(26) Westover, L. B., Tou, J. C., Mark, J. H., Anal. Chem., 46, 568-71 (1974). (27) Chem. Eng. News, p 18, April 28,1975. (28) Dilling, W. L., Tefertiller, N. B., submitted for publication. (29) Lange, N. A,, “Handbook of Chemistry,” 10th ed., p 1091, McGraw-Hill, New York, N.Y., 1961. (30) Hamming, W. J., “Photochemical Reactivity of Solvents,” paper presented a t Aeronautic and Soace Engineering and Manuf&turing Meeting, Society of Automotive Engineers, Los Angeles;Calif., October 2-6, 1967. (31) Wilson. K. W.. Dovle. G. J.. Hansen. D. A.. Endert. R. D.. “Photochemical Reactivity of Trichloroethylene a n i Other Sol: vents,” paper presented a t 158th American Chemical Society National Meeting, New York, N.Y., September 7-12, 1969; Abstracts of Papers, ORPL 38.
(32) Wilson, K. W., Doyle, G. J., Hansen, D. A., Englert, R. D., Amer. Chem. SOC.,Diu. Org. Coat. and Plast. Chem. Preprints, 29, No. 2,445-9 (1969). (33) Wilson, K. W., “Photoreactivity of Trichloroethylene,” Summary Report for Manufacturing Chemists Association on SRI Project PSC-6687, Stanford Research Institute, South Pasadena, Calif., September 1969. (34) ‘Altshuller; A. P., Bufalini, J. J., Enuiron. Sci. Technol., 5, 39-64 (1971). (35) Dilling, W. L., Bredeweg, C. J., Tefertiller, N. B., submitted for publication.
Received for review January 15,1975. Accepted May 21,1975
Molecular Composition of Secondary Aerosol and Its Possible Origin Dennis Schuetzle,” Dagmar Cronn, and Alden
L. Crittenden
Chemistry Department, University of Washington, Seattle, Wash. 98195
Robert J. Charlson Civil Engineering Department, University of Washington, Seattle, Wash. 98195
w Several aerosol samples were collected during a diurnal period of inversion and aerosol production in Pasadena, Calif. Particles were collected in two size ranges: particles of diameters less than 1-2 pm and particles of diameters greater than 1-2 pm. Computer-controlled mass spectrometric thermal analysis was used for molecular organic and inorganic analysis. The results described in this paper are semiquantitative with a precision of f 3 0 % on a relative comparison basis, but accuracies may range up to two times for some of the organic secondary aerosols with estimated response factors. X-ray fluorescence and atomic absorption were w e d to obtain inorganic elemental composition. The diurnal variation in aerosol composition was studied for the two size ranges and used to postulate the primary and/or secondary origin of the aerosol. The most probable precursors for the measured secondary aerosol products are presented in this paper and postulated from the results of smog chamber studies and the gaseous composition of gasoline, auto exhaust, and ambient air samples. The primary pollutants included alkanes, polycyclic aromatics, substituted phenols, and several elements. Organic secondary pollutants included acids, aldehydes, alcohols, chlorides, and nitrates. Inorganic secondary pollutants identified included sulfates, nitrates, and chlorides. The results are discussed with respect to meteorological conditions.
