Assessing the human health risks of indoor PM2.5 exposure in urban and rural households in two provinces of South Africa

Background: Exposure to fine particulate matter (PM2.5) is linked to many adverse outcomes, including respiratory and cardiovascular diseases. South Africa's reliance on coal combustion has led to poor air quality. Indoor air pollution exacerbates health risks in low-income households, necessitating thorough assessment. In this study, a human health risk assessment (HHRA) provided an understanding of health risks posed by indoor and outdoor PM2.5 concentrations in rural and urban settings. Methods: During two campaigns, PM2.5 concentrations were monitored indoors (low-cost sensors in households) and outdoors (Zephyr sensors). We employed the method of the US Environmental Protection Agency in 22 urban households and 22 rural households. Results: During a cooler period, indoor PM2.5 concentrations in all households exceeded the World Health Organization (WHO) Air Quality Guidelines. In Soweto, the winter 24-h PM2.5 concentrations reached as high as 491.4 μg/m³ (Household 19), surpassing all the WHO guideline targets, with the highest at 75 μg/m³. Even with conditions of higher atmospheric dispersion and less solid fuel burning, almost half of rural households had Hazard Quotients (HQs) > 1. In both seasons in urban areas and winter in rural areas, HQ values consistently remained >1, signalling greater health risks. Indoor PM2.5 concentrations almost consistently exceeded outdoor reference limits in both rural and urban locations throughout the year, underscoring the additional pollution burden due to indoor solid fuel burning and personal smoking habits. One Agincourt household recorded a warm period 24-h peak PM2.5 concentration of 1054 μg/m³ indoors, far higher than any corresponding outdoor values. Conclusions: There is an urgent need for interventions to mitigate indoor air pollution that presents significant health risks to household occupants. Reducing health risks associated with high PM2.5 concentrations require interventions to mitigate outdoor PM2.5 levels and solid fuel use indoors. (347 words)