I
PAUL P. MADER, JOSEPH GLIKSMAN, MARCEL EYE, and LESLIE A. CHAMBERS Air Pollution Control District, County of Los Angeles, Los Angeles, Calif.
Photochemical Formation of Air Contaminants from Automobile Exhaust Vapors Effects of Different Motor Fuels Amounts and types of olefins in fuel blend are most important in formation of smog composition of exhaust gases produced during operation of a n automobile engine may be significantly influenced by the composition of the charging fuel (6). I n a comparison of two fuels under controlled experimental conditions strong indication was obtained that the participation of the exhaust gases in photochemical reactions resulting in smog was reduced by omission of unsaturated compounds from the fuel blend. Such a finding is consistent with the principle that the photochemical reaction capacity is dependent on the molecular configuration of the hydrocarbon reactants (7) and the knowledge that a significant portion of exhaust hydrocarbons is contributed by unburned gasoline. Significant differences in exhaust content of internally double-bonded and branchedchain olefins occurred in exhausts produced in the same engine by the two gasolines, and atmospheric reactivities in terms of ozone production and eye irritation seemed correlated with unsaturate content. Practical implication lies in the consistent and rather larger difference in the smog-forming capacity of the exhausts. Extensive analytical work in other laboratories is now directed toward detailed analyses of the exhaust gases, and to identify the compounds responsible for these differences. T H E
*
hausts produced by burning different fuels were tested for eye irritants, aldehydes, formaldehyde, organic peroxides, and ozone after exposure to sunlight in the presence of oxides of nitrogen. The eye irritation potential of exhaust gases from individual cycles was determined as follows : A measured volume of exhaust was introduced into a 50-liter flask. Oxides of nitrogen within the flask were adjusted to 1 p.R.m. by volume. The contents of the flask were irradiated for 1 hour, during which time the temperature within the flask reached 85” to 95” C. Irradiation was accomplished by four mercury vapor Iamps (Kern-Rand, 400 W EH-1). After the flask had been cooled to about 60” C., a panel of eight laboratory chemists were exposed to its contents. The number of
Two fuels were used to compare the smog-forming capacities of exhausts: A blend of six “premium” grade gasolines which contained 51% paraffins and naphthenes, 27% aromatics, and 23.5y0 olefins; and a full range catalytically reformed gasoline which contained 6770 paraffins and naphthenes, 32% aromatics, and less than 1% olefins. A 1954 model Chevrolet engine, in good mechanical condition, mounted on a Clayton chassis dynamometer, was used to obtain representative exhausts under controlled engine and sampling conditions. Parallel sets of samples were collected for all four cycles of engine operation. The individual ex-
Experimental Results T h e results of eye irritation tests on irradiated exhaust gases from four engine cycles are shown in Figure 1. B. I D L I N G CYCLE
--.
0
Experimental Conditions
seconds it took each individual to experience eye irritation was then recorded, and the average of eight values was taken as a measure of the eye irritation potential to the exhaust sample tested. Hydrocarbons introduced into the exposure flask were determined by infrared absorption a t 3.45 microns ( 8 ) . Aldehydes were measured by the Goldman-Yagoda method ( Z ) , formaldehyde by the Ozburn chromatropic acid procedure (5), ozone by the rubber cracking (7), and organic peroxides by a peroxidase gum guaiac procedure ( 4 ) .
10
20
30
40
50
-
60
1 0
10
20
30
40
50
60
U
C . ACCELERATING CYCLE
2 q 20
30
REACTION TIME IN SECONDS
Figure 1. Irradiated exhaust from reformed gasoline (less irritating than that from premium blend fuel (-) VOL. 50, NO. 8
- -)
was
AUGUST 1958
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during the entire period of irradiation. Differences in the smog-forming potential of exhaust gases were substantial regardless of irradiation time or irradiation temperature (Table I). Exhausts from premium mixture were approximately three times as potent in producing eye irritation as reformed fuel. Differences in formation of total aldehydes, formaldehyde, and organic peroxides were substantial.
HYDROCARBONS VS. REACTION TIME
-
1o
-r
1
dl-
io
20
30
40
50
60
e
R E A C T I O N TIME I N S E C O N D S
Figure 2. Irradiated composite exhaust from reformed gasoline was less irritating than that from premium fuel
T h e irradiated automobile exhaust from the premium blend produced more eye irritation than that from the reformed gasoline. The most pronounced differences were obtained from the decelerating and idling exhausts. Fairly substantial differences were found for the acceleration cycle, but were less evident for the cruising cycle. I n a series of experiments exhaust gases from all four cycles were blended and irradiated. The blended sample consisted of 45% acceleration, 45% cruising, 5.57, deceleration, and 4.5% idling exhaust gas by volume. These volumes were obtained by multiplying the flow rate for any one cycle by the percentage of time the average driver spends on this cycle on a representative route. The driving cycle data, from which the blending factors were calculated, were obtained by using manifold vacuum recording equipment on test automobiles operated over a n average route used by both the Air Pollution Control District and the Automobile Manufacturers Association. Data obtained on this test route by the Automobile Manufacturers Association were later evaluated on a speed change basis and with different definitions of the various driving cycles ( 9 ) . O n this basis the figures for per cent of time
Table 1.
