Study of Peroxyacetyl Nitrate (PAN) in Suburban and Remote Areas of Western China

摘要

Peroxyacetyl Nitrate (PAN) is an important secondary photochemical air pollutant. It received particular interest as a reservoir for atmospheric odd nitrogen as well as an excellent indicator of photochemical air pollution. In this study, continuous measurements of PAN using an automatic GC-ECD analyzer with an on-line calibration device were made at a suburban site of Lanzhou (LZ) and a remote site of Mt. Waliguan (WLG) in the summer of 2006, with supporting measurements of ozone (O_3), total reactive nitrogen (NOy) and carbon monoxide (CO). The study was aimed to explore the source, transport and chemical processes of PAN in both polluted and remote areas of China. At LZ, the average mixing ratio (plus or minus standard deviation) was 0.76 (±0.89) ppbv for PAN with the maximum of 9.13 ppbv observed, compared to an average value of 0.44 (±0.16) ppbv at WLG. The PAN mixing ratios exhibited strong diurnal variations with a maximum at noon in LZ, while it showed enhanced concentrations in the evening at WLG. The daily O_3 and PAN maximum showed a strong correlation (r~2=0.91) in LZ, and the mean ratios of PAN daily max/O_3 daily max were 0.091. Analysis of back trajectories at WLG shows that air masses from east urban regions contains the highest PAN and suggests that the high-PAN events at WLG were mostly derived from the transport of air masses passing LZ. These analyses indicate that urban areas are important sources of photochemical pollutants such as PAN and can have a large impact on remote areas through regional transport.