Analysis of the sulfate aerosol scavenging processes in the metropolitan area of Porto Alegre (MAPA), RS, Brazil

The present work aims to study the in-cloud and below-cloud sulfate (SO42-) scavenging processes by applying numerical models. The BRAMS (Brazilian Regional Atmospheric Modeling System) model was used to simulate the vertical structure of clouds in the metropolitan area of Porto Alegre (MAPA), in southern Brazil, together with the B.V.2 (below-cloud Beheng version 2) scavenging model for wet removal processes, which occur in–cloud (rainout) and below-cloud (washout). Six rainfall events between 2005 and 2007 were selected. They occurred at three sites within the MAPA–Porto Alegre, Canoas, and Sapucaia do Sul–where the SO42- concentrations measured experimentally in wet precipitation, as well as the SO2 concentrations in the air, were measured. The data were used in the modeling. Results of SO42- scavenging process modeling were in good agreement with those observed experimentally, showing a correlation of 0.73. Results also showed a prevalence of in-cloud scavenging processes, which are responsible for about 70 to 90% of the SO42- concentration found in rainwater, corroborating with data found in the literature.