Determination of the distribution of elements as a function of particle size in aerosol samples by sequential leaching†

Abstract

A study of the fractionation of aerosols according to particle size and chemical bonding is reported. A three-stage sequential leaching procedure was applied to establish the distribution of metals between the environmentally mobile fraction, the fraction bound to carbonates and oxides and the fraction bound to silicates and organic matter (environmentally immobile). Different particle size fractions were collected and sequential leaching was applied to the filter-collected aerosols in eight particle size ranges. It was shown that several species of Pb, Cd and Cr were concentrated in the particle size range 0.18–0.71 µm. Different metals were strongly fractionated between different aerosol size fractions, and this has important implications for all aspects of atmospheric transport from public health to global metal cycling. Elements such as Pb, Cr and Cd were adsorbed on sub-micrometre diameter particles and they could be deposited in the pulmonary area. Cadmium compounds have been found to occur extensively in the environmentally mobile fractions, whereas As compounds accumulated in the environmentally immobile portions. The results of sequential leaching indicate the mobility of the elements once the aerosol is mixed directly into natural waters or during scavenging of the aerosol by wet deposition.