Enhancing the understanding of air pollutant emission reductions from coal-fired industrial boilers under the China’s Clean Air Action Plans

Coal-fired industrial boilers (CFIBs) constitute a priority area of the China’s Clean Air Plans. This study first detailed the effects of two Clean Air Plans implemented during 2012 to 2020 on the air pollutant emissions of Chinese CFIBs based on the establishment of an up-to-date emission inventory covering primary air pollutant species. Specifically, we analysed the spatiotemporal heterogeneity of air pollutant reductions, quantified the measure-specific emission reductions, and further investigated the synergistic effects for hazardous trace elements (HTEs) in the base years 2012, 2017 and 2020. Results showed that national emission reductions in PM, M_2.5, SO₂, NOx, and HTEs (sum of Hg, As, Cd, Cr, and Pb) were 3678.8 kt, 942.0 kt, 6672.5 kt, 1446.1 kt, and 5981.7 t from 2012 to 2020, respectively, with the largest reductions occurred in the period 2012-2017 (66.4–90.5%). East China, Northeast China, and South-Central China were the most beneficial regions to achieve emission reductions of air pollutants, and their share of the contribution to emission reductions ranged from 80.1% to 86.9%. The measure of phase-out boilers resulted in the highest reductions in air pollutant emissions from 2012 to 2017 with the share of 58.7–66.3% over the entire period, while its contribution was weakened by the upgrading of air pollution control devices during 2017-2020. The synergistic effect of NOx on HTEs was weaker than that of PM, PM_2.5, and SO₂ with the lowest cross-elasticity coefficient, and the degree of synergistic effects also exhibited stage-specific heterogeneity. The findings could provide new insights into the effectiveness of air pollution control policies in reducing pollutant emissions in major sectors.