Air pollution and climate response to aerosol direct radiative effects: a modeling study of decadal trends across the northern hemisphere

Changes in anthropogenic aerosol loading can perturb the energy balance of the atmosphere via aerosol direct, indirect and semi-direct effects, thus influencing weather, climate and air quality. Quantification of the magnitude of those impacts is critical for better understanding the importance of air pollution – climate interactions. A new two-way coupled meteorology and atmospheric chemistry model, i.e., Weather Research and Forecast (WRF) model coupled with the Community Multiscale Air Quality (CMAQ) model, has been developed by U.S. Environmental Protection Agency. This model system can be applied as an integrated regional climate and chemistry model to assess the interactions between atmospheric chemistry and radiative forcing and effects on meteorology and air concentrations. Decadal hemispheric WRF-CMAQ simulations from 1990-2010 were conducted and evaluated through comparisons with long-term observations of surface gaseous and particle species as well as AOD and clear-sky short-wave radiation (SWR) in a recent study. In this study, the aerosol direct impacts on meteorological variables and chemical species derived from these 21-year hemispheric WRF-CMAQ simulations will be discussed. Our results suggest that summer-time regional average ground temperature, PBL height, wind speed and SWR tends to be reduced by aerosol direct radiative effects, with an almost linear response to aerosol loading of -0.3 to -0.4 K/AOD, -69 to -79 m/AOD, -0.06 to -0.11 m s-1/AOD and -71 to -93 W m-2/AOD, respectively over three land areas (i.e., eastern China, eastern U.S. and Europe). Diurnal analysis suggests that impacts are most significant around 8am and 8pm local time when the inversion layer breaks down in the morning and builds up in the evening, resulting in an enhancement of air pollution levels. The response of ambient SO2, NO2 and PM components as well as O3 production efficiency will be quantified.