t should not diminish the calibration accuracy.

The instrumental conformities to predicted values established

the accuracy of the transmittance and photoacoustic techniques over the

range cited for the standard material. (See Figure 3.17 for the c a li

bration curves.) The large deviation of the PAS measurement for the

highest standard indicated that signal saturation probably occured.

Spraying f 1uorocarbons over the cell cooled the cell and yielded a

RESP

ONSE

54

CM

° PAS (volts)

CM

ABS

§-

16 24CARBON (Vig/cm2)

Figure 3.17. Calibration Curves for PAS and Gilford 240.

maximum response of approximately 2.9 volts as long as the spray was

maintained. Upon cessation of cooling the response returned to about

1.3 volts in less than one minute. Although this is a limitation at

the chopping frequency employed (80.5 Hz), tripling the chopping fre

quency should reduce the signal and the sample-generated heat to an

acceptable level (Rosencwaig 1975).

A sample of aerosol graphitic carbon from motor brushes was

collected on a quartz f i l te r to evaluate the possible use of such

samples as standards. Six repetitions on f i l t e r sections yielded

values of 0.114+0.004 absorbance unit and a PAS response of 0.268+0.010

volt. Equation 1.4 predicts that pyrolytic carbon with indices of

refraction equal to 1.9-0.35i (Chippett and Gray 1978) w ill exhibit

responses approximately 0.46 times the standard responses for materials

with indices of refraction equal to 2.75-0.72i. When the slopes of

Equations 3.2 and 3.7 are employed as the ratios of absorbance to total

carbon and PAS response to total carbon, respectively, the absorbance

value predicts that f i l te r sections contain slightly more than 6 ug C/cm2

and PAS predicts slightly less than 6 yg C/cm2. However, elemental

analysis determines that approximately 16 pg C/cm2 and 3 pg H/cm2 are

present on these f i l t e r sections. This implies that the material may

not be pyrolytic graphite with similar refractive indices to those of

environmental soot. Consequently, this material provides no obvious

advantage over the standards chosen for analysis calibrations.

CHAPTER 4

EXPERIMENTS WITH FILTER SAMPLES

Various sample relationships were studied. A Perkin-ETmer .240

Elemental Analyzer provided total carbon values, and a Diohex 10 Ion

Chromatograph provided total nitrate and sulfate measurements. Esti

mated accuracies are ±0.3 percent for total carbon values (Perkin-

Elmer Corporation 1974), 6 percent standard deviation at .09 ppm for

nitrates, and TO percent standard deviation for 0.10 ppm in sulfates - ■■ ■ ,

(Dionex Corporation 1978). Instrumentation described in Chapter 3

provided the remaining measurements.

4.1. Evaluation of Reference F ilter Properties

Blank quartz f i l t e r properties were evaluated primarily through

the use of ISR spectroscopy. When the quartz f i l t e r blank is placed

into the sample holder without a backing, the transmittance and absor

bance components of the sample signal are instrumentally cancelled.

(See Figure 4,1.) The blank in this situation was evenly illuminated on

both sides and yielded an average reflectance value of 95.5 percent or a

total calculated transmittance plus absorptivity value of 4.5 percent

(see Table 4.1) from the relationship

1 = R + T + A . (4.1)

where R is reflectance, T is transmittance, and A is absorptivity.

' 56 ' .

Reference Side of ISR

$ QuartzBlank/ / / / / / / 7 7 Z

tt-Luunnu ii r u n u i

Z \

♦ Black Backing

zzzzQuartzBlank

77771

7 \

Sample Side of ISR

Figure 4.1. Experimental Configurations for ISR Study of Quartz Blanks.

Largest arrows represent incident source l ig h t; smaller arrows represent transmitted l ig h t .

58

Table 4.1. Reflectance Measurements on a Quartz Blank.

Wavelength(nm)

No Reference Backing R T+A (Calc)

B1ack Reference Backing R-Aa R-(T-A)b T (calc)

400 96.2 3.8 88.4 84,0 4.4

412 95.9 4.1 88.0 83.1 5.1

425 95.6 4.4 87.7 83.1 4.6

438 95.9 4.1 88.0 83.2 4,8

450 96.0 4.0 87.6 83.2 4.4 ...

