Global aerosol concentration and size parameters derived from MODIS sensors onboard the Terra and Aqua satellites are continuously being evaluated with ground-based measurements and used for various aerosol studies. These parameters have enabled a two-year assessment of aerosol loading and seasonal trends over several important regions on land and ocean, based on 5 x 5degrees monthly averages. Similar studies were conducted at higher spatial (50 x 50-km) and temporal (daily) resolutions over selected sites representative of pollution, smoke, dust, and sea-salt aerosol types. Also, a two parameter clustering technique has been employed successfully for categorizing the predominant aerosol types and events affecting selected locations over the Atlantic and Pacific Oceans. In addition, results of regional aerosol radiative forcing calculations over a few regions are reported. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.