Tracking CO2 Emissions and Air Pollution in 13,000 Cities Worldwide Using Large Geospatial Datasets

Urban areas are a key contributor to global climate change and air pollution. Currently, urban areas—comprising over half of the global population—face increasing public health challenges attributable to environmental and climate hazards. Various worldwide urban initiatives have been implemented to address the health threats arising from air pollution and climate change, for example, setting sustainable development goals and forming global city networks to address climate change through collaborative actions. Nonetheless, there is still substantial uncertainty regarding the effectiveness and benefits of these actions in relation to both air pollution and greenhouse gas (GHG) emissions. This study identifies and compares temporal trends of CO2 emissions and air pollutant (PM2.5, NO2, and O3) concentrations across 13,000 cities worldwide from 2000 to 2021. We aggregate gridded estimates of CO2 emissions and pollutant concentrations to urban areas with newly available datasets based on satellite data, geophysical modeling, and statistical approaches. We also explore the influence of different commonly used urban boundary definitions on estimated air pollution concentrations and CO2 emissions. Results from this study provide the first city-scale systematic comparison of temporal trends in CO2 emissions and three health-damaging and ubiquitous air pollutants encompassing all urban areas globally. We expect our results will allow international, national, and sub-national actors to evaluate progress towards GHG and air quality targets and further develop long-term mitigation strategies.