Characterization of Fine Particulate Matter mass Concentration and Sources using Aerosol Mass Spectrometry in Eastern Africa

Limited infrastructure and resources in Sub-Saharan African (SSA) countries have led to a scarcity of in situ air pollution measurements, hampering our understanding of pollution concentrations and sources. This challenge persists despite the pervasive influence of non-clean cooking fuels, outdated imported vehicles, rapid urbanization, and biomass burning on air quality, health, and the environment. In 2019, ambient air pollution was estimated to cause 4.2 million premature deaths globally, with 89% occurring in low and middle-income countries (LMICs). Thus, air pollution poses a significant public health burden, particularly in SSA and LMICs. To address this gap, we deployed an Aerosol Chemical Speciation Monitor (ACSM) and Magee Scientific Black Carbon Analyzers in Kigali, Rwanda's capital, for continuous monitoring starting in March 2023. Rwanda, an East African country, is undergoing rapid urbanization and industrialization, with pollution influenced by both local and regional emissions. The ACSM measures particulate organic aerosol (OA), sulfate (SO4⁺), ammonium (NH4⁺), nitrate (NO3⁺), and chloride (Cl⁺), while Magee Scientific black carbon measures light-absorbing particles at seven wavelengths. The measured annual PM₁ concentration in Kigali during the campaign was 34 µg m⁻³, with OA contributing 71% of particulate matter mass, inorganic species contributing 10%, and black carbon accounting for 19% of the measured PM mass concentration. Marker ions in the average ACSM mass spectrum provide insights into important OA sources at this site, including traffic emissions, biomass/fossil fuel burning, cooking emissions, and photochemistry. Source apportionment of organic only PM₁ identified three source profiles dominated by Oxygenated Organic Aerosol (OOA, 50%), Hydrocarbon-like Organic Aerosol (HOA, 26%), and Biomass Burning-like Organic Aerosol (BBOA, 24%). Heavily oxidized OOA was observed with peaks in the afternoon, irrespective of the shallower boundary layer and higher particle dilution. A minor seasonal variation in PM mass concentration, chemical composition, and source profiles was observed during this campaign. The results of this study can complement the often-misinterpreted air pollution levels in African countries and inform policy measures to mitigate air pollution and its adverse health effects