Concentration of black carbon and particulate matter air pollution and source apportionment in Rwanda, East Africa

Abstract Fine particulate matter (PM 2.5 ) and black carbon (BC) are major air pollutants with impacts on human health and regional climate, yet very little information on spatiotemporal distributions in African cities currently exists. This study analysed spatiotemporal variations in the concentration of PM 2.5 and BC in African urban and rural areas, with special attention to Kigali, in Rwanda. The data revealed average values for PM 2.5 of 22 to 38 μg m −3 , well above the WHO recommended thresholds, with higher values recorded in the dry season. The average concentration level of BC was 13.4 ± 9.7 μg m −3 in urban areas and 7.7 ± 4.4 μg m −3 in rural areas, demonstrating strong seasonal variation and with morning and evening peaks reflective of traffic density and household fuel usage, respectively. Source identification showed fossil fuels contributed approximately 60% of the total BC at urban sites. These findings highlight the growing influence of urbanization and transport emissions in Rwandan cities and emphasize the importance of continuous air quality monitoring to guide mitigation strategies.