Measurements of some low molecular-weight oxygenated, aromatic, and chlorinated hydrocarbons in ambient air and in vehicle emissions

Environment International, Vol. 11, pp. 383-392, 1985 Printed in the USA. All rights reserved.

0160-4120/85 $3.00 + .00

Copyright ©1985 Pergamon Press Ltd.

MEASUREMENTS OF SOME LOW MOLECULARWEIGHT OXYGENATED, AROMATIC, AND CHLORINATED HYDROCARBONS IN AMBIENT AIR AND IN VEHICLE EMISSIONS A. Jonsson, K. A. Persson, and V. Grigoriadis Department of Analytical Chemistry, Arrhenius Laboratory, University of Stockholm, S-106 91 Stockholm, Sweden (Received 15 December 1984; Accepted 1 February 1985) Low-molecular-weight oxygenated, aromatic, and chlorinated organic air pollutants were measured at different sites in urban air and in motor vehicle emissions. The analytical method used is based upon cryogenic sampling using a thermogradient over a packed, well-deactivated sampling tube. Analysis of the samples was made by two-dimensionalgas chromatography. Formaldehyde was trapped on molecular sieve 13 × and analyzed by gas chromatography with photoionization detection. At sites near dense traffic a strong correlation was found between vehicleexhaust components such as CO and NO with aromatic compounds (benzene, toluene, ethyl benzene, m/p-xylene), formaldehyde, acrolein, methacrolein, and 3-buten-2-one. At the dense traffic sites, significant amounts of methanol (0.58-72 nL/L), ethanol (1.5-247 nL/L), 2-propanol (0.28-44 nL/L), acetone (1.0-129 nL/L), 2-butanone (0.26-32 nL/L), ethylacetate (0.15-21 nL/L), trichloroethylene (0.03-37 nL/L), tetrachloroethylene (0.04-53 nL/L), butanal (0.06-3.1 nL/L), pentanal (0.04-1.9 nL/L), and 3-methylbutanal (0.01-0.45 nL/L) were measured. However, these compounds did not generally correlate to typical vehicle exhaust compounds. Other potential sources such as solvent usage, dry cleaning, and bakeries are plausible sources for these compounds. For the low molecular weight aldehydes (C,-Cs), photochemical production as well as natural emissions may be significant sources.

Introduction Much concern has been shown in recent years regarding the possible health effects caused by long-term exposure to low levels o f genotoxic air pollutants in urban environments. A n u m b e r o f the volatile organic compounds c o m m o n l y found in the polluted atmosphere are suspected of being carcinogenic to man, e.g., formaldehyde (Robins and Bingham, 1980), benzene (Occupational Health and Safety Administration, 1977), and tetrachloroethylene (Altshuller, 1980). Other adverse effects, mainly associated with oxygenated hydrocarbons (formaldehyde and other aldehydes, ketones, alcohols, etc.), include irritation o f eyes and mucous membranes (Altshuller, 1978) and the ability of m a n y species to act as radical sources in photochemical smog production (Graedel, 1978). Except for a few lower oxygenates, mainly formaldehyde, and peroxyacetyl nitrate (PAN), the distribution and variabilities o f oxygenated hydrocarbons in typical urban atmospheres is not well known t o d a y (Altshuller, 1983). One probable reason for this are the considerable problems associated with quantitative analysis o f small

amounts o f volatile polar compounds in such a complex matrix as ambient air (Jonsson and Berg, 1983). The use o f dedicated sampling equipment and advanced analytical techniques (i.e., two-dimensional gas chromatography (2D-GC) in combination with highly sensitive a n d / o r specific detectors, as well as 2 D - G C - m a s s spectrometry) has made possible the accurate identification and quantitation of a wide range of low-molecularweight oxygenates in ambient air; hydrocarbons and chlorinated hydrocarbons m a y also be determined. This paper provides a s u m m a r y o f the results obtained during a one-year study of Stockholm air. Quantitative data on volatile alcohols, aldehydes, ketones, ethyl acetate, light aromatics, and two chlorinated ethylenes are presented. D a t a f r o m auto and diesel exhaust measurements are also included.

