Measurement of atmospheric peroxyacetyl nitrate (PAN) and the implications to photochemical pollution

vii, 134 leaves : ill. (some col.), maps (some col.) ; 30 cm.PolyU Library Call No.: [THS] LG51 .H577M CSE 2009 ZhangKnowledge of the atmospheric abundance of peroxyacetyl nitrate (PAN) is important for assessing the severity of photochemical pollution and for understanding the chemical transformation of reactive odd nitrogen and its impact on the tropospheric ozone (O₃) budget. Although available monitoring data on O₃ have shown serious photochemical pollution in China, there have been few published continuous measurements of PAN in the country. In this project, continuous measurements of PAN were made using an automatic GC-ECD analyzer with an on-line calibration device at an urban site in Hong Kong (HK, southern China) and a rural site at Mt. Tai (TS, eastern China), in 2007. O₃ and other trace gases measured as part of TS study were used to support the interpretation of PAN data. Data obtained from previous measurements at a suburban site in Lanzhou (LZ, western China), a remote site at Mt. Waliguan (WLG, western China), and the HK site in 2006 were also analyzed to obtain a more comprehensive picture of PAN in China. The data were examined in terms of time series, statistical analysis, diurnal patterns, correlations between PAN and other species, nitrogen budgets, and regional transport.Strong photochemical production was found at urban sites, with average PAN mixing ratios of 0.76, 0.74, and 0.94 ppbv in LZ, HK 2006, and HK 2007 studies. Of the two mountain top sites, Mt. Tai, which is situated in the polluted North China Plains, had average PAN concentrations of 1.17 and 0.77 ppbv in spring and summer, whereas the remote WLG site had an average value of 0.44 ppbv, which represents the background level of photochemical pollution in East Asia. The PAN mixing ratios at the two urban sites (LZ and HK) exhibited strong diurnal variations, with peaks at noon and in the early afternoon. At the polluted mountain top site (TS), PAN levels showed peaks in the afternoon and troughs in the early morning, whereas increased concentrations were observed in the evening at WLG. The correlations between PAN and O₃, were analyzed to shed light on the photochemical processes occurring in different regions. The regression slopes of the daily maximum PAN versus O₃, ranged from 0.091 to 0.020 ppbv ppbv⁻¹ in LZ, HK, and at TS. The differences in slopes are in part due to different compositions of volatile organic compounds in these areas. Nitrogen budgets were computed for Mt. Tai, for which data on individual reactive nitrogen (NOy) compounds were available, and PAN was found to contribute a small fraction to NOy compared with nitric acid and particulate nitrate. Data from the two mountain top sites were also examined to determine the regional transport of air pollution. At polluted Mt. Tai in eastern China, transport of pollutants from different regions to the summit was found using back trajectory analysis, with a notable impact from Korea and Japan being identified. At remote Mt. Waliguan in western China, backward particle release simulation showed that high-PAN events were mostly associated with the transport of air masses that had passed over Lanzhou.Department of Civil and Environmental EngineeringM.Phil., Dept. of Civil and Structural Engineering, The Hong Kong Polytechnic University, 200