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 we t 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 midlatitude s in the northern hemisphere. The regional acidity of rainwater (pH si milar to 5) is mainly due to formic and acetic acids; however, the sou rces 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 pre sent anthropogenic acidification of rain, but no measurements have bee n made. Since most soils in tropical America are sensitive to acid dep osition, the evaluation in areas affected by local urban-industrial em issions should be emphasized.