It has been suggested by several investigators that photochemical aerosol produced from reactions of hydrocarbons and oxides of nitrogen are major pollutants in Southern California ( I ) . Insight into processes occurring to form aerosols have been made using smog chambers. The composition of aerosols formed during the photochemical oxidation of several alkanes in a smog chamber was first determined by Wilson et al. ( 2 ) . O’Brien et al. (3, 4 ) have also found organic acids and nitrates in aerosols, formed from the smog chamber reactions of octadiene and NO,. To Scientific Research Laboratories, Ford Motor Co., P.O. Box 2053, Dearborn, Mich. 48121. 838
Environmental Science & Technology
date, few measurements on the molecular organic composition of atmospheric aerosols have been made during periods of atmospheric stability and photochemical aerosol formation. Recently, new techniques have been established by Schuetzle (5-7) using computerized high-resolution mass spectrometry, which make such a study more feasible. Semiquantitative results on submicrogram quantities of pollutants were possible using this technique, which allowed pollutant concentrations to be followed using 2- or 3-hr sampling intervals. The sampling of air particulate matter was made in conjunction with the 1972 California Aerosol Characterization Study (ACHEX) (8).Aerosol samples were collected over a two-month period from September 19, 1972, to November 25, 1972. Due to unusual meteorological conditions, there were few days during which the atmosphere was stable enough to allow the formation of photochemical aerosols. Fortunately, there was one three-day period of sampling, during which meteorological conditions were ideal for studying the molecular composition of aerosols before, during, and after photochemical smog production. Experimental Atmospheric Sampling. Air sampling techniques for particulate and gaseous pollutants were used which were compatible with a sampling probe designed for the mass spectrometer system. A single-stage impactor was designed which collects particles greater than 1-2 pm on 0.30-in. diam gold plates. Gold was used as a sampling medium because of its nonreactivity to acid aerosols. The remainder of the particulate matter was collected on a glass fiber filter. A mobile sampling van was equipped with a 20-ft mast upon which the sampling assembly could be hoisted and directed into the prevailing winds (Figure 1).After sampling, the filter and impactor plates were stored at dry ice temperature in glass containers sealed with a Teflon gasket to prevent losses due to volatilization and interreaction of pollutants. (Total particle concentrations were determined using a 37-mm Nuclepore filter.) Impactor plates and Nuclepore filters were weighed to &2 pg before and after sampling. Submicron particle concentrations were determined from the difference between total particle concentrations and the supermicron particle concentrations. An integrat-
VARIABLE IMPACTOR
Fil T F P
AS ABSORBER C H R O M O S O R B IO2 i
R 07
G L A S S FRIT
I
I
2400
I200
9/21 / I 7 2 Figure 2.
1
I 2400
91221'72
I9/23/'72
Variation of the light-scattering coefficient, bScat
analyzed for inorganic and organic constituents using comI * Flgure 1.
Ambient air sampling system
ing nephelometer was used to infer particle concentrations from the light-scattering coefficient bscat. Aerosol samples were collected for four intervals during the period from September 21, 1972, to September 23, 1972. Sampling times and particle concentrations for these four periods are summarized in Table I. From September 21 a t 1002 to September 22 a t 0710 there was a continental air mass in the Los Angeles basin; bscat values for this period of time were relatively constant and averaged 0.95 X (Figure 2). An onshore pressure gradient increased overnight giving a weak influx of marine air the morning of the 22nd. The marine air extended inland about 10 miles as far as downtown Los Angeles and was 300-500 f t deep. At the surface, in the vicinity of the sampling site, the relative humidity was 70% and dropped to 30% at 300 ft. During this period of time there was a rapid increase in aerosol concentration as observed by the increase in bscat and total weight of aerosols. Southeast winds developed in Pasadena during early afternoon causing a rapid decrease in aerosol concentration. The relative humidity dropped to 24% during the afternoon, and mixing heights increased to 18002000 f t with unlimited mixing late in the afternoon. Mixing heights were 11.5OC in the morning and 0.5OC in the afternoon at El Monte. Visibilities in the western part of the basin were reduced to about three miles as the peak of smog moved through the area. Molecular and Elemental Analysis. The samples were
puter-controlled high-resolution mass spectrometry, X-ray fluorescence, atomic absorption, and wet chemical techniques. Up to 200 molecular compounds or elements were determined for the eight aerosol samples collected. Special emphasis was placed on the secondary photochemical aerosols since there is little or no information on these pollutants in the literature. The quantitative results obtained from the mass spectrometric studies are estimated to be precise to within f 3 0 % on a relative comparison basis, but accuracies may vary by two times for some compounds with estimated response factors. An AEI-MS9 high-resolution mass spectrometer interfaced with a PDP-12 digital computer was used for the organic molecular analysis. A temperature programmed probe was designed to accommodate both impactor plate samples and portions of glass fiber filter, 0.30 in. in diameter. A 4.0-pg aliquot of biphenyl in methanol was added to the samples as an internal standard for quantitative determinations of the pollutants. The probe was inserted into the vacuum insertion lock system of the mass spectrometer and the particles were heated from 20-400°C into the source region of the mass spectrometer. Various pollutants were volatilized into the mass spectrometer according to their vapor pressure. Computer acquisition of mass spectra was obtained concurrent with the volatilization of sample into the source region. Mass spectra were stored on magnetic tape for processing at a later date. Many of the secondary organic pollutants were identified using their molecular mass and/or three major identifying masses, which were calculated to an accuracy of f0.003 mass units. This infor-
Table I. Sampling Times and Particle Concentrations, Pasadena, Calif. Aerosols, pg/m3 Total particle concn
Sample period (PST) Sample no.