Experimental A m b i e n t air sampling and analysis Sampling for all compounds except formaldehyde was accomplished using a cryogenic sampling technique 383

384 in which a cryogradient is established over a well-deactivated sampling tube packed with a sorbent bed (Jonsson and Berg, 1983). Cryogradient sample tubes were made of Pyrex glass tubing (380 x 6 mm o.d., 3 mm i.d.). The glass tubes were thoroughly cleaned, silanized, and filled to a length of 300 mm with sorbent material, this bed being held in place with small plugs of silanized glass wool. The sorbent bed material was prepared as follows: Chromosorb WAW (30-60 mesh) (JohnsManville, Denver, CO) was deactivated with 3,3,3trifluoropropyl-methyl-cyclotrisiloxane as previously described (Jonsson and Berg, 1983) and coated with 5o/0 of a trifluoropropyl-methyl-silicone liquid (SP-2401, Supelco, Bellefonte, PA). After preparation, the sample tubes were conditioned overnight under a stream of purified nitrogen at 200 °C, and were finally sealed with Swagelock caps and nylon ferrules. In order to minimize contamination of the sample tubes before sampling, the sample tubes were stored in a glass vessel containing activated carbon and molecular sieve 13X. During sampling a cryogradient from - 50 °C (at the upstream end of the tube) to - 100 °C was maintained over the sample tube. Usually 2-3 L of ambient air was sampled during a 1-h period. This sample volume could be used without the trap becoming plugged by ice, even in warm and humid periods. After sampling, the cryogradient sample tubes were sealed and stored in a Dewar vessel cooled with solid carbon dioxide ( - 7 9 °C) until analysis. The samples were transferred to the gas chromatograph by gentle heat desorption (150-175 °C) and analyzed by two-dimensional gas chromatography (2D-GC) (Jonsson and Berg, 1983; Berg and Jonsson, 1984). Compounds were separated on a packed column (glass; 2 m x 1.8 mm i.d.) with a highly polar stationary phase (1,2,3-tris (2-cyanoethoxy) propane, Alltech, Deerfield, IL) on Chromosorb WAW (100-120 mesh), then refocused on-line in a fused silica capillary cold-trap, followed by on-line splitless reinjection onto a fused-silica capillary column (50 m x 0.3 mm i.d., Hewlett-Packard, Palo Alto, CA) coated with a nonpolar methylsilicone liquid (OV101). A variable restrictor, situated immediately after the first column, split approximately 6°70 of the effluent to a photoionization detector (PID) (HNU, PI-52-02, HNU Systems, Newton, MA). The rest of the effluent was directed to a laboratory made flame ionization detector (FID) or to the capillary trap. Switching was accomplished by flow switching according to Deans (1968). The PID and FID, used as monitoring detectors for the first column, were also used to quantify the higher aromatics, i.e., ethyl benzene and xylenes. These latter compounds were co-eluted with water and could not be transferred to the second (capillary) column, because this would have caused plugging of the capillary trap by ice. Compounds transferred to the capillary column were quantified by a second FID. Data recording and

A. Jonsson, K. A. Persson,and V. Grigoriadis peak processing were made with an integrator (Shimadzu Chromatopac C-R1A). For identification of unknown compounds the 2D-GC was connected to a double-focussing mass spectrometer (JEOL JMS-D300) (Jonsson and Berg, 1983). Formaldehyde was trapped on a solid adsorbent (molecular sieve 13X, 40-60 mesh; Alltech, Deerfield, IL) and analyzed by gas chromatography with photoionization detection using a high energy UV-lamp (11.7 eV). Sample tubes for formaldehyde were made of pyrex glass tubing (200 x 6 mm o.d., 3 mm i.d.). After silanization, the tubes were filled to a length of 95 mm with sorbent material. The sample tubes were conditioned overnight under a stream of purified nitrogen at 280 °C, and then stored in the same way as described above for cryogradient tubes. Typically, 3L of ambient air was sampled during a 1-h period. Formaldehyde was then transferred to the gas chromatograph by heat desorption (220 °C) and analyzed on a packed column (glass, 3 m x 1.8 mm i.d.) packed with 0.50/0 Carbowax 20M (Applied Science, State College, PA) on Porapak T (80-100 mesh) (Waters, Milford, MA). Details of this method will be published elsewhere.

