Other homogeneous reactions of cresols to be considered are the reactions with 03 and 0 atoms. For p-cresol we have obtained a second-order rate constant for reaction with ozone equal to about 1.4 x 10-18 cm3 molec-1 s-1. At 0.05 ppm 03, this reaction is about 1 percent of the OH-cresol reaction, assuming the o- and p-cresol have the same reactivities. While the reaction may prove unimportant as a loss mechanism for cresols, it can be a dominant source of free radicals at high ozone concentrations if it produces radicals efficienctly. We hope to determine if this is the case in our studies of cresol-0, reactions. Atkinson and Pitts [23] studied the reaction of O atom plus o-cresol and found it to have a rate constant of 5.8 x 10 13 cm3 molec1 s1. Since the OH reaction is 100 times faster and since OH is 100 times more abundant than 0 atom, this reaction with o-cresol is insignificant. 5. Modeling of Toluene Smog Chamber Data Xwe The Statewide Air Pollution Research Center SAPRC) at the University of California, Riverside as carried out a series of runs with toluene in heir smog chamber facility. Concentrations of oluene range from 0.2 to 2.0 ppm while the NO oncentration was varied from 0.1 to 1.0 ppm. ave developed a mechanism to simulate these data. he mechanism includes the standard inorganic eactions and those organic reactions which have een discussed in previous sections. We have also ncluded reactions for formation and decomposition f the major peroxynitrates as well as the terminaSon reactions of HO2 with RO⚫ and RO2 radicals. Concentration, ppm 0.60. 0.30 0.15. 0.00 •С СС (b) Fig. 1. (c) Simulation of SAPRC EC-77: Ozone (* experimental, 3 = simulation) and Formaldehyde (+ experimental, = simulation). = Currently, data show very low material balances which may be indicative of the formation of aerosols or deposition of products on the chamber walls. The chamber data should be obtained over a wide range of conditions because the sensitivity of individual reactions varies with the conditions. Thus, by using a wide range of conditions, different parts of the model can be tested. The current study of individual reactions of various intermediates should be continued. This work has been one of the most helpful sources of information in developing the toluene mechanism. Finally, the inability to simulate the ozone data in smog chamber runs, indicate a need for a better understanding of the chemistry that controls the ozone concentration. Since this effect appears to be common to the simulation of data for other hydrocarbons, the problem may not be solely with the organic part of the mechanism. References [1] Calvert, J. G., Environ. Sci. Tech. 10, 256 (1976). [2] Lonneman, W. A., Kopczynski, S. L., Danley, P. E., and Sutterfield, F. D., Environ. Sci. Tech. 8, 229 (1974). [3] Crabtree, J. H., private communication. [5] Davis, D. D., Bollinger, W., and Fischer, S., [6] Hansen, D. A., Atkinson, R. and Pitts, [7] Perry, R. A., Atkinson, R. and Pitts, J. N., Jr., J. Phys. Chem. 81, 296 (1977). [8] Atkinson, R. and Pitts, Jr., J. N., J. Phys. Chem. 79, 295 (1975). [9] Nakagawa, T. W., Andrews, L. J., and Keefer, R. M., J. Amer. Chem. Soc. 82, 269 (1960). [10] Hendry, D. G., Mill, T., Piszkiewicz, L., Howard, J. A., and Eigenmann, H. K., J. Phys. Chem. Ref. Data 3, 937 (1974). [11] Doyle, G. J., Lloyd, A. C., Darnall, K. R., Winer, A. M., and Pitts, J. N., Jr., Environ. Sci. Tech. 9, 237 (1975). [12] Kenley, R. A., Davenport, J. E., and Hendry, D. G., J. Phys. Chem. 82, 1095-1096 (1978). [13] Kenley, R. A. and Hendry, D. G., manuscript in preparation. [14] O'Brien, R. J., Green, P. J., and Doty, R. A., [15] Fitz, D. R., Grosjean, D., Van Cauwenberghe, K., and Pitts, J. N., Jr., Photo-oxidation Products of Toluene-NO, Mixtures Under Simulated Atmospheric Conditions, 175th Meeting of the American Chemical Society, March 1978. [16] Niki, H., Maker, P. D., Savage, C. M., and Breitenbach, L. P., J. Phys. Chem. 82, 132 (1978). [17] Kenley, R. A., Lan, B., and Herdry, D. G., unpublished data. [18] Niki, H., Maker, P. F., Savage, C. M., and Breitenbach, L. P., Fourier Transform IR Studies of Gaseous and Particulate Nitrogeneous Compounds of Atmospheric Interest, 175th National Meeting of the American Chemical Society, March 1978. [19] Berger, M., Goldblatt, I. L., and Steel, C., J. Amer. Chem. Soc. 95, 1717 (1973). [20] Porter, G. B., J. Chem. Phys. 32, 1587 (1960). [21] Bouchy, M. and Andre, J. C., Molec. Photochem. 