Comparison of atmospheric polycyclic aromatic hydrocarbons (PAHs) over six years at a CAWNET background site in central China: Changes of seasonal variations and potential sources.

Total suspended particles (TSP) and gaseous samples were collected by using a high-volume sampler from March 2012 to March 2013 and January 2018 to January 2019 at a background site (Jinsha, JSH) in central China to study the chemical characteristics, seasonal variations, and potential sources of polycyclic aromatic hydrocarbons (PAHs). The average concentrations of ∑15PAHs were 24.55 ± 9.19 ng m-3 in 2012/2013 and 20.98 ± 9.77 ng m-3 in 2018/2019. Low-ring PAHs were more concentrated in gas phase while high-ring PAHs were prone into particle phase. The concentrations of PAHs in the two sampling years were high in winter but low in summer and autumn. The relationships between the gas concentrations of PAHs and temperature indicated that most PAHs were influenced by long-range atmospheric transport (LRAT) in 2012/2013 and in 2018/2019, excluding anthracene (Ant) and pyrene (Pyr) were partially affected by air-surface re-volatilization in 2012/2013. The source of atmospheric PAHs at JSH was similar in 2012/2013 and 2018/2019,which was mainly due to the LRAT of PAHs emitted from biomass/fossil fuel combustion in the northern area of JSH. From 2012/2013 to 2018/2019, there was no significant difference between the concentrations of PAHs in spring and winter, whereas the concentrations of PAHs decreased from 2012/2013 to 2018/2019 in summer. In all, the control of PAHs at the source region was partially effective from 2012/2013 to 2018/2019.

Atmospheric deposition and air-soil exchange of polybrominated diphenyl ethers (PBDEs) in a background site in Central China.

Jinsha (JSH) is one of the regional background sites in Central China. In this study, eight polybrominated diphenyl ethers (PBDEs) were measured in atmospheric deposition samples (dry particle, wet particle, and wet dissolved), air (gaseous and particle) samples, and soil samples that were collected from March 2012 to March 2013. Of all eight PBDEs, BDE-209 was the most abundant congener in both deposition samples and air/soil samples. Average dry particle, wet particle, and wet dissolved deposition fluxes of Σ8PBDEs were 270 ± 310 pg m-2 day-1, 130 ± 210 pg m-2 day-1, and 250 ± 330 pg m-2 day-1, respectively, while those of BDE-209 were 210 ± 290 pg m-2 day-1, 80 ± 120 pg m-2 day-1, and 160 ± 290 pg m-2 day-1, respectively. Dry deposition velocities of individual PBDE ranged from 0.11 ± 0.15 cm s-1 (BDE-183) to 0.24 ± 0.38 cm s-1 (BDE-209), and total washout ratios ranged from 5.0 × 103 (BDE-28) to 4.2 × 104 (BDE-209). The calculated net air-soil gas exchange flux of Σ8PBDEs was - 16 ± 13 pg m-2 day-1, suggesting the deposition status of PBDEs. The gas exchange flux at the air-soil interface was significantly lower than the deposition flux, which only accounted for 2.5% of the total deposition flux, implying that atmospheric deposition was an important input pathway for PBDEs to soils. Overall, the pollution level of the soil was relatively low, and the soil serves as a sink for PBDEs from adjacent regions.

Occurrence and air-soil exchange of organochlorine pesticides and polychlorinated biphenyls at a CAWNET background site in central China: Implications for influencing factors and fate.

Ambient air and soil samples were collected between March 2012 and March 2013 at Jinsha, a regional background site in central China, to measure the concentrations of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). The average concentrations of total OCPs and total PCBs were 191 ± 107 and 39.4 ± 27.1 pg/m3 in air (gaseous and particulate phase) and 0.585 ± 0.437 and 0.083 ± 0.039 ng/g in soil, respectively. The higher concentrations of p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT) and p,p'-DDT/p,p'-DDE ratios in the soil indicated recent p,p'-DDT input to the soil. A strong positive temperature dependence and average fugacity fraction value > 0.5 were observed for p,p'-DDT, suggesting that volatilization of residual DDT in the soil was the main influencing factor on atmospheric p,p'-DDT. Highly average fugacity fractions (>0.7) of trans-chlordane (TC) and cis-chlordane (CC) and high TC/CC ratios both in the soil and atmosphere suggested fresh inputs. Higher gaseous concentrations of hexachlorobenzene (HCB) were observed in winter and negative temperature dependence was directly attributed to the surrounding ongoing source (e.g. fuel consuming activities), especially in winter. Overall, most targeted OCPs and PCBs were influenced by long-range transport, and fugacity fraction values indicated highly volatile compounds (e.g. α-hexachlorocyclohexane (α-HCH) and lower chlorinated PCBs) were volatilized and low volatility compounds (e.g. p,p'-DDE and higher chlorinated PCBs) were deposited at the air-soil interface. Knowing the source and sink of OCPs and PCBs can help to control their pollution in this area and provide a reference for other studies.