Regional aerosol chemistry of the Amazon Basin during the dry season

Abstract

Our data suggest that there is remarkable compositional and spatial homogeneity of the atmospheric aerosol on an extensive regional scale. We describe the aerosol regime associated with emissions from the moist tropical forest during early to middle dry season conditions. The moist forest ecosystem is a source of aerosols, composed of material directly released by vegetation, together with species originating from biogenic emissions of various reduced atmospheric gases. Particulate organic carbon is the dominant component of the atmospheric aerosol, exhibiting an average concentration of 740 +/- 190 nmol C m -3 in the mixed layer and 220 +/- 60 nmol C m -3 in free tropospheric air. On the average the atmospheric concentration of aerosol constituents was enhanced in mixed layer air fivefold over free tropospheric levels. Oxalate and SO 42- exhibited the greatest enrichment in the mixed layer, while Cl - showed essentially no enrichment in mixed layer aerosols. For many constituents their enhancement in mixed layer air was greatest in the aerosol coarse fraction, exceeding a factor of 10 in some cases. -from Authors