| Per-and polyfluoroalkyl substances(PFASs)are widely used in industry and daily life.Due to the toxicity and persistence,perfluorooctane sulfonate(PFOS),perfluorooctanoic acid(PFOA)and their salts were listed in the Stockholm Convention.Hence,the production and use of them are subject to strict restrictions.As a result,new fluorine alternatives gradually occupy more markets.The functional groups and physicochemical properties of alternatives are different from those of perfluoroalkyl acids.Such as Fluorotelomer alcohols(FTOHs)and perfluorooctane sulfonamides(FOSA/Es),they are more likely to evaporate into atmosphere,and these precursors can be photodegraded into perfluoroalkyl acids.However,the pollution characteristics,phase partitioning influencing factors and scavenging effect of wet deposition on PFASs in the atmosphere have not been thoroughly studied.Therefore,passive atmospheric samplers were deployed to collect PFASs during summer and winter from 21 cities of China,Japan and Malaysia.In addition,a new sampling method,cryogenic air sampler(CAS),was used to collect gaseous and particulate samples from June 2018 to May 2019 from Xiamen.Wet deposition samples were also collected from June 2018 to May 2019 from Xiamen.The occurrence,seasonal variations,transport,gas/particle partitioning,scavenging effect of wet deposition on atmospheric PFASs and influencing factors were studied,which provided a scientific basis for the environmental management of atmospheric PFASs and the formulation of pollutants reduction policies.The main results of this study are as follows:1.Concentrations of neutral PFASs(n-PFASs)in Asian cities were 6.5-3200 pg m3,with an average of 340 pg m-3.8:2 FTOH accounted for the largest proportion,with an average of 59%,while the detection frequencies of FOSA/Es were low.Concentrations of ionic PFASs(i-PFASs)were 2.0-110 pg m-3,with an average of 19 pg m-3.Perfluorobutanoic acid(PFBA)accounted for the largest proportion,with an average percentage of 74%,followed by PFOA,with an average value of 19%.Economically developed cities,such as Shanghai,Guangzhou,and Hong Kong,had higher PFASs concentrations,while Urumqi and Lhasa had lower PFASs concentrations.Concentrations of most individual i-PFASs during summer were significantly(p<0.05)higher than that during winter.Significant positive correlations between concentrations of 8:2 FTOH,10:2 FTOH and PFOA,perfluorodecanoic acid(PFDA)were found,indicating that FTOHs as precursors were photodegraded into even-numbered carbon chains perfluorocarboxylic acids(PFCAs)in the atmosphere.2.Concentrations of i-PFASs in the atmosphere from Xiamen in gas phase ranged from 0.23 to 12 pg m-3,with an average of 4.3 pg m-3,of which PFBA accounted for the highest proportion,with a value of 56%.Concentrations of i-PFASs in particulate phase were 4.1-67 pg m-3,with an average concentration of 27 pg m-3,of which PFOS and PFOA had high proportions,45%and 18%,respectively.The detection frequencies of 6:2 chlorinated polyfluorinated ether sulfonate(6:2 Cl-PFESA)in particles were relatively high,and the average concentration of it was 2.1 pg m-3,while 4:2 fluorotelomer sulfonate(4:2 FTSA)and 8:2 fluorotelomer sulfonate(8:2 FTSA)were not detected in the atmosphere.From September 2018 to January 2019(dry season),concentrations of particulate PFASs were relatively high,while there was no obvious seasonal variation of them in gas phase.PFCAs were mainly found on fine particles(PM1),while PFOS and 6:2 Cl-PFESA containing sulfonic acid group were mainly found on coarse particles(PM1-2.5 and PM2.5-10).The reason for the difference in particle size distribution of these two types of compounds may be that PFASs containing sulfonic acid group are more likely to chemically adsorb with clay minerals on coarse particles.3.Organic carbon(OC)and element carbon(EC)on particles were mainly found on PM1.They had significant positive correlations with medium and long carbon chain PFCAs,which were consistent with the mechanism of KOA absorption model.The partition coefficients of PFCAs increased linearly with the increase of carbon chain length.PFCAs also had good correlations with KOA and PL,indicating that these two parameters controlled their distribution between gaseous phase and particulate phase.4.Concentrations of i-PFASs in the rainwater from Xiamen were between 0.20-180 ng L-1,with an average value of 11 ng L-1.Among them,PFBA and PFOA account for large proportions,reaching 35%and 19%.Concentrations of PFASs were higher during wet season(March to September 2018),while PFASs were lower from October 2018 to February 2019(dry season).The backward trajectory model of air mass indicated that high concentrations PFASs in rainwater samples came from a northwest fluorination plant.The annual flux of PFASs wet deposition was 5200 mg km-2,and fluxes were higher during wet season than that during dry season.PFBA had the highest annual flux,with a value of 1800 mg km-2,followed by PFOA,with a value of 1200 mg km-2.5.During precipitation,concentrations of PFASs in the gas and particle were reduced compared to that on sunny days.In the two long-term rainfall events,concentrations of PFASs in the gas and particle were reduced by 78%and 78%for the first rainfall event,73%and 96%for the second rainfall event.The dissolution of rainwater was the main way for short-chain PFASs to be removed in the atmosphere,and the wash-out of rainwater was the main way for long-chain PFASs to be removed from the atmosphere.Scavenging efficiency of particulate PFASs by wet deposition depended on their particle size distribution characteristics.The removal of PM1 by wet deposition promoted the reduction of PFCAs,and the removal of PM1-2.5 and PM2.5-10 by wet deposition promoted the reduction of per-and polyfluorinated sulfonic acids.Rainfall duration and rainfall intensity affected the scavenging efficiency of PFASs in the atmosphere by wet deposition. |
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