Wintertime characteristic of peroxyacetyl nitrate in the Chengyu district of southwestern China
Atmospheric concentrations of peroxyacetyl nitrate (PAN) were measured in Ziyang in December 2012 to provide basic knowledge of PAN in the Chengyu district and offer recommendations for air pollution management. The PAN pollution was relatively severe in Ziyang in winter, with the maximum and average PAN concentrations of 1.61 and 0.55 ppbv, respectively, and a typical single-peak diurnal trend in PAN and theoretical PAN lost by thermal decomposition (TPAN) were observed. PAN and O3 concentrations were correlated (R2 = 0.52) and the ratios of daily maximum PAN to O3 ([PAN]/[O3] ratio) ranged from 0.013 to 0.108, with an average of 0.038. Both acetone and methyl ethyl ketone (MEK) were essential for producing the acetylperoxy radicals (PA) and subsequently PAN in Ziyang in winter, and PAN concentrations at the sampling site exhibited more sensitivity to volatile organic compound (VOC) concentrations than nitrogen oxide (NOx) levels. Therefore, management should focus on reducing VOCs emissions, in particular those that produce acetone and MEK through photolysis and oxidizing reactions. In addition, the influence of relative humidity (RH) on the heterogeneous reactions between PAN and PM2.5 in the atmospheric environment may have led to the strong correlation between observed PM2.5 and PAN in Ziyang in winter. Furthermore, a typical air pollution event was observed on 17–18 December 2012, which Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) and PSCF simulations suggest that it was caused by the local formation and the regional transport of polluted air masses from Hanzhong, Nanchong, and Chengdu.
KeywordsPAN Chengyu district PM2.5 and RH Sensitivity Regional transport
We gratefully thank Pro. Limin Zeng and Yusheng Wu for the technical support with the PAN instrument. We also thank the support of National Oceanic and Atmospheric Administration (NOAA) and National Centers for Environmental Prediction (NCEP) who provide HYSPLIT 4 model and meteorological data, respectively. This work was supported by the State Key R& D Program (grants numbers 2016YFC0202200 and 2017YFC0212400).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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