Characterization of peroxyacetyl nitrate (PAN) under different PM_2.5 concentration in wintertime at a North China...

As a secondary pollutant of photochemical pollution, peroxyacetyl nitrate (PAN) has attracted a close attention. A four-month campaign was conducted at a rural site in North China Plain (NCP) including the measurement of PAN, O₃, NO_x, PM_2.5, oxygenated volatile organic compounds (OVOCs), photolysis rate constants of NO₂ and O₃ and meteorological parameters to investigate the wintertime characterization of photochemistry from November 2018 to February 2019. The results showed that the maximum and mean values of PAN were 4.38 and 0.93 ± 0.67 ppbv during the campaign, respectively. The PAN under different PM_2.5 concentrations from below 75 μg/m³ up to 250 μg/m³, showed different diurnal variation and formation rate. In the PM_2.5 concentration range of above 250 μg/m³, PAN had the largest daily mean value of 0.64 ppbv and the fastest production rate of 0.33 ppbv/hr. From the perspective of PAN's production mechanism, the light intensity and precursors concentrations under different PM_2.5 pollution levels indicated that there were sufficient light intensity and high volatile organic compounds (VOCs) and NO_x precursors concentration even under severe pollution level to generate a large amount of PAN. Moreover, the bimodal staggering phenomenon of PAN and PM_2.5 provided a basis that PAN might aggravate haze through secondary organic aerosols (SOA) formation.