8, 345 (1977). [22] Perry, R. A., Atkinson, R., and Pitts, J. N., Jr., J. Phys. Chem. 81, 1607 (1977). [23] Atkinson, R. and Pitts, J. N., Jr., J. Phys. Chem. 79, 541 (1975). Summary of Session The presentation by Hendry emphasized the importance of aromatic compounds in the chemistry of urban air pollution. Single ring aromatic compounds account for 25-40 percent of the carbon species found in urban air. From chamber studies these compounds are known to be reactive in the production of ozone (03). Therefore a knowledge of the atmospheric chemistry of simple aromatics is required for inclusion of these compounds in tropospheric models to predict their role and contribution to photochemical smog formation. The importance of a better understanding of the chemistry was illustrated in comments by Atkinson and Hendry on the uniqueness of the 03 formation curve and the current inability to simulate 03 smog chamber data. The major theme of the discussion and the majority of the uncertainties centered around mechanisms of reactions of primary and secondary aromatics in the atmosphere. There was general agreement that the initial reaction can be accounted for almost solely by attack of the hydroxyl (OH) radical. For methyl substituted benzenes, the accepted mechanisms are hydrogen abstraction at the methyl group and OH addition at the ortho position. However, there was a degree of It was evident from the discussion that some problems exist with regard to analytical measurements of products. All of the analyses reported during the discussions were performed by gas chromatography (GC). O'Brien reported some difficulty with some product measurements at low concentrations, e.g. cresols. No analyses were reported by other techniques such as mass spectroscopy or Fourier transform infrared spectroscopy. Either of these techniques could give better time resolution and the possibility of observing intermediates. Finally there is the larger question of the amount and nature of products in the aerosol phase. This Elimination of CH3 from radical III can be calculated to be 9 kcal mol1 endothermic. together with an activation energy for the addition of CH3 radicals to toluene of 4 kcal mol [1], leads to an activation energy of ~13 kcal mol1 for reaction (3). Hence reaction (3) will be favored over elimination of an OH radical (analogous to reaction (1)) from this OH-toluene adduct. The occurrence of this reaction pathway would hence mean that the values of ki and k1/(k1 + k2) obtained by Perry, Atkinso and Pitts [2,3] are upper limits. This may be especially true for o-xylene where, by analogy with the 0(3P) atom reaction [4], OH radical addition at the methyl substituted positions is likely to be appreciable, and for which the repor ed value of k1/(k1 + k2) appears to be high, with a low value of E16, compared to the other aromatic hydrocarbons. 2) At the Statewide Air Pollution Research Center, University of California, Riverside, we [5] have recently determined rate constants for the reaction of OH radicals with o-, m- and p-cresol from the rates of disappearance of the cresols and n-butane in irradiated NO-organic-a mixtures of atmospheric pressure and 300 ± 1 K. Using a value of k(OH+ n-butane) of 2.73 x 107 cm3 molec at 300 K [6] rate constants k (cm3 molec1 s1) of (4.7 ± 0.4) × 10 12; (6.7 ± 0.7) x 10 12 and (5.2 ± 0.5) x 10 obtained [5] for o-cresol, m-cresol and p-cresol Further experiments [7] have shown that the NO I photooxidations of the cresols form hydroxynitroluenes as the major observed gas phase 1 212 were |