Carbonaceous components, levoglucosan and inorganic ions in tropical aerosols from Tanzania, East Africa: implication for biomass burning contribution to organic aerosols

Abstract

Abstract. Atmospheric aerosol samples of PM2.5 and PM10 were collected at a rural site in Tanzania in 2011 during wet and dry seasons and they were analysed for carbonaceous components, levoglucosan and water-soluble inorganic ions. The mean mass concentrations of PM2.5 and PM10 were 28.2±6.4 μg m−3 and 47±8.2 μg m−3 in wet season, and 39.1±9.8 μg m−3 and 61.4±19.2 μg m−3 in dry season, respectively. Total carbon (TC) accounted for 16–19% of the PM2.5 mass and 13–15% of the PM10 mass. On average, 85.9 to 88.7% of TC in PM2.5 and 87.2 to 90.1% in PM10 was organic carbon (OC), of which 67–72% and 63% was found to be water-soluble organic carbon (WSOC) in PM2.5 and PM10, respectively. Water-soluble potassium (K+) and sulphate (SO42−) in PM2.5 and, sodium (Na+) and SO42− in PM10 were the dominant ionic species. We found, that concentrations of biomass burning tracers (levoglucosan and mannosan) well correlated with non-sea-salt-K+, WSOC and OC in the aerosols from Tanzania, East Africa. Mean contributions of levoglucosan to OC ranged between 3.9–4.2% for PM2.5 and 3.5–3.8% for PM10. This study demonstrates that emissions from biomass- and biofuel-burning activities followed by atmospheric photochemical processes mainly control the air quality in Tanzania.