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

THEOBARD HABINEZA, Albert A. Presto, Allen Robinson, Carnegie Mellon University

     Abstract Number: 209
     Working Group: Chemicals of Emerging Concern in Aerosol: Sources, Transformations, and Impacts

Abstract
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 This challenge persists despite the pervasive influence of non-clean cooking fuels, outdated imported vehicles, rapid urbanization, and biomass burning on air quality, health, and the environment.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 an Aethalometer 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 the aethalometer 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 PM 1 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%). A minor seasonal variation in PM mass concentration, chemical composition, and source profiles was observed during this campaign. The results of this study can inform policy measures to mitigate air pollution and its adverse health effects in SSA.