Sensitivity of Ozone Concentrations to Rate Constants in a Modified SAPRC90 Chemical Mechanism Used for Canadian Lower Fraser Valley Ozone Studies

The SAPRC90 chemical mechanism implemented in CALGRID is modified and updated for the specific emissions and applications of the Lower Fraser Valley (LFV) of British Columbia, Canada. Explicit reactions related to biogenic emissions and alternative fuels are added. The sensitivity of ozone formation to rate parameters in the mechanism is determined for an episode specific trajectory which originates under relatively clean marine conditions and passes over the urban core of Vancouver during the morning rush hour. Of the 137 reactions in the modified mechanism, the rate constants of 44 reactions are found to have a high sensitivity on ozone formation. The 44 reactions are further divided into general sensitive reactions, for which rate constant changes near the base case values have observable effects on maximum ozone concentrations, and limit-sensitive reactions, for which rate constant changes of more than an order of magnitude are required to have an observable impact on ozone concentrations. For the sensitive reactions, both ozone sensitivity coefficients for small changes (20%) in the rate constants and effects on ozone caused by large rate constant changes (factors of 0, 0.5, and 2) are calculated. Of note is the importance of several photolysis reactions and the reactions of OH with a class of reactive aromatics, including xylenes, on ozone concentrations in the LFV.