Spatiotemporal variations and inequalities in global traffic-sourced PM_2.5 exposure

Traffic emission is a major source of ambient fine particulate matter with aerodynamic diameter less than 2.5 µm (PM_2.5) pollution. However, little is known about the global population exposure to traffic-sourced PM_2.5 at high spatiotemporal resolutions. This study, utilizing chemical transport and machine learning models, estimated global daily traffic-sourced PM_2.5 at a 0.25° × 0.25° spatial resolution during 2000-2019. The results showed that global population-weighted average traffic-sourced PM_2.5 concentrations increased, aligning with the trend in total PM_2.5 concentrations, rising from 5.8 µg/m³ (contributing to 15.3 % of global total PM_2.5) in 2000-2009 to 6.6 µg/m³ (16.4 % of total PM_2.5) in 2010-2019. Our analysis showed that the increasing trend of traffic-sourced PM_2.5 contributed 36.0 % to the global increasing trend of total PM_2.5. The increasing traffic-sourced PM_2.5 were primarily in Asia, while Europe, North America, and Oceania experienced decreasing trends. Higher concentrations or proportions of traffic-sourced PM_2.5 generally occur during colder months, especially in Asia, and in countries with higher socioeconomic levels. The top ten countries with the highest traffic PM_2.5 proportion in both decades are all high-income countries. Inequalities existed both between and within countries/territories assessed by the Gini index. Compared to total PM_2.5 exposure, traffic-sourced PM_2.5 exposure demonstrated greater inequalities at the global level, within and between countries. Our study provides essential data for identifying high-risk traffic-related PM_2.5 exposure areas, assessing regional pollution control effectiveness, exploring health impacts, and promoting environmental justice.