Regional Air Quality Under Climate Change Using a Nested Global-Regional Modeling System

Strong links between climate, particulate matter and ozone make it likely that climate change will have impacts on air quality. This study examines the effects that climate change will have on concentrations of PM2.5 and ozone in the Eastern US. The changes examined are between the present day and the 2050s. This is accomplished by developing the Global-Regional Climate Air Pollution Modeling System (GRE-CAPS). GRE-CAPS couples a general circulation model (GCM) / global chemical transport model (CTM), a regional meteorological model, and a regional chemical transport model. Present and future climates are simulated by the GISS-II' GCM with an embedded gas-phase and aerosol chemistry model. Meteorology generated by the GCM is downscaled to the regional modeling domain using the MM5 regional climate model. The downscaled meteorology is passed to the regional chemical transport model PMCAMx. In addition to the downscaled meteorology, chemical boundary conditions for the regional model are derived from the global model. The coupled model system is evaluated for the present day by comparing model-predicted concentrations of O3 and PM2.5 to measured concentrations during the last decade. This comparison between typical present- day measurements and model predictions is made for three modeled present-day Julys (both PM2.5 and O3) and three modeled Januaries (PM2.5). Future concentrations (using the IPCC A2 scenario) are compared to present-day concentrations. Concentrations in specific sites and statistical distributions of concentrations will be examined.