[Variation characteristics of ambient volatile organic compounds (VOCs) in Nanjing northern suburb, China].

Based on the data of volatile organic compounds (VOCs) collected continuously from Mar 1, 2011 to Feb 29, 2012 in the northern suburb of Nanjing, characteristics of their temporal variation, photochemical reactivity of their compositions and source characteristics of VOCs were analyzed. The results showed that the mean value of VOCs mixing ratios was 43.52 x 10(-9) (volume fraction). There was an obvious seasonal cycle of VOCs, with the maximum in summer and minimum in winter. Diurnal variation of VOCs mixing ratios showed a very clear cycle, with higher average VOCs mixing ratios at nighttime than at daytime. The seasonal trend of VOCs mixing ratios at night was in the order of summer > autumn > spring > winter, whereas the order during daytime was winter > summer > spring > winter. Mixing ratio of VOCs had greater diurnal amplitude in autumn and lesser in winter. Alkanes and alkenes had greater diurnal amplitude in autumn. Aromatics and alkenes had greater diurnal amplitude in spring. Using the propylene-equal mixing ratios method, alkenes was found to be the largest part of VOCs, followed by aromatics, and alkanes was the least. The ratios of T/B, E/B and X/B were 1.23, 0.95 and 0.81, respectively, possibly due to the aging of the air mass at this site. The robust vehicular indicator, 3-methylpentane, which is an intrinsic component gasoline, was used to estimate the contributions of traffic versus non-traffic sources. The non-traffic source contribution was significant for ethene (85%), toluene (71%) and m, p-xylene (82%).