Analysis of trends in observations of aerosol concentration and radiation, also development of 20-year emission inventories and trend analysis of emissions

 

Authors

Chuen Meei Gan — National Exposure Research Laboratory
Jia Xing — U.S. Environmental Protection Agency
Jonathan Edward Pleim — U.S. Environmental Protection Agency
Rohit Mathur — U.S. Environmental Protection Agency

Category

Aerosol-Cloud-Radiation Interactions

Description

Anthropogenic aerosols play a key role in dictating global and regional trends in “dimming and brightening.” However, the decadal variation in the distribution of atmospheric aerosols and clouds and their effect on the radiation budget are not well understood. In order to better evaluate and characterize the behavior of aerosol and clouds in atmosphere, a long-term study of their optical properties (e.g., optical thickness, single-scattering albedo, and extinction coefficient) and physical properties (e.g., size distribution and spectral refractive index) as well as their effects on surface radiation is critical. Simulation of these trends requires an accurate description of emissions of aerosol precursors.

Title IV of the U.S. Clean Air Act Amendments required annual emissions of SO2 and NOx to be reduced by ten and two million tons, respectively, from their 1980 levels. It is believed that these reductions of SO2 and NOx emissions have caused considerable effects on anthropogenic aerosol loading and regional radiation budgets over the past two decades, which is a good reference period to be researched. The main task of this study is to understand the multi-decadal changes in surface solar radiation and its relationship with the historic emission trends and associated aerosol burdens during 1990–2010.

By utilizing surface measurements (e.g., ARM sites, AERONET, and CASTNET) with satellite measurements such as MODIS, CERES and CALIPSO, we obtain a better picture of the aerosol effects and radiation trend. Approximately 20 years of measurements from several sources (e.g., CASTNET, SURFRAD, and AERONET) are presented. The 20-year emission inventories over North America are developed correspondingly. National emissions inventory (NEI) air pollutant emissions trends data as well as selected years of NEI data sets and detailed hourly continuous emissions monitoring (CEM) data were used to best-estimate the emissions in both total amounts and spatial/temporal variations. This newly developed 20-year emission inventory is now being used for 3D CTM simulations of this period. From our results, the anthropogenic emissions of SO2 and NOx were significantly decreased by 66% and 49%, respectively, over the past two decades in the United States. Trends in aerosol loading and radiation inferred from surface and remotely sensed platforms will be analyzed in conjunction with estimated trends in SO2 and NOx emissions.