Chemical Characterization and Seasonality of Ambient Particles (PM_2.5) in the City Centre of Addis Ababa

Ambient air pollution is a growing public health concern in major African cities, including Addis Ababa (Ethiopia), where little information is available on fine particulate matter (PM_2.5, with aerodynamic diameter <2.5 µm) pollution. This paper aims to characterize annual PM_2.5, including bulk composition and seasonal patterns, in Addis Ababa. We collected 24-h PM_2.5 samples in the central city every 6 days from November 2015 to November 2016. The mean (±SD) daily PM_2.5 concentration was 53.8 (±25.0) µg/m³, with 90% of sampled days exceeding the World Health Organization's guidelines. Principal components were organic matter (OM, 44.5%), elemental carbon (EC, 25.4%), soil dust (13.5%), and SNA (sulfate, nitrate, and ammonium ions, 8.2%). Higher PM_2.5 concentrations were observed during the heavy rain season, while crustal dust concentrations ranged from 2.9 to 37.6%, with higher levels during dry months. Meteorological variables, vehicle emissions, biomass fuels, unpaved roads, and construction activity contribute to poor air quality. Compared to the Air Quality Index (AQI), 31% and 36% of observed days were unhealthy for everyone and unhealthy for sensitive groups, respectively. We recommend adopting effective prevention strategies and pursuing research on vehicle emissions, biomass burning, and dust control to curb air pollution in the city.