The Southern African Regional Science Initiative (SAFARI 2000) was a major surface, airborne, and spaceborne field campaign carried out in southern Africa in 2000 and 2001 that addressed a broad range of phenomena related to land‐atmosphere interactions and the biogeochemical functioning of the southern African system. This paper presents a thematic analysis and integration of the Journal of Geophysical Research SAFARI 2000 Special Issue, presenting key findings of an intensive field campaign over southern Africa in August and September of 2000. The integrating themes deal with surface emissions characterization; airborne characterizations of aerosols and trace gases; regional haze and trace gas characterization; and radiant measurements by surface, aircraft, and remote sensing platforms. Enhanced regional fuel loads associated with the moist La Niña phase of the El Niño‐Southern Oscillation (ENSO) cycle produced above average biomass burning emissions, which consequently dominated all other aerosol and trace gas emissions during the dry season. Southward transport of a broad plume of smoke originating in equatorial Africa and exiting off the east coast toward the Indian Ocean (the river of smoke) is attributed to unusual synoptic airflows associated the ENSO phase. New and revised biogenic and pyrogenic emission factors are reported, including a number of previously unreported oxygenated organic compounds and inorganic compounds from biomass combustion. Emission factors are scaled up to regional emission surfaces for biogenic species utilizing species specific and light‐dependent emission factors. Fire scar estimates reveal contradictory information on the timing of the peak and extent of the biomass‐burning season. Integrated tall stack coordinated measurements (between ground, airborne and remotely sensing platforms) of upwelling and downwelling radiation in massive thick aerosol layers covering much of southern Africa yield consistent estimates of large negative forcing for both surface and top of atmosphere radiative forcing. Radiation calculations are supported by novel information on chemical speciation and internal aerosol particle structure. The overall conclusion is that SAFARI 2000, as an integrating theme, has been able to give significant new insights into the regional scale biogeochemical cycling of southern Africa and contributed in important ways to the validation of remote sensing instruments on board the NASA Terra spacecraft.
Abstract. We investigated smoke emissions from fires in savanna, forest, and agricultural ecosystems by airborne sampling of plumes close to prescribed burns and incidental fires in southern Africa. Aerosol samples were collected on glass fiber filters and on stacked filter units, consisting of a Nuclepore prefilter for particles larger than -• 1-2 gm and a Teflon second filter stage for the submicron fraction. The samples were analyzed for soluble ionic components, organic carbon, and black carbon. Onboard the research aircraft, particle number and volume distributions as a function of size were determined with a laser-optical particle counter and the black carbon content of the aerosol with an aethalometer. We determined the emission ratios (relative to CO2 and CO) and emission factors (relative to the amount of biomass burnt) for the various aerosol constituents. The smoke aerosols were rich in organic and black carbon, the latter representing 10-30% of the aerosol mass. K + and NH• were the dominant cationic species in the smoke of most fires, while C1-and so•-were the most important anions. The aerosols were unusually rich in CI-, probably due to the high C1 content of the semiarid vegetation. Comparison of the element budget of the fuel before and after the fires shows that the fraction of the elements released during combustion is highly variable between elements. In the case of the halogen elements, almost the entire amount released during the fire is present in the aerosol phase, while in the case of C, N, and S, only a small proportion ends up as particulate matter. This suggests that the latter elements are present predominantly as gaseous species in the fresh fire plumes studied here.