Date-time start
85
9/21/72 1002 9/22/72 0730 9/22/72 1250 9/2 217 2 2300
86 87 88
Date-time stop
9/2 2/7 2 0710 9/22/72 1235 9/22/72 2245 9/23/72 0717
IF
Nuclepore filter
Calculatedb
lp
,50
-
53.0
37
-
157
10.4
167.4
205
15.1
59
9.7
68.7
74
6.1
73.0
113
2.8
54
19
a D i f f e r e n c e b e t w e e n t h e N u c l e p o r e f i l t e r a n d i m p a c t o r . b c a l c u l a t e d f r o m b,,,t: [ C h a r i s o n e t ai. ( 9 ) l .
(bav X
X (39 X IO4) = aerosol c o n c e n t r a t i o n i n p g / m 3
Volume 9, Number 9, September 1975 839
Table II. Diurnal Variation in Organic Primary Aerosol Concentration in l g / m 3 Submicron Compound
Naphthalene Methyl naphthalene Dimethyl naphthalene Trimethyl naphthalene AI kyl piperidenes (C5+) Phenyl pi per i dene Piperazine Carbazole Alkanes (C18-C35)
Supermicron
a5
86
a7
0.06 0.03
0.30 0.17
0.002
85
0.23 0.04
0.15 0.08
0.02 0.02
0.07
0.05
0.06
0.01
0.08
0.08
0.03
0.06
0.34
0.69
0.36
0.13
0.04
0.22
0.03
0.09
0.02
0.005
0.01
0.003
0.01
0.02
0.02 0.05 2.42
0.05 0.03 1.77
0.06
-
0.96
0.002 0.26
-
0.68
mation together with product volatilization temperatures allowed unequivocal identification of the pollutants. Standards were run for several of the compounds in order to check mass fragmentation patterns, volatilization temperatures, and for a determination of compound response factors. There were several nitrated organic compounds whose sensitivity values were not available in the literature; response factors with respect to the internal standard, biphenyl, were thus estimated and this estimate was used to calculate quantitative results. Other details of the analytical technique appear elsewhere (5-7). Analysis for several elements on the Nuclepore filters were made using a Quanta/Metrix 77-800A Materials Analysis System. The system was equipped with a 50-kv, &ma, X-ray generator with a rhodium target X-ray tube, 12-position sample changer and had the provision for vacuum path. An on-line computer program was calibrated using 1.2- and 12-pg/cm2 standards of chlorine, iron, and zinc deposited on Whatman 541 filter paper. Chlorine standards were run after removing the rhodium filter from the primary beam and pumping the sample chamber down to 100 p. The generator was then adjusted to 20 kv a t 0.3 ma. The lower limit of detection for chlorine was 0.2 pg/cm2. An automated Siemens X-ray fluorescence unit was used for the analysis of lead and bromine on the glass fiber filters. All sodium present in the particulate matter was assumed to be water soluble. The Nuclepore filters were washed with 10 ml of deionized water and analyzed using an Instrument Laboratory, Inc., atomic absorption spectrometer. Sodium standards were obtained from Fisher Scientific as 1000-ppm solutions and diluted to the appropriate concentration. Values of sulfate obtained from the mass spectrometric analysis were checked using classical analytical techniques. Sulfate concentrations were determined via titration with standardized Ba(C104)2. A visual end point indicator, thorin, was used in the titrations. The barium perchlorate titrant was standardized against standard sulfuric acid. Table IV compares the values of sulfate obtained using the mass spectrometric and classical analytical techniqes. The levels of sulfate using the titration technique were low by an average of 38 f 8%when compared to sulfate concentrations obtained from the mass spectrometric technique. It has recently been found that some loss of the biphenyl mass spectrometric standard may occur. A less volatile 840
86
88
Environmental Science & Technology
87
0.004 0.01
0.05 0.01
0.03 0.01
0.03
0.02
0.003
-
88
0.004
-
0.01 0.005 0.82
0.79
0.12
0.26
standard, hexahydropyrene, is now in use. Loss of internal standard may account for the difference in sulfate values. Results and Discussion