Calibration, precision and accuracy Both gas phase standards and liquid solutions were used for calibration. Gas phase standards in the nL/L-#L range of aldehydes, ketones, and benzene were prepared by means of diffusion tubes and dynamic gas-phase dilution as previously described (Jonsson and Berg, 1983). Aliquots of the gas standard were injected onto the 2D-GC, and response factors relative to benzene were determined. The response factors for oxygenated compounds relative to benzene were found to be, within experimental error, constant over long periods. Thus, for repeated determinations during a 1-yr period, the following average response factors and standard deviations were found: acrolein, 0.44, 7070; acetone, 0,54, 507o; 2-methyl acrolein, 0.49, 6°70; 3-buten-2-one, 0.51, 3°70; and 3-methyl butanal, 0.54, 1°70 (benzene, 1.00). Day-to-day calibration was performed by injecting known amounts of benzene, from the dynamic gasphase standard generator, onto the gas chromatograph. The amount of each compound was determined by dividing the peak area of the compound with the corresponding response factor and with the peak area of the standard benzene peak, and multiplying with the amount of standard benzene injected. A permeation tube containing paraformaldehyde was used for generation of calibrated gas mixtures of formaldehyde. The permeation tube was maintained at 84 ±0.25 °C under a constant flow of nitrogen. Permeation rate was determined by regularly weighing the permeation tube during at least one month. Calibration was performed by sampling 3 L of accurately diluted and humidified formaldehyde primary gas standard on

Low-molecular-weighthydrocarbons molecular sieve sample tubes, which were then analyzed by the above described procedure. The accuracy of the sampling and analytical methodology (2D-GC) is dependent on many factors and may be difficult to determine. However, it was estimated for those factors that were thought to be the most critical, i.e., gravimetric calibration of the diffusion tubes (accuracy better than 1%), measuring and controlling of dilution flow rates (accurate to within 3%), syringe transfer of the gas phase standard to the gas chromatograph (accurate to within 5 %), and determination of the sample volume (accurate to within 3 %). For compounds in the low n L / L range, the total sampling and analytical recovery was close to 100% (Jonsson and Berg, 1983). Thus, the analytical accuracy is estimated to be within 12% of the true value. The minimum detectable quantity (peak height = 2 x noise width) was approximately 80 pg for a typical oxygenate, e.g., 3-methylbutanal, which corresponds to 0.008 n L / L in a 3-L sample volume. The precision of the method was 12% relative standard deviation or less for compounds in the low n L / L range. The detection limit of formaldehyde was 0.5 nL/L.

Measuring sites Sampling within Stockholm city was made at a mobile air-quality measuring station belonging to the Environment and Health Administration in Stockholm. Air samples were collected at a height of 3 m above ground level. Concentrations of inorganic pollutants such as CO, NO, and NOx were continuously measured at the station and some local meteorological parameters were registered. Ozone data within the city were obtained from a fixed station on the roof of the Environment and Health Administration building. Measurements were also conducted at a reference station (a recreation area 12 km outside central Stockholm). CO was not measured at this site.

Sampling and analysis of vehicle exhaust Test procedure. Measurements were made on a heavyduty diesel truck (Volvo TD 100, 9.6 L, six-cylinder) and gasoline powered cars. Late-year model vehicles complying with Swedish specifications (a SAAB 900 and a Volvo 244, both with carburetors) and U.S. Federal specifications (an Audi 4000, fuel injection) were used; the Audi was equipped with a three-way catalyst. The gasoline (motor octane number 90.8) contained 36.6% aromatics (1.5% benzene), 7.5% olefines, and no oxygenated additives. Regular diesel fuel was used with the heavy-duty vehicle. All tests were carried out on a chassis dynamometer at the National Swedish Environment Protection Board, Motor Vehicle Emission Laboratory. An exhaust gas sampling system for testing according to the CVS (constant volume sampling) procedure was used (U.S. En-