462 95.9 4.1 88.0 83.2 4.8

475 95.5 ; 4,5 87.7' 83.1 4.6

488 95.3 4.7 87.9 . 83.1 4,8

500 95.3 4.7 87.5 83.1 4.4

517 95.1 4.9. 87.3 82.8 4.5

533. 95.1 4,9 87.1 82.8 4.3

550 95.1 4.9 87.2 82.9 4.3

566 95.1 4.9 87.2 82,8 4.4

583 95.5 4.5 87.2 82.9 4.3

600 95.6 4.4 87.2 82.9 4.3

aATuminum sample backing.

bBlack sample backingi

59

Two additional sets of measurements were employed as another

means of obtaining blank reflectance data. One set was run with an

aluminum f irs t surface mirror facing the sample channel through the

blank and a black absorbing plate facing the reference channel. This

reintroduces most of the transmitted light to the sample channel i f the

blank absorptivity is, low. Another set was run with a black absorbing

plate facing both the reference channel and the sample channel through

the blank. The difference between the two sets of readings yields a

total transmittance of 4.5 percent which agrees: with the 4.5 percent

value for transmittance plus absorptivity.- Therefore, the calculated

blank absorptivity is negligible.

Comparisons}of the quartz blank transmittance with air trans

mittance from 300: to beyond 700 ran on the spectrophotometer yielded

values in excess of the absorbance meter's upper lim it of 2,145 units.

This indicates that the transmitted Tight to the detector is less than

0.72 percent. Because light through air and the blank cuvette was

collimated, essentially 100 percent of the incident light was detected.

However, the quartz, blanks diffusely reflect much of the light, and only

a small solid angle of transmitted light is monitored by the detector.

I f this angle were increased to 180°, the entire 4.5 percent transmitted

Tight should be detected.

The PAS measurements typically were 0.000 volt on all settings

for freshly cut blanks. This verifies that f i l te r absorbances are

normally negligible.

Table 4.2 shows blank reference values used in determinations of

Mauna Loa sample responses. The observed difference between highest and

60

Table" 4.2. Comparison o f Reference Blanks.

BlankNumber

(Arbitrary)Absorbance

(625 nm)Response

Log ( R 0 / R ) (625 n m )

PAS(volts x 100)

1 -.006 .020 .091

2 .002 .020 .095

3 -.030 .015 . 1 0 0

: '4 :'-.036 ; ,.016: .095

5 .085

6 - - ' . ■ .090

Average. -.018 + .018 .018 ± .003 .093 + .005

61

lowest PAS blank responses was approximately 10~4 volt which amounts to

about 4x10r 4 absorbance unit when the slope of the Equation 3.6 is used

to indicate the ratio of absorbance to PAS response. Since PAS is

insensitive to reflected and transmitted light, the high degree of con

sistency exhibited by the blanks was expected. The range, of logfRg/R)

amounted to 1.1 percent reflectance, and this indicates that the blanks

were essentially uniform in reflectance. Absorbance values obtained by

transmittance techniques should be sensitive to changes in reflectance

qua!ities and absorbance qualities of the f ilte rs . The 8.4 percent

range in-apparent absorptivity showed that this is probably valid. The.

data suggest that response uncertainties for blanks is greatest for the

transmittance technique, less for the reflectance, technique, and least

for PAS.

4.2. Spectroscopic Sample Studies

Several sets of f i l te r samples were examined. Mauna Loa,

Hawaii samples (ML0-, Table 4.3) represent the most Tightly loaded

samples. Samples collected at Missoula, Montana are the best charac

terized samples (Table 4.4) available: for this study and represent a

wide range of loadings. Other collection sites include Research Tri

angle Park, North Carolina (Table 4 .5), Tucson, Arizona (Table 4.6),

Betatakin Ruins (Table 4.7) and Black Mesa (Table 4.8) in the Four

Corners area of Arizona. Samples originated from a variety of regions

ranging from polluted to pristine.

Because optical alignment is crucial to PAS measurement pre

cision, adjustments were made so that the 3.1 ug/cm2 standard yielded

62

Table 4.3. Comparison of Absorbance and Reflectance Values.

Sample Designation Absorbance Log (Rq/R) (625 nm) (625 nm)

MLO-DSQ-12-1

12-2

13-1

13-2

D1-UAC-6TC

61F

.041 .039

.008 .015

.087 .092

.014 .016

.075 .128

.343 .348

Table 4 M . Missou1 a Sample Data.Sample Date PAS Signal (volts)

Absorbance (550 niii) (625 nm)

Total Carbon(ygA f i lte r )

CNPs3(pg/ml)

[s o n(yg/mi)