Thermal Behavior of the Aerosols. The thermal behavior of the aerosol was depicted in this study by plotting the total ion current signal from the mass spectrometer as a function of temperature as the sample was volatilized from the aerosol sample introduction probe and approximates the total quantity of material injected into the ion source. There are very few organic compounds which do not volatilize under the conditions used in this study (380°C and torr pressure). The possibility of compound decomposition does exist in a few cases but is minimized because the components were volatilized into a high vacuum a t a temperature which was much lower than the normal decomposition temperatures of most compounds. Decomposition would be much more likely to occur if the products identified in this study were eluted through a gas chromatographic column, for example. The identification of a number of unstable peroxides using this technique suggests a low probability of decomposition. Only at the higher temperatures ( >35OoC) will polymeric materials such as rubber tire fragments (i.e., butadiene-styrene copolymers) begin to decompose. The only other carbon-containing compounds which will not be detected are carbonates and ele10,000
-
8,000
V
.N
6,000
- 4,000 0
+
t v)
2
z
2,000 0
0
25 Figure 3.
5 100
IO
15
20
25
I
275
370-
I
30 t ( n n )
Ternp.('C) Isothermal
Total ion mass thermogram for the submicron aerosol
mental carbon. In conclusion, the area under each total ion thermogram should be related to the total quantity of material volatilized, mainly organic compounds and inorganic sulfates and nitrates. Figure 3 gives the total ion mass thermograms for the four submicron aerosol samples. The quantity of material volatilized from each sample is proportional to the area under each curve, because each plot was normalized to total mass loading on the sample and corrected for variations in instrument response. By this technique, the relative abundance of volatilized materials for the submicron aerosols was 1.00, 1.42, 1.08, and 0.92 for samples #85-88, respectively. The diurnal change in the fraction of volatilized material was not as dramatic as expected, partly because of the different diurnal variations of the major volatile components of the aerosol [primary organics, secondary organics, and sulfate (see Table X)]. Mass Distribution of the Pasadena Aerosol. The volume distribution of particulate matter in the atmosphere may be bimodal in character as reported by Husar et al. (10).They determined there is a growth in total volume of the particles in the size range from 0.1-1 km (diam). The maximum in volume is reached a t noon in synchronism with the maximum in solar radiation. This may be the result of photochemical atmospheric reactions or the effect of atmospheric motion. The volume distribution function AV/Alog D, is related to the mass distribution function AM/Alog D, by the average density (a) of the aerosol since AV = A M l p . The mass distribution function AMlAlog D, would therefore be expected to follow a similar trend. There was a significant decrease in submicron aerosol mass after the peak of smog formation but little change in the mass of the supermicron aerosol. The mass ratio of the submicron to supermicron sized particles was a maximum a t noon (15.1) on September 22, 1972, and decreased during the next two sampling periods (6.1 and 2.8). Several investigators have predicted that the increase in submicron aerosol mass at periods of maximum solar radiation are due primarily to the formation of photochemical aerosol. Analysis for secondary aerosol products was performed to determine if this was the case. Organic Primary Aerosols. The organic fractions of Table I I I. Concentrations of Several Elements Obtained from Analysis of Pasadena Aerosol (All Sizes) Elemental concentration, p g / m 3
Sample no.
