Anthropogenic Influence on Decadal Aerosol Trends over the Western North Atlantic Ocean

Aerosols from both natural and anthropogenic sources contribute to atmospheric variability and impact Earth's radiative balance around the globe. Atmospheric aerosols can also indirectly influence the radiative balance through interactions with clouds. Industry and other human activities during the last century have led to an increase in the release of trace gases and anthropogenic aerosol particles. More recently, policies aimed at reducing air pollutants for human health concerns have seen success at improving local air quality. Regional anthropogenic contribution to the atmospheric aerosol loading is presumed to be altered as a by-product.

In this work we examine variations in aerosol loading over the eastern seaboard of the United States and the North Atlantic Ocean from 2000 to 2012. This period is significant due to anthropogenic emissions control measures that are in place. We use monthly mean data from satellite (MODIS), ground (AERONET, IMPROVE), and model (GOCART) sources. From MODIS observations, a statistically significant -0.020 decade^-1 trend in aerosol optical depth (AOD) over the mid-latitudes is seen. Correlation of AOD between MODIS and AERONET sites in the upwind regions as well as trend analysis of GOCART component AOD reveal the anthropogenic origin of this trend downwind of the eastern U.S. IMPROVE network surface PM_2.5 observations from the eastern U.S. confirm statistically significant decreases in total PM_2.5 driven primarily by decreases in anthropogenic PM_2.5 species. In contrast to the mid-latitudes, MODIS observations reveal a statistically significant 0.015 decade^-1 trend in AOD over the sub-tropics. AERONET correlation, GOCART component trends, and an estimation of summertime dust flux suggest that this trend is of natural origin. Finally, preliminary results are presented for both aerosol direct and indirect effects. This work offers an assessment of aerosol trends and aerosol-cloud interactions in the context of decreasing anthropogenic aerosol contribution and on timescales relevant to climate processes.