AirâSeawater Gas Exchange and Dry Deposition of Chlorinated

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Environmental Processes

Air-seawater gas exchange and dry deposition of chlorinated paraffins in a typical inner sea (Liaodong bay), North China Xindong Ma, Yawei Wang, Wei Gao, Yingjun Wang, Zhen Wang, Ziwei Yao, and Guibin Jiang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b01803 • Publication Date (Web): 25 Jun 2018 Downloaded from http://pubs.acs.org on June 28, 2018

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Environmental Science & Technology

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Air-seawater gas exchange and dry deposition of chlorinated paraffins in a

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typical inner sea (Liaodong bay), North China

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Xindong Ma,† ‡ Yawei Wang,† ξ §* Wei Gao,† Yingjun Wang,† Zhen Wang,‡ Ziwei

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Yao,‡ Guibin Jiang†

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†

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Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing

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100085, China

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‡

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Coastal Areas, National Marine Environmental Monitoring Center, Dalian 116023,

State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research

State Oceanic Administration Key Laboratory for Ecological Environment in

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China

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§

12 13 14 15 16 17 18 19 20 21 22 23 24 25

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Institute of Environment and Health, Jianghan University, Wuhan 430056, China University of Chinese Academy of Sciences, Beijing 100049, China

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*Corresponding author

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Dr. Yawei Wang

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State Key Laboratory of Environmental Chemistry and Ecotoxicology

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Research Center for Eco-Environmental Sciences

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Chinese Academy of Sciences

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P.O. Box 2871, Beijing 100085, China

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Tel: 8610-6284-9124

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Fax: 8610-6284-9339

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E–mail: [email protected]

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ACS Paragon Plus Environment


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TOC

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ABSTRACT

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As a group of new persistent organic pollutants, short-chain chlorinated paraffins

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(SCCPs) and medium-chain CP (MCCPs) have attracted extensive worldwide interest

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in recent years. However, the data regarding to the environmental behavior, especially

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in atmospheric transfer and air-seawater exchange are still sparse. In this study,

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seasonal marine boundary layer air and seawater samples were collected from

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Chinese Bohai sea and fugacity model was built to evaluate the air–seawater diffusion

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and deposition flux of CPs. Generally, the total CPs levels in atmosphere and

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seawater samples in summer were higher than those in Spring, and CPs existed mostly

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in gaseous phase in air and dissolved phase in seawater. For SCCPs, C10 and C11

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components were the most abundant homologue groups. For MCCPs, the C14

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homologue dominated in particle−phase of atmosphere and particulate-phase of

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seawater. The logarithmic fugacity ratios (logfa/fw) of higher chlorinated congeners

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(Cl8 to Cl10: 0.71 to 1.32 in May and 1.38 to 2.29 in August) indicated that net

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deposition was the predominant process, whereas lower chlorinated congeners,

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especially Cl5 homologue groups in August, showed a trend of net volitization

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(logfa/fw < -0.5). The results of diffusion and dry deposition fluxes indicated that

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air-seawater gas exchange of CPs was significantly higher than dry deposition in the

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sampling areas.

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Keyword: Chlorinated paraffins; Fugacity Ratio; diffusion; dry deposition; Liaodong

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Bay

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INTRODUCTION

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As the most complex halogenated contaminants, chlorinated paraffins (CPs) can be

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subdivided into short-chain (C10−13, SCCPs), medium-chain (C14−17, MCCPs), and

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long-chain chlorinated paraffins (C18−30, LCCPs) according to the carbon atom

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number of chlorinated derivatives.1 Compared to MCCPs and LCCPs, SCCPs (with

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chlorine contents of 30%−70% by mass) have attracted more scientific and regulatory

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scrutiny as a new persistent organic pollutants (POPs), and the draft profile including

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the major POPs characteristics, i.e. environmental persistence,2 toxicological

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properties,3 bioaccumulation,4,5 and long−range atmospheric transport (LRAT)6-8 has

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been reviewed since 2006 by POPs review committee (POPRC) of Stockholm

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Convention (SC). In May of 2017, the eighth Conference of Parties (COP8) of SC

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decided to list SCCPs in Annex A as a group of new POPs.9 This ultimate decision

