PM2.5 infiltration from controlled burns in dwellings in a rural community within Mpumalanga, South Africa

Air pollution poses a significant health risk globally, particularly in Sub-Saharan Africa. While domestic fuel burning is a well-known source of air pollution, outdoor sources beyond an individual’s control, such as large-scale biomass burning, can also significantly impact on indoor air quality. In South Africa's Kruger National Park, controlled burns are conducted during the winter months for ecological reasons and to mitigate the risk of wildfires, but their impact on local air quality is underexplored, especially in low- and middle-income countries. As part of a broader study, we monitored indoor PM 2.5 concentrations in a rural community in Agincourt, Mpumalanga province, South Africa, over two weeks using low-cost sensors in nine dwellings. Ambient (outdoor) PM 2.5 levels were simultaneously measured with a Zephyr air quality sensor. On 9 July 2023, we observed a peak in indoor PM 2.5 in all households, as well as a peak in ambient PM 2.5 . On this day, 24-hour indoor concentrations averaged 50 μg/m 3 (range: 43–55 μg/m 3 ), exceeding national guidelines. Satellite imagery and aerosol index data identified smoke plumes originating from Kruger National Park two days earlier. Using meteorological data from nearby Hoedspruit Air Force Base and HYSPLIT back-trajectory analysis, we identified that a wind shift on 9 July transported the plume over the community, showing air masses passing over the park before reaching the study site. Communities in South Africa already face high pollution levels from industrial and anthropogenic sources. These findings emphasise the need to further investigate relationships between controlled burning and human exposure, in order to aid refinement of controlled biomass burning practices to limit exposure to harmful pollutants and highlight the importance of developing strategies to inform and protect vulnerable communities.