Heterogeneous variations in wintertime PM2.5 sources, compositions and exposure risks at urban/suburban rural/remote rural areas in the post COVID-19/Clean-Heating period

Inevitably, both unblocking of the COVID-19 (UNCOV) and uncertainty in the clean heating policy (2017–2021) in winter 2022 imposed complex impacts on PM2.5 variations. Together, the urban-rural and rural-rural disparities in these impacts remain unclear. To address this gap, we conducted a synchronous observation at urban (UA)/suburban rural (SRA)/remote rural (RRA) areas to probe PM2.5 evolutions in the post COVID-19/clean-heating (PCOV/PCH) period for further site-specific policy implications. Similar meteorological conditions among sites benefited examining the effects of emission variations. On average, PM2.5 presented a decline order as RRA > UA > SRA. Invoking the positive matrix factorization (PMF) results, specially, the primary emissions (PE) rebounded again after experiencing a continuous decline since the stringent emission-control polices initiated in 2013. PE contributions were up to 80.2 %–83.0 % for three points. SRA benefited most from coal-to-gas and coal combustion (CC) has become its minimum contributor (10.8 %). Concurrently, subsidy reduction and natural-gas (NG) shortage compelled biomass burning (BB) to be the largest origin (21.9 %) marked by the highest K+, Cl− and OC/EC. Regarding RRA, CC (26.5 %) and BB (19.6 %) have been the first and second largest origins despite that the coal-to-electricity policy, indicating the slowdown of policy enforcement. The highest SO42−, As, Sb, Tl, OC, EC and the lowest NO3−/SO42− further verified the dominant CC. Production recovery made industrial emissions (IE) become the largest source (26.8 %) at UA. The metal associated health risks peaked at RRA due to large impacts of CC, though the most of metals related to small-scale industries peaked at UA. This is the first work to highlight that more targeted site-specific strategies in prevention/control of dominant primary sources should be formulated in the PCOV/CH period.