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further hints an extensive attraction for SCCPs. However, to our knowledge, the data

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regarding to the environmental behavior, especially in terms of the atmospheric

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transfer and exchange in the marine environment are still sparse, limiting the

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comprehensive understanding of CPs environmental behavior and fate.10

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Some studies indicated that air–water exchange is one of the most important

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processes determining the environmental behavior and fate of many typical and

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emerging chemicals.13-17 Hence, to study the interfacial interaction between air and

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seawater is a crucial way to understand the oceanic behavior and the possible source

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analysis of POPs in marine environment. A few field studies indicated that

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atmospheric transport is the main transporting mechanism for SCCPs to remote areas,

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including high-altitude and polar regions.7,11,12 Our previous work also has proved that

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atmospheric deposition affected the occurrence of SCCPs in sediment around the

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offshore of the Chinese Bohai and Yellow seas.17 However, researches regarding to

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the air–seawater exchange and deposition flux of CPs are still limited.15,18

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Fugacity is defined as the escaping tendency of a chemical from a compartment,

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which is always used to describe the transport mechanism and estimate the air–water

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exchange flux of POPs at the environmental interfaces.16,18,19 Intuitively, the fugacity

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quotient between two medias can determine transport trends and assess equilibrium -3-



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status of organic pollutants. Zhong et al.16 revealed that air–sea gas exchange of

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chlorpyrifos varied from net volatilization in East Asia to equilibrium or net

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deposition in the North Pacific and the Arctic through the fugacity ratio. For SCCPs,

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the wide range of logarithmic sub-cooled liquid vapor pressure (logp°L, −2.29 to −6.58)

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and octanol/air partition coefficient (logKOA, 6.92 to 10.18) are close to other typical

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POPs (e.g. PCBs, OCPs, PCDD/Fs, PBDEs).20,21 However, the typical linear

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paraffined and halogenated structure characteristics of CPs might hint some different

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air–water exchange process.1,22

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To improve the knowledge gap of CPs including SCCPs and MCCPs air-water

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exchange and deposition flux, in this study, marine boundary layer air samples and

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seawater samples were collected during the cruises in Chinese Bohai Sea in spring

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and summer 2016, respectively. Fugacity model was applied to estimate the direction

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(or equilibrium status) of the gas exchange and calculate the net air–seawater

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diffusion and deposition flux of CPs. The objectives of this work were: (1) to examine

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the concentration, spatial distribution, formula group profiles and characteristics of

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CPs in marine air samples and seawater samples (including dissolved and particulate

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phase); (2) to estimate the net air–seawater exchange flux and dry deposition of CPs

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in a typical inner sea in China. The results are meaningful to comprehensively

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understand the source analysis and atmospheric transport and air–water exchange

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between the atmospheric and marine environment.

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EXPERIMENTAL SECTION

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2.1 Sampling.

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Air and seawater sampling were conducted in May and August in 2016,

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respectively, onboard the scientific research vessel (YiXing in Chinese). The sampling

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campaign were carried out in middle of spring and summer, with the average

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temperature of 15.1℃ and 27.7℃. Detailed cruise route and sampling locations are

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listed in Supporting Information (SI). There are four matrixes including gaseous and

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particle phase of atmosphere, dissolved and particulate phase of seawater.

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Correspondingly, the collecting materials were polyurethane foam plugs (PUF, 6.5 cm -4-


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in diameter and 7.5 cm in thickness), quartz fiber filter (QFF, 20 cm × 25 cm, Pall

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Gelman, USA), C18 membrane (47 mm disk, 3M Empore, USA) and QFFs (150 mm

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diameter, Pall Gelman, USA). Atmospheric samples were conducted constantly by the

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high-volume sampler (HiVol, Type 2031, Qingdao, China) with a flow rate of 0.8 m3

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min-1 and the average volume was about 800 m3 (24h interval). Particulate and

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dissolved seawater samples were filtered onboard with the volume of 50 L and 20 L

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sequently. Totally, 20 gaseous samples (accompanied with 20 particle-phases, 10 in

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May and 10 in August) and 34 dissolved samples (accompanied with 34 particulate

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seawater samples, 16 in May and 18 in August) were collected. Meanwhile, triplicate

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field blanks were prepared for each matrix during the sampling. To avoid the

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interference from the ship itself, air sampler was placed on the upper-most deck of the

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ship, approximately 10 m above sea level, and the sampler was guaranteed to run

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during the voyage to ensure the air always come from the bow of the ship during the

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process of collection.

