title: Intercomparison of chemical mechanisms for air quality policy formulation and assessment under North American conditions.
abstract: The 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% NOxand VOC reductions with the different mechanisms, despite the striking similarities between the base-case ozone production rates. The 30% reductions in NOxand VOCs also produced changes in OH. The responses in OH to 30% reductions in NOxand VOCs appeared to be more sensitive to mechanism choice, compared with the responses in the photochemical ozone production rates. Although 30% NOxreductions generally led to decreases in OH, 30% reductions in VOCs led to increases in OH, irrespective of mechanism choice and background environmental conditions. The different mechanisms therefore gave different OH responses to NOxand VOC reductions and so would give different responses in terms of changes in the fate and behavior of air toxics, acidification and eutrophication, and fine particle formation compared with others, in response to ozone control strategies. Policymakers need to understand that there are likely to be inherent differences in the responses to ozone control strategies between different mechanisms, depending on background environmental conditions and the extents of NOxand VOC reductions under consideration.
  
  
  
  The purpose of this paper is to compare predicted ozone responses to NOxand VOC reductions with seven chemical mechanisms under North American conditions. The good agreement found between the tested mechanisms should provide some support for their application in the air quality models used for policymaking.
authors.affiliation: a rdscientific , Newbury , Berkshire , United Kingdom.
authors.forename: Richard
authors.identifier: 0000-0003-2383-1360
authors.initials: R
authors.lastname: Derwent
mesh_terms: D000393:Air Pollutants / Q000032:analysis / Q000737:chemistry*; D000397:Air Pollution / Q000032:analysis* / Q000331:legislation & jurisprudence; D004784:Environmental Monitoring / Q000379:methods; D008962:Models, Theoretical; D009589:Nitrogen Oxides / Q000032:analysis / Q000737:chemistry; D009656:North America; D010126:Ozone / Q000032:analysis / Q000737:chemistry*; D014481:United States; D055549:Volatile Organic Compounds / Q000032:analysis / Q000737:chemistry
chemical_list: D000393:Air Pollutants; D009589:Nitrogen Oxides; D055549:Volatile Organic Compounds; D010126:Ozone