A comprehensive field experiment measuring aerosol chemical and physical properties at a suburban site in Beijing around the 2019 Spring Festival was carried out to investigate the impact of reduced anthropogenic emissions on aerosol formation. Sharply reduced sulfur dioxide (SO.sub.2) and nitrogen dioxide (NO.sub.2) concentrations during the festival holiday resulted in an unexpected increase in the surface ozone (O.sub.3) concentration caused by the strong O.sub.3 -titration phenomenon. Simultaneously, the reduced anthropogenic emissions resulted in massive decreases in particle number concentration at all sizes and the mass concentrations of organics and black carbon. However, the mass concentrations of inorganics (especially sulfate) decreased weakly. Detailed analyses of the sulfur oxidation ratio and the nitrogen oxidation ratio suggest that sulfate formation during the holiday could be promoted by enhanced nocturnal aqueous-phase chemical reactions between SO.sub.2 and O.sub.3 under moderate relative humidity (RH) conditions (40 % RH 80 %). Daytime photochemical reactions in winter in Beijing mainly controlled nitrate formation, which was enhanced a little during the holiday. A regional analysis of air pollution patterns shows that the enhanced formation of secondary aerosols occurred throughout the entire Beijing-Tianjin-Hebei (BTH) region during the holiday, partly offsetting the decrease in particle matter with an aerodynamic diameter less than 2.5 Âµm. Our results highlight the necessary control of O.sub.3 formation to reduce secondary pollution in winter under current emission conditions.