Global Urban Temporal Trends in Fine Particulate Matter (PM <sub>2.5</sub>) and Attributable Health Burdens

Background: With much of the world's population residing in urban areas, an understanding of city-level air pollution exposures can inform mitigation approaches. Prior studies of global urban air pollution have not considered trends in air pollutant concentrations nor corresponding attributable health burdens.Methods: We use high-resolution annual average PM2.5 concentrations, epidemiologically derived concentration response functions, and country-level baseline disease rates to estimate population-weighted PM2.5 concentrations and attributable cause-specific mortality in 13,160 urban centers between 2000 and 2019.Findings: While regional averages of urban PM2.5 concentrations decreased over this time period, we find considerable heterogeneity in trends of PM2.5 concentrations between urban areas. Approximately 86% of urban inhabitants (2·5 billion people) lived in urban areas exceeding the World Health Organization's (WHO) guideline for annual average PM2.5 (10 µg/m3) resulting in an excess of 1·34-2·3 million deaths in 2019. Regional averages of PM2.5-attributable deaths increased in all regions except for Europe and the Americas, driven by population, age structure, and disease rate changes. In some cities, PM2.5-attributable health burdens increased despite decreases in PM2.5 concentrations, resulting from shifting age distributions and non-communicable disease rates.Interpretation: We find the majority of the world's urban population lived in areas with unhealthy levels of PM2.5 between 2000 and 2019, leading to substantial contributions to non-communicable disease burdens. Results highlight that avoiding the large public health burden from urban PM2.5 will require strategies that reduce exposure through emissions mitigation as well as strategies that reduce vulnerability to PM2.5 by improving overall public health.Funding Information: NASA Grant No. 80NSSC19K0193 and Wellcome Trust Grant No. 216075-Z-19-Z. RVM acknowledges support from NASA Grant No. 80NSSC21K0508.Declaration of Interests: The authors declare they have no actual or potential competing financial interests.