Characterization of PM2.5-bound nitrated and oxygenated polycyclic aromatic hydrocarbons in ambient air of Langfang during periods with and without traffic restriction

Abstract

PM2.5-bound nitrated polycyclic aromatic hydrocarbons (nPAHs) and oxygenated polycyclic aromatic hydrocarbons (oPAHs) in ambient air were analysed in Langfang during periods with and without traffic restriction. During traffic restriction periods, 20% of gasoline vehicles and all diesel vehicles were restricted to travel within downtown. The 2-nitrofluoranthene/1-nitropyrene ratios obtained during the sampling periods implied that direct emission, especially from diesel vehicles, is the main source for the nPAHs in Langfang. The primary sources of nPAHs and oPAHs, including diesel vehicle emissions and gasoline vehicle emissions, were reduced in the P2 period. Thus, the concentrations of 1-nitropyrene, 3-nitrobenzanthrone, 9-nitrophenanthrene, 2-nitrofluorene, 7-nitrobenz[a]anthracene, 9,10-anthraquinone and benzanthrone were reduced up to 73.3% under this traffic restriction policy. However, the concentrations of 2-nitrofluoranthene and 9-fluorenone formed from gas phase reactions increased slightly. Meanwhile, the chemical profiles of nPAHs and oPAHs changed with traffic fleet variation, and cancer risk levels decreased under the traffic restriction policy. Hence, the traffic restriction policy did effect the ambient concentrations of nPAHs and oPAHs.