Elemental and carbonaceous composition of PM10 and its oxidative potential in schools in Luanda

Abstract

Chemical speciation and oxidative potential (OP) analysis of airborne particles in African schools has not been previously conducted. In this study, daily atmospheric particulate matter (PM10) sampling was carried out in classrooms of four primary schools in Luanda, Angola. Samples were analysed for elemental composition, organic and elemental carbon (OC and EC) and water-soluble organic carbon (WSOC). OP was measured using two acellular assays: dithiothreitol (DTT) and ascorbic acid (AA). PM10 concentrations ranged from 10.2 to 183 μg m􀀀 3, exceeding the WHO guideline on ~70 % of days, with weekday averages (61.0 μg m􀀀 3) more than twice those recorded on Saturdays (26.2 μg m􀀀 3). Carbonaceous constituents accounted for 21.3 % of PM10 mass, with a consistent OC/EC ratio of 2.26 ± 0.74. On average, 77 % of OC was estimated to be secondary, while WSOC/ OC ratios ranged from 0.15 to 0.90, averaging 0.42 ± 0.18. The most abundant elements were Ca, S, Cl, and K, with the highest concentrations observed in a school affected by structural issues and proximity to an unpaved road. Enrichment factor analysis revealed extremely high anthropogenic contributions for Br, S, Cl, Ni, Zn, Pb, Cu, V, and Cr, while correlations between elements indicated major sources such as resuspended mineral dust, vehicular emissions, fuel combustion, and industrial activities, with additional contributions from road dust, construction sites, and sea spray. Average OPAA values ranged from 1.36 to 2.21 nmol min􀀀1 m􀀀3, while OPDTT values spanned from 0.507 to 0.854 nmol min􀀀1 m􀀀3. OC, WSOC, and several transition metals were key con tributors to OPDTT, whereas OPAA showed significant correlations only with Ni and Sr.