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2.2. Sample pretreatment and instrument analysis.

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Before the sampling, the PUF was cleaned using methanol, acetone and

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dichloromethane (DCM) sequentially by ultrasonic extraction. The QFF (for air and

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seawater) were both heated at 450 °C for 6 h to remove the organic interferences. For

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the air samples, PUF and QFF were extracted and analyzed separately to obtain

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information about gas and particle phases, and for seawater samples, C18 membrane

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and QFF (150 mm diameter) provided the information about dissolved and particulate

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phases.

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Prior to extraction, a surrogate standard of 10 µL 13C6-α-HCH (100 ng mL-1) was

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added as a recovery standard. The four samples were both extracted by the ultrasonic

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bath for 30 min with 400 mL (PUF) and 50 mL (C18 and QFF) hexane/DCM (1:1, v:v),

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with three times for each. The combined raw extracts were concentrated to about 5

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mL, solvent-exchanged into hexane, and added about 5 g activated copper to remove

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elemental sulfur, sequentially. Then the concentrates were transferred to a multilayer

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column (10 mm i.d.) for further clean-up. Detailed information of regents, standards,

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materials, and clean-up procedure are listed in SI. -5-



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The CPs instrumental analysis was performed on quadrupole time-of-flight

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high-resolution mass spectrometry (Agilent Technologies 7200, Santa Clara, USA)

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operated in negative chemical ionization mode(GC-QTOF/NCI-HRMS). A DB-5MS

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Ultra Inert capillary column (30 m × 0.25 mm i.d. × 0.25 µm film thickness, J&W

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Scientific, USA) was used with the temperature program: 100ºC (held for 1 min), up

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to 160 at 5℃/min (2 min), then up to 310 at 30℃/min (12 min). Helium (99.999%

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purity) with a constant flow of 1.0 mL min−1 and methane (99.999%) with a constant

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flow of 2.0 mL min−1 were used as the carrier and reagent gases, respectively. An

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aliquot of 2 µL of the final extract was injected in splitless mode with an injector

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temperature of 280℃. The quick quantification of 24 SCCPs (C10-13Cl5-10) and 24

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MCCPs (C14-17Cl5-10) formula congener groups was conducted by one injection. And

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the identification of different CP congener groups was conducted by screening the

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accurate masses (high resolution > 10 000) and comparing the retention time and the

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signal shape with matching standards. Detailed quantitative and qualitative m/z values

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and retention time were summarized in the SI as described in our previous work.23

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2.3. Quality control.

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Strict quality steps were implemented to ensure the accuracy and reliability of the

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data. Field blanks and laboratory procedural blanks were extracted and analyzed in

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the same way as the samples. The results showed no significant difference between

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these two kinds of blank and the average CPs amount was significantly lower than

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that in air and seawater samples. The result of linear experiment, as reported in our

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previous work,6 with different sampling volume (48 h, 96 h, and 144 h) indicated that

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there was no breakthrough for all field samples. The repeated filtration of filtered

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water also indicated that there was no breakthrough for all dissolved samples. The

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method detection limit (MDL) was defined as three times the standard deviation of

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field blanks and procedural blanks (each type of sample: n=8). The MDLs for ∑CPs,

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converted by an average volume of 800 m3 and 50 L, were estimated to 0.2 ng m−3

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(gaseous), 0.1 ng m−3 (particle), 4.0 ng L−1 (dissolved), and 2.0 ng L−1 (particulate),

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respectively. The surrogate recoveries of 13C6-α-HCH in gaseous, particle, dissolved,

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and particulate phase were in range of 74.8% to 120.3% (mean: 92.3%), 80.5% to -6-


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117.8% (105.3%), 60.4% to 91.2% (75.5%), and 72.4% to 97.7% (85.5%),

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respectively. The ﬁnal concentrations of CPs presented in this study were recovery but

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not blank corrected.