385 vironmental Protection Agency, 1980). Light-duty (gasoline) vehicles were investigated over transient driving cycles according to (a) the 1973 Federal Test Procedure (FTP) (US 72 driving cycle: cold start and stabilized portion), and (b) the ECE (Economic Commission for Europe) test procedure. The heavy-duty diesel was investigated over transient driving cycles according to (a) a "terminal cycle" similar to the ECE procedure but at a lower maximum driving speed, and (b) a "bus cycle" with numerous repeated accelerations and decelerations. All driving cycles had a duration of between 20 to 30 min. Tailpipe emissions were continuously diluted with filtered ambient air to give a constant volume according to the FTP or the ECE procedure. The cryogradient sampling equipment was connected to the diluted exhaust gas stream with a 1-m length of stainless steel tubing which was kept above 100 °C in order to prevent water from condensing. One sample for analysis of oxygenates and aromatics was collected for each driving cycle. After sampling, the sample tubes were sealed, stored in the dark at solid carbon dioxide temperature ( - 7 9 °C), and transported to the laboratory for analysis. Since diluted exhaust levels of ethanol did not exceed blank levels in the dilution tunnel, this compound was not quantified. Formaldehyde was measured by another research group and the results are not published here. Results and Discussion Table 1 summarizes the data obtained for all of the organic compounds measured at four different urban sites (Stockholm, sites I-IV) and at one site 12 km outside central Stockholm (site V). Average concentration, relative standard deviation, and minimum and maximum values are given. The averages (arithmetic mean) are based on all 1-h samples collected at each site. Some reference parameters, i.e., concentrations of NO, NO2, CO, 03, and windspeed, are also given in Table 1. Information on sampling periods, the number of samples at each site, and a brief description of the sites is presented in Table 2.

Consideration of chemical categories Carbonyl compounds. Significant amounts of carbonyl compounds (aldehydes, ketones, ethylacetate) were found at all urban sites as well as at the reference site (Table 1). Extensive measurements of carbonyl compounds in urban atmospheres have been made only for formaldehyde and peroxyacetylnitrate (PAN) (Altshuller, 1983). Concentrations of formaldehyde (0.5-12 nL/L) in Stockholm air are somewhat lower than hourly average levels reported from Tokyo (1.4-18 nL/L) (Higuchi et al., 1979). High levels of formaldehyde (3-71 nL/L) have been reported from measurements

386

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387 Table 2. Descriptionof sampling sites.

Site/Description

Numbera

Period

Traffic Intensityb

Days

R6dabergsgatan, calm street in central Stockholm Hornsgatan, busy street in central Stockholm

IV

82.08.03-82.09.01

1700

3

II

82.09.22-82.12.16

49500

12

96

Kastellholmen, small island with little traffic in central Stockholm Sveaviigen, busy street in central Stockholm Kanaan, recreationarea 12 km WNW of central Stockholm

III

83.01.20-83.03.10

no data available

7

56 (68)d

I

83.03.29-83.05.10

27000

7

56

V

83.05.18-83.06.30

no data available

7

56

Samplesc 24 (40)d

aThese numbers are referredto in Table 1. bNumber of vehicles/workingday. Data from 1981. cEach sample taken during 1 h; normallyeight samples each day. dNumbers in parantheses includesamples taken in the earlymorning and at night.

during photochemical smog periods in the Los Angeles area (Tuazon et al., 1981, Grosjean, 1982; Hanst, 1982). Acrolein levels in Stockholm (0.04-12 nL/L) (Table 1) are in fair agreement with levels reported from Los Angeles during the period 1961-68 (average values 4-7 n L / L with a maximum of 14 n L / L (Altshuller, 1983). Butanal and methylethylketone have been measured in Los Angeles by Grosjean (Grosjean, 1982; Grosjean et al., 1983). Data on butanal (from below detection limit to 8 n L / L and 0.1-7 n L / L during smog period) are somewhat higher than our data from Stockholm (0.06-3.1 nL/L). On the other hand, data on methylethylketone in Los Angeles (from below detection limit to 15 nL / L , and from below detecion limit to 14 n L / L during smog period) are somewhat lower than our data from Stockholm (0.25-32 nL/L). For the other carbonyl compounds reported in Table 1 there seems to be little data available for comparison. Methacrolein, 3-buten-2-one, pentanal, 3-methylbutanal, and ethylacetate have to our knowledge not been quantified before in the open air of cities. Background levels of acetone have been reported from Point Barrow, Alaska (0.3-2.9 nL/L) (Cavanagh et al., 1969). Average acetone concentrations measured at sites I and II were an order of magnitude higher.

