Abstract
This paper describes the application of tracer species and process analysis to study the simulated effects of regional climate change on air quality over the eastern United States. The coupled modeling system utilized in this study consists of the NASA Goddard Institute for Space Studies General Circulation Model (GISS-GCM), Fifth Generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (MM5), Sparse Matrix Operator Kernal Emissions (SMOKE) modeling system, and the US Environmental Protection Agency Community Multiscale Air Quality (CMAQ) model. Results show that climate change for the 2050s is expected to cause an increase in summertime average concentrations for a variety of primary and secondary pollutants. Through the use of CO-like chemically inert tracer species it is found that changes in physical parameters such as boundary layer ventilation and stagnation cause an increase in primary pollutant concentrations, but that actual CO concentrations show an even larger increase that points to a contribution from increased chemical reaction as well. This finding is corroborated through the use of process analysis that reveals increased chemical production of O3 and total odd oxygen as well as an increase in the rate of radical initiation. In an attempt to study the robustness of the simulated changes in pollutant concentrations towards the choice of physics options in the MM5 regional climate model, CMAQ simulations were performed with two sets of MM5 configurations under both current and future climate scenarios. While the magnitude of changes in climate parameters and pollutant concentrations shows differences between the two sets of simulations, the directionality of concentrations changes was found to be robust towards the choice of physics options in the MM5 regional climate model. This finding implies that performing future regional climate ensemble modeling studies could help to quantify the uncertainty around simulated pollutant changes as a result of regional climate change.
