Variability of biomass burning aerosol optical characteristics in southern Africa during the SAFARI 2000 dry season campaign and a comparison of single scattering albedo estimates from radiometric measurements

Abstract

[1] Measurements of the column-integrated aerosol optical properties in the southern African region were made by Aerosol Robotic Network (AERONET) Sun-sky radiometers at several sites in August-September 2000 as a part of the Southern African Regional Science Initiative (SAFARI) 2000 dry season field campaign. Fine mode biomass burning aerosols dominated in the northern part of the study region (Zambia), which is an active burning region, and other aerosols including fossil fuel burning, industrial, and aeolian coarse mode types also contributed to the aerosol mixture in other regions (South Africa and Mozambique), which were not as strongly dominated by local burning. The large amount of smoke produced in the north lead to a north-south gradient in aerosol optical depth (t a ) in September, with biomass burning aerosol concentrations reduced by dispersion and deposition during transport. Large average diurnal variations of t a (typical diurnal range of 25%) were observed at all sites in Zambia as a result of large diurnal trends in fire counts in that region that peak in midafternoon. However, for all sites located downwind to the south, there was relatively little ($5-10%) average diurnal trend observed as the aerosol transport is not strongly influenced by diurnal cycles. AERONET radiometer retrievals of aerosol single scattering albedo (w 0 ) in Zambia showed relatively constant values as a function of t a for t a440 ranging from 0.4 to $2.5. The wavelength dependence of w 0 varied significantly over the region, with greater decreases for increasing wavelength at smoke-dominated sites than for sites influenced by a significant coarse mode aerosol component. Retrievals of midvisible w 0 based on the fitting of Photosynthetically Active Radiation (PAR; 400-700 nm) flux measurements to modeled fluxes for smoke in Mongu, Zambia yielded an average value of 0.84. This is in close agreement with the estimated average of 0.85 derived from interpolation of the AERONET retrievals made at 440 and 675 nm for August-September 2000. The spectral dependence of w 0 independently retrieved with the AERONET measurements and with diffuse fraction measurements in Mongu, Zambia was similar for both techniques, as a result of both methods retrieving the imaginary index of refraction ($0.030-0.035 on one day) with very little wavelength dependence.

Measurements of aerosol properties from aircraft, satellite and ground‐based remote sensing: a case‐study from the Dust and Biomass‐burning Experiment (DABEX)

“…This compares with values of 0.85-0.90 measured during the Southern African Regional Science Initiative (SAFARI-2000) (Eck et al, 2003;Haywood et al, 2003a;Leahy et al, 2007). In contrast, the dust aerosol was very weakly absorbing with single-scattering albedos of around 0.98 at 550 nm .…”

South African EUCAARI measurements: seasonal variation of trace gases and aerosol optical properties

“…Example of this circulation is visible in Fig. 1, which represents the statistical distribution of HYSPLIT 96-h back trajectories (Draxler and Hess, 2004) for the observational period of this paper.…”

“…especially optical properties of submicron aerosol particles have mainly been investigated during the SAFARI 1992 and SAFARI 2000 measurement campaigns Ross et al, 2003;Eck et al, 2003). On a long-term basis, the South African Weather Service and NOAA-ESRL have conducted observations of aerosol number concentrations and optical properties such as light scattering and absorption as part of the Global Atmosphere Watch (GAW) program at the station in Cape Point (e.g.…”

Optical and microphysical characterization of aerosol layers over South Africa by means of multi-wavelength depolarization and Raman lidar measurements

“…Previous studies have indicated that South Africa is one of the countries in the world that is largely affected by aerosol load, due to various natural and anthropogenic sources (Piketh et al, 2000Formenti et al, 2002Formenti et al, , 2003Campbell et al, 2003;Eck et al, 2003;Freiman and Piketh, 2003;Ichoku et al, 2003;Ross et al, 2003;Winkler et al, 2008;Queface et al, 2011;Tesfaye et al, 2011;Venter et al, 2012;Tiitta et al, 2014). Intensive efforts have been undertaken during recent years to characterize aerosol pollution in South Africa.…”