Regional collaboration to simultaneously mitigate PM 2.5 and O 3 pollution in Beijing-Tianjin-Hebei and the surrounding area: Multi-model synthesis from multiple data sources.

Beijing-Tianjin-Hebei and the surrounding area (BTHSA) shows the poorest air quality in China, reflected in sub-standard PM _2.5 and increasingly pronounced O ₃ pollution, stressing the urgency for regional cooperation and collaborative control of PM _2.5 and O ₃ . With the aim to explore the cooperative regions and response mechanisms of PM _2.5 and O ₃ in BTHSA, this study applied multiple mathematical models and analytical indicators to multiple data sources, including applying self-organizing map (SOM), response surface model (RSM), random forest (RF), distributed lag nonlinear models (DLNMs), and meta-analysis, on ground observations of air quality and meteorology, ozone monitoring instrument (OMI) observations, and air pollutant emission inventory. The results revealed that BTHSA exhibited clear regional characteristics of air pollution and can be divided into four clusters for enhanced intercity cooperation. Over 2015-2020, anthropogenic factors played more important roles than meteorological ones on the alleviation of PM _2.5 and the deterioration of O ₃ . RSM based on observations and RF based on emissions both suggested that, in the near future, strengthened abatement of SO ₂ , PM _2.5 and VOC can be beneficial for controlling PM _2.5 and O ₃ pollution, while intensive NOx reduction in PM _2.5 -dominant months and mitigatory NOx reduction in O ₃ -dominant months should be formulated before certifying an obvious transition of O ₃ -NOx-VOC sensitivity. This study, with multi-model and multi-data fusion, can be expected to provide synthesized fact- and science-based guidance for the next-stage collaborative control of PM _2.5 and O ₃ in BTHSA.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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