Na
85 86 87 88
0.9
1.0
3.1 2.0 3.2
1 p ) HC1
+
NH,
--
O'
m
2
24b0
I 2400
9/21/'721
9/22/'72
I9/23/'72
Diurnal variation in submicron alkanes, naphthalene,and
trimethyl naphthalene
the identification parameters for the five dicarboxylic acids identified in aerosols, their identifying masses (molecular masses), and the temperature at which these acids were volatilized from the aerosol matrix. Two major groups of organic secondary compounds correlated well with the increase and decrease in solar radiation and total aerosol production. These were the difunctionally substituted alkanes (I) and the monofunctionally substituted aromatic (11) compounds. These compounds are shown with the hydrocarbon chain existing as either the normal or secondary isomer.
N a , S O I O 1 p) -t BHCl? NH,C1(-(CH?)),-X
@
(CH,),,--X (CH?),,-X
IV I11 Several products of Type I were identified where the X substituent was found to be CHzOH, CHO, COOH, CHzONO, COONO, and COON02 with n varying from one to five. Several of these products have also been identified in the smog chamber oxidation of cyclohexene by Wilson et al. ( 2 ) . Tables VI1 and VI11 give the diurnal variation for each of these products in the submicron and supermicron aerosol size ranges. Greater than 95% (by weight) of the Type I products was found in the submicron aerosol size range. These data are consistent with the theory that photochemical products are primarily present in the submicron aerosols. The compounds identified may have originated from the photochemical oxidation of cycloalkenes and/or dienes with a variety of possible reaction schemes ( I O ) . The proposed gas phase precursors and the resulting aerosol products are depicted by the following reaction scheme:
X-(CH,),-X
+
X-(TH2),-i-X
( n = 4,s) where
k
= 1.2; I = 0 , l
and m = 0 , l
To date there are insufficient ambient data on the possible precursors of secondary aerosols identified in this study. There are two possible reasons for the lack of data: The gaseous precursors are too reactive to remain in the atmosphere for a significant period of time and the gas chromatographic techniques used to date do not have sufficient resolution or sensitivity. Stephens (14) has reported a cyclopentene concentration of 4.4ppb in the atmosphere with a sensitivity of 0.1-0.2 ppb. This concentration of cyclopentene could produce up to 23.8 bg/m3 of aerosol if all of the Volume 9, Number 9, September 1975
843
cyclopentene were converted to glutaric acid. This conversion illustrates the fact that only sub-ppb concentrations of the proposed precursors were necessary to form the secondary aerosols identified in this study. Four cyclic olefins have been identified in gasoline and/or auto exhaust: cyclopentene, 1-methyl cyclopentene, 3-methyl cyclohexene, and 4-methyl cyclohexene (15-21). These gases could account for the formation of the products (I) with n = 3-5. Smog chamber studies of several alkenes (2, 22) have shown that decarboxylation occurs and could account for the production of difunctional organics with n = 1,2. The only diolefins found to date in gasoline and/or auto exhaust have four to five carbons. This eliminates the possibility that dienes serve as a precursor for difunctional organics where n = 2-5. 1,4-Pentadiene has been identified in auto exhaust and may contribute to the formation of the products (I) where n = 1. Monofunctionally substituted aromatics (11) were identified primarily in the submicron size ranges where n. varied from zero to three and the X substituent was COOH (Table V). No compounds of Type I1 were detected when the X substituent was either CHO or CH20H and is possibly the result of their higher vapor pressures. Benzoic and phenylacetic acids have been previously identified in “auto exhaust material” (21, but these two acids were not detected in air particulate matter samples in the