Emission Reductions Have Led to Significant Decrease in Sulfate: An Example of Severe Pollution Episode in Henan Province During The Period Around The New Year's Eve of 2023–2024

Abstract In late December 2023, the Ministry of Ecology and Environment of China implemented a joint reginal air pollution prevention and control initiative in key areas encompassing Beijing, Tianjin, Hebei, Shandong, and Henan to mitigate severe pollution episodes. Taking Henan Province as a case study, this research employs the WRF-SMOKE-CAMx modeling system to assess the impacts of emergency emission reductions during a heavy pollution period spanning late December 2023 to early January 2024 (Y2023). Despite unfavorable meteorological conditions, observed PM 2.5 concentrations in Henan during Y2023 declined by 20.9% compared to a comparable heavy pollution episode during the 2022–2023 year-end transition (Y2022), attributable to stringent control measures. Sulfate exhibited the most pronounced response to emission controls, showing a 95.4% reduction in relative concentration change after meteorological normalization, followed by ammonium at 50.3%. These results demonstrate the effectiveness of the Y2023 intervention in curtailing sulfate and ammonium formation. Moreover, earlier activation of orange alert measures in northern Henan cities yielded significantly greater emission reduction benefits compared to southern cities. The findings underscore that in industrialized, energy-intensive regions such as Henan, controlling sulfate precursors remains a critical strategy for achieving rapid PM 2.5 reductions. Graphical Abstract