Alcohols. High levels of methanol (0.45-72 nL/L), ethanol (1.48-247 nL/L), and 2-propanol (0.25-44 nL/L) were frequently found in Stockholm air. The high maximum and average concentrations of ethanol measured at several sites in Stockholm indicates that this compound is one of the most abundant organic species excepting methane, in Stockholm air. No data were available for comparison. However, urban air levels of methanol have been reported in the range of

4-40 n L / L (Hanst, 1982) and 8-100 n L / L (Graedel, 1978). This is in fair agreement with our measurements. Alcohol-blended fuels have only recently (i.e., after completion of this study) become available on the Swedish market. Furthermore, gasoline and diesel vehicles running on regular fuels emit only minor amounts of low-molecular-weight alcohols (Jonsson et al., 1982). Thus, it is not likely that the high levels of ethanol derive from vehicle emissions. This assumption is further confirmed by the lack of correlation to typical exhaust components such as CO or benzene, which will be discussed in the section below. In Fig. 1, concentrations of 2-propanol and ambient temperatures are plotted against time during measurements at site II (fall and early winter 1982). The figure reveals a dramatic increase in the 2-propanol levels, which coincides with a fall of ambient temperature towards zero. 2-Propanol is a main component of antifreezing agents for windscreen washers. Thus, a rapid increase in the use of antifreezing agents as the temperature approaches zero might explain this phenomenon. Substantial amounts of methanol and ethanol (100-226 mg/km) were measured in the exhaust emissions from non-catalyst vehicles fueled with isobutanol/ methanol/gasoline (2/15/83; M 15) and ethanol/gasoline (23/77; E23) (Jonsson et al., 1982). Methanol emissions from a light-duty diesel vehicle fueled with 95°70 methanol were one order of magnitude higher (3.4 g/km). The use of a three-way conversion catalyst with a closed-loop control system may reduce alcohol emissions significantly (Jonsson et al., 1982). However, in European countries where this type of exhaust control system is not used, the penetration of alcohol-blended fuels into the marketplace today implies another potential source of alcohols to the urban atmosphere.

388

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Table 3. Linear regression analysis (Y = k X + m) on individual chemical species at an u r b a n site near dense traffic (site II). Y = concentration o f species; X = concentration o f benzene.

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Aromatic hydrocarbons. Light aromatics have been measured on several occasions in urban atmospheres, and a large amount of data is available for comparison. Levels of benzene, toluene, and the Cs aromatics found in Oslo (<1-60 nL/L) (Wathne, 1983), in Helsinki (3-30 nL/L) H ~ i n e n et aL, 1981), and in Berlin (3-105 nL/L) (Dulson, 1978) are in fair agreement with the levels found at sites I to IV in Stockholm (Table 1). The concentrations of aromatics found at the dense traffic sites (sites I and II) were significantly (usually one to two orders of magnitude) higher than the concentrations found immediately outside Stockholm (site V). Chlorinated ethylenes. Trichloroethylene and tetrachloroethylene were found in highly varying concentrations (0.03-37 nL/L) and (0.03-53 nL/L), respectively, at the four urban sites. Much lower concentrations were determined at site V (0.006-1.6 n L / L and 0.02-2.4 n L / L , respectively) (see Table 1). Singh et al. (1981) have measured chloroethylenes at three different urban sites in the United States and report concentrations that were significantly lower than our urban data, i.e., trichloroethylene, 0.01-3.1 n L / L and tetrachloroethylene, 0.05-3.7 nL/L. Tri- and tetrachloroethylene are important industrial solvents used for, e.g., degreasing of metals (Organization for Economic Cooperation and Development, 1982). Furthermore, tetrachloroethylene is widely used for dry cleaning. Thus, evaporative emissions might be an important source of these compounds in urban air. The high level of tetrachloroethylene occasionally measured at site II (Table 1) were found to coincide with the local wind blowing in the direction from a dry-cleaning facility situated less than 25 m down the road from the sampling station. The contribution from local sources near the sampling site may thus explain the high concentration of chloroethylenes measured in Stockholm air.

