Global Shifts in PM2.5 Chemical Composition over decade (from 2010 to 2020)

The chemical composition of fine particulate matter (PM_2.5) critically shapes its impacts on climate, air quality and human health, yet its high-resolution spatiotemporal variability covering continental to global scales remains poorly constrained owing to sparse ground observations. Here we develop a 10-km-resolution global dataset of PM_2.5 chemical composition for 2010-2020, including sulfate (SO₄^2-), nitrate (NO₃^-), ammonium (NH₄⁺), organic matter (OM) and black carbon (BC), using a physically constrained deep transfer learning framework. Model evaluation against surface observations yields high accuracies, with correlation coefficients ranging from 0.80 to 0.91 across compositions. We identify pronounced spatiotemporal heterogeneity in PM_2.5 composition distribution and long-term evolution. During the study period, the global reduction in PM_2.5 concentration was driven primarily by decreases in SO₄^2-, with Europe and Asia contributing most prominently. The fractional contributions of BC and OM increased significantly and exhibited a sustained upward trend in North America (by 4.72% and 5.86%, respectively) and Africa (by 2.32% and 6.94%), whereas secondary inorganic aerosols declined in all the continents except Africa. Recent studies have reported substantial differences in toxicity among PM_2.5 compositions. Composition-specific exposure data therefore enable more accurate assessments of PM_2.5-related health risks and underscore the importance of sustained and comprehensive monitoring of PM_2.5 composition.