Irrad. Time,
spent in each cycle differ from the manifold vacuum recorder data. The irradiated composite exhaust from reformed gasoline was less irritating than that from the premium fuel (Figure 2). Plotting reaction time for eye irritation against exhaust volumes instead of hydrocarbon conceiitration did not affect the general nature of the results. T h e amounts of total aldehydes, formaldehyde, ozone, and hydroperoxides which were measured in parallel samples showed the same trend toward formation of substantially higher quantities of each reaction product with the burning of the premium fuel blend. Long Exposure of Exhausts to Sunlight
Because the foregoing experiments were confined to a 1-hour irradiation a t somewhat elevated temperatures, experiments were made to determine whether similar differences between the two types of exhausts could be observed over a range of several hours’ exposure or by irradiation a t more normal temperatures. Exhaust vapors representing the decelerating cycle were introduced into the flasks and irradiated for 1, 2, and 3 hours in sunlight. The temperature within the flasks was 33-4” C.
Differences in Smog-Forming Potential Are Substantial Regardless of Irradiation Time or Temperature
Orn. Per-
Hr.
H-C, P.P.M.
Before
1 2 3
20 20 20
1.02 0.98 0.99
Eye Irr.,
(NO):c
After
Sec.
Ald., P.P.M.
Formald., oxides”, P.P.M. P.P.H.M.
Blend of Premium Grade Fuels 0.26 0.28 0.29
18.2 19.0 25.2
3.46 4.17 5.55
0.66 0.96 0.96
6.7 7.4 6.9
0.46
2.3 3.0 2.8
Catalytically Reformed Gasoline 1 2 3
20 20 20
1.04 1.02 0.97
0.32 0.30 0.29
56.3 57.6 56.1
Based on irradiation of 15 p.p.ni. of hydrocarbons.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
1.60 1.30 1.85
...
0.70
Discussion
T h e experimental results reported support earlier indications that the smog-forming potentialities of automobile engine exhausts are related to the composition of the charging fuel. The analytical procedures were independent of techniques used for fuel analysis, and exhaust sampling procedures of such variety as to minimize the probability of systematic sampling error. The conditions of formation of the exhausts and their photochemically produced reaction products differed in only the motor fuels used to power a dynamometer engine. h-o attempt was made to identify specific constituents in the exhaust which could be held responsible for the observed differences. However, the relative olefin concentrations in the two fuels, with the knowledge of extreme reactivity of certain types of these compounds, suggest that differences may be due to this group of compounds. References
(1) Bradley, C. E., Haagen-Smit, A. J . , Rubber Chem. and Technol. 24, 750 (1951). (2) Goldman, F. H., and Yagoda, Herman, IND.ENG. CHEM., ANAL.ED. 15, 377 (1943). (3) Haagen-Smit, A. J., Fox, M. M., I N D . ENG.CHEM. 48,1484 (1956). (4) Haagen-Smit, A . J., Van Meter, R., Bradley, C. E., Report to Los Angeles County -Air Pollution Control District. (5) MacDonald, W. E., Ind. Hyg. Quart. 15, 217 (September 1954). (6) Mader, P. P., Chambers, L. A., “Motor Exhaust Composition Relation to Selected Fuels,” Proceedings, West Coast Section, Air Pollution Control Association, pp. 13-28,1957. (7) Mader, P. P., Heddon, M. W., Eye, M. G., Hamming, W. J., IND. ENG.CHEW48, 1508 (1956). (8) Mader, P. P., Heddon, M. W., Lofierg, R. T., Kochler, R. H., Anal. Chem. 24, 1899 (1952). (9) Teague, D. M., others, “Los Angeles Traffic Pattern Survey,” Society of Automotive Engineers, Seattle, Wash., August 1957. RECEIVED for review Xo\*ember 15, 1957 ACCEPTED June 17, 1958 Divisions of Industrial and Engineering and Water, Sewage, and Sanitation Chemistry, Symposium on Air Pollution, 132nd Meeting, .4CS, S e w York, N. Y., September 1957.
