Spatiotemporal variations and inequalities in global traffic-sourced PM exposure.

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