Short term effect of rainfall on elemental composition and size distribution of aerosols in north Florida

Abstract

Aerosol and rain samples were collected during winter 1978–1979 in Tallahassee, Florida and analyzed by particle induced X-ray emission (PIXE) to determine 12–15 elements from Al to Pb. The aerosol sampling was carried out before, during, and after rainfall episodes using time sequence filter samplers (streakers) and cascade impactors to investigate the variation of aerosol composition with rainfall. Al, Si, Ca, Fe, Mn, and Cl, predominantly large particle aerosol constituents (> 1 μm), were strongly affected by rain, their before/during rainfall concentration ratio being greater than 4, whereas K, Zn, Br, Pb and S, predominantly in small particle fractions (< 1.0 μm), had ratios of less than 2. The degree of apparent removal followed the order Cl > Al, Si, Mn > Ca > Fe > K > S, Pb, Zn, Br. Differences in the speed of recovery after rain for elements, to their before rainfall values were also observed. The recovery of soil-derived elements such as Al, Si, Fe, and Mn was delayed, probably because of the wetting of the soil by rain, while S, Zn, Pb, and Br, emitted from anthropogenic sources, recovered more rapidly. The enrichments (fractionation factors) in rain of Ca, K, Zn, Cu, S, Br, and Pb normalized to Fe, relative to particulate matter in the air, were 13, 7.0, 4.3, 3.4, 2.9, 0.96, and 0.36, respectively. High enrichments of K, Zn, Cu, and S suggest that these elements might be at relatively greater concentrations than Fe at higher altitudes and be transported from more distant sources, since their apparent extent of removal is less near ground level compared to soil derived elements.