D.F. a

Formaldehyde Acrolein Methacrolein Pentanal 3-Methylbutanal Acetone Methylethylketone 3-Buten-2-one Methanol

62 76 78 79 75 76 76 79 76

Ethanol 2-Propanol Ethylacetate Toluene Ethylbenzene m/p-Xylene Trichloroethylene Tetrachloroethylene CO NO

76 76 79 76 79 79 78 76 79 55

k b x 100 13 5.2 0.99 0.040 0.040 20 - 0.28 0.59 15 15 5.3 12 3.6 190 51 130 -0.13 9.2 15000 1400

±5.0 ± 1.3 ±0.040 -4-0.29 ±0.10 ± 120 -4-11 ±0.21 ±22 ± 13 c -4-160 ±33 ± 19 ± 14 -4-5.1 -4-12 ± 1.3 ±41 ±3400 ±360

m (ppb, n L / L )

r

2.4 0.28 0.048 0.15 0.039 15 2.5 0.060 5.7

0.764 0.841 0.943 0.055 0.158 0.071 0 0.746 0.259

29 3.9 1.4 0.54 0.93 1.96 0.29 2.9 707 0.17

0 0.148 0.077 0.985 0.970 0.975 0.032 0.089 0.862 0.868

aD.F. (degrees o f freedom, n - 2) = sample n u m b e r - 2 . bA 99.9% confidence interval for k is given. If this interval does not include 0 then k is different from 0 with 99.9% confidence. Thus, a correlation exists between X and Y. cA 95% confidence interval is given.

Co-variation o f measured chemical species At sites near dense traffic (site I and II) there was a strong correlation between vehicle exhaust components such as CO and NO with aromatic compounds (benzene, r = 0.959, r = 0.862; toluene, r = 0.940, r = 0.865; ethylbenzene, r = 0.921, r = 0.903; m/p-xylene, r = 0.980, r = 0.892), formaldehyde (r = 0.748. r = 0.747), acrolein (r = 0.806, r = 0.754), methacrolein (r = 0.919, r = 0.807) and 3-buten-2-one (r = 0.791, r = 0.744); here, r is the correlation coefficient for the correlation to CO at sites I and II, respectively. The co-variation of benzene and CO at site II is illustrated graphically in Fig. 2b. The aromatic compounds correlated highly to each other at the urban sites as shown for benzene and toluene at site II (Fig. 2a). Light aromatics are typical exhaust components from gasoline-powered automobiles and thus account for the high degree of co-variation within this group and with CO at sites near dense traffic. The abovementioned oxygenated species, showing a high degree of correlation to CO, were also highly correlated to benzene at sites near dense traffic. In Table 3 are summarized some linear regression data for individual organic species at site II. It is evident from Table 3 that there is a strong positive correlation between benzene and oxygenated compounds such as formaldehyde, acrolein, methacrolein, and 3-buten-2-one at site II. The correlation between benzene and these oxygenates was at least as strong at site I (formaldehyde, r = 0.790; acrolein, r = 0.857;

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Fig. 2. Plots of compound (Y) versus compound ( X ) at selected sites in the Stockholm area (ppm = t,L/L; ppb = nL/L). The results from linear regression analysis on such plots are given in Table 3. a. Plot of benzene versus toluene at a site near dense traffic (site II). b. Plot of benzene versus CO at site II. c. Plot of methacrolein versus benzene at site II. d. Plot of methacrolein versus benzene at a recreation area immediately outside Stockholm (site V). e. Plot of formaldehyde versus benzene at site II.

390

A. Jonsson, K. A. Persson, and V. Grigoriadis

methacrolein, r = 0.964, and 3-buten-2-one, r = 0.80(0. Thus, the direct emission from traffic is thought to be an important source of these oxygenates. At sites further away from dense traffic (sites III-V) there was no statistically significant correlation between benzene and the four oxygenates mentioned above. This is illustrated for methacrolein at site V, in Fig. 2d. Here, the slope of the linear regression is not statistically significant (95070 confidence level). Sources other than direct emissions from vehicles may contribute significantly to the measured levels at these sites. Since formaldehyde, acrolein, methacrolein, and 3-buten-2-one have all been reported as products of photochemical oxidation processes in laboratory studies (Altshuller, 1983; Kleindienst et al., 1982), photochemical production may be a potential source of these compounds in Stockholm air during periods with photochemical activity. For the alcohols, C4-Cs aldehydes, saturated ketones, chloroethylenes, and ethylacetate there was in general no statistically significant correlation to exhaust com-

G/KM

G/KM

'

