<b>Chemical characterization and source apportionment of fine particulate matter in Kigali, Rwanda, using aerosol mass spectrometry. </b>

<p dir="ltr">This research project conducted a detailed chemical analysis of fine particulate matter (PM) in Kigali, Rwanda, a rapidly urbanizing city in East Africa. The study aimed to identify the major pollution sources and factors influencing air quality in the region.</p><p dir="ltr">In this project, we deployed advanced air monitoring instruments at a central super-site in Kigali, collecting data on particulate matter (PM) mass and chemical composition in real-time for 12 months, from April 2023 to May 2024.</p><p dir="ltr">A Quadrupole Aerosol Chemical Speciation Monitor (Q-ACSM) was used to measure the chemical components of non-refractory PM1 (particles smaller than 1 micrometer), such as organics, sulfate, nitrate, ammonium, and chloride. An Aethalometer (model AE33) was used to measure Black Carbon (BC), a tracer for combustion, which also distinguished the proportion of BC originating from fossil fuel versus biomass burning. We integrated our findings with publicly available PM2.5 data from the US Embassy in Rwanda to provide a broader context.</p><p dir="ltr"><b>Key Findings:</b></p><ul><li><b>Primary Pollutant:</b> Organic Aerosols were the dominant component, making up approximately 73% of the total PM mass.</li><li><b>Pollution Sources:</b> These organics originated from both primary emissions (directly released from traffic and biomass burning, ~50%) and secondary organic aerosol (formed in the atmosphere from chemical reactions).</li><li><b>Seasonal Pattern:</b> PM mass concentrations significantly increased during the dry season due to the lack of rain, which normally removes aerosols from the air ("precipitation scavenging").</li><li><b>Policy Impact:</b> The city's "car-free day" initiative (on the first and third Sundays of each month) demonstrated a clear potential to reduce PM concentrations, directly linking traffic reduction to improved air quality.</li></ul><p dir="ltr">The research concludes that Kigali's air pollution is primarily driven by combustion sources. We recommend:</p><ul><li>Stricter enforcement of air quality policies.</li><li>Improving the quality of fossil fuels and biomass energy sources.</li><li>A transition to cleaner energy sources for transportation and domestic use.</li></ul><p dir="ltr"><b>Funding and Collaboration:</b><br>This project was funded by the National Science Foundation (NSF), with the Rwanda Space Agency providing the instrumental infrastructure.</p>