Intentionally Produced And Unintentionally Produced Persistent Organic Pollutants At Ningbo Atomospheric Environment Observatory

Persistent organic pollutants(POPs)are a long-term challenge for human beings.There are two major sources for POPs in the environment:(1)historical emissions from pesticides or industrial chemicals which were intentionally produced and used in industry(referred to as IP-POPs);(2)unintentionally produced from combustion and thermal processes(referred to as UP-POPs).IP-POPs show a constantly decreasing trend since the ban on produce and use of commercial products by the Stockholm Convention.The impact of UP-POPs emissions on the environment is becoming more important,and will even gradually replace IP-POPs as the main source of POPs in the environment.Industrial thermal processes,fossil fuels combustion,and biomass burning have been recognized as the major sources of UP-POPs.Polycyclic aromatic hydrocarbons(PAHs)and elemental carbon(EC)are generated by the incomplete combustion process of fossil fuels and biomass.Three anhydrosugars(levoglucosan,galactosan,and mannosan)are pyrolysis products of cellulose.They have been recognized as biomarkers of biomass burning.Therefore,PAHs,EC,three anhydrosugars can be used as molecular indicators of combustion and thermal processes when analyse the sources and environmental impact of UP-POPs.To investigate the pollution levels of UP-POPs in the atmosphere and firure out which sources are controlling PCB burdens in ambient atmosphere(IP-POPs or UP-POPs?),air samples were collected from August 2012 to August 2015 at Ningbo Atmospheric Environmental Observatory(NAEO).Concentrations of typical POPs,such as polycyclic Aromatic Hydrocarbons(PAHs),polychlorinated biphenyls(PCBs),polychlorinated naphthalenes(PCNs),and hexachlorobenzene(HCB),were measured in air samples.In the selected POPs,PCBs,PCNs,and HCB can be emitted form both intentional sources and unintentional sources.As molecular indicators of combustion and thermal processes,the concentrations and seasonal variations of levoglucosan,galactosan,mannosan,OC,and EC were also analyzed.Additionally,the correlations between PAHs vs.levoglucosan,PCBs,PCNs,and HCB and the source apportionments of these compounds were investigated.The contribution of UP-POPs to the POPs in the atmospheric environment were also discussed.Thourgh the study on 15 PAHs,3 anhydrosugars(levoglucosan,galactosan,and mannosan),OC and EC,higher concentrations of these combustion indicators were observed in fall and winter.Indoor biofuel combustion in north China was considered to be the major contributor to the high concentrations of anhydrosugars in fall and winter,because there were few fires detected on a fire count map for this period.A tracer-based approach,using the ratio of PAHs to levoglucosan(PAHs/Lev)in fresh biomass burning aerosols,was proposed and used to estimate the contribution of biomass burning to PAHs.The results showed that biomass burning contributed nearly11%of the total particulate PAHs.The estimation of the contribution from biomass burning using PAHs/Lev agreed well with the results obtained from an independent positive matrix factorization(PMF)analysis.Through the analysis of 209 PCBs,extremely high concentrations of PCB47+48+75,51,11,and 68,which are non-Aroclor PCBs,were detected in the atmosphere,accounting for 48±16%?10±4%?8±6%,and 7±3%of the total concentration of PCBs,respectively.It suggested that UP-PCBs were predominat sources of PCBs in the atmosphere in this study.Seasonal variations with high levels in summer and lowest in winter were observed for PCB47+48+75,51,and 68.These tetrachlorobiphenyl congeners were strongly correlated with temperature(r~2>0.7),suggesting the control of temperature-dependent volatilization process from contaminated surfaces.The weak correlations with PAHs and PCB11 suggested unique unintentional sources that differ from combustion and industrial thermal processes or pigment for PCB47+48+75,51,and 68 in the ambient air.The concentration of 42 typical Aroclor PCBs accounted for 14±8%of the total concentration of PCBs in the atmosphere,with tetrachlorobiphenyl being the main component.PMF-based source analysis showed that the legacy of historical emissions of industrial PCBs(Aroclor1242 and Aroclor1248),coal and wood combustion process emissions and e-waste recycling process emissions were the main sources of42 typical Aroclor PCBs in Ningbo atmosphere,of which legacy of historical emissions of industrial PCBs(IP-PCBs)contributed 52%,coal and wood combustion process emissions(UP-PCBs)contributed 30%,and e-waste recycling process emissions(EW-PCB)contributed 18%.PCNs and HCB showed similar seasonal characteristics to PAHs that with high concentrations be in winter and autumn and low concentration be in summer.The good relationship between PCNs,HCB,and PAHs and the principal component analysis of PCNs suggested that UP-PCNs contributed more than 50%of atmospheric PCNs in this study,and HCB in the atmosphere mainly originated from combustion or industry thermal process.There were no obvious seasonal variations of?-HCH and?-HCH.But?-HCH showed high levels in summer and autumn.The HCHs ratio analysis suggested that the legacy of historical technical HCHs were the major soure of atmospheric HCHs in this study.The seasonal variation of?-HCH may be related to secondary emissions from soil.Atmospheric DDTs exhibited seasonal variations with high concentrations be in summer.The ratio analysis showed that DDTs in the atmosphere mainly attributed to the legacy of historical technical DDTs.But fresh inputs of DDTs still exist during summer.