reaction of the paraffins in the atmosphere. Further experimental work is needed to resolve the problems and elucidate the important mechanisms. Our examination of Calvert’s analysis of the involvement of various hydrocarbons in the Los Angeles smog reaction points up the importance of continuing to test and modify reaction theories with real world experimental data. On the basis of the present analysis, we conclude that while a case can be made for olefin involvement in the smog reaction, there does not appear to be significant paraffin involvement.
Literature Cited (1) Rasmussen, R. A., Westburg, H. H., “Measurements of Light Hydrocarbon in the Field and Studies of Transport of Oxidant Beyond an Urban Area”, Washington State University, College of Engineering, Research Division-Air Pollution Section, Contract No. 68-02-1232, September 4, 1974. (2) Polgar, L. G., Londergan, R. J., “Ozone Formation and Transport”, TRC, Research Corp. of New England, presented a t the 79th National Meeting AIChE, Paper No. 45C, Houston, Tex., March 19, 1975. (3) Jaffe, R. J., Last, K. W., “Study of Factors Affecting Reactions in Environmental Chamber”, prepared for CRC and EPA by Biotechnology-Lockheed Missiles and Space System, Inc., Sunnyvale, Calif., Final Report, Phase 111, September 30, 1974. (4) Herzberg, G., “Spectra of Diatomic Molecules”, 2nd ed., p 560, Van Nostrand, New York, N.Y., 1950.
Kenneth H. Ludlum Bruce S. Bailey Environmental Protection Department Texaco Inc. P.O. Box 509 Beacon, N.Y. 12508
SIR: The letter of Ludlum and Bailey states that I overlooked t h e f a c t that n-pentane and isopentane do not react to a significant extent in the Los Angeles atmosphere. I am afraid that Ludlum and Bailey are guilty of the same oversight which they suggest I had. I t is not a fact that n-pentane and isopentane do not react in the Los Angeles atmosphere; certainly, one cannot come to this conclusion based on the data from the one day of the LARPP operations which I treated, or any other published scientific data of which I am aware. Although the rates of change of the C5H12/C2H2ratio are small and uncertain in the LARPP study, the values which I estimated by no means prove that the pentanes do not react. The same argument based on uncertainty in the rate data which Ludlum and Bailey invoke to claim no reactivity, actually requires that the pentane removal rates (at the 68% confidence limit level) be within a rather broad range which includes both significant rates and zero rates in most cases. Furthermore, it is not evident to me why one would discard certain selected points in the data as Ludlum and Bailey suggest to enhance their case. It is not just one bag analysis which we must discard to support the Ludlum and Bailey case, but other independent bag sample analyses which were obtained from the other elevations as well. Let us accept the fact that the operation #33 LARPP data are not highly accurate, but we should not discard certain data points without some scientifically sound reason. Of course, present theories of hydrocarbon involvement in photochemical smog predict only a very small change in the pentanelacetylene ratio with time. Certainly the accuracy of the operation #33 LARPP data is not sufficient to prove unambiguously either that there is no reaction or that there is a small extent of reaction of the pentanes. I contend only that the observed rates of change of this ratio in the operation # 33 of the LARPP study are consistent with present theoretical expectations for which the HO-radical-pentane reac-
tion is not insignificant. It is my hope that a less ambiguous answer to this question will be possible using more extensive data from the 34 other days of successful LARPP studies. I find a more serious point of concern in the discussions of Ludlum and Bailey. They apparently are convinced that alkanes do not react observably in the atmosphere. This conclusion is difficult for me to understand. Of course, one must treat theories of atmospheric reactions with a great deal of suspicion in view of the great complexity of the chemistry and physics of these systems. However, there is extensive experimental and theoretical evidence today which favors the significant involvement of the HO-radical in smog development (1-6). Furthermore, there are both direct (7) and indirect (6) observations of the HO-radical concentration in the polluted lower atmosphere. In view of all of the evidence, there can be little doubt that the HO-radical is present in the sunlightirradiated polluted lower atmosphere and that the estimated HO-radical concentration is reasonably consistent with that predicted in theory. Furthermore, the rate of HO-radical attack on a given hydrocarbon (RH) present in the atmosphere can be estimated accurately from a product of the concentrations of HO and RH and the known rate constant for the reaction of HO with the specific hydrocarbon. Although the absolute [HO] may not be known better than to within a factor of five or so for any given atmospheric conditions, the relative rates of attack of HO-radical on the various alkenes, alkanes, aromatic hydrocarbons, carbon monoxide, etc., can be estimated with little uncertainty from an accurate knowledge of the specific rate constants for the HO-radical reactions and the concentrations of the specific impurity reactants. It is this latter estimate of relative rates of HO-attack on hydrocarbons and CO which I have made using the LARPP analytical data and published accurate rate constant estimates; see Table IV of ref. 6. I conclude that for the conditions present in the LARPP operation #33 at about 0823, the rate of reaction of HO-radicals with the alkanes constitutes about 33% of the total HO-reaction with all hydrocarbons and CO. The LARPP data do not prove this, as Ludlum and Bailey correctly point out in their letter, but the data are consistent with this conclusion. I look forward to the publication of the reports cited by Ludlow and Bailey which show the alkanes to be unreactive in the atmosphere. Present evidence provides me with a different view which suggests the alkanes do react in the lower atmosphere at a finite but not insignificant rate. I gain some solace in this view in that no new potential problems should be anticipated through the buildup of these species in our atmosphere.
Literature Cited (1) Weinstock, B., “Chemical Reactions in the Urban Atmosphere”, p 54, C. S. Tuesday, Ed., American Elsevier, New York, N.Y., 1971. (2) Niki, H., Daby, E. E., Weinstock, B., in “Photochemical Smog and OzoneReactions,”Chap. 2, R. F. Gould, Ed., Adu. Chem. Ser., 113, 16 (1972). (3) Heicklen, J., Westberg, K., Cohen, N., Publication No. 115-60, Center for Air Environmental Studies, University Park, Pa., 1969. (4) Demerjian, K. L., Kerr, J. A,, Calvert, J . G., Adu. Enuiron. Sci. Technol., 4 , l (1974) and references therein. ( 5 ) Calvert, J. G., McQuigg, R. D., Int. J . Chem. Kinet., Symp. 1, 113 (1975). (6) Calvert, J . G., Enuiron. Sci. Technol., 10,256 (1976). (7) Wang, C. C., Davies, L. I., Jr., Wu, C. H., Japar, S., Niki, H., Weinstock, B., Science, 189, 797 (1975).
Jack G. Calvert Department of Chemistry Ohio State University Columbus. Ohio 43210 Volume IO, Number 12, November 1976
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