'Fine Particulate Matter source apportionment in Easter Africa /Rwanda.'

Limited infrastructure and resources in African countries have resulted in a scarcity of in situ air pollution measurements, hindering our understanding of the concentrations and sources of air pollution. This burden persists despite the extensive influence of non-clean cooking fuels, outdated imported vehicles, rapid urbanization, and biomass burning on air pollution, health, and the environment.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). Therefore, air pollution is a significant public health burden, especially in Africa and in LMICs. To help address this gap, we deployed an Aerosol Chemical Speciation Monitor (ACSM) and Magee Scientific Black Carbon Analyzer in Kigali, the capital of Rwanda, for continuous measurement starting from March 2023. Rwanda is an East African country with undergoing rapid urbanization and industrialization whose pollution can be influence by both local and regional emissions. The ACSM measured particulate organic aerosol (OA), sulfate (SO₄⁺), ammonium (NH₄⁺), nitrate (NO₃⁺), and chloride (Cl^-) whereas Magee scientific black carbon measure light absorbing particles at 7 different wavelengths. The measured study-average PM₁ concentration in Kigali during the campaign was 19.7 µg m⁻³. OA contributed 71% of particulate matter mass, inorganic species contributed 10% and Black carbon counted for 19% of the measured PM mass concentration. Marker ions in the average ACSM mass spectrum provide insight into important sources of OA at this site, including traffic emissions, biomass/fossil fuel burning, cooking emissions, and photochemistry. Positive matrix factorization (PMF) identified 3 source profiles dominated by Hydrocarbon-like Organic Aerosol (HOA, 38%), Biomass Burning-like Organic Aerosol (BBOA,33%) and Oxygenated Organic Aerosol (OOA, 29%), Heavily oxidized OOA was observed with peaks in the afternoon, regardless of the shallower boundary layer and higher particle dilution. The result of this work can be used to complement the misinterpreted air pollution level thought inventories in most of the African countries.