| In southern Africa, emissions from industrial fossil fuel combustion and extensive, often anthropogenic, biomass burning tend to accumulate and recirculate in the well-defined synoptic pattern that persists for long time periods over the subcontinent. This study, conducted as a part of the Southern African Regional Science Initiative (SAFARI 2000), utilized a three-tiered approach involving bulk stable isotope analysis, gas chromatography/mass spectrometry (GC/MS) and compound specific isotope analysis (CSIA) to describe southern African aerosols collected at source regions and rural locations. A site-specific comparison of bulk stable isotopic ratios and mean annual precipitation revealed that there were geographical differences among both the wet and dry season sites. These results were related to the relative contributions of C 3 and C4 vegetation to aerosols at each site and to differences in the isotopic signature of nitrogen and sulfur source pools. Conclusions include that location specific processes drive aerosol production in the wet season, whereas regional processes contribute more importantly in the dry season. The CSIA of fatty acids complemented these results by further clarifying source differences not clearly understood through bulk isotope analysis alone. Urban aerosols, such as those collected in Johannesburg have significantly enriched delta13C values of short chain fatty acids (C < 20) as compared to aerosols produced during biomass combustion. Differences between daytime and nighttime aerosol samples were also observed. Both chemical and isotopic techniques identified diurnal differences in aerosols from Mongu, Zambia. GC/MS analysis showed compositional differences in the abundance of C20:0 and C24 fatty acids; bulk carbon isotopic values were significantly depleted at night and C16:0 was similarly depleted at night. These results, showing differences in geographical, diurnal and source specific composition of southern African aerosols confine the utility of a combined chemical and isotopic approach to aerosol research. |