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2.4. Other parameters and statistical analysis.

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The concentration of suspended particular matters (SPM) was determined by the

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method of weight subtraction. Particular organic carbon (POC) was measured by the

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high temperature combustion method using a total organic carbon analyzer (Vario

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TOC cube, Elementar Co. Ltd., Germany). DOC was determined with a Shimadzu

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TOC-VCPH analyzer. For the linear and nonlinear fittings, the P value below 0.05

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was considered statistically significant. All analyses and drawings in present work

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were conducted by the software Origin 8.5 (OriginLab Inc., USA) and SPSS 20.0

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(SPSS Inc., USA) and ArcGIS 10.3 (Esri Inc., USA).

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RESULTS AND DISCUSSION

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3.1 CPs Concentrations in Air.

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Detailed CP concentrations and meteorological parameters of the air are shown in

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Figure 1 and Table S1. The total CPs (∑CPs, SCCPs+MCCPs) in gas−phase of air

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samples range from 3.8 to 13 ng m-3 with an average value of 6.9 ng m-3 in May, and

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8.3 to 39 ng m-3 with an average of 24 ng m-3 in August. The ∑CPs in particle−phase

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range from 1.1 to 8.5 ng m-3 with an average value of 3.2 ng m-3 in May, and 0.72 to

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2.4 ng m-3 with an average of 1.3 ng m-3 in August. Compared with other reports, the

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total SCCPs (∑SCCPs) in air of Bohai sea are significantly higher than those from the

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Polar regions,6,8 remote and high altitude regions,7 but lower than those from the

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urban area, such as Beijing in China.24 Notably, ∑SCCPs is comparable to the level of

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semi−rural area, such as Unite King,11 and East Asia countries (China, Japan and

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Korea).12

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The seasonal variation of gaseous ∑SCCPs, as well as ∑MCCPs is obvious (Figure

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1). For meteorological parameters, the temperature divergence between May and

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August, with the average values of 15.1℃ and 27.7℃, is apparent, whereas not for

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the total suspended particle (TSP), with average values of 98.2 µg m-3 and 103.4 µg -7-



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m-3 (Figure1 and Table S1). Furthermore, both the gaseous ( ∑ gCPs) and total

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concentrations (∑g+pCPs) significantly increase with the increasing of temperature (p

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< 0.01, Figure S2), implying that the meteorological parameter temperature is the

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main factor affect the occurrence of CPs in marine atmosphere, which is similar to the

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changing rules in urban air of North China report by Wang et al.24 Compared between

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the ∑SCCPs and ∑MCCPs, gaseous ∑SCCPs in both seasons (mean: 5.6 and 17 ng

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m-3) is higher than ∑MCCPs (1.3 and 7.1 ng m-3, Figure S3). However, for

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particle−phase, ∑SCCPs is slightly lower than ∑MCCPs in May (1.4 and 1.8 ng m-3),

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and no obvious difference is found in August (0.68 and 0.61 ng m-3). Furthermore, the

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correlation analysis between the gas-particle partition coefficient (Kp) and logKOA

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shows a significantly positive correlation (Figure S4). All these results indicate that

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longer carbon chain congeners, i.e. higher molecular weight CPs, have higher affinity

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to atmospheric particulates, especially during the springtime, which is also consistent

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with the result of urban air of North China24.

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As shown in Figure1, CPs exists mostly in the gas−phase in both seasons. The

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particle−phased fraction of ∑CPs in May ranges from 12.3 to 55.9% with a mean

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value of 30.1%, and in August ranges from 2.9% to 13.7% with a mean of 5.7%.

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Compared with urban atmospheric SCCPs, the average particle fraction of ∑SCCPs in

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August was similar to that of Beijing (China) during summertime (6%), and the

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average fraction in May is between that of Beijing during summertime and wintertime

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(6% ~ 67%).24

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There are no obvious spatial characteristics for gaseous CPs in May and August.

