The chemistry in the tropics is severely undersampled. The Indian subcontinent and surrounding nations are rich sources for many kinds of aerosols, including those produced from industrial and auto emissions, biomass burning, and soil dust. With Asia's population rising at a dramatic rate, the amount of sulfur dioxide released into the atmosphere is expected to increase. Sulfur dioxide is converted into sulfate aerosol in the atmosphere. The ability of sulfate aerosols to reflect the sun's radiation may be one reason that increasing greenhouse gases have not warmed the earth as much as some climate models have predicted.
Sulfates also contribute to local pollution and acid rain.
Some physical and chemical processes in the earth system are so complicated that modelers cannot simulate each detailed step. The observation region is downwind of the Indian subcontinent during the spring and extends into the pristine Southern Hemisphere. The direct effect of aerosols is the scattering that occurs when solar radiation bounces off particles in clear air. The indirect effects have to do with sulfates' interactions with clouds. Globally, aerosols are an important source of nuclei around which cloud droplets can condense, and in the tropics they are the chief source.