Abstract: Following the relaxation of coronavirus disease 2019 restrictions and the subsequent full economic recovery, Shandong Province experienced a 4.3% rebound in the air quality index in 2023, with both fine particulate matter (PM2.5) and ozone (O3) concentrations exhibiting noticeable upward trends. Quantifying the drivers of this rebound is essential for developing targeted air quality management strategies. To this end, the analysis focused on the early spring period (ESP, February-April) and autumn harvest period (AHP, September-October) for PM2.5 pollution and the photochemical season period (PSP, July-October) for O3 pollution. We developed an interpretable random forest-Shapley additive explanation (RF-SHAP) framework optimized with a tree-structured Parzen estimator (TPE) to assess the impacts of anthropogenic emissions and meteorological factors. The introduction of the TPE optimization technique enhanced RF model performance across these pollution periods. anthropogenic emissions played the dominant role in PM2.5 pollution rebounds, contributing 14.1% during the ESP and 19.0% during the AHP, for example, industrial recovery (9.2% increase in energy consumption) and agricultural waste burning (70.0% increase in crop residue burning incident). In contrast, O3 pollution was more strongly influenced by meteorological conditions, which contributed a 5.8% increase during the PSP. Critical meteorological drivers included strengthened atmospheric oxidation capacity, reduced total cloud cover, and changes in boundary layer height, although precursor emissions from the transportation and petrochemical industries remained indispensable for O3 formation. This study provides an important scientific basis for precise air quality management in Shandong Province in the postpandemic period.

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