Construction of Surrogate CHEmical MEchanisms (SCHEMEs) for Atmospheric Photochemical Systems

摘要

During the past several years it has become apparent that homogeneous gas-phase reactions of pollutants in the troposphere, i.e., the formation of photochemical smog and the oxidation of SO sub 2 , occur to a great extent by elementary reactions involving chain carrying free-radicals (HO, HO sub 2 , RO, RO sub 2 , RCOO sub 2 ) whose concentrations are governed by the concentrations of trace molecular constituents including NO, NO sub 2 , CO, O sub 3 , and organics, as well as sunlight. For the purpose of modeling chemical transformations in the ambient atmosphere, which requires incorporating a reaction mechanism within an atmospheric transport model, it is necessary to develop a mechanism that includes a minimum number of chemical species, since the computational time and cost involved in solving the set of partial differential equations describing the diffusion-advection-reaction problem increases dramatically with the number of species modeled. Although photochemicl mechanisms employing fewer than 15 species have been developed previously for use within urban airshed models, those reduced, or surrogate, mechanisms do not include sulfur chemistry and do not appear applicable to the more widely varying conditions possible as gases become chemically depleted while being transported away from emission sources. Therefore, in order to meet the time and cost constraints of an atmospheric transport model, we have constructed a 12-species Surrogate CHEmical MEchanism (SCHEME) incorporating reactions for the homogeneous gas-phase oxidation of SO sub 2 . A preliminary but much more detailed and comprehensive ATmospheric Model for Sulfur (ATMOS) has been used to generate SCHEME and test its applicability to a broad range of chemical conditions. (ERA citation 03:055829)