Abstract
Peroxyacetyl nitrate (PAN) acting as a typical indicator of photochemical pollution can redistribute NOx and modulate O3 production. Coupled with the observation-based model (OBM) and a generalized additive model (GAM), the intensive observation campaigns were conducted to reveal the pollution characteristics of PAN and its impact on O3, the contributions of influencing factors to PAN formation were also quantified in this paper. The F-values of GAM results reflecting the importance of the influencing factors showed that ultraviolet radiation (UV, F-value = 60.64), Ox (Ox = NO2+O3, 57.65), and air temperature (T, 17.55) were the main contributors in the PAN pollution in spring, while the significant effects of Ox (58.45), total VOCs (TVOCs, 21.63) and T (20.46) were found in autumn. The PAN formation rate in autumn was 1.58 times higher than that in spring, relating to the intense photochemical reaction and meteorological conditions. Without considering the transformation of peroxyacetyl radical (PA) and PAN, acetaldehyde contributed to the dominant production of PA (46 ± 4 %), followed by methylglyoxal (28 ± 3 %) and radical cycling (19 ± 3 %). The PAN formation was highly VOC-sensitive, and sufficient NOx (compared with VOCs abundance) would not be the limited factor for atmospheric photochemistry. PAN could promote or inhibit O3 formation under high or low ROx levels, respectively. The PAN promoting O3 formation mainly occurred during the periods of 11:00–16:00 (local time) when the favorable meteorological conditions (high UV and T) stimulated the photochemical reactions to offer ROx radicals, which accounted for 17 % of the whole monitoring periods in spring and 31 % in autumn. In this study, the formation mechanism of PAN and its effect on ozone were identified, which might be helpful to improve the scientific understanding of photochemical pollution in coastal areas.
Highlights
Peroxyacetyl nitrate (CH3C(O)O2NO2, PAN) is a key product of photochemical smog (Penkett andBrice, 1986; Li et al, 2019)
Field observation was continuously conducted in spring and autumn in a coastal city of Southeast
We clarified the seasonal variations of PAN pollution, formation mechanisms, influencing factors and impacts on O3 production
Summary
Peroxyacetyl nitrate (CH3C(O)O2NO2, PAN) is a key product of photochemical smog (Penkett andBrice, 1986; Li et al, 2019). Peroxyacetyl nitrate (CH3C(O)O2NO2, PAN) is a key product of photochemical smog PAN is generated through photochemical reactions of precursors emitted by human activities only, and the atmospheric PAN is a reliable and scientific indicator of photochemical pollution (Lonneman et al, 1976; Han et al, 2017). PAN acts as a temporary reservoir for NOx and radicals, and can transport to remote regions to redistribute NOx and intervene in O3 production at regional or even global scale (Kleindienst, 1994; Atkinson et al, 2006; Fischer et al, 2010). The reaction of peroxyacetyl radical (CH3C(O)O2, PA) with NO2 is solely formation pathway of PAN (Han et al, 2017; Xue et al, 2014). PAN affects radical chemistry and modulates O3 production mainly by affecting PA radical, which is one of the most abundant organic peroxy radicals in the troposphere (Tyndall et al, 2001). A small group of oxygenated volatile organic compounds (OVOCs)
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