Chemical composition and mass closure for PM10 aerosols during the 2005 dry season at a rural site in Morogoro, Tanzania

Abstract

AbstractAn intensive aerosol field campaign was carried out from 11 July to 11 August 2005 (dry season) at a rural site in Morogoro, Tanzania. The objectives were to determine the chemical composition of the atmospheric particulate matter (PM) and to examine to which extent the gravimetric PM mass can be explained by the measured aerosol components. Two low‐volume filter samplers were deployed, a PM10 filter holder with two Whatman QM‐A quartz fibre filters in series and a Gent PM10 stacked filter unit (SFU) sampler with coarse and fine Nuclepore polycarbonate filters. The samplers operated in parallel and a total of 51 parallel collections were made. All samples were analysed for the PM mass by weighing. Depending on the sampler type and/or collection substrate, further analyses were performed for 25 elements by particle‐induced x‐ray emission spectrometry, for major water‐soluble inorganic ions by ion chromatography, and for organic carbon and elemental carbon by a thermal—optical transmission technique. The PM10 mass, as derived from the SFU samples, was, on an average, 46 ± 12 µg/m3. Aerosol chemical mass closure calculations were made for this PM10 mass; eight aerosol components were considered and they explained 93% of the average PM10 mass. Organic matter (OM) and crustal matter were the dominant aerosol components; they accounted for, on an average, 44% and 33%, respectively, of the PM10 aerosol. The large contribution from OM is thought to originate mainly from the burning of biomass, especially of charcoal and agricultural residues. Copyright © 2009 John Wiley & Sons, Ltd.