No abstract

Summary Background With much of the world's population residing in urban areas, an understanding of air pollution exposures at the city level can inform mitigation approaches. Previous studies of global urban air pollution have not considered trends in air pollutant concentrations nor corresponding attributable mortality burdens. We aimed to estimate trends in fine particulate matter (PM 2·5 ) concentrations and associated mortality for cities globally. Methods We use high-resolution annual average PM 2·5 concentrations, epidemiologically derived concentration response functions, and country-level baseline disease rates to estimate population-weighted PM 2·5 concentrations and attributable cause-specific mortality in 13 160 urban centres between the years 2000 and 2019. Findings Although regional averages of urban PM 2·5 concentrations decreased between the years 2000 and 2019, we found considerable heterogeneity in trends of PM 2·5 concentrations between urban areas. Approximately 86% (2·5 billion inhabitants) of urban inhabitants lived in urban areas that exceeded WHO's 2005 guideline annual average PM 2·5 (10 μg/m 3 ), resulting in an excess of 1·8 million (95% CI 1·34 million–2·3 million) deaths in 2019. Regional averages of PM 2·5 -attributable deaths increased in all regions except for Europe and the Americas, driven by changes in population numbers, age structures, and disease rates. In some cities, PM 2·5 -attributable mortality increased despite decreases in PM 2·5 concentrations, resulting from shifting age distributions and rates of non-communicable disease. Interpretation Our study showed that, between the years 2000 and 2019, most of the world's urban population lived in areas with unhealthy levels of PM 2·5 , leading to substantial contributions to non-communicable disease burdens. Our results highlight that avoiding the large public health burden from urban PM 2·5 will require strategies that reduce exposure through emissions mitigation, as well as strategies that reduce vulnerability to PM 2·5 by improving overall public health. Funding NASA, Wellcome Trust.

Observing the spatial heterogeneities of NO 2 air pollution is an important first step in quantifying NO X emissions and exposures. This study investigates the capabilities of the Tropospheric Monitoring Instrument (TROPOMI) in observing the spatial and temporal patterns of NO 2 pollution in the continental United States. The unprecedented sensitivity of the sensor can differentiate the fine‐scale spatial heterogeneities in urban areas, such as emissions related to airport/shipping operations and high traffic, and the relatively small emission sources in rural areas, such as power plants and mining operations. We then examine NO 2 columns by day‐of‐the‐week and find that Saturday and Sunday concentrations are 16% and 24% lower respectively, than during weekdays. We also analyze the correlation of daily maximum 2‐m temperatures and NO 2 column amounts and find that NO 2 is larger on the hottest days (>32°C) as compared to warm days (26°C–32°C), which is in contrast to a general decrease in NO 2 with increasing temperature at moderate temperatures. Finally, we demonstrate that a linear regression fit of 2019 annual TROPOMI NO 2 data to annual surface‐level concentrations yields relatively strong correlation ( R 2 = 0.66). These new developments make TROPOMI NO 2 satellite data advantageous for policymakers and public health officials, who request information at high spatial resolution and short timescales, in order to assess, devise, and evaluate regulations.