ATMOSPHERIC DEPOSITION TO A RURAL TROPICAL SITE - ANALYSIS OF THE RELATIONSHIP BETWEEN AMOUNT OF PRECIPITATION AND CHEMICAL-COMPOSITION

Chemical analysis of Na, K, Ca and Mg in bulk deposition, using 230 events, showed that variations in atmospheric deposition are explained better by measured concentration than by precipitation amount. In addition, measured concentration is related to precipitation by a significant power function with the exponent near -1. These observations led us to propose an inverse linear model which makes it possible to calculate two parameters: one of them is indicative of the mean composition of "cloud rain" and is assumed to be typical for the study area; the other parameter is representative of particulates, aerosols and gases that are washed out from the atmosphere in the initial phases of precipitation, including dry deposition. This initial component represents an average of 64% of the bulk deposition for the cations studied. The functions that explain the relations between atmospheric deposition and measured concentration are, within statistical limits, equal for the four cations.