Trends in urban air pollution over the last two decades: A global perspective

Document Type

Journal Article

Publication Date



The Science of the total environment




Pt 2




Air pollution trends; Global burden of diseases; Human health; Population exposure; Risk assessment; Urban areas


Ground-level ozone (O), fine particles (PM), and nitrogen dioxide (NO) are the most harmful urban air pollutants regarding human health effects. Here, we aimed at assessing trends in concurrent exposure of global urban population to O, PM, and NO between 2000 and 2019. PM, NO, and O mean concentrations and summertime mean of the daily maximum 8-h values (O MDA8) were analyzed (Mann-Kendall test) using data from a global reanalysis, covering 13,160 urban areas, and a ground-based monitoring network (Tropospheric Ozone Assessment Report), collating surface O observations at nearly 10,000 stations worldwide. At global scale, PM exposures declined slightly from 2000 to 2019 (on average, - 0.2 % year), with 65 % of cities showing rising levels. Improvements were observed in the Eastern US, Europe, Southeast China, and Japan, while the Middle East, sub-Saharan Africa, and South Asia experienced increases. The annual NO mean concentrations increased globally at 71 % of cities (on average, +0.4 % year), with improvements in North America and Europe, and increases in exposures in sub-Saharan Africa, Middle East, and South Asia regions, in line with socioeconomic development. Global exposure of urban population to O increased (on average, +0.8 % year at 89 % of stations), due to lower O titration by NO. The summertime O MDA8 rose at 74 % of cities worldwide (on average, +0.6 % year), while a decline was observed in North America, Northern Europe, and Southeast China, due to the reduction in precursor emissions. The highest O MDA8 increases (>3 % year) occurred in Equatorial Africa, South Korea, and India. To reach air quality standards and mitigate outdoor air pollution effects, actions are urgently needed at all governance levels. More air quality monitors should be installed in cities, particularly in Africa, for improving risk and exposure assessments, concurrently with implementation of effective emission control policies that will consider regional socioeconomic imbalances.


Environmental and Occupational Health