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However, the particle CPs in May performs an apparent terrestrial input feature,

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which the concentrations from the coastal sampling areas (A09 and A10) were

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apparently higher than those from middle areas (Figure S5). The air mass back

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trajectories from altitudes of 250, 500 and 1000 m at coastal sites and middle sea sites

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(Figure S6) and the significant correlation between particle CPs and TSP in May (r =

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0.92，p < 0.01) and August (r = 0.78, p < 0.01, Figure S7) both indicated the feature of

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land source. Besides, the regression analysis of gaseous CPs against particle CPs, and

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gaseous CPs against TSP also showed the linear relationships (Figure S7). These -8-


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could somewhat infer the similar source and/or transport direction of CPs in marine

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atmosphere around the Bohai Sea.

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Figure 1. Concentrations of CPs (SCCPs and MCCPs) in atmosphere collected from

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Bohai Sea. TSP represents the total suspended particle.

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3.2 CP Concentrations in Seawater.

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Detailed CP concentrations and meteorological parameters of the seawater are

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shown in Figure 2 and Table S2. The ∑CPs in dissolved−phase range from 9.6 to 28

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ng L-1 with an average value of 18 ng L-1 in May, 2016 and 29 to 126 ng L-1 with an

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average of 67 ng L-1 in August, 2016. The ∑CPs in particulate−phase range from 6.0

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to 26 ng L-1 with an average value of 13 ng L-1 in May, and 14 to 42 ng L-1 with an

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average of 28 ng L-1 in August. Compared with other reports, the dissolved ∑SCCPs

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in seawater from Bohai sea are far lower than those in influent waters of municipal

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sewage treatment plant reported in Beijing (184 ng L-1)25 and Japan (279 ng L-1).27

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However, ∑SCCPs in August shows a little higher than the effluents from these two

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plants (27 and 26 ng L-1).25,26 Another report about Pulandian Bay, also in Bohai Sea,

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revealed that the average SCCPs concentrations in seawater, influenced by domestic

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industry wastewater and untreated wastewater, were up to 953 ng L-1 (494 to 1490 ng

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L-1).27 The ∑MCCPs in both phases are lower than those of ∑SCCPs, with the average -9-



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percentages of 21.1% (May) and 28.0% (August) in dissolved−phase, and 34.7% and

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33.1% in particulate−phase. Besides, ∑MCCPs in both phases significantly correlate

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with ∑SCCPs (r = 0.56, p < 0.01 in May and r = 0.83, p < 0.01 in August).

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Furthermore, the spatial distributions (Kriging interpolation) in May and August show

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that the ∑CPs around the Liaohe River estuary and Pulandian Bay are significantly

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higher than those of other areas (Figure S8). All these results indicate the significant

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influence of riverine input on CPs concentration in estuary and inner bay areas during

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the summer (flood season).

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As shown in Figure 2, CPs exists mostly in the dissolved−phase in the sampling

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period. The particulate fraction of ∑CPs in May ranges from 28.6 to 53.7% with a

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mean value of 41.0%, and in August ranges from 18.1% to 50.9% with a mean of

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31.5%. The correlation analysis between the particulate-water partition coefficients

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(Kp) and logKOW (Figure S9) indicates that longer carbon chain congeners, i.e. higher

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molecular weight CPs, have higher affinity to particulates in water column. Due to

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limited data about CPs distributions in the dissolved−phase and particulate fraction in

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water sample, we compared this result to the PBDEs in Pearl River estuary reported

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by Chen et al., and the ratios between dissolved and particulate phase is consistant.28

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Besides, ∑CPs in both two phases in seawater in August are higher than those in

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May, and the seasonal difference of dissolved CPs (31.7 ng L-1 in August and 14.0 ng

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L-1 in May) are higher than those of particulate CPs (12.3 and 7.3 ng L-1, Figure S2).

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Moreover, compared between SCCPs and MCCPs, the dissolved ∑SCCPs in the two

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seasons with average values of 14.7 ng L-1 and 47.1 ng L-1 are higher than the

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dissolved ∑MCCPs (3.8 and 19.8 ng L-1), corresponding to the concentration ratios of

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3.2 and 5.2. Similar results are also observed for particulate ∑SCCPs and ∑MCCPs,

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with concentration ratios of 2.2 and 2.1 (Figure S2). These results indicate that the

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seasonal change of the occurrence of CPs (including SCCPs and MCCPs) in seawater

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is significant, especially for the dissolved CPs.

