T o find out what effect suspended sediments have on the photolysis rate of a compound that absorbs sunlight, the degradation rate of methoxychlor in the Rayonette photoreactor a t 300 nm was studied as a function of suspended sediment concentration. Figure 2 shows that the rate of photodecomposition of methoxychlor from a saturated aqueous solution (0.12 ppm) is considerably reduced in the presence of the suspended sediments. The half-life of methoxychlor in the photoreactor seems to increase linearly with suspended sediment concentration but a t different rates for the two sediments studied. Although there is a large difference in organic carbon content between the two sediments (40-Mile Creek. 21%; Black River, 4.1%),the major reason for the difference in behavior appears to be differential light absorption. The extinction coefficients a t 300 nm, as measured in the secondary cell compartment of the spectrophotometer close to the photomultiplier, are 13.8 X L mg-l cm-l for 40Mile Creek and 4.1 X L mg-l cm-l for Black River sediment. The true extinction coefficients of such suspensions are impossible to measure using a standard spectrophotometer because of sample light scattering. For example, if the measurement is made using the primary sample compartment of this spectrophotometer located some 15 cm from the photomultiplier, the apparent extinction coefficients are about twice the above values. In any case, the ratio of the extinction coefficients a t 300 nm (30-Mile Creek/Black River) is about 3.3. The ratio of the slopes of the half-life vs. concentration plots (40-Mile Creekl’Black River) is 3.8. Therefore, to a reasonably close approximation, the suspended sediments appear to be simply shielding the methoxychlor from the available light. In summary, even though suspended sediments and clays
can contain Ti02 and other semiconductors in the 5-10% range and even though they absorb sunlight, suspended sediments and clays do not appear to photocatalyze the decomposition of organic pollutants in water but reduce the rate of photolysis by shielding the pollutant from the available light. Literature Cited (1) Wolfe, N. L., Zepp, R. A., Baughman, G. L., Fincher, R. C., Gordon, J. A., “Chemical and Photochemical Transformation of Selected Pesticides in Aquatic Systems”, US.-EPA Report-600/376-067, 1976. ( 2 ) Zepp, R. G., Cline, D. M., Enbiron. sci. Technol., 11, 359 (1977). (3) Dolcater, D. L., Syers, J. K., Jackson, M. L., Clays Clay Miner., 18, 71 (1970). (4) Courbon, H., Formenti, M., Pichat, P., J . Phys. Chem., 81,550 (1 j - _977) . . ,.
( 5 ) Koster, R., Asmus, K. D., J . Phys. Chem., 77,749 (1973). (6) Carey, J. H., Lawrence, J., Tosine, H. M., Bull. Enuiron. Contam. Toxicol., 16,697 (1976). (7) Oster, G., Yamamoto, M., J . Phys. Chem., 70, 3033 (1966). (8) Zepp, R. G., Wolfe, N. L., Gordon, J. A., Fincher, R. C., J . Agric. Food Chem., 24,727 (1976). (9) Zepp, R. G., Wolfe, N. L., Baughman, G. L., Hollis, R. C., Nature (London),267,421 (1977). (10) Hatchard, C. G., Parker, A. C., Proc. R. SOC.London, Ser. A, 235, 518 (1956). (11) Langford, C. H., Carey, J. H., Can. J . Chem., 53, 2430 (1975). (12) Houle, M. J., Long, D. E., Smithe, D., Anal. Lett., 3, 401 (1970). (13) Walling, C., Kato, S., J . Am. Chem. Soc., 93,4275 (1971). (14) Carey, J. H., Cosgrove, E. G., Oliver, B. G., Can. J . Chem., 55, 625 (1977).
Received for review September 28, 1978. Accepted January 8, 1979.
Factor Analysis and Derivation of an Experimental Equation on Polynuclear Aromatic Hydrocarbon Emissions from Automobiles Takashi Handa”, Takaki Yamamura, Yoshihiro Kato, Shoichiro Saito, and Tadahiro lshii Department of Chemistry, Faculty of Science, Science University of Tokyo, 1-3, Kagurazaka, Shinjuku-ku, Tokyo, 162, Japan
Factor analysis on polynuclear aromatic hydrocarbon (PAH) emissions from gasoline engine automobiles was made on the data from test runs of more than 50 000 km on each of 26 cars. The average emission rate of PAH from cars was directly linked to average car mileage. The consumption of engine oil was a significant factor governing PAH emissions from cars in ordinary city service. An experimental equation which can give the average emission rate of PAH from cars was derived as a function of car mileage and engine oil mileage. The validity of this equation was supported by field data.
T o determine a quantitative relation between PAH emission rate and car mileage, test runs of more than 50 000 km were carried out on each of 26 Japanese gasoline engine cars in ordinary city service ( 5 ) .In this paper, from the results of the test runs, we elucidated the main factors governing PAH emissions, and derived an experimental equation on PAH emissions as a function of car mileage and engine oil mileage. Finally, the validity of this equation was evaluated by field data.
Recently, carcinogenic polynuclear aromatic hydrocarbons (PAHs) from automobiles have become a significant problem for public health, especially in big cities troubled by heavy traffic. The present research is part of ongoing research on the emissions of PAHs from automobiles. Generally, older cars with higher mileage have higher PAH emissions (1-4). For example, Begeman and Colucci ( I ) measured the emission rates of PAH from 25 cars. They showed that the average emission rate of benzo[a]pyrene (BaP) from 1 2 cars of 1951-1959 model years was 3 times higher than that from 13 cars of 1959-1963. Thus, PAH emissions are closely related to car age, i.e., car mileage. 0013-936X/79/0913-1077$01.00/0
@ 1979 American Chemical Society
Experimental T o investigate the effect of used oil on PAH emission, two cars, car A and car B, were operated for 6000 km on single oil changes. For car A, a similar test run was repeated. The specifications of these cars are as follows. Car A: 1972 model year, 4-cycle and 4-cylinder gasoline engine, 1400-cm3 displacement, spark retarded for emission control of HC and NO,, initial car mileage in the test run, 39 000 km, and consumption rate of engine oil, operating a t 40 km/h using new oil, 1.44 m L L of fuel (oil economy, 10.9 km/mL). Car B: 1974, 4-cycle and 4-cylinder gasoline engine, 1200 cm3, spark retarded, 19 000 km, and 0.14 mL/L of fuel (143 km/mL) a t 40 km/h using new oil. The PAH measurements were made a t 2000-km intervals Volume 13, Number 9, September 1979
1077
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