Light absorbing carbonaceous aerosols: Concentrations and sources in an under-monitored setting

Light-absorbing carbonaceous (LAC) aerosols, particularly black carbon (BC), impact human health and climate, yet their sources are understudied in sub-Saharan Africa (SSA). This study presents the first source apportionment of LAC aerosols in Malawi, using locally determined Absorption Ångström Exponent (AAE) values for the first time in the SSA region. From May to August 2023, mobile monitoring covered eight settlements and highways, with stationary monitoring at two sites in Blantyre, Malawi's second-largest city. We used the MA200 micro-aethalometer to measure equivalent black carbon (eBC) as a BC proxy. Fossil fuel and biomass burning sources were distinguished based on locally determined AAE thresholds (<1.29 for fossil fuel, >1.63 for biomass and intermediate values indicating mix of both). Stationary monitoring revealed mean eBC levels of 4.1 ± 4.1 µg m^-³ in planned and 3.6 ± 2.6 µg m^-³ in unplanned settlements. Mobile monitoring showed spatial variations, with highways averaging 11.3 µg m^-³ and settlements mean ranging from 2.4 to 9.9 µg m^-³ eBC. Across settlements, biomass burning contributed 7 %-46 %, and fossil fuel combustion contributed 10 %-73 % of the total average eBC. The dominant eBC source between fossil fuel and biomass remained consistent across AAE values 1.21-1.37 for fossil fuel and 1.55-1.71 for biomass in sensitivity analysis, except in one settlement. Blantyre's eBC concentrations were comparable to some large and more populated urban cities in SSA, highlighting air quality challenges as the city urbanizes. The study emphasizes area-specific interventions and demonstrates a transferable source apportionment methodology for diverse urban contexts globally.