Variation and key reactive species of ambient VOCs in the urban area of Shanghai, China
上海市城区VOCs的年变化特征及其关键活性组分

The ambient concentration of 56 VOCs species were measured continuously in the urban of Shanghai, China from Jan. 1 to Dec. 31, 2010 by GC-FID instrument. The hourly mixing ratio of ambient VOCs in the urban of Shanghai is (2.47~301.48)×10-9, and the average mixing ratio is (26.45±23.36)×10-9. The major compositions of VOCs were alkanes, alkenes, aromatics, and acetylenes, accounting for 46.72%, 33.18%, 11.33%, and 8.76% of the total VOCs, respectively. The ratios of T/B (toluene/benzene) was found at the level of 3.51±2.40, indicating that vehicles were not the only source of ambient VOCs. Others sources, e.g. solvent use, evaporation of gasoline and LPG, made large contribution to VOCs as well. The ratio of E/E (ethane/ethyne) was 0.98±0.68, indicating that the plumes were aged. According to the ratio of E/C (ethyne/CO), the plumes were fresh in spring and winter, and photochemical ages were relatively long in summer and autumn. The constant of ambient VOCs radical loss rate (KOH) was 8.05×10-12cm3·molecule-1·s-1 and the maximum O3 incremental reactivity (MIR) was 4.00 mol·mol-1, which stated that the chemical reactivity of ambient air in urban Shanghai was similar as ethylene. The mixing ratio and composition of VOCs varied with wind direction and wind speed, as a result of different locations of VOCs emission sources. For the OH radical loss rate (LOH), the alkenes and aromatics were the most important contributors, and accounted for 42.21% and 40.83%, respectively. In the case of ozone formation potential (OFP), the alkenes and aromatics accounted for 21.70% and 62.75%, respectively. The key reactive species were xylene, toluene, ethylbenzene, ethylene, propylene, trans-2-butene, and isoprene.