Photochemical smog. Rate parameter estimates and computer simulations

Abstract

DiscussionW. H. Duewer (Lawrence Livermore Laboratory). The stationary state assumption for various free radicals has been tested by other modelers and found to be satisfactory for several. The large discrepancies found by the authors suggest errors either in the formulation of the model or of the steady state expression. Because only a few terms were included in the steady state approximations used, I suspect the latter. If there is no error (e.g., omitted significant terms) then the significant differences between your model and other models that cause your model not to behave 2483 as a steady state species should be described. In the case of

Computer modeling of smog chamber data: Progress in validation of a detailed mechanism for the photooxidation of propene and n‐butane in photochemical smog

“…This expression was used to obtain the 303'K rate constant used in this study. The A factor of sec-l is significantly lower than expected for a bond scission decomposition reaction [ 1331 and Baldwin and co-workers [7] had estimated the A factor to be sec-I. The lower experimental A factor may be due to this reaction not being a t the high-pressure limit a t 1 atm total pressure.…”

“…In order to fit the data, we assume that 12111 and 12112 are both -100 times faster than the estimates of Baldwin and co-workers [7]. Thus the relative but not the absolute values of their estimates are assumed to be correct.…”

“…Thus the relative but not the absolute values of their estimates are assumed to be correct. If this is the case, then the 1-hydroxy-2-propoxy radical primarily decomposes (path C), while the 2-hydroxy-1-propoxy radical, which is estimated to decompose -100 times slower [7], primarily reacts with O2 (path B). Since the precursor of the 2-hydroxy-1-propoxy radical is predicted to be formed -35% of the time following addition of OH to propene [91], we therefore assume that path B occurs -35% of the time, with path C occurring the rest of the time.…”

“…The latter decomposition is expected to be fast, based on the estimation techniques of Baldwin and co-workers [7] and the estimated reaction exothermicity 1901. The competing decomposition forming methyl radicals is estimated t o be less favored thermochemically, and is ignored.…”

Effect of NO<sub>x</sub> level on secondary organic aerosol (SOA) formation from the photooxidation of terpenes

“…One of the possible explanations for the higher SOA yield under high-NO x conditions is the formation of large alkoxy radicals that isomerize rather than fragment. Isomerization is plausible if the alkoxy radical has four or more carbon atoms and can form a 6-membered transition state (Baldwin et al, 1977;Carter and Atkinson, 1985). The isomerization pathway leads to the formation of large hydroxycarbonyls, multifunctional products that are likely low in volatility.…”