Diagnostic analysis of the three-dimensional sulfur distributions over the eastern United States using the CMAQ model and measurements from the ICARTT field experiment

Abstract

Previous comparisons of air quality modeling results from various forecast models with aircraft measurements of sulfate aerosol collected during the ICARTT field experiment indicated that models that included detailed treatment of gas-and aqueous-phase atmospheric sulfate formation, tended to overestimate airborne SO42- levels. To understand the three-dimensional distributions and fate of atmospheric SO42- and to diagnose the possible reasons for these over-predictions, we perform detailed analysis of modeled SO42- budgets over the eastern U.S. during the summer of 2004 using an instrumented version of the Community Multiscale Air Quality (CMAQ), namely the sulfur-tracking model. Two sets of three-dimensional model calculations are performed using different gas-phase chemical mechanisms: (1) the widely used CBM4 mechanism, and (2) the SAPRC mechanism.