| A pulsed large volume(6×20μL) injection gas chromatography coupled with electron-capture negative ionization quadrupole mass spectrometry for simultaneously determining the 30 halogenated POPs was established.The method avoided common chromatographic interferences by selected monitoring the characteristic ions of large mass-to-charge ratio but not the base peak ions,while relatively low sensitivity was compensated by increasing the sample injection volume up to 120μL.The method detection limits reached pg-fg/mL level.Besides,using perdeuterated and/or 13C-labeled compounds as internal standards ensured the reliability of quantification.The mechanism of persistent organic pollutants(POPs) accumulation from air into tree bark was systematically studied.The POPs of IogKOA≤8.5 predominately existing as gas-phase are accumulated through interactions with lipid substances in bark,which is primarily controlled by their KOA and influenced by bark lipid content and ambient temperature;while the POPs of logKOA＞8.5 predominately existing as particle-phase are accumulated through stochastic entrapment by the lenticels on the surface of the bark,which is mainly controlled by their Vp and influenced by the surface area of the bark and precipitation.A new concentration ratio of target polycyclic aromatic hydrocarbons(PAHs) to perylene(PER),RPAH/PER,was proposed as an alternative methodology for more objective evaluation of spatial distribution of atmospheric PAHs pollution levels on a large scale when using tree bark as passive sampling medium,in which PER was proposed to be a natural internal compound of atmospheric PAHs accumulation processes from air into tree bark.RPAH/PER minimizes the evaluation uncertainties arising from the variations in both bark characteristics and meteorological conditions.A mathematic model describing the bark/air partitioning of POPs was established taking into consideration the accumulation processes of POPs from air into bark and compound-,species- and site-specific air-to-bark accumulation factors.It allows the assessment of the concentrations of atmospheric POPs based on those recorded in tree bark.The POPs analyzed in this study include 17 brominated flame retardants(BFRs, including 15 polybrominated diphenyl ethers,1 polybrominated biphenyl and tetrabromobisphenol A TBBPA),10 polychlorinated biphenyls(PCBs),5 organic chlorinated pesticides(OCPs,including 4 hexachlorocyclohexane isomers and hexachlorobenzene) and 18 PAHs.By applying the POPs' bark/air partitioning model,we investigated the spatial distribution of atmospheric POPs across Mainland China using 163 bark samples collected from 68 sites.The atmospheric POPs were estimated to he 0.9-624,4.5-130, 11.3-553 pg/m3 air and 4.1-399 ng/m3 air for the total concentrations of the BFRs (∑17BFRs),the PCBs(∑10PCBs),the OCPs(∑5OCPs),and the PAHs(∑18PAHs), respectively.The logarithm transformed atmospheric POPs concentrations have linear relationship positively with gross domestic production of the cities,with the correlation coefficients of 0.812,0.616,0.524 and 0.618(p＜0.01,n = 68) for the∑17BFRs,∑10PCBs,∑5OCPs and∑18PAHs respectively.Moreover,the hexachlorocyciohexane (HCH) isomer concentration ratios ofα-HCH toγ-HCH(α/γ-HCH ratios) were fractionated with latitude(from 49.22°to 18.27°N) indicating the spatial distribution of HCHs in China is now governed by the nationwide redistillation of the HCHs residues used in the past but not by their recent use patterns.We also revealed the centurial historical evolution of atmospheric POPs pollution in Southeast China using bark pocket and peat bog samples from Jiangxi and Fujian provinces,Southeastern China. The∑18PAHs,∑5OCPs and∑10PCBs,as well as∑17BFRs remained at their background levels of 0.7±0.1 ng/m3,4.0±1.1 and 2.2±0.4 pg/m3,0.2±0.1 pg/m3 air,respectively, from the 1870th to the 1880th,mid-1940th and 1940th;and then they steeply increased reaching 8,18,12 and 25 times of their respective background levels at the beginning of the 21th century;meanwhile,the∑5OCPs and∑10PCBs respectively peaked at the 1970th and 1980th with the concentrations of 20 and 18 times of their background levels.
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