Impacts of climate change on regional and urban air quality in the eastern United States: Role of meteorology

[1] The effects of climate change on ozone and PM2.5 concentrations over the eastern United States were investigated using the Global-Regional Coupled Air Pollution modeling System (GRE-CAPS). GRE-CAPS consists of the Goddard Institute for Space Studies (GISS) II' general circulation model with aerosol processes and ozone chemistry, the fifth-generation PSU/NCAR mesoscale model (MM5) regional meteorological model, and the Comprehensive Air Quality Model with Extensions (CAMx) with aerosol (PM) processes developed at Carnegie Mellon University (PMCAMx) regional chemical transport model. A set of five present-day Januaries and six present-day Julys was simulated using GRE-CAPS. The present-day model predictions (2000s) were compared to model predictions for a set of five future Januaries and Julys. The future time period investigated was the 2050s, using the Intergovernmental Panel on Climate Change A2 scenario. U.S. emissions of biogenic and anthropogenic precursors were held constant so that the effects of climate change alone could be calculated. Climate change led to a decrease in U.S. land cell average January PM2.5 concentrations of 0.3 μg m−3 and an increase of July PM2.5 of 2.5 μg m−3. The changes in PM in the Northeast were of the opposite sign of the domain-wide averages. The response in January was due largely to increased precipitation, while the response in July was due primarily to decreased ventilation, as indicated by decreases in mixing height and wind speed, with increases in sulfate being the largest response by a single species. The U.S. land cell average change in July daily maximum 8-h ozone concentration was +1.7 ppb, though the increases in cities in the Southeast were up to 15 ppb. In spite of the large differences in ozone in many areas, the changes in ozone concentration were not statistically significant over most of the domain because of large interannual variability. In separate simulations to test the sensitivity of ozone concentrations to biogenic emissions, a 25% increase in biogenic U.S. volatile organic compound emissions led to an additional increase in land cell average ozone of 0.7 ppb, though the increased ozone resulting from increased biogenics was largely statistically insignificant.