What question did this study set out to answer?

To model and characterize particulate matter and black carbon pollution in Accra's urban settings.

March 14, 2026ACS ES&T Air0 citations

Urban Pollution Burden in Sub-Saharan African (SSA) Cities: Characterizing PM 2.5 , PM 10 , and Black Carbon in Two Contrasting Environments in Accra, Ghana

JNJames NimoAlbany State University YIYussif Ibrahim-AnyassUniversity of Ghana EAEmmanuel K-E AppohUniversity of Ghana

Key Points

To model and characterize particulate matter and black carbon pollution in Accra's urban settings.
Conducted year-long measurements at a busy urban core and a low-density urban background site.
Utilized reference-grade monitors to assess PM2.5, PM10, and black carbon levels.
Employed linear mixed effects models to analyze pollution data.
PM2.5 and PM10 levels exceeded recommended guidelines with higher concentrations in the urban core than the background site.
Significant seasonal variations in pollutant levels, particularly during the dry-Harmattan period due to Saharan dust.
Findings indicated that PM10 constitutes a persistent pollutant with 70% excess at the high-density site.

Abstract

Fine and coarse particulate matter (PM2.5, PM10) and black carbon (BC) pose significant health risks in rapidly urbanizing cities in low- and middle-income countries, particularly in sub-Saharan Africa. However, studies pertaining to their local impacts and disparities are less understood in these cities. This study modeled PM2.5, PM10, and BC differences in Accra, Ghana, to separate the impacts of local urban emissions from regional weather patterns and identify the specific drivers of pollution. Using reference-grade monitors, we conducted year-long, concurrent measurements of PM2.5, PM10, and BC at two sites with distinct land-use characteristics: a busy high-density urban core and a low-density urban backgroundThe results show significant urban pollution burden exceeding recommended guidelines for PM2.5 and PM10, with annual mean concentrations at the urban core site higher than the background site for PM2.5 (38.6 vs 27.9 μg m–3), PM10 (99.3 vs 71.0 μg m–3), and BC (7.5 vs 3.7 μg m–3), underscoring the impact of local traffic and residential activities. A strong seasonal variation was also observed, with pollutant levels increasing significantly at both sites during the dry-Harmattan period (November–March) due to the transport of Saharan dust. Analysis of pollutant ratios (PM2.5/PM10 and BC/PM2.5) confirms a shift in aerosol type: coarse mineral dust dominates during the dry-Harmattan, while fine particles from local combustion sources are more prominent in the wet season. Using linear mixed effects models with PM10, the dry season, and daytime (06:00–17:59) as baseline variables, we demonstrated that PM10 pollution constitutes a persistent pollutant more than PM2.5 and BC at the high-density site, remaining significantly elevated (∼70% excess) regardless of the season. This study provides quantitative evidence of the dual impact of local land-use sources and regional weather on Accra’s air quality. Our findings highlight the need for a two-track management approach that addresses both hyper-local emission sources and the large-scale impacts of seasonal phenomena like the Harmattan.

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