Seasonal variation and source attribution of ambient air pollution in an industrial sub-city of Addis Ababa, Ethiopia

Ambient air pollution remains a major environmental health challenge in rapidly urbanizing African cities. This study examined the seasonal and spatial variation of PM2.5, PM10, SO2, NO2, and CO across six land-use types (industrial, transportation, commercial, residential, institutional, and recreational) in Akaki Kality Sub-City, Addis Ababa. Sixty-six geo-referenced sites were monitored during the dry (December–February) and wet (June–August) seasons using an AeroQual Series 500 analyzer. Pollutant concentrations were significantly higher during the dry season than during the wet season (p < 0.05). Dry-season mean values reached 60.4 µg/m3 (PM2.5), 138.8 µg/m3 (PM10), 532.1 µg/m3 (SO₂), and 160.6 µg/m3 (NO2). PM2.5 and SO₂ exceeded (in WHO global air quality guidelines: particulate matter (PM₂.₅ and PM₁₀), ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide, World Health Organization, Geneva, 2021) limits by approximately four-fold and twenty six-fold, respectively. The Air Quality Index (AQI), computed using (U.S. EPA (United States Environmental Protection Agency). Technical assistance document for the reporting of daily air quality—the Air Quality Index (AQI). Office of Air Quality Planning and Standards, Research Triangle Park, NC. 2021. https://www.epa.gov/air-quality-index ) and (in National ambient air quality standards and air quality index guideline for Ethiopia, Environmental Protection Authority of Ethiopia, Addis Ababa, 2023) standards, indicated “Unhealthy” conditions in industrial (AQI = 186) and transportation (AQI = 178) zones. Concentrations decreased by 30–45% during the wet season due to rainfall-induced dispersion and wet deposition. Industrial fuel combustion, vehicular exhaust, biomass burning, and road-dust resuspension were identified as dominant emission sources. Targeted interventions such as enforcing industrial stack emission standards, transitioning to low-sulfur fuels, improving vehicle inspection and maintenance, and applying dust control on unpaved roads are recommended. This study provides the first land-use stratified and seasonally resolved AQI map for Addis Ababa, offering evidence to support air-quality management and public-health protection in rapidly urbanizing African cities.