[Impact Factors of O

O3 and PM2.5 pollution remains a challenge for further improvement of air quality in the Shandong Province. Based on the online observations of O3 and PM2.5 of four typical cities of Jinan, Zibo, Tai'an, and Weihai in the Shandong Province in 2021, we analyzed the relative importance of meteorological factors, conventional pollutants, and VOCs using the random forest （RF） model. The results indicated that in terms of the impact on O3 pollution, the most influential factor was temperature, followed by precursors such as NOx and VOCs. The importance of NOx in Jinan and Weihai was lower than that of VOCs, and that in Zibo and Tai'an was the opposite. The VOC species affecting O3 in different cities were related to emission source structure. Aromatic hydrocarbons and alkenes from solvent use and traffic emissions had a high impact in Jinan. C2-C5 alkanes, alkenes, and aromatic hydrocarbons emitted from petrochemicals and chemical pharmaceuticals had the greatest impact in Zibo. Plant-derived isoprene was of great importance to Tai'an. OVOCs and halogenated hydrocarbons from industries, such as ship/fishing gear manufacturing, rubber production, and electronics manufacturing, were crucial to Weihai. In terms of PM2.5 pollution, the more influential factors were in the order： CO, NOx, SO2, meteorological factors, and VOCs. Long-chain alkanes, OVOCs, halogenated hydrocarbons, and acetylene emitted from petroleum refining, chemical pharmaceuticals, and coal and diesel combustion were species of high importance for PM2.5 pollution. This study provides useful reference for cities to develop targeted pollution control strategies.