Low‐Level Urban Anthropogenic Sources Contribute to Strong Aerosol Light Absorption on the South African Highveld

This study investigated the chemical composition and shortwave absorption coefficient, βabs(λ), of aerosols collected from sites on the Highveld, a major industrial and highly polluted region of South Africa. Local anthropogenic mineral dust was found to be the dominant chemical component, accounting for (53 ± 14)% of the aerosol mass concentrations. Carbonaceous aerosols (34 ± 12)%, mainly from domestic and waste biomass burning, and secondary inorganic aerosols (13 ± 6%) from anthropogenic combustion sources were also found. High βabs(λ) was observed at all sites, with an estimated mass absorption efficiency, MAE(λ), from (1,296 ± 472) 10−3 m2 g−1 at 375 nm to (621 ± 239)10−3 m2 g−1 at 850 nm. The contributions of the primary light-absorbing aerosols to βabs(λ) were determined using chemical tracers for two optical clusters identified based on the estimated MAE for black carbon (BC). BC was the major contributor to βabs(λ) at all wavelengths (>60%). The brown carbon contribution decreased with λ from (8–40) % at 375 nm to (1–23) % at 532 nm, and was higher in Cluster 1 than Cluster 2. Anthropogenic mineral dust in Cluster 2 appeared to be more light absorbing than pure desert dust and was a significant contributor to βabs(λ), constant with wavelength at ∼16%. The levels of light-absorbing aerosols identified have implications for the radiation budget and atmospheric stability. Although BC dominates light absorption on the South African Highveld, mineral dust contributes significantly to aerosol mass concentrations and enhanced light-absorption.