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

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. 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. 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. Key Findings: Primary Pollutant: Organic Aerosols were the dominant component, making up approximately 73% of the total PM mass.Pollution Sources: 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).Seasonal Pattern: PM mass concentrations significantly increased during the dry season due to the lack of rain, which normally removes aerosols from the air ("precipitation scavenging").Policy Impact: 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.The research concludes that Kigali's air pollution is primarily driven by combustion sources. We recommend: Stricter enforcement of air quality policies.Improving the quality of fossil fuels and biomass energy sources.A transition to cleaner energy sources for transportation and domestic use.Funding and Collaboration: This project was funded by the National Science Foundation (NSF), with the Rwanda Space Agency providing the instrumental infrastructure.本研究针对东非快速城市化城市卢旺达基加利的细颗粒物（fine particulate matter, PM）开展了详尽的化学组分分析，旨在明确该区域主要污染来源与影响空气质量的关键因素。 本项目在基加利的中央超级监测站点部署了先进的空气监测仪器，于2023年4月至2024年5月期间连续12个月实时采集细颗粒物质量浓度与化学组分数据。 本研究采用四极气溶胶化学组分监测仪（Quadrupole Aerosol Chemical Speciation Monitor, Q-ACSM），对非难熔PM1（粒径小于1微米的颗粒物）的化学组分进行测定，涵盖有机物、硫酸盐、硝酸盐、铵盐及氯化物等。同时使用型号为AE33的黑碳仪（Aethalometer, AE33）测定作为燃烧示踪物的黑碳（Black Carbon, BC），并区分出黑碳中源自化石燃料与生物质燃烧的占比。此外，本研究结合美国驻卢旺达大使馆公开的PM2.5数据，以提供更全面的研究背景。 核心研究结果： 主要污染物：有机气溶胶为占比最高的组分，约占细颗粒物总质量的73%。 污染来源：此类有机物既来自一次排放（约占50%，直接由交通活动与生物质燃烧释放），也来自二次有机气溶胶（通过大气化学反应在空气中生成）。 季节变化特征：旱季时细颗粒物质量浓度显著升高，原因在于缺乏通常可通过"降水清除（precipitation scavenging）"去除大气气溶胶的降雨。 政策影响：该市推行的"无车日"活动（每月第一个与第三个周日举办）展现出显著降低细颗粒物浓度的潜力，直接证明了减少交通排放可有效改善空气质量。 本研究结论显示，基加利的空气污染主要由燃烧源驱动，据此提出以下建议： 1. 严格落实空气质量相关政策； 2. 提升化石燃料与生物质能源的使用品质； 3. 推动交通与民用领域向清洁能源转型。 资助与合作： 本项目由美国国家科学基金会（National Science Foundation, NSF）资助，卢旺达空间局（Rwanda Space Agency）提供了监测仪器基础设施。