Bronx, New York. These data, may indicate that the concentration of these two acids in auto exhaust is not of sufficient magnitude to allow measurement of ambient air concentration. The diurnal variation of these pollutants is indicative of their secondary origin and is highly correlated with the diurnal variation in the Type I products. Both alkenylbenzenes and alkyl benzenes may be photochemically oxidized to form these products, but no ambient air data on gaseous alkenylbenzenes exist to date. Both benzaldehyde and tolualdehyde have been identified in auto exhaust and may be oxidized to their respective acids. There are several factors that may affect the concentration of secondary organics found in the aerosol. Undoubtedly some of these products must exist in both the gas and aerosol phases if one considers both their vapor pressure and concentrations. On the basis of vapor pressure alone, it would be expected that some of the pollutants (Le., naphthalene) could not exist in the aerosol phase. However, studies in this laboratory have shown that atmospheric aerosols are highly adsorptive, especially with respect to polar compounds. Table IX illustrates the effect of aerosol matrices on the vaporization or elution temperature of four pollutants. One microgram of each material was added to a clean brass disk with particles and a glass fiber filter with particles. The matrices were inserted into the mass spectrometer and heated a t 22OC/min. -The temperatures a t which the compounds were vaporized from the particle matrix were significantly higher than in the absence of the particle matrix. Negligible differences were observed for particles collected on the brass disks (impactor) or on glass fiber filters. The largest effect was observed for the two most polar compounds, phenol and glutaric acid. The possible presence of chlorinated and brominated organic compounds in the aerosol was determined by searching the mass spectra for ions containing carbon, hydrogen, chlorine, and/or bromine. One chlorinated mass fragment identified was C.&Cl+ (m/e, 91.031), a major mass fragment derived from compounds of the type R-GHsCl. The fragment C&Br+ was in trace quantities only. The temperature a t which the C4HsC1+ peak appeared was nearly the same for all the samples, which indicates that the same type of alkyl chloride(s) was present in each. The abun844
Environmental Science & Technology
Table IX. Effect of Aerosol Matrix on Vaporization Temperature of Several Pollutantsa Compound
Brass disk
Particles o n brass disk
Particles on filter
Naphthalene Phenol Glutaric acid Phenanthrene
60 20 125 80
110 172 250 124
85 170 230 140
‘/$
(20°C)
0.01 0.02 0.001 0.001
aHeating rate at 2Z0/min, aerosol sampling probe. b 760-mm pressure.
Table X. Average Relative Diurnal Concentration (Wt %) Change for Primary and Secondary Submicron Aerosols A v relative ( w t %) changea Pollutant group
85
86b
87
88
Primary aerosols-
inorganicc Na
Pb
Zn Fe Primary aerosols--organic (Table 1 1 ) Secondary aerosolsinorganic “,NO, NH,CI
Sulfates as (“,),SO, Secondary aerosolsorganic Alkyl difunctional (Table VI I ) Phenyl alkyl monofunctional (Table V)
0.91 1.84 3.66 1.84
1.00 1.00 1.00 1.00
0.96
1.00 2.20)
2.21
1.41
0.22 0.55 0.45
1.00 1.54) 1.00 1.54) 1.00 13.6)
0.79 0.76 2.60
0.23 0.53 1.24
0.55
1.00 11.5)
1.00
0.11
0.35
1.00 (0.85)
0.51
0.00
(1.85) (1.92)
1.59 1.56 (0.18) 1.39 (1.35) 2.15
2.34 1.41 2.50 0.95
a V a l u e ~for a85,8 7 , and 88 calculated with’respect t o #86 (1.00).T h e values given are the relative concentration change of submicron aerosol products. expressed as a uercentaae of the total submicron aerosol, excluding the inorganic rimary aerosols expressed as a percentage o f the total aerosol.%The values in parentheses are the w t % concentration of the products in t h e aerosol. CTotal of submicron and supermicron aerosoi.
