Quantification and seasonal pattern of atmospheric reaction products of gas phase PAHs in PM2.5

► Quantification of unique reaction products of gas phase PAH in real ambient PM2.5. ► Observation of seasonal pattern of PAH reaction products for the first time. ► Evaluation of the significance for the formation of SOA from gas phase PAH reaction. ► Suggestion of unique indicators for the reactions of PAH in the real atmospheres.