An accurate fine-resolution surface of the chemical composition of fine particulate matter (PM_2.5) would offer valuable information for epidemiological studies and health impact assessments. We develop geoscience-derived estimates of PM_2.5 composition from a chemical transport model (GEOS-Chem) and satellite observations of aerosol optical depth, and statistically fuse these estimates with ground-based observations using a geographically weighted regression over North America to produce a spatially complete representation of sulfate, nitrate, ammonium, black carbon, organic matter, mineral dust, and sea-salt over 2000-2016. Significant long-term agreement is found with cross-validation sites over North America (R²=0.57—0.96), with the strongest agreement for sulfate (R²=0.96), nitrate (R²=0.90), and ammonium (R²=0.86). We find that North American decreases in population-weighted fine particulate matter (PM_2.5) concentrations since 2000 have been most heavily influenced by regional changes in sulfate and organic matter. Regionally, the relative importance of several chemical components are found to change with PM_2.5 concentration, such as higher PM_2.5 concentrations having a larger proportion of nitrate and a smaller proportion of sulfate. This dataset offers information for research into the health effects of PM_2.5 chemical components.

Here we retrieve global daily 1 km gapless PM_2.5 concentrations via machine learning and big data, revealing its spatiotemporal variability at an exceptionally detailed level everywhere every day from 2017 to 2022, valuable for air quality monitoring, climate change, and public health studies. We find that 96%, 82%, and 53% of Earth’s populated areas are exposed to unhealthy air for at least one day, one week, and one month in 2022, respectively. Strong disparities in exposure risks and duration are exhibited between developed and developing countries, urban and rural areas, and different parts of cities. Wave-like dramatic changes in air quality are clearly seen around the world before, during, and after the COVID-19 lockdowns, as is the mortality burden linked to fluctuating air pollution events. Encouragingly, only approximately one-third of all countries return to pre-pandemic pollution levels. Many nature-induced air pollution episodes are also revealed, such as biomass burning.

Ambient fine particulate matter (PM_2.5) is the world’s leading environmental health risk factor. Quantification is needed of regional contributions to changes in global PM_2.5 exposure. Here we interpret satellite-derived PM_2.5 estimates over 1998-2019 and find a reversal of previous growth in global PM_2.5 air pollution, which is quantitatively attributed to contributions from 13 regions. Global population-weighted (PW) PM_2.5 exposure, related to both pollution levels and population size, increased from 1998 (28.3 μg/m³) to a peak in 2011 (38.9 μg/m³) and decreased steadily afterwards (34.7 μg/m³ in 2019). Post-2011 change was related to exposure reduction in China and slowed exposure growth in other regions (especially South Asia, the Middle East and Africa). The post-2011 exposure reduction contributes to stagnation of growth in global PM_2.5-attributable mortality and increasing health benefits per µg/m³ marginal reduction in exposure, implying increasing urgency and benefits of PM_2.5 mitigation with aging population and cleaner air.

The World Health Organization (WHO) recently released new guidelines for outdoor fine particulate air pollution (PM _2.5 ) recommending an annual average concentration of 5 μg/m ³ . Yet, our understanding of the concentration-response relationship between outdoor PM _2.5 and mortality in this range of near-background concentrations remains incomplete. To address this uncertainty, we conducted a population-based cohort study of 7.1 million adults in one of the world’s lowest exposure environments. Our findings reveal a supralinear concentration-response relationship between outdoor PM _2.5 and mortality at very low (<5 μg/m ³ ) concentrations. Our updated global concentration-response function incorporating this new information suggests an additional 1.5 million deaths globally attributable to outdoor PM _2.5 annually compared to previous estimates. The global health benefits of meeting the new WHO guideline for outdoor PM _2.5 are greater than previously assumed and indicate a need for continued reductions in outdoor air pollution around the world.