OC 2-6-80 .000 .000 .000 10.02 0.4 1.2OF .000 ,064 .063 9.49 0.3 0.91C 2-7-80 .257 .128 .095 33.04 2.6 2.2IF .803 ,846 .723 77.61 2.8 10.92C 2- 18-80 .458 .370 .296 41.95 5.7 10.22F 1.054 .981 .772 123.75 3.7 24.03C 2-19-80 .504 ,397 .338 41,64 6.2 4.13F 1.018 1.497 1.332 130.57 5.3 11 •2;4C 2-20-80 .431 .364 .307 57.16 4.25 2.64F: .989 ' 1.446 1.202 184.06 6,7 20.75C 2-21-80 .363 .215 .188 46.67 2.5 2.45F .776 1,080 .940 111.76 1.0 2.56C 2-22-80 .000 -.083 -.067 8.91 0.6 0.86F .000 -.084 -.053 9.44 1.0 0.67C 2-23-80 .358 . .205 .165 60.30 2.6 2.17F .692 .864 .738 82.24 7.2 4.28C 2-26-80 .455 .644 .566 97.54 7,7 3.38F 1.023 1.713 1.506 159.41 13.6 18.89C 2-27-80 .527 .471 .392 66.07 6.9 4,29F .891 1.541 1.406 173.96 11.5 13.1

IOC 2-28-80 .479 .612 .517 95.44 10.0 5.010F .957 1.608 1.417 180.28 10.0 16.2lie 2-29-80 .351 .141 .122 36.90 1,2 2.4IIF .694 .833 .708 61.35 3.4 8.9

Jab]e 4 .4 ., continued

Sample Date PAS Signal (volts)Absorbance

(550 nm) (625 nm)Total Carbon (ugA f i lte r )

[NO 3] (ltg/ml)

[s o n(yg/ml)

12C 3-1-80 .000 -.050 -.036 12.06 7.7 3.312F .000 .015 - .032 43.75 3.5 1.114C 3-6-80 .289 .198 .179 30.41 2.3 4.714F .818 .830 .725 101.73 4.6 19.815C 3-7-80 .316 .205 • 179 35.85 4.0 4.615F .836 1.108 .999 146.83 5,5 27.218F .000 -.050 -.050 10.54 0.4 0.930C .000 .

tooI -/033 6.85 3.7 0.6

cr>-e

65:

Table. 4.5. Research Triangle Park Samples.

SampleNumberGA-

DateCollected

Response PAS Absorbance

(volts) (625 nm)Total C (yg/cm2)

Total SO2- (yg/cm2)

1 August1978

0.053 0.000

99 0.236 0.270 19.6; 10.7

94 0.498 0.447 17.6 8.6

82 1.060 1.470. 60.0

66

Table 4.7. Betatakin Sample Responses.

SampleNumberBT-

DateCollected

PAS(volts)

Absorbance (625 nm)

Total Carbon: (pg/cm2)

100 7-22-79 .233 .144 ; 11.86

101 7-27-79 .244 .142 11.86

102 8-2-79 .164 .115 11.62:

103. 8-8=79 .400 .253 14.26

104 8-14-79 .420 .182 13.35

105 8-26-79 .372 .287 8.84

106 9-1-79 .094 / .033 2,29

107 9-7-79 .369 „260 8.22

108 9-13-79 .333 ,268 9.65

109 9-19-79 .355 ,299 8.85

67

Table: 4.8. Black Mesa Sample Responses =

SampleNumberHQ-

DateCollected

PAS (volts)

Absorbance (550 nm) (625 nm)

Carbon(pg/cm2-)

Blank ” — .001 .000 .000 -»■“

44 4-6-78 .160 .388 .355 21.51

45 4-18-78 .182 .887 .792 87.77

46 4-24-78 . .253 . 1.167 1.108 47.28

47 5-4-78 .191 .758 .700 33.32

48 5—10—78 .196 .830 .772 31.58

49 5-16-78 . .143 .405 .361 194.7

50 5-22-78 .151 .577 .521

: 51 5-28-78 .135 .349 .325

52 6-3-78 .225 .850

53 6-9-78 .185 .650

54 6-15-78 .102 — . .. .193

55 6-22-78 .165 .442

68

a value: of approximately 0.67 volt before any- samples were measured.

The xlO preamplification setting provided sufficient signal strength for

sample measurements, and this setting was used for all sample runs

reported.

4.2.1. Optimum Wavelength Range for Analysis

Comparisons of responses fo r several samples at a single wave

length should provide estimates: of graphitic carbon masses on quartz

f i l te r substrates since: the graphitic component should dominate the

absorption coefficient in the visible region. Absorption measurements

ideally should exclude all reflectance and transmittance components.

Therefore^ an optimum wavelength region was: sought to minimize particle

scattering: contributions to the obs