Development and evaluation of a photooxidation mechanism for isoprene

Abstract

A detailed mechanism for isoprene photooxidation is developed that includes the recent developments on each of isoprene's atmospherically important reactions: O 3 , OH, O( 3 P), and NO 3 as well as the OH reactions of methacrolein and methyl vinyl ketone. The mechanism also attempts to account for the gaps in the product distributions for a few reactions. The CO yield from isoprene oxidation in the presence of NO x , more than about 50 ppt, is calculated as about 3.4. The mechanism is tested against chamber data that include a range of mixtures of the primary oxidants, isoprene concentrations, and hydrocarbon/NO x ratios. It performs well under conditions where the OH and O( 3 P) reactions dominate and predicts peak O 3 concentrations within about 25% under all conditions. The mechanism underpredicts methyl vinyl ketone yields as well as O 3 levels under conditions of low available NO x . Sensitivity of the mechanism to assumptions about the NO 3 and O 3 reactions are examined, and possible sources of the discrepancies are discussed. A condensed mechanism is developed and compared to the explicit mechanism.