Abstract
Abstract. Ambient particulate matter (PM) can contain a mix of different toxic species derived from a wide variety of sources. This study quantifies the diurnal variation and nocturnal abundance of 16 polycyclic aromatic hydrocarbons (PAHs), 10 oxygenated PAHs (OPAHs) and 9 nitrated PAHs (NPAHs) in ambient PM in central Beijing during winter. Target compounds were identified and quantified using gas chromatography–time-of-flight mass spectrometry (GC-Q-ToF-MS). The total concentration of PAHs varied between 18 and 297 ng m−3 over 3 h daytime filter samples and from 23 to 165 ng m−3 in 15 h night-time samples. The total concentrations of PAHs over 24 h varied between 37 and 180 ng m−3 (mean: 97±43 ng m−3). The total daytime concentrations during high particulate loading conditions for PAHs, OPAHs and NPAHs were 224, 54 and 2.3 ng m−3, respectively. The most abundant PAHs were fluoranthene (33 ng m−3), chrysene (27 ng m−3), pyrene (27 ng m−3), benzo[a]pyrene (27 ng m−3), benzo[b]fluoranthene (25 ng m−3), benzo[a]anthracene (20 ng m−3) and phenanthrene (18 ng m−3). The most abundant OPAHs were 9,10-anthraquinone (18 ng m−3), 1,8-naphthalic anhydride (14 ng m−3) and 9-fluorenone (12 ng m−3), and the three most abundant NPAHs were 9-nitroanthracene (0.84 ng m−3), 3-nitrofluoranthene (0.78 ng m−3) and 3-nitrodibenzofuran (0.45 ng m−3). ∑PAHs and ∑OPAHs showed a strong positive correlation with the gas-phase abundance of NO, CO, SO2 and HONO, indicating that PAHs and OPAHs can be associated with both local and regional emissions. Diagnostic ratios suggested emissions from traffic road and coal combustion were the predominant sources of PAHs in Beijing and also revealed the main source of NPAHs to be secondary photochemical formation rather than primary emissions. PM2.5 and NPAHs showed a strong correlation with gas-phase HONO. 9-Nitroanthracene appeared to undergo a photodegradation during the daytime and showed a strong positive correlation with ambient HONO (R=0.90, P < 0.001). The lifetime excess lung cancer risk for those species that have available toxicological data (16 PAHs, 1 OPAH and 6 NPAHs) was calculated to be in the range 10−5 to 10−3 (risk per million people ranges from 26 to 2053 cases per year).
Highlights
Outdoor air pollution contains a complex set of toxicological hazards and has become the largest detrimental environmental effect on human health (WHO, 2016)
1/16 of each filter was cut using a hole puncher (Ø = 27 mm), and for each batch of six samples, one sample was spiked with a mixture of two deuterated Polycyclic aromatic hydrocarbons (PAHs), two deuterated-oxygenated PAHs (OPAHs) (9fluorenone-d8; 9,10-anthraquinone-d8) and two deuterated NPAHs (1-nitronaphthalene-d7; 3-nitrofluoranthene-d9), as surrogate standards for PAHs, OPAHs and NPAHs, respectively, with concentration on filters corresponding to 400 ng (40 μL, 10 ng μL−1 in acetonitrile)
Analysis was performed in 29.2 min, and the gas chromatograph (GC) settings were as follows: 1 μL of each sample was injected in pulsed splitless mode at 310 ◦C; helium flow was set to 1.2 mL min−1; the initial oven temperature of 70 ◦C was held for 4 min, followed by a heating rate of 60 ◦C min−1 until 190 ◦C, which was raised to 270 ◦C at a rate of 25 ◦C min−1, ending with 5 ◦C min−1 until 320 ◦C, held for 10 min
Summary
Outdoor air pollution contains a complex set of toxicological hazards and has become the largest detrimental environmental effect on human health (WHO, 2016). OPAHs and NPAHs are often more toxic than the parent PAHs, showing a direct-acting mutagenicity on human cells (Durant et al, 1996; Hannigan et al, 1998; Purohit and Basu, 2000; Wang et al, 2011a; BenbrahimTallaa et al, 2012) Beside their formation in the gas phase, OPAHs and NPAHs can be produced by heterogeneous reactions (Ringuet et al, 2012a, Jariyasopit et al, 2014; Zimmermann et al, 2013; Wenyuan and Zhu, 2014; Keyte et al, 2013). This paper explores the feasibility of higher frequency sampling in Beijing, to support the identification of emissions sources from diagnostic ratios and correlations with atmospheric gas pollutants These measurements raise the potential importance of the chemical relationship between NPAHs and HONO, which may impact the HONO budget in the atmosphere and, if included, improve related models. This study comes 3 years after declaring the anti-pollution action plan and strategy taken by the municipal government of Beijing and published in September 2013 (Ministry of Ecology and Environment The People’s Republic of China, 2013), trying to increase the number of days with good air quality index by prohibiting coal combustion, promoting clean energy vehicles and public transport, helping industrial transformation and upgrading to new technologies
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