Influence of calcareous soil particulates on acid rain:: Belo Horizonte Metropolitan Region, Brazil

This paper describes the characteristics of acid rain in the Belo Horizonte Metropolitan Region/RMBH, Brazil, a region influenced by sulfur dioxide and nitrogen oxides emitted by industries and automotive vehicles. The region also receives the prevailing winds from the large karstic area where an intensive calcareous exploitation occurs. The supply of alkaline calcareous dust to neutralize anthropogenic acids in the atmosphere can control the acidity of the RMBH precipitation. Rainfall was collected from 3 monitoring stations, on a daily basis, using bulk collectors, from October 1993 to February 1994. The volume-weighted mean pHs ranged from 4.98 to 5.27. Ca2+ was the dominating ion followed by SO42-, NH4+ and NO3-. Acidity in precipitation was well correlated with SO42-:Ca2+ and NO3-:Ca-2(+) ratios. In the dry periods, these calcium particles are continuously emitted to the atmosphere and as a result the acidity of the first rain that passes through this buffered atmosphere is lower. However, in a continuous rainy period the rain acidity tends to increase progressively. The results showed the great acid neutralizing capacity of the RMBH atmosphere by calcium particles.