Synergistic PM and O control to address the emerging global PM-O compound pollution challenges.

In recent years, the issue of PM-O compound pollution has become a significant global environmental concern. This study examines the spatial and temporal patterns of global PM-O compound pollution and exposure risks, firstly at the global and urban scale, using spatial statistical regression, exposure risk assessment, and trend analyses based on the datasets of daily PM and surface O concentrations monitored in 120 cities around the world from 2019 to 2022. Additionally, on the basis of the common emission sources, spatial heterogeneity, interacting chemical mechanisms, and synergistic exposure risk levels between PM and O pollution, we proposed a synergistic PM-O control framework for the joint control of PM and O. The results indicated that: (1) Nearly 50% of cities worldwide were affected by PM-O compound pollution, with China, South Korea, Japan, and India being the global hotspots for PM-O compound pollution; (2) Cities with PM-O compound pollution have exposure risk levels dominated by ST + ST (Stabilization) and ST + HR (High Risk). Exposure risk levels of compound pollution in developing countries are significantly higher than those in developed countries, with unequal exposure characteristics; (3) The selected cities showed significant positive spatial correlations between PM and O concentrations, which were consistent with the spatial distribution of the precursors NOx and VOCs; (4) During the study period, 52.5% of cities worldwide achieved synergistic reductions in annual average PM and O concentrations. The average PM concentration in these cities decreased by 13.97%, while the average O concentration decreased by 19.18%. This new solution offers the opportunity to construct intelligent and healthy cities in the upcoming low-carbon transition.