Variations in Rural PM2.5 Sources and Composition in the Post Coal-to-Gas Period Based on a Three-Year Observation

Abstract

Abstract Introduction Various studies were conducted focused on the coal-to-gas (CTG) impacts on urban PM2.5 during its implementation. However, the continuity of CTG effectiveness on PM2.5 control in the post CTG remained unclear, especially in rural area, retarding the further emission-control policy optimization. To address this gap, we examined the wintertime rural PM2.5 variations within the Beijing–Tianjin–Hebei during the non-epidemic-lockdown period of winter 2020–2022. Of which, 2020 holds the most stringent CTG enforcement, 2021 marks the conclusion of CTG, and 2022 represents the post CTG. Methods In this study, the PM2.5 levels in rural areas of the Beijing–Tianjin–Hebei region were monitored during the winters of 2020, 2021, and 2022. Meanwhile, multiple chemical analysis methods were employed to determine its chemical components. The Positive Matrix Factorization (PMF) modeling and Potential source contribution function (PSCF) analysis were employed to analyze the contributions of different sources to PM2.5. Results and Discussion PM2.5 exhibited an average decrease of 30.4%, and PMF modeling indicated the contributions of coal combustion (CC) to PM2.5 fell from 22.4% in 2020 to 17.8% in 2021, and further to 10.8% by 2022, highlighting the enduring CTG effectiveness. The continuously decreasing CC-specific As, Pb, and SO4 2– was another evidence for scattered coal prohibition. Reluctantly, the biomass burning (BB) contributions held higher increase of 17.2% in 2021–2022 than 8.86% in 2020–2021, and it has leapt to be the largest PM2.5 contributor (25.4%) in winter 2022. The natural gas shortage and subsidy reduction in winter 2022, as well as the man, and forced demolition of coal-stoves in winter 2022 should be the main inducements. Contrary to the recent upward trend of secondary aerosols, SO4 2–, NO3 –, and NH4 + showed a downward trend, with annual average dropped of 52.6%, 23.4%, and 53.8%, respectively. This should be ascribed to the enhanced primary emissions from BB and vehicle exhaust (VE). Increments of VE fraction might be related to the gradually unblocking of COVID-19. Correspondingly, the fractions of BB-dependent K+/Cl– and VE-specific Cu/Zn/NO3 – obviously rose from 2020 to 2022. Conclusions This work highlighted that the priorities should be given to the emission control from BB, and guarantee of natural gas supply and certain financial CTG subsidies on the basis of retaining the original pollution control policies, for further rural air quality improvement in the post CTG period. Graphical abstract

Keywords

• Beijing-Tianjin-Hebei
• Rural PM2.5
• Coal-to-gas
• Biomass burning
• Coal combustion