Insights into air pollution at an urban site in the Greater Cairo Megacity: Minor PM2.5 sources with significant health risks

This study presents a comprehensive chemical characterization and source apportionment of PM 2.5 in the Greater Cairo Area (GCA), one of the world's most polluted megacities. A total of 59 PM 2.5 samples were collected continuously and on a 24-h basis during the winter of 2019–2020 at an urban background site and analyzed for a wide range of organic and inorganic species. The Positive Matrix Factorization model was applied to identify and quantify as many as eleven sources contributing to PM 2.5 , highlighting the highly complex mixture of aerosols over the GCA. These sources include industrial emissions (coal combustion, lead and copper smelting), vehicular exhaust and non-exhaust emissions, open waste and wood burning, cooking, processed secondary aerosols, transported crustal dust, and mixed regional pollution. Local primary particulate controllable sources dominated elemental health risks, contributing 60% of the total NCR (1.7) and 52% of the total CR (2.1×10 -5 ), despite representing a much smaller fraction of PM 2.5 mass. Industrial emissions, though contributing only ∼12% of PM 2.5 mass, were responsible for 37% of elemental NCR and 29% of CR. These findings underscore the need for targeted mitigation strategies addressing the burden of air pollution in GCA. • Source apportionment revealed 11 PM 2.5 sources in the Greater Cairo Area • Industrial sources of coal, copper, and lead have a PM 2.5 share of 12.2% • Elemental PM 2.5 in GCA exceeds safety thresholds, with NCR 2.9 and CR 3.9×10 -5 • Local primary particulate controllable sources dominate PM 2.5 health risks • Traffic and industry accounted for 40% elemental-NCR and 37% elemental-CR