Ambient PM<sub>2.5</sub>, soot, black carbon and organic carbon levels in Kimberley, South Africa

Purpose: Ambient air pollution, particularly fine particulate matter (PM2.5), is a major threat to human health and the environment. South Africa faces a burden of PM2.5 exposure, leading to non-communicable diseases and premature mortality. International and national organisations have set air quality guidelines to protect public health. Although studies indicate that compliance with these guidelines carries some risk, meeting them can substantially reduce premature mortality rates. Several studies in different South African regions have highlighted the challenges of PM2.5 pollution, emphasising the importance of monitoring air quality and implementing mitigation measures. This study aims to provide valuable data on the air quality in Kimberley. Results: 24-hour PM2.5 filter samples were collected manually every sixth day from 25 March 2021 to 25 January 2022 in Kimberley, Northern Cape Province, South Africa. The mean PM2.5 concentration recorded in Kimberley was 6.3 μg/m3 (range: 0.7 – 25 μg/m3), slightly exceeding the World Health Organization (WHO) annual air quality guideline of 5 μg/m3. Additionally, the daily WHO guideline of 15 μg/m3 was exceeded on three occasions during the sampling period. The average soot (absorption coefficient), black carbon and organic carbon levels were 0.46 m-1 x 10-5, 0.6 μg/m3 and 0.4 μg/m3, respectively. Six geographic origins of air masses were identified after clustering 4476 generated 72-hour backward trajectories: North West (NW), North (N), East (E), South West (SW), South (S) and Long-range Indian Ocean (LRIO), suggesting diverse long-range transported air pollution from distant source areas. Conclusions: This study is the first of its kind in Kimberley and provides valuable information on PM2.5, soot, black carbon and organic carbon levels and the geographic origin of air masses that passed the sampling site. The findings indicate that the city's PM2.5 pollution poses a risk to human health.