Environmental determinants of ambient air pollution in Urban East Africa: Unveiling critical insights from Kigali, Rwanda

Ambient air pollution, driven by natural and anthropogenic sources, poses serious threats to health and ecosystems, particularly in rapidly developing cities with limited monitoring networks. This study assessed how environmental factors affect air quality in urban East Africa, with Kigali, Rwanda, as a case study. Low-cost air quality monitors were installed at six stations across the city to measure the concentration of PM 10 , PM 2.5 , NO 2 , SO 2 , and CO from January to December 2021. Daily (24-hour) quality indicator (QI) for each pollutant was evaluated. Additionally, the rapid impact assessment matrix methodology analyzed 46 environmental components categorized into physical-chemical, biological-ecological, social-cultural, and economic-operational factors, revealing negative and positive impacts on urban air quality. Across the stations, the 24-hour average levels ranged as follows: PM 10 (42.0–56.0 µg/m³), PM 2.5 (25.0–47.9 µg/m³), NO 2 (15.5–20.4 µg/m³), SO 2 (34.8–62.0 µg/m³), and CO (6182.0–7216.0 µg/m³), all exceeding the 2021 WHO 24-hour limits of 45, 15, 25, 40, and 4000 µg/m³, respectively, with QI values ranging from 0.3 to 1.6—highlighting especially critical conditions for PM₂.₅ (QI: 0.3–0.6) and CO (QI: 0.6–0.8), and underscoring the need for urgent intervention. The impact analysis highlighted local topography, dust emissions, and traffic as significant contributors to poor air quality in Kigali while noting the positive impacts of Rwanda's UMUGANDA community work program. These findings underscore the need for evidence-based air quality solutions in Kigali, a case study in urban East Africa. The method's global novelty clarifies environmental factors, guiding effective public health and environmental interventions.