Carbonyls can be emitted by human activities or produced by photochemical oxidation. However, there is a lack of accurate methods for separately analyzing the primary and secondary sources of carbonyls, which is important for industrial cities with large carbonyls emission. Combined the method of multiple linear regression, positive matrix factorisation (PMF) and observation-based model (OBM), this study improved the source apportionment method of carbonyl and conducted research in a typical industrial city in North China during different seasons. In the method, the source of primary emissions and secondary formation of carbonyls were analysed separately. The concentrations of carbonyls in summer were 47 % higher than those in winter, and acetaldehyde was present in the highest concentrations. Acetaldehyde was mainly formed by secondary formation in summer (51 %) but by primary emissions (40 %) in winter, owing to high temperatures and strong photochemical reactions during summer. The PMF results demonstrated that gasoline vehicle emissions were the major contributors (16 %) in summer. The contribution of diesel vehicle emissions was higher (7 %) in winter than in summer, which related to higher coal transport requirements in winter for industrial city. Chemical budget result indicated that RO· (from alkene) + O