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Other geochemical parameters including POC, DOC and SPM were simultaneously

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determined to investigate the possible effecting factors to the distribution of CPs in

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different phase (Figure 2, Table S2 and Figure S10).∑CPs in the seawater increased -10-


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with the decreasing of salinity in both seasons, indicating the influence of the riverine

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input of terrestrial sources.27∑CPs in both two phases increased with the increasing of

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POC and SPM in May, but the trends in particulate in August were not significant

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(Figure S11). Considering all samples of two seasons, ∑CPs in both phases positively

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correlated to DOC (p < 0.01, Figure S10), as well as dissolved ∑CPs against

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particulate ∑CPs (r = 0.62, p < 0.01), indicating the DOC is an important factor

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affecting the distribution of CPs between dissolved-phase and particulate-phase.28

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Another interesting phenomenon is that the dissolved ∑CPs positively correlates to

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the wind speed in both seasons (Figure S10), indicating the wind speed is also an

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important factor influencing the occurrence of CPs in seawater. This is consistent with

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the result of organochlorine pesticides (OCPs) reported by Lin et al., i.e. the

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increasing of wind speed can increase the air−seawater diffusion.29

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300 301

Figure 2. Concentrations of CPs (SCCPs and MCCPs) in seawater collected from

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Bohai Sea. SPM represents the suspended particle material, POC represents the

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particle organic content.

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3.3 Formula Group Abundance Profiles.

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The CP formula group patterns in gaseous samples showed that the C10 and C11

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formula groups are the predominant carbon congeners (Figure 3) with an average -11-



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abundance of 48.5% for C10 and 18.6% for C11 in May, 43.1% for C10 and 20.3% for

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C11 in August respectively. However, C14 homologue group in particle phase in both

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two seasons is the most abundant group with an average abundance of 36.8% and 40.2%

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respectively. Among the chlorine groups, Cl6 and Cl7 are the dominant formula groups

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in air samples with an average value of 41.4% for Cl6 and 32.2% for Cl7 in May, 37.3%

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and 35.2% in August respectively. Similar homologue group patterns were observed

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in seawater samples. Overall, the homologue profiles in both two types of samples

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were comparable to those found in the air, soil/sediment, and seawater around

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China,12,17,27 which was also consistent with the compositions of the three major

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industrial CP products manufactured in the coastal and central regions of China.30,31

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One difference should be noted was that the chlorine congener profiles of CPs in air

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were different from those in Antarctica6,8 and high altitude regions on the Tibetan

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Plateau.7 The homologue group abundance of C10, C11, Cl6 and Cl7 homologue groups

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from these two typical remote areas were relatively higher than those from the

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sampling area in this study. The possible reasons might be ascribed to effect of long

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range atmospheric transport, which the CP congeners with shorter carbon chain and

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lower degree of chlorination (corresponding to higher p°L values or lower octanol-air

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partition coefficients (KOA)) had higher ability of atmospheric migration.24,32,33

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To further investigate the difference of formula group profiles between the different

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matrices, Correspondence analysis (CA, Figure S12) of congener group abundance

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and Pearson correlation (Table S3) between different matrixes were conducted. The

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result shows the gaseous in both seasons and dissolved CPs in May clustered with C10,

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Cl5 and Cl6 congener groups, whereas the particle in both seasons and part of

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particulate CPs in May clustered with C14, C15, Cl9 and Cl10 congener groups.

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However, the correlation efficient between gaseous and dissolved in August (r = 0.85,

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p < 0.001) are higher than that between particle air and particulate seawater in May (r

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= 0.62, p < 0.001), indicating the influence of gaseous CPs on dissolved seawater

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during the summer is higher than that of particle CPs on particulate seawater during

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the spring. The dissolved ∑CPs in August are correlated with C11 and C12 congener

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groups, which is different from that in May. The possible reason might be due to the -12-


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riverine input during the flood season. Besides, significant correlations of gaseous

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CPs between May and August (r = 0.98, p < 0.001) and particle atmosphere (r = 0.96,

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p < 0.001) also indicate the similar source and comparable atmospheric transport

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behavior between spring and summer.16

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343 344

Figure 3. Composition abundance profiles for CPs congeners in May and August.

