The chemical composition of tropospheric aerosols and their contributing sources to a continental background site in northern Zimbabwe from 1994 to 2000

Abstract

Atmospheric aerosols were collected in separate coarse (2–10 μm diameter) and fine (diameter less than 2 μm) size fractions at Rukomechi Research Station (16.1°S, 29.4°E), Zimbabwe, in the central part of southern Africa, from September 1994 to January 2000. The samples were analysed for the particulate mass (PM), black carbon, and 47 elements. The overall data set and the separate wet and dry season data sets were examined with absolute principal component analysis (APCA). Natural and anthropogenic aerosol sources were identified in both seasons, but the sources and their contributions to the total PM were found to vary between seasons and between size fractions. Crustal matter, sea salt (SS), a mixed biogenic (BIO) emission/biomass burning (BB) component, and a copper component were identified for the coarse aerosols during the wet season. APCA attributed 29% of the total wet season coarse PM to the mixed BIO/BB component, and 32% to SS. The copper component is likely due to the copper smelters in the Zambian Copperbelt. The dry season coarse PM originated from crustal matter, BB, BIO, and SS sources, with the major contribution (32%) coming from BB. Four components (crustal matter, BB, non-ferrous smelters, and SS) were identified for the fine particles for both the wet and dry seasons. The BB component provided the major contribution to the total fine PM, accounting for 44% and 79% in the wet and dry seasons, respectively. The relative contributions to the total PM (both fine and coarse) for all sources were greater in the dry season than the wet season, except for SS.