The Country Trends in Major Air Pollutants data set is a framework of public-health-focused air quality indicators that quantifies over 200 countries' trends in exposure to Particulate Matter (PM2.5), Ozone (O3), Nitrogen Oxides (NOx), Sulfur Dioxide (SO2), Carbon Monoxide (CO), and Volatile Organic Compounds (VOCs). Pollutant concentration data are derived from the European Centre for Medium-Range Weather Forecasts (ECMWF) Atmospheric Composition Reanalysis 4 (EAC4) data sets, freely available from the Copernicus Atmospheric Monitoring Services' Atmospheric Data Store (https://ads.atmosphere.copernicus.eu). CIESIN's Gridded Population of the World, Version 4 (GPWv4): Population Count Adjusted to Match 2015 Revision of UN WPP Country Totals, Revision 11 was used in the population weighting algorithm.