dance of the C4H&1+ ion was integrated for each sample and used to estimate the concentration of aliphatic chlorides assuming the molecular species was octadecyl chloride. For submicron aerosol samples #85-88, the concentrations were 0.14, 0.15, 0.32, and 0.02 pg/m3, respectively. It is difficult to predict the origin of these chlorides on the basis of their diurnal variation. A possible secondary mechanism could be the release of chloride from the sea salt aerosol as HC1 and reaction of HCl with particulate or gaseous alkenes. Other peaks containing chlorine were identified in sample #86 as C7HsC13 (m/e 192.938) and CcH3C12 (m/e, 144.961). These fragments most likely arise from a primary origin, as chlorinated benzenes and polychlorinated biphenyls. An estimated concentration for the parent compounds would range from 0.5-3 ng/m3.
Conclusions Many secondary organic and inorganic constituents of aerosols have been identified for the first time during periods of smog formation in ambient air. The results indicate that the composition of secondary aerosol is very complex and comprised of scores of different compounds. The distribution of difunctionally substituted alkanes in ambient air was similar to products found in earlier smog chamber
studies ( 2 ) and more recent smog chamber studies (22). However, the origin of some of the other products is only speculative and further work is necessary to determine their source and mechanism of formation. Table X summarizes the average relative concentration ( w t %) change for the primary and secondary aerosol samples. Values for samples #85, 86 and 88 are compared to #86 (1.00). During sampling period #85, secondary aerosols were formed, but high concentrations of aerosol were not allowed to accumulate owing to unfavorable meteorological conditions. Sampling period # 85 covered nearly the same time span (1002-0710) as sampling periods #86-88 (0730-0717). An examination of the data in Table X shows that the percentage abundance of organic secondary compounds in the aerosol for the first sampling period (#85) was nearly the same as that for the succeeding periods (#86-88). These data imply that the rapid increase in aerosol production observed on September 22, 1972, was primarily the result of meteorological conditions. Sample #88 was collected only during the nighttime and early morning hours (2300-0717), thus eliminating the possibility of photochemical reactions from occurring. In addition, relatively clean air was injected into the area from the southeast. During this time, the concentration of organic secondary products in the aerosols was reduced by more than nine times, from the peak aerosol period ( #86). There was little change in the concentration of the organic primary aerosols during this period, which is consistent with the fact that the concentration of the primary aerosols will be dependent upon their source strength. The highest concentration of primary organics was observed in sample #87, during a period of time which encompassed the evening rush hour traffic. The diurnal variation in sulfates did not appear to show a dependence upon photochemistry and was not correlated with the variation in organic secondary aerosols. However, there was a good diurnal correlation between sulfate and organic primary aerosol. Greater than 95 wt % of the organic secondary products were present in the submicron aerosols. This compares with an average of 44 wt % for the organic primary products in this size range. These data are consistent with the theory that photochemical products are primarily present in the submicron aerosols. Previous workers have shown that air particulate matter is a good adsorbent for gases such as sulfur dioxide. I t is possible that some of the products identified in this study were adsorbed from the gas phase by particulate matter in the atmosphere or during sampling. In addition, gas phase concentrations of the identified species may exist. For this reason, future studies should include product identification for both the gas and aerosol phases, simultaneously. Work of this nature is now in progress.
