Composition and Atmospheric Reactivity of Ambient Volatile Organic Compounds(VOCs)in the Urban Area of Nanjing, China

Abstract

Online gas chromatography with flame ionization detection (GC-FID) systems were employed to observe 56 species of volatile organic compounds (VOCs) in the environmental atmosphere in Nanjing in 2015. The results showed that the annual volume fraction of VOCs was (17.49±11.35)×10-9. The highest concentration of VOCs was in April (22.21×10-9), and the lowest in July (12.39×10-9). Diurnal values of VOCs concentration had no obvious variations. Alkanes, alkenes, aromatics, and acetylene accounted for 56.51%, 11.06%, 24.62%, and 7.81%, respectively. Propane (15.26%), ethane (14.14%), acetylene (7.81%), toluene (6.97%), n-butane (6.23%), ethylene (5.23%), isobutane (4.34%), propylene (4.13%), isoprene (4.12%), and m/p-xylene (4.06%) were the most abundant VOCs species. The average ratio of toluene/benzene (T/B) was 2.02, indicating that the atmospheric VOCs were mainly affected by emissions of motor vehicles, especially gasoline vehicles. The average ratio of ethane/ethyne (E/E) was 2.24, showing that the plume had aged. The hydroxyl radical (·OH) loss rate(L·OH) and ozone formation potential(OFP)were applied to assess the chemical reactivity of VOCs. The atmospheric activity of VOCs was higher in the winter and spring than in the summer and autumn. Aromatics and alkenes were the most important contributors to L·OH and OFP. Their contributions to L·OH and OFP were 46.96% and 41.58%, and 33.73% and 39.86%, respectively. Propylene, ethylene, and xylene were the most active species.