Atmospheric Wet Depositions in Tropical America

The chemical composition of wet depositions at a “natural” regional scale and in local polluted areas in tropical America is reviewed. The available data indicate that at large regional scales, atmospheric wet depositions in tropical America are little affected by anthropogenic emissions, and that rain concentrations of non-sea-salt sulfate (SO4*), NO3−, and NH4* are much lower than the ones observed at midlatitudes in the northern hemisphere. The regional acidity of rainwater (pH −5) is mainly due to formic and acetic acids; however, the sources of these acids (probably natural) are not well identified as yet. Some “local-regional” problems are observed in Brazil and Venezuela, and it is likely that other tropical urban-industrial areas also present anthropogenic acidification of rain, but no measurements have been made. Since most soils in tropical America are sensitive to acid deposition, the evaluation in areas affected by local urban-industrial emissions should be emphasized.