As part of the Southern Africa Fire‐Atmosphere Research Initiative (SAFARI‐92), size‐fractionated aerosol samples were collected during September–October 1992 at three fixed ground‐based sites in the eastern Transvaal, i.e., at two sites within the Kruger National Park (KNP) and at a third site on the Transvaal highveld (about 150 km WSW of the KNP sites), and near a number of prescribed fires in the KNP. The collection devices consisted of stacked filter units, which separate the aerosol into a coarse (2–10 μm equivalent aerodynamic diameter (EAD)) and a fine (<2 μm EAD) size fraction, and of eight‐stage cascade impactors, which provide more detailed size fractionation. The samples were analyzed for particulate mass (PM), black carbon (BC), and up to 47 elements. The prescribed fires gave rise to high levels of airborne soil dust, but several species (elements) were particularly enriched in the pyrogenic emissions. This was the case for BC, P, K, Ca, Mn, Zn, Sr, and I in the coarse fraction, and for BC, the halogens (Cl, Br, I), K, Cu, Zn, Rb, Sb, Cs, and Pb (and in the flaming phase also Na and S) in the fine fraction. The aerosol concentrations, compositions, and time trends at the two KNP sites were quite similar, suggesting that regionally representative samples were collected. Receptor modeling calculations, using both absolute principal component analysis and chemical mass balance, indicated that the KNP coarse PM was essentially attributable to mineral dust and sea salt, with average relative apportionments of 75% and 25%, respectively. At the highveld site, mineral dust and sea salt contributed in a 99‐to‐1 ratio to the coarse PM. In the fine size fraction at all three fixed sites, four components were identified, i.e., mineral dust, sea salt, biomass burning products, and sulfate. The pyrogenic component was the dominant contributor to the atmospheric concentrations of BC, K, Zn, and I, a major source for PM, Cl, Cu, Br, and Cs, but only a minor source for S. About 40% of the fine PM was, on the average, attributed to the pyrogenic particles, and about one third of it to the sulfate component. Relation of the time trends of the various components with three‐dimensional air mass back trajectories indicated that elevated levels of pyrogenic products were mostly found in air masses arriving from the north. The levels of the sulfate component tended to be higher at the highveld site than at the two KNP sites, and this component was generally associated with continental air. It was concluded that the major contribution to this fine sulfate came from fossil fuel burning and various industrial activities on the Transvaal highveld.
The International Geosphere‐Biosphere Programme/International Global Atmospheric Chemistry (IGBP/IGAC) Southern Africa Fire‐Atmosphere Research Initiative (SAFARI‐92) field experiment was conducted in the 1992 dry season in southern Africa. The objective of the experiment was a comprehensive investigation of the role of vegetation fires, particularly savanna fires, in atmospheric chemistry, climate, and ecology. During SAFARI‐92 experimental fires were conducted in Kruger National Park, South Africa, and at some sites in Zambia, in order to study fire behavior and trace gas and aerosol emissions. Regional studies on atmospheric chemistry and meteorology showed that vegetation fires account for a substantial amount of photochemical oxidants and haze over the subcontinent, and that the export of smoke‐laden air masses contributed strongly to the ozone burden of the remote atmosphere in the southern tropical Atlantic region. The relationships between fire, soil moisture status, and soil trace gas emissions were investigated for several climatically and chemically important gases. Remote sensing studies showed that advanced very high resolution radiometer/local area coverage (AVHRR/LAC) imagery was valuable for fire monitoring in the region and in combination with biomass models could be used for the estimation of pyrogenic emissions.
Abstract. The southern African haze layer is a ubiquitous subcontinental-scale feature of the lower atmosphere that extends to a depth of • 5 km (• 500 hPa level) on non rain days, particularly in winter. Aerosols derived from biomass burning are commonly thought to contribute substantially to the total background aerosol loading within the layer. It is shown that in both summer and winter this supposition is without foundation over South Africa. Summer and winter aerosol loadings are derived from gravimetric analysis of stacked filter units and from proton-induced X ray emission (PIXE) analysis of one to four hourly resolved streaker samples. From concentrations of eleven inorganic elements, apportionment into four primary sources, biomass burning particulates, aeolian dust, industrial sulphur aerosols, and marine aerosols, has been effected. It is shown that the background biomass burning component of the total aerosol loading over South Africa in general, and within the plume of material being recirculated over South Africa and from there exported from the subcontinent south of 22øS to the Indian Ocean in particular, is minimal in both summer and winter. Except over coastal and adjacent inland areas, marine aerosols likewise make up a small fraction of the total loading. This is particularly so over the inland pl.ateau areas. Crustally -derived aeolian dust and industrially -produced sulphur aerosols are demonstrated to be the major summer and winter constituents of the haze layer over South Africa and the particulate material being transported to the Indian Ocean region. Sulphur is transported within the aerosol plume exiting southern Africa to the Indian Ocean as agglomerates on aeolian dust nuclei.
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