Intercomparison of chemical mechanisms for air quality policy formulation and assessment under North American conditions

ABSTRACTThe intercomparison of seven chemical mechanisms for their suitability for air quality policy formulation and assessment is described. Box modeling techniques were employed using 44 sets of background environmental conditions covering North America to constrain the chemical development of the longer lived species. The selected mechanisms were modified to enable an unbiased assessment of the adequacy of the parameterizations of photochemical ozone production from volatile organic compound (VOC) oxidation in the presence of NOx. Photochemical ozone production rates responded differently to 30% NOx and VOC reductions with the different mechanisms, despite the striking similarities between the base-case ozone production rates. The 30% reductions in NOx and VOCs also produced changes in OH. The responses in OH to 30% reductions in NOx and VOCs appeared to be more sensitive to mechanism choice, compared with the responses in the photochemical ozone production rates. Although 30% NOx reductions generally...