Variability of Aerosols over the United States due to Anthropogenic Activities

Attributing the aerosol abundance to natural or anthropogenic activity is important for aiding climate predictions and air quality policy decisions given the influential role of aerosols on climate and air quality. This study investigates the trends of aerosol abundance and polluted gas emission between 2000 and 2011, a period that experienced unprecedented changes in regulatory action leading to significant influences on anthropogenic emission of aerosol precursors. It is shown that regulatory policies and technological improvement dominated the decrease of polluted gases emissions, aerosol optical depth (AOD) and particulate matter less than 2.5 microns (PM2.5) in United States (US) during the twelve-year study period. The US average SO2, NO2, PM2.5 and AOD was found decreasing since2000. It was found the deceasing of US average SO2 was dominated by the decreasing of SO2 emissions at the US east coast while the deceasing of NO2 was mainly due to the decreasing at the US west coast. Regression analysis suggests that climatic indices and anthropogenic activities can explain 76.4 percent of variation of deseasonalized AOD and 90.3 percent variation of deseasonalized PM2.5. Individually, anthropogenic activities can explain 64.9 percent of AOD and 87.2 percent of PM2.5 while the climatic variability can explain 31.4 per cent of AOD and only 9.2 per cent of PM2.5. These findings suggest that recent emission regulations drove the reduction of AOD and PM2.5 over the US. The magnitude of influence of large-scale climatic variability on AOD is comparable to that of anthropogenic activities on AOD and cannot be ignored in the estimation of AOD. The estimates of future concentrations of aerosols will be improved by accurately quantifying the extent to which both climatic and anthropogenic effect on them.