Tracking air pollution and CO emissions in 13,189 urban areas worldwide using large geospatial datasets.

Air pollution and climate change are urgent global concerns, with urban areas contributing heavily to both air pollutants and greenhouse gas emissions. Here we calculate fine particulate matter, nitrogen dioxide, and ozone concentrations and fossil-fuel carbon dioxide emissions per capita in 13,189 urban areas worldwide from 2005 to 2019 and analyze correlations between trends for these pollutants, leveraging recently-developed global datasets. Globally, we found significant increases in ozone (+6%) and small, non-significant changes in fine particulate matter (+0%), nitrogen dioxide (-1%), and fossil-fuel carbon dioxide emissions (+4%). Also, over 50% of urban areas showed positive correlations for all pollutant pairs, though results varied by global region. High-income countries with strong mitigation policies experienced decreases in all pollutants, while regions with rapid economic growth had overall increases. This study shows the impacts of urban environmental initiatives in different regions and provides insights for reducing air pollution and carbon dioxide emissions simultaneously.