The seasonal variations of Peroxyacetyl nitrate (PAN) in Seoul, South Korea

Peroxyacetyl nitrate (PAN), and other photochemically reactive species including O₃, CO, NO, H₂O₂, HCHO, and non-methane hydrocarbons (NMHCs) have been measured at two downtown sites (Gui and Guro) in Seoul over a year period since June, 2010. Hourly PANs were determined by gas chromatographs with ECD detector and a self contained calibration unit. As Gui site is located at downwind side from Guro, Average PAN of 0.49 ppbv with maximum 4.93 ppbv at Gui was slightly higher than those at Guro ( 0.44 ppbv average, 4.30 ppbv maximum). PAN hourly maxima were usually observed 2 - 3 hours earlier than much broader O₃ maxima in the mid afternoon. Interestingly, PAN seasonal maximum was also found 2 month early (April) than Ozone with June maximum. This PAN seasonal maximum shift indicated that thermal destruction of PAN during the summer overwhelmed its photochemical production in Seoul. The summertime PAN average (0.59 ppbv) measured this campaign were about 25% lower than those of 2004 and 2005 campaign measured at the other site in Seoul. Although it is not clear that this concentration difference is significantly meaningful, the detailed investigation on changes of PAN and its precursors since last six years are required for further analysis.