Envlron. Sei. Technol. 1983, 77,762-762
(8) Atkinson, R.; Darnall, K. R.; Lloyd, A. C.; Winer, A. M.; Pitts, J. N., Jr. Adv. Photochem. 1979, 11, 375-488. (9) Dimitriades, et al. “Development and Utility of Reactivity Scales from Smog Chamber Data”; U.S.Department of the Interior: Washington, DC, 1975.
James P. Killus,” Gary 2. Whltten
Systems Application, Inc. San Rafael, California 94903
SIR: We have been interested in establishing general relationships between photochemical ozone formation and the initial concentrations of hydrocarbons (HC) and NO, so as to enable inter-smog chamber comparison more quantitatively and get guidelines for ozone control strategy (1-4). We introduced “ozone formation potential (P)” defined as [O,],,/[O,],, as a measure of ultimate maximum concentration of ozone after prolonged irradiation. Here [O,],, was defined by -kl
[O,l,, =
+ (kL2 + 4k1k2[N0,]o)’/2 2k2
(1)
where kl and k2 are the rate constant of NOz photolysis and the NO-0, reaction, respectively. The basis for our proposal to use the nondimensional parameter was that P is approximately a constant which is determined specifically for each hydrocarbon in HC-excess region as revealed from our experimental (1-3) and computer simulation ( 4 ) studies. Killus and Whitten plotted K (which corresponds to our P) against [O,],, for the UCR chamber data in their comment on our previous paper (I). The constancy of Kp against [O,],, does not seem to be verified in Figure 1 of their comment. Although the experimental conditions ([HC],/[NO,], ratio) of the UCR chamber data employed are not specified, those experiments would not have always been performed at the HC-excess region. The tendency that the P value decreases as the [HC]o/[NO,]o ratio decreases has been predicted in our computer simulation for
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propylene (4) and also verified experimentally (5). Thus, the decreasing trend of Kp as [O,],,increases depicted in the figure would be due to a lower [HC],/[NO,], ratio for the runs with higher [O,],,. Also, the definition of [O,],, by Killus and Whitten is somewhat different from that we are using conventionally. They used a NO2 peak concentration instead of initial NO, concentration in eq 1. The use of NOz peak concentration might give more consistent results when comparing runs with different NO-to-N02 initial ratios, while the use of [NO,], is more versatile when comparing smog chamber experiments for which only a chemiluminescent NO, analyzer is employed and no “NO2” data are supplied. The use of NO2 peak concentration instead of [NO,], value would increase slightly a value of Kp as compared to a value of P. Our recent experimental results (5) revealed that the ozone formation potential as defined in the HC-excess region is the highest for paraffins, the lowest for aromatics, and intermediate for olefins. Further, m-xylene has a higher P value than toluene but lower than propylene. These trends agree fairly well with the results given by Killus and Whitten. The details of our study on the ozone formation potential for various hydrocarbons will be published elsewhere (6). Registry No. Nitrogen oxide, 11104-93-1;ozone, 10028-15-6.
Literature Cited (1) Sakamaki, F.; Akimoto, H.; Okuda, M. Environ. Sci. Technol. 1981, 15, 665.
(2) Akimoto, H.; Sakamaki, F.; Hoshino, M.; Inoue, G.; Okuda, M. Enuiron. Sci. Technol. 1979, 13, 53. (3) Sakamaki, F.; Akimoto, H.; Okuda, M. Enuiron. Sci. Technol. 1980, 14, 985. (4) Sakamaki, F.; Okuda, M.; Akimoto, H.; Yamazaki, H. Enuiron. Sci. Technol. 1982, 16, 45. (5) Samakaki, F.; Akimoto, H.; Okuda, M.; presented at the 22nd Annual Meeting of Japan Society of Air Pollution, Akita, Japan, Oct 7-9, 1981. (6) Sakamaki, F.; Akimoto, H., manuscript in preparation for publication.
Fumio Sakamaki, Hajlme Akimoto” The National Institute for Environmental Studies P.O. Tsukuba-gakuen, Ibaraki 305,Japan
0013-936X/83/0917-0762$01.50/0
0 1983 American Chemical Society
