Trend analysis in aerosol optical depths and pollutant emission estimates between 2000 and 2009

We evaluated global and regional aerosol optical depth (AOD) trends in view of aerosol (precursor) emission changes between 2000 and 2009. We used AOD data products from MODIS, MISR and AERONET and emission estimates from the EMEP, REAS and IPCC inventories. The trends in global monthly AOD of MODIS (L3), MISR (L3) and AERONET (L2) are significantly negative over Europe and North America, whereas over South and East Asia they are mostly positive. The calculated 2000-2009 trends from the monthly L3 products correspond well with the more detailed daily MODIS L2 AODs for three selected regions (Central Mediterranean, North-East America and East Asia). Furthermore, daily and monthly AERONET L2 AOD trends agree well. The trends in AOD are compared to estimated emission changes of SO2, NOx, NH3 and black carbon. We associate the downward trends in AOD over Europe and North America with decreasing emissions of SO2, NOx and other pollutants. Over East Asia the MODIS L2 trends are generally positive, consistent with increasing pollutant emissions by fossil energy use and growing industrial and urban activities. It appears that SO2 emission changes dominate the AOD trends, although especially in Asia NOx emissions may become increasingly important. Our results suggest that solar brightening due to decreasing SO2 emissions and the resulting downward AOD trends over Europe may have weakened in the 2000s compared to the 1990s. (C) 2012 Elsevier Ltd. All rights reserved.