Space-Time Air Quality Disparities in Sub-Saharan Africa: PM₂.₅, PM₁₀, and Black Carbon Trends in the Greater Accra Metropolitan Area

Le résumé fourni par la source

Particulate matter (PM₂.₅ and PM₁₀) and black carbon (BC) significantly affect climate and public health, especially in rapidly urbanizing regions. This study examines the spatial and temporal variations of PM₂.₅, PM₁₀, and BC in the Greater Accra Metropolitan Area (GAMA), Ghana, from January to December 2021. Measurements were conducted at a busy, high-density residential site and a low-density residential background site using two federal equivalent monitors, alongside meteorological parameters (relative humidity, temperature, wind speed, and wind direction).Annual mean concentrations of PM₂.₅, PM₁₀, and BC were significantly higher at the high-density site characterized by heavy traffic and residential congestion than at the predominantly residential background site. These discrepancies underscore the influence of distinct land-use patterns, local emissions, and site-specific activities on air quality. Seasonal differences were also evident, particularly during the Harmattan—a dry, dusty trade wind unique to sub-Saharan Africa that substantially degrades air quality. During this period, both sites experienced elevated pollutant levels, with consistently higher measurements at the urban site, highlighting the marked increase in PM₂.₅ and BC concentrations in busy urban areas.Analysis of the PM₂.₅/PM₁₀ ratio showed lower values during the Harmattan, reflecting the predominance of coarse dust particles from natural sources, whereas higher ratios during the wet season indicated greater contributions from fine particles generated by anthropogenic activities such as traffic and industrial processes. Conditional Bivariate Polar Plot analysis further revealed that pollutant levels at the urban site were more strongly driven by wind speed, indicating substantial local emissions and particle resuspension due to heightened human activity. In contrast, concentrations at the background site remained relatively uniform, indicating minimal local emissions and a stronger influence of regional background levels.Overall, this study illustrates the significant spatial and temporal variability of air pollution in GAMA, with important implications for public health and climate change. The elevated levels of PM₂.₅ and BC during the Harmattan period underscore the need for targeted air quality management strategies to mitigate health risks and environmental impacts in sub-Saharan Africa’s rapidly urbanizing environments

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