Characteristics of Photochemical Loss and VOCs Source Apportionment of Urban Area of Xiangtan City in Summer.

Owing to the fact that chemical activity of numerous VOCs (volatile organic compounds) differs greatly, the contributions of the more active species VOCs could be weakened in case the source apportionment of VOCs is carried out merely using the observed data of VOCs concentration, which is detrimental to the VOCs emission reduction and ozone pollution alleviation. To effectively reduce the influence of photochemical loss on VOCs source apportionment, in this study the initial concentrations of VOCs were estimated by photochemical aging method to correct the photochemical loss of ambient VOCs species, and then the positive matrix factorization (PMF) was used to conduct source apportionment of ambient VOCs. The findings of the study suggested that the average observed concentration of ambient VOCs during the observation period was (23.90±5.79)X10^-9, and the initial concentration was (31.28±15.17)x10^-9; and among others, variation of olefins was most drastic, being 4.33 times greater than the observed concentration, which was followed by aromatic hydrocarbons (1.87 times). The total average photochemical consumption of VOCs in daytime was 14.66X10^-9, the photochemical consumption of olefin was the greatest, accounting for 70.7% of the total consumption. The daily variation trend of the initial concentration of ambient VOCs, O₃ and temperature were basically consistent, reaching the maximum value of the initial concentration at 15: 00 with the biggst hourly maximum photochemical loss value (22.69X10^-9). The photochemical loss of olefins and aromatics during O₃ pollution days was greater than that during non-pollution days, and which became an important source of ozone generation. According to the results of the VOCs source apportionment of initial concentrations by use of PMF, the industrial pollution source in Xiangtan's urban area was the most remarkable contribution source during summer, while the secondary transformation was the biggst contributor source in accordance with the observed concentrations. [ABSTRACT FROM AUTHOR]