This study used online observation instruments to analyze and compare the chemical composition of PM1 and PM2.5 during a heavy pollution event in Zhengzhou in 2021.Differences in the sources of PM1 and PM2.5,and the formation mechanisms of secondary inorganic aerosols,were investigated using a positive matrix factorization model,potential source contribution function,thermodynamic modeling,and chemical reaction rate equations.The results showed that the main components of both PM1and PM2.5were nitrate and organic matter,with higher concentrations in PM1(35.1％and 23.6％)than in PM2.5(26.3％and 18.2％).Compared to PM25,PM1 had larger contributions from secondary sources(37.7％),biomass buming(10.5％),industrial emissions(5.2％),and vehicle emissions(37.0％),while coal combustion(9.3％)and dust(0.4％)contributed less.Additionally,the impact of transport on PM1 was greater than on PM2.5.The dominant pathway for aqueous-phase sulfate formation in both PM1 and PM2.5 was H2O2 oxidation,with transition-metal ion catalysis playing a greater role in PM1 and O3 oxidation being more significant in PM2.5.Nitrate formation in PM1 appeared to be more influenced by gas-phase reactions,and high gas-particle partitioning of NH3 was likely at low aerosol water content in PM1.
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