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 an d nitrogen oxides emitted by industries and automotive vehicles. The region also receives the prevailing winds from the large karstic area where an in tensive calcareous exploitation occurs. The supply of alkaline calcareous d ust to neutralize anthropogenic acids in the atmosphere can control the aci dity of the RMBH precipitation. Rainfall was collected from 3 monitoring st ations, on a daily basis, using bulk collectors, from October 1993 to Febru ary 1994. The volume-weighted mean pHs ranged from 4.98 to 5.27. Ca2+ was t he dominating ion followed by SO42-, NH4+ and NO3-. Acidity in precipitatio n was well correlated with SO42-:Ca2+ and NO3-:Ca-2(+) ratios. In the dry p eriods, these calcium particles are continuously emitted to the atmosphere and as a result the acidity of the first rain that passes through this buff ered atmosphere is lower. However, in a continuous rainy period the rain ac idity tends to increase progressively. The results showed the great acid ne utralizing capacity of the RMBH atmosphere by calcium particles.