Literature Cited (1) Whitby, K. T., Husar, R. B., Liu, B. Y. U., “Physical Mecha-
nisms Governing Dynamics of Los Angeles Smog Aerosol,” presented a t the Kendell Award Symposium ACS Meeting, Los Angeles, Calif., April 1971. (2) Wilson, W. E., Schwartz, W. E., Kinzer, G. W., “Haze Formation. Its Nature and Oriein.” Battelle Columbus Laboratories Rep: # CPA 70,1972. (3) Obrien, R. J., Holmes, J. R., Crabtree, J . H., Hoggan, M. C., Bockian. A. H.. “The Organic Fraction of Smog Aerosol: Collection, Extraction, Separgion and Preliminary-Identification of Hi-Vol Filter Samples,” Joint Pacific Conference on Chemistry and Spectroscopy, San Francisco, Calif., October 16-20, 1972. (4) Obrien, R. J., Holmes, J . R., Bockian, A. H., “Formation of Photochemical Aerosol from Diolefins,” ibid. (5) Schuetzle, D., “Computer Controlled High Resolution Mass Spectrometric Analysis of Air Pollutants,” PhD dissertation, University of Washington, 1972. (6) Schuetzle, D., Crittenden, A. L., Charlson, R. J., “Application of Computer Controlled High Resolution Mass Spectrometry to the Analysis of Air Pollutants,” J . Air Pollut. Contr. Assoc., 23 (1973). ( 7 ) Schuetzle, D., “Analysis of Complex Mixtures by Computer Controlled High Resolution Spectrometry-I. Application to AtmosDheric Aerosol ComDosition.” submitted to Biomed. Mass Spectrom., 1975. (.8.) Hidv. G. M.. “Characterization of Aerosols in California-Interim Report for Phase I Covering the Period October 25, 1971 to April 1,1973,” Air Resources Board, State of California. (9) Charlson, R. J., Ahlquist, N. C., Horvath, H., “On the Generality of Correlation of Atmospheric Aerosol Mass Concentration and Light Scatter,” Atmos. Enuiron., 2,455-64 (1968). (10) Husar, R. B., Whitby, K. T., Liu, B. Y. U., “The Size Distribution of Los Angeles Smog,” presented a t the Kendell Award Symposium ACS Meeting, Los Angeles, Calif., April, 1971. (11) Niki, H., Daby, E. E., Weinstock, B., “Photochemical Smog and Ozone Reactions,” Advan. Chem. Ser., Number 113, 1972. (12) Miller, M. S., Friedlander, S.K., Hidy, G. M., “A Chemical Element Balance for the Pasadena Aerosol,” J. Colloid Interface Sci., 39,165-76 (1972). (13) Hirschler, D. A., Gilbert, L. F., Lamb, F. W., Niebylske, L. M., Ind. Eng. Chem., 49,1131 (1957). (14) Stephens, E. R., “Hydrocarbons in Polluted Air,” Coordinating Research Council Project Summary Rep. CAPA-5-68 (1973). (15) McEwen, D. J., Anal. Chem., 38,1047 (1966). (16) Maynard, J. B., Sanders, W. N., J . Air. Pollut. Contr. Assoc., 19,505 (1969). (17) Sanders, W. N., Maynard, J. B., Anal. Chem., 40,527 (1968). (18) Papa, L. J., Densel, D. L., Haris, W. C., J . Gas Chromatog., 6, 270 (1968). (19) Stephens, E. R., Burleson, F. R., J . Air Pollut. Contr. Assoc., 17,147 (1967) and ibid., 19,929 (1969). (20) Grob, K., Grob, G., J . Chromatog., 62,1(1972). (21) Jacobs, E. S., Anal. Chem., 38,43 (1966). (22) Rasmussen, R., Schuetzle, D., “Formation and Composition of Aerosol Products from the Reaction of Terpenes with Ozone and NO2 in the Presence of Sunlight,” unpublished data, 1974. Received for review August 15, 1974. Accepted April 18, 1975. Paper presented at the 166th National Meeting of the American Chemical Society, Symposium on Surface and Colloid Chemistry in Air Pollution Control, Chicago, Ill., August 1973. Work supported in part by Environmental Protection Agency Grant #SO1119. I
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