Trade-driven changes in China's air pollutant emissions during 2012-2017.

Trade plays an important role in driving regional production and the associated pollutant emissions. Revealing the patterns and underlying driving forces of trade may be critical for informing future mitigation actions among regions and sectors. In this study, we focused on the "Clean Air Action" period from 2012 to 2017 and revealed the changes and driving forces in trade-related air pollutant emissions (including sulfur dioxide (SO), particulate matter with a diameter equal to or less than 2.5 μm (PM), nitrogen oxides (NO), volatile organic compound (VOC), and carbon dioxide (CO)) among regions and sectors in China. Our results showed that emissions embodied in domestic trade decreased considerably in absolute volume nationwide (23-61 %, except for VOC and CO), but the relative contribution ratios from consumption in central and southwestern China increased (from 13 to 23 % to 15-25 % for various species), and those for eastern China decreased (from 39 to 45 % to 33-41 % for various species). From the sector perspective, trade-driven emissions from the power sector decreased in relative contribution ratios, while those from other sectors (including chemical, metal, nonmetal and services) were outstanding for specific regions, and became new targeted sectors when seeking mitigation through domestic supply chains. For changes in trade-related emissions, reduction in emission factor dominated the decreasing trends for almost all regions (27-64 % for the national total, except for VOC and CO), and optimization in trade and/or energy structures also played marked reduction roles in specific regions, far offsetting the increasing effect of increasing trade volume (26-32 %, except for VOC and CO). Our study provides a comprehensive picture of how trade-associated pollutant emissions changed during the "Clean Air Action" period, which may facilitate the formulation of more effective trade-associated policies to mitigate future emissions.