Spatial-temporal patterns and influence of land-use and socioeconomic factors on fine particulate matter pollution in Accra, Ghana

Abstract

Background: Air pollution levels in cities in Sub-Saharan Africa (SSA), the world’s most rapidly urbanizing region, are among the highest globally due to influences from diverse local and regional sources. However, very little is known about within-city disparities at fine spatial-temporal resolution. We examined the space-time patterns of fine particle pollution (PM2.5) in relation to land-use variables and socioeconomic factors in Accra, Ghana, and evaluated trends over a decade.Methods: We measured and analysed weekly gravimetric and minute-by-minute PM2.5 (optical sensor) concentrations from 150 unique locations (10 fixed [1-year] and 140 weekly [7-day] sites) covering a range of land-use, socioeconomic features and source influences.Results: PM2.5 concentrations were highest between December - February, during the “Harmattan” when transported dust and changes in regional and local meteorology affect Accra. In this period, levels were as high as 267 μg/m3 (mean 94.1 μg/m3), compared to annual PM2.5 concentrations ranging from 14.4 to 31.3 μg/m3 at fixed sites. Across all 150 sites, weekly concentrations ranged from <10 μg/m3 to >250 μg/m3. Sites near roadsides had the highest overall mean PM2.5 (43 μg/m3), followed by high-density (poor) and low-density (affluent) residential sites; peri-urban background sites had the lowest levels. By time of day, daily PM2.5 at all sites rose at dawn and peaked at daybreak, followed by a gradual decline till afternoon and a modest evening peak. There were indications of decreased PM2.5 concentrations at residential sites when compared to matching data from a decade ago (39 vs 25 μg/m3), suggesting likely reductions in biomass emissions.Conclusion: Fine particle pollution in Accra may be decreasing over time but remains 2 to 4-fold higher than the WHO guideline with significant variations in relation to spatial, socioeconomic, and land-use factors. Equitable local policies and interventions are needed to reduce air pollution levels and protect the vulnerable.