Characterization of sources for southern African aerosols through fatty acid and trajectory analyses

Abstract

Biogeochemical cycles in southern Africa are affected by emissions from extensive biomass burning. Emitted trace gases and aerosols frequently accumulate and recirculate in the well‐defined synoptic pattern that persists for long time periods over southern Africa. The role of organic aerosols during atmospheric transport and the influence of neighboring air masses on biogeochemical dynamics in this nutrient‐limited region are insufficiently studied. The Southern African Regional Science Initiative (SAFARI 2000) was conducted in part to investigate the impacts of this large‐scale transport and deposition of increasingly anthropogenic emissions on southern African biogeochemical cycling. This study explores the understanding of regional atmospheric transport through the identification of chemical biomarkers to describe aerosols collected during the SAFARI 2000 dry season research campaign. Total suspended particulate aerosol samples were collected diurnally for a period of two weeks in Mongu, Zambia. Mongu is bordered by the Zambezi River on the west and the Miombo woodland savanna in all other directions. It also lies on the northern extent of the Kalahari Desert. This region is characterized by high biomass burning emissions of river floodplain grasses and woodland savanna during the dry season. Fatty acids were extracted from the collected aerosols and analyzed using gas chromatography. The resultant fatty acid compositions were examined for temporal patterns and trends. Furthermore, these results were compared to both synoptic meteorological patterns over the region, as well as to modeled air parcel trajectories, to gain insight into changes in aerosol composition resulting from changes in atmospheric transports from regions of different vegetation. The results of these analyses confirm that abundances of fatty acids are dependent on local and synoptic meteorology and can thus be used as an additional geochemical tracer to better describe aerosol sources and transport processes within the region.