The abundance and inter-relationship of atmospheric peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), O, and NO during the wintertime in Beijing, China.

Although atmospheric peroxyacetyl nitrate (PAN) and O have been extensively measured in Beijing during the summertime, the abundances of PAN, peroxypropionyl nitrate (PPN) and the total odd-reactive nitrogen budget (NO) and their inter-relationship have been studied comparatively less in the winter. Here we measured atmospheric PAN, PPN, O, NO, and NO in Beijing from Nov. 2012 to Jan. 2013. Compared with our previous results in the summertime, much lower levels were observed in the winter, with the mean and maximum values of 311.8 and 1465 pptv for PAN, 52.8 and 850.6 pptv for PPN, and 11.6 and 36.7 ppbv for O. In contrast, high levels were found as 94.2 and 374.9 ppbv for NO, with a major constituent of NO (75.9%). The source to the west and northwest made the significant contribution to the relatively high O concentrations during nighttime. PAN concentrations were highly related with the PAN-rich air mass transported from the southeast during the nighttime, whereas predominated by local photochemical production during the daylight. The distributions of NO and NO were dominated by local emission and photochemical production during daylight but also influenced by air masses transported from south direction during nighttime. Significant positive correlation (R = 0.9, p < 0.0001) between PAN and PPN with a slope (∆PPN/∆PAN) of 0.17 indicated that anthropogenic volatile organic compounds (AVOCs) dominated the photochemical formation of PANs in Beijing, and the independent relationship between the PPN/PAN ratio and PAN (>500 pptv) implied a steady state between PAN and PPN achieving rapidly in the polluted air masses. Negative correlation and slopes between PAN and O likely resulted from their weak photochemical productions in the winter, coupled with the large NO sources which acted as a local sink for O, but much less so for PAN due to its enhanced thermal stability under low temperature.