Characterizations on polycyclic aromatic compounds (PACs) during frequent haze periods have been conducted in an urban site of Beijing, China. Particulate polycyclic aromatic hydrocarbons (PAHs) and oxygenated-PAHs (OPAHs) and other carbonaceous matters were quantified. The average PM2.5 during haze events (256.3 ± 103.7 μg/m3) were one magnitude over than that of clear periods (CRs, 24.7 ± 27.7 μg/m3).The average total quantified PAHs (ΣPAHs) and OPAHs (ΣOPAHs) during haze events were 423.9 ± 178.4 ng/m3 and 581.4 ± 299.8 ng/m3, respectively, which were approximately 10 times higher than those of 40.3 ± 68.2 ng/m3 and 54.4 ± 82.4 ng/m3 in clear days. Four-rings PAHs had the highest compositions. 1,8-Naphthalic anhydride (1,8-NA) is the most abundant OPAHs, accounted for 49.8% of ∑OPAHs, followed by 9,10-anthraquinone (9,10-AQ) (13.8%) and benzo(a)anthracene-7,12-dione (BaAQ) (8.31%). In haze events, the contents of 5- to 7-rings PAHs decreased by 2.32% compared with those of clear days, while lower molecular weight fractions of 3- and 4-rings PAHs increased. The relationships between PAHs, OPAHs and relative humidity (RH) were found to be exponential. High oxygenation rate (R0) ratios of OPAH/PAH represents higher rates in secondary formation or degradation and gas- particle conversion for each PAH or OPAH during the wintertime. Significant positive correlation between BeP and OPAHs (r = 0.97), combined with the results of photochemical aging and negatively correlation with O3, suggest that secondary atmospheric reactions of PAHs played an important role in the burden of OPAHs.
Keywords: Haze; Oxygenated PAHs; Oxygenation rate; PAHs; PM(2.5); Secondary organic formation.
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