5.1 Individual and Combined Impacts of Projected Climate and Emission Changes on Future Air Quality over the U.S.

Jena, Chinmay, Yang Zhang, Kai Wang, Patrick Campbell, Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Fang Yan, Zifeng Lu, and David Streets, Energy Systems Division, Argonne National Laboratory, Argonne, IL

Rapid increases in modern society activities, economics, and population are becoming complex and vulnerable to changes in weather, climate, and air quality. Emission projections are critical elements to the understanding of future climate impacts on regional air quality. In the past, emission projections have often been estimated by combining fuel consumption with an averaged emission factor that represents the whole emitting sector while neglecting relationship between socioeconomic factors and projected technology changes. Following a comprehensive evaluation of the regional Weather research and forecasting model with Chemistry (WRF/Chem v 3.7), we use the emissions projected by the Technology Driver Model (TDM) under two IPCC scenarios (i.e., A1B and B2) and WRF/Chem v3.7 to investigate the individual and combined impacts of climate change and anthropogenic emission projections on the future regional air quality over the continental U.S. (CONUS) during present (2001 - 2010) and future (2046 - 2055) decades. Sensitivity simulations are conducted with projected anthropogenic emission changes only, which are used to compare with baseline results to quantify the relative importance of impacts from climate change only, emission change only, and combined changes on air quality. The TDM takes into account the impacts of socio-economic factors, technological changes, and federal and regional environmental policies and overcomes to some extent the aforementioned limitations in projecting emissions. Dynamical downscaling method is applied to link the global Community Earth System Model/Community Atmosphere Model (CESM/CAM5) and bias correction technique with WRF-Chem. Results show that the temperature at 2-m (T2), planetary boundary layer height, wind speed at 10-m, and precipitation will increase for the future decade under both TDM A1B and B2 scenarios. The projected future surface ozone (O3) levels will increase across the CONUS region under the TDM/A1B scenario and in the urban centers under the TDM/B2 scenario, ranging from 2 to 7 ppbv due to enhanced carbon dioxide and methane concentrations and subsequently higher T2, increased biogenic volatile organic compounds (VOC) emissions, larger nitrogen oxides (NOX) emission reduction than VOC emission reduction over VOC-limited regions (the so-called dis-benefit of NOx emission reduction), and weakened nitric oxide titration to O3 formation. The reduced primary anthropogenic emissions and the increase in precipitation lead to decreases in the surface PM2.5 concentrations under both scenarios. The climate change dominates the changes in surface O3 concentration under the TDM A1B scenario across the CONUS, whereas the changes in anthropogenic emissions dominates surface O3 levels under the TDM B2 scenario and fine particulate matter levels under both TDM A1B and B2 scenarios. The results of this study provide important information about the impacts of projected climate change and emissions on air quality and will be useful for policy makers to develop integrated strategies to control anthropogenic emissions and mitigate adverse climate change.