Spatio–temporal trends of air quality, Kampala City, Uganda, 2020–2022

Fine particulate matter (PM2.5) is among the health damaging air pollutants that pose health risks to humans, with levels >15 µg/m3 being associated with adverse health effects. PM2.5 has been recommended as the best measure of air quality. Cities are more prone to poor air quality compared to non–urban areas. We assessed the spatio–temporal trends in air quality in Kampala City during January 2020–June 2022. We abstracted PM2.5 concentrations generated by twenty–four Clarity© Node Solar–Powered monitors from January 1, 2020, to June 30, 2022, from the Clarity© dashboard. We computed 24–hour average PM2.5 concentrations at city and division levels by combining data from all monitors. Average PM2.5 concentrations per hour were compared by the hour of the day. We generated choropleth maps and line graphs to show trends in 24–hour average PM2.5 concentrations in Kampala City over the study period. The seasonal Mann–Kendall statistical test was applied to assess the significance of observed trends based on Kendall’s tau correlation coefficient (r) and p–values. Overall, the 24–hour average PM2.5 concentration from January 1, 2020, to June 30, 2022, was 59 µg/m3 (range: 18–182 µg/m3). PM2.5 concentrations exceeded 15 µg/m3 in all city divisions: Kawempe (63 µg/m3), Central (61 µg/m3), Rubaga (60 µg/m3), Nakawa (55 µg/m3) and Makindye (53 µg/m3). A statistically significant decline in PM2.5 occurred throughout the assessment period from January 2020 to June 2022 (r = –0.27, p < 0.001). PM2.5 increased from April to June each year [2020 (55 µg/m3, r=0.56, p=0.006), 2021 (45 µg/m3, r=0.26, p=0.030), and 2022 (37 µg/m3, r=0.37, p=0.030)] and declined from July to September in 2021 (57 µg/m3, r=–0.43, p=0.008) and January to March in 2022 (60 µg/m3, r=–0.41, p=0.011). PM2.5 concentration peaked from 10am–midday (74–73 µg/m3) and 8pm–9pm (73–77 µg/m3). PM2.5 concentrations exceeded targeted safe levels on all days in Kampala City during 2020–2022. In 2022, Kampala Capital City Authority developed the Kampala City Clean Air Action Plan with interventions to be undertaken by multiple partners aimed at improving air quality, including further monitoring.