Longitudinal Ambient PM2.5 Measurement at Fifteen Locations in Eight Sub-Saharan African Countries Using Low-Cost Sensors

Air pollution is a major global public health issue causing considerable morbidity and mortality. Measuring levels of air pollutants and facilitating access to the data has been identified as a pathway to raise awareness and initiate dialogue between relevant stakeholders. Low-and middle-income countries (LMICs) urgently need simple, low-cost approaches to generate such data, especially in settings with no or unreliable data. We established a network of easy-to-use low-cost air quality sensors (PurpleAir-II-SD) to monitor fine particulate matter (PM2.5) concentrations at 15 sites, in 11 cities across eight sub-Saharan Africa (sSA) countries between February 2020 and January 2021. Annual PM2.5 concentrations, seasonal and temporal variability were determined. Time trends were modelled using harmonic regression. Annual PM2.5 concentrations ranged between 10 and 116 mu g/m(3) across study sites, exceeding the current WHO annual mean guideline level of 5 mu g/m(3). The largest degree of seasonal variation was seen in Nigeria, where seven sites showed higher PM2.5 levels during the dry than during the wet season. Other countries with less pronounced dry/wet season variations were Benin (20 mu g/m(3) versus 5 mu g/m(3)), Uganda (50 mu g/m(3) versus 45 mu g/m(3)), Sukuta (Gambia) (20 mu g/m(3) versus 15 mu g/m(3)) and Kenya (30 mu g/m(3) versus 25 mu g/m(3)). Diurnal variation was observed across all sites, with two daily PM2.5 peaks at about 06:00 and 18:00 local time. We identified high levels of air pollution in the 11 African cities included in this study. This calls for effective control measures to protect the health of African urban populations. The PM2.5 peaks around 'rush hour' suggest traffic-related emissions should be a particular area for attention.