Extreme Aerosol Events Over Eastern North America: Part 2. Responses to Changing Emissions

Abstract

AbstractThe Weather Research and Forecasting model with coupled Chemistry is used to study the impact of anthropogenic emission changes between 2005 and 2015 on historical extreme aerosol optical depth (AOD) events that occurred during 2003–2007 over the eastern USA. An ensemble of simulations is generated where individual and all combined emissions of SO2, NOx, and NH3 are perturbed relative to the 2005 levels for three subregions (Midwest, Northeast, and Southeast). These simulations are used to quantify fractional changes in the spatial and temporal characteristics of mean and peak AOD and near‐surface particulate matter (PM2.5), as well as changes in radiative forcing. Simulated AOD exhibits a spatially averaged decrease of 39%–63% during the six extreme events in response to the combined perturbed emissions. The impact on near‐surface PM2.5 concentrations is larger, with average decreases of ∼41%–69%. Peak AOD is reduced to below 1 in the perturbed simulations from initial values of 1.73–3.02 in the control runs driven by 2005 emissions. Radiative fluxes at the ground and top‐of‐the‐atmosphere exhibit considerably smaller and less consistent fractional changes across events, although changes in radiative fluxes during these extreme events are found to be larger than previously reported changes in seasonal mean values over the period 2005 to 2015.