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Carbon number ranged from 10 to 15 (up) due to the low detection of C16 and C17

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formula group congeners, and chlorine number ranged from 5 to 10 (down).

347 348

3.4 Fugacity Ratios Between Air and Seawater.

349

To estimate the direction (or equilibrium status) of the gas exchange, the fugacity

350

ratio (FR) fa/fw was calculated and the aggregated uncertainty associated with the

351

calculation was evaluated according to error propagation. A logfa/fw > 0.5, = 0, and
0 indicates net deposition and

399

net volatilization, respectively. The aggregated uncertainty associated with the

400

calculation was also evaluated according to error propagation. The final flux

401

uncertainty for all CP formula group congeners was ±96%. The dry particle

402

deposition flux (Fdry, ng m-2 day-1) was estimated by multiplying the concentration of

403

particle-phase CPs (Cp, ng m-3) by a dry deposition velocity (vd, m/d). Detailed air-sea

404

gas exchange flux, uncertainty calculation and dry deposition flux are listed in

405

SI.16,34,38

406

As shown in Figure 5, the air-sea gas exchange for different formula group -15-



407

congeners were generally dominated by net deposition. During the springtime, the

408

average Faw values of all sites range from -1072 (C10Cl7) to 112 ng m-2 day-1 (C16Cl5),

409

with the standard deviation of 772 and 94 ng m-2 day-1. The diffusion flux varies

410

relatively wider during the summertime with the average Faw values of -2433 ± 685

411

ng m-2 day-1 (C14Cl8) to 562 ± 255 ng m-2 day-1 (C11Cl5). This result is higher than

412

PCBs and OCPs at a coastal site in Izmir Bay, Turkey14 and PCBs in the lower Great

413

Lakes.34 Generally, the CP congeners with highest deposition flux are Cl8 congener

414

groups, followed by Cl7 and Cl8 congener groups, which is consistent to the CP

415

formula group patterns both in air and seawater samples (Figure 5). The CP congeners

416

with higher volatilization flux mostly focus on Cl5, and Faw values during the summer

417

are much higher than those during the spring. The result further indicates that the

418

concentration level of CPs and the temperature are important factors effecting the

419

air-sea diffusion flux.14,39-41

420

The total dry deposition fluxes in different sites range from 92 to 738 ng m-2 day-1

421

in spring and 62 to 205 ng m-2 day-1 in summer, respectively. The dry deposition

422

fluxes are both far lower than those of air-sea gas exchange (-13606 to -1760 ng m-2

423

day-1 in spring and -31144 to -148 ng m-2 day-1 in summer, Figure 5). To further

424

investigate the influence of atmospheric inputs on CP profiles in the water column, a

425

flux ratio between diffusion and dry deposition versus the carbon chain length was

426

conducted (Figure S16). The absolute values of Faw/Fdry both increase with the

427

decrease of carbon atoms, however the increasing trend in August is more obvious,

428

especially for C10 formula groups. This result indicates that the diffusive inputs relate

429

to concentrations and profiles of dissolved phase CPs in the water column than that of

430

dry deposition to particulate phase CPs, which is consistent to the result of CA

431

analysis (Figure S12). Furthermore, compared between different sites, the diffusion

432

and dry deposition fluxes adjacent to the coastal areas are higher than those in middle

433

of the sea during the spring, indicating that the contribution from the land sources

434

through atmospheric transport is significant.

-16-


Page 16 of 23


1000 0 -1000

May August

-2000 -4000 -6000 May -12000

Air-sea gas exchange dry deposition

0 -200 -400 -600 -13000

A 0 A1 0 A2 03 A 0 A4 0 A5 06 A 0 A7 0 A8 09 A 10

-2000 0

Total flux

Cl5 Cl6 Cl7 Cl8 Cl9 Cl10 Cl5 Cl6 Cl7 Cl8 Cl9 Cl10 Cl5 Cl6 Cl7 Cl8 Cl9 Cl10 Cl5 Cl6 Cl7 Cl8 Cl9 Cl10 Cl5 Cl6 Cl7 Cl8 Cl9 Cl10 Cl5 Cl6 Cl7 Cl8 Cl9 Cl10 Cl5 Cl6