Air quality and attributable mortality among city dwellers in Kampala, Uganda: results from 4 years of continuous PM2.5 concentration monitoring using BAM 1022 reference instrument.

Background: Air pollution is a known risk factor for non-communicable diseases that causes substantial premature death globally. Rapid urban growth, burning of biomass and solid waste, unpaved sections of the road network, rising numbers of vehicles, some with highly polluting engines, contribute to the poor air quality in Kampala.

Objective: To provide evidence-based estimates of air pollution attributable mortality in Kampala city, with focus on ambient fine particulate matter (PM_2.5).

Methods: We utilized a time series design and prospectively collected data on daily ambient PM_2.5 concentration levels in micrograms per cubic meter (μg/m³) using a Beta Attenuation Monitor (BAM-1022) in Kampala city, Uganda. We combined the PM_2.5 data with all-cause mortality data obtained from the Uganda Bureau of Statistics and the Ministry of Health in Kampala. We calculated attributable risk estimates for mortality using the WHO AirQ+ tools.

Results: Overall, the annual average concentration for PM_2.5 for the period of 4 years, 2018-2021, was 39 μg/m³. There was seasonal variation, with the rainy season months (March-June and October-December) having lower values. PM_2.5 concentrations tend to be highest in the morning (09.00 h) and in the evening (21.00 h.) likely due to increased vehicular emissions as well as the influence of weather patterns (atmospheric temperature, relative humidity and wind). Saturday has the most pollution (daily average over 4 years of 41.2 μg/m³). Regarding attributable risk, we found that of all the deaths in Kampala, 2777 (19.3%), 2136 (17.9%), 1281 (17.9%) and 1063 (19.8%) were attributable to long-term exposure to air pollution (i.e., exposure to PM_2.5 concentrations above the WHO annual guideline of 5 μg/m³) from 2018 to 2021, respectively. For the 4 years and considering the WHO annual guideline as the reference, there were 7257 air pollution-related deaths in Kampala city.

Impact: Our study is the first to estimate air pollution attributable deaths in Kampala city considering the target as the WHO annual guideline value for PM_2.5 of 5 μg/m³. Our monitoring data show that fine particulate matter air pollution in Kampala is above the WHO Air Quality Guideline value, likely resulting in substantial adverse health effects and premature death. While further monitoring is necessary, there is a clear need for control measures to improve air quality in Kampala city.