MG/KM

ponents such as CO and benzene at site I or at site II (see Table 3). For methanol, the slope of the linear regression equation (methanol versus benzene) was positive on a 95°70 confidence level (Table 3). However, the correlation coefficient (r = 0.259) was low, indicating a weak correlation. Alcohols, saturated ketones, ethyl acetate and chloroethylenes were frequently found in high concentrations in Stockholm air (Table 1). Sources other than vehicle exhaust emissions, such as solvent usage (alcohols, ketones, chlorinated compounds), dry cleaning (chlorinated hydrocarbons), and bakeries (ethanol) are possible sources of these compounds. Photochemical oxidation of aliphatic hydrocarbons may be a source of the C4-C5 aldehydes found in Stockholm air. However, emissions from microbes and plants may also contribute (Babich and Stotzky, 1974) Vehicle exhaust measurements

In Fig. 3 are presented data from some of the organic compounds measured in auto and diesel emissions.

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IPROH

Fig. 3. Vehicle exhaust mass emissions of a number o f the chemical c o m p o u n d s measured in u r b a n air. Emission data on regulated pollutants, i.e., CO, H C , and NO,, are also given. A = gasoline powered automobile; empty bar, without catalyst; filled bar, with three-way catalyst. D = heavy-duty diesel. BENZ = benzene, T O L = toluene, A C R = acrolein, M E A C R = methacrolein, B U T = butanal, M E B U T = 3methylbutanal, P E N T = pentanal, A C E = acetone, M E K = methylethylketone, MVK = 3-buten-2-one, M E O H = methanol, I P R O H = 2propanol.

Low-molecular-weighthydrocarbons Levels o f regulated compounds such as hydrocarbons (HC), CO, and NO, are also shown. Bars in Fig. 3 indicate average emissions (in mass/km) for the three different vehicle types, e.g., gasoline-powered automobile (average o f 13 samples; two test procedures, two makes of car), gasoline-powered a u t o m o b i l e - t h r e e - w a y catalyst (average of 3 samples; one test procedure, one vehicle), heavy-duty diesel (average o f 4 samples; two test procedures, one vehicle). The one-sigma standard deviations are also indicated in the figure. This figure is quite self-explanatory and only a few comments will be made here. The large difference in emission pattern between non-catalyst gasoline-powered automobile and diesel can be clearly seen. Significantly higher amounts o f oxygenated species (not only aldehydes) and much lower amounts of aromatic compounds (benzene and toluene) are emitted by the diesel compared with the non-catalyst gasoline-powered vehicle. A reduction of both oxygenated and aromatic compounds is given by the 3-way catalyst. Both the emission data and the ambient air data suggest that direct vehicular emissions is an important source o f such oxygenated species as acrolein, methacrolein, and 3-buten-2-one in the urban air. The C4-C5 aliphatic aldehydes were found only in small amounts in the exhausts from gasoline-powered vehicles; diesel emissions o f these compounds were much more pronounced. However, the lack o f correlation to exhaust components (CO, NO, benzene) at urban sites indicates that other sources are more important than direct vehicular emissions, even at sites with dense traffic. The "solvents" acetone, MEK, and methanol were found in significant amounts in the exhausts from gasoline-powered vehicles as well as in diesel exhausts; weight emissions were o f the same order as, e.g., methacrolein and 3-buten-2-one. However, levels in urban air were much higher for the first group o f compounds (Table 1). Again, this indicates that direct vehicular emissions contribute only marginally to the ambient levels o f these solvent-type compounds in Stockholm air. This situation may be modified by an increased use o f alcohol-blended fuels, as discussed in the previous section.

Conclusion We conclude that volatile oxygenated hydrocarbons as well as aromatic and some chlorinated hydrocarbons are present in significant amounts in urban air. Motor vehicle emissions are thought to be an important direct source o f aromatic and some oxygenated hydrocarbons. However, some oxygenates appear to have other potential sources, e.g., photochemical oxidation o f hydrocarbons, solvent evaporation, and possibly natural emissions. More research is needed in order to clarify the role o f different sources as well as the fates of this important group o f chemicals in the urban atmosphere.

391 work was supported by The National Swedish Environment Protection Board. The authors are indebted to K. E. Egebiickand his staff at the Motor VehicleEmissionLaboratory for their cooperation. We also express appreciation to the Environment and Health Administration in Stockholm for the use of the air quality monitoring station. Mrs. Beryl Holm is gratefully acknowledged for help in correcting this manuscript.

Acknowledgements-This

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