Dry deposition of photochemically reactive species to architectural materials

摘要

Dry deposition of acidic species and oxidants enhances the deterioration of vulnerable architectural materials. The dry deposition velocity is a net masstransfer coefficient that can be used to compare dry deposition rates of atmospheric species under different surface and meteorological conditions. Photochemical reaction kinetics are typically not incorporated in conventional dry deposition resistance models. Rapid gas-phase reactions in urban environments may modify flux-gradient relationships and, hence, the dry deposition fluxes of acidic species and oxidants to vulnerable surfaces. The current study examines the effects of surface moisture, friction velocity, and photochemical reactions on the effective dry deposition velocities of nitrogen dioxide, nitric acid, hydrogen peroxide, ozone, and peroxyacetyl nitrate to architectural surfaces. Effective dry deposition velocities for each species are calculated as the negative ratio of the vertical turbulent mass flux and the concentration as a function of elevation. Two Eulerian models with first-order flux closure are used in the analysis; one model includes 22 gas-phase reactions; the other model does not include chemical kinetics. Damkohler numbers for each species are calculated as function of elevation to distinguish the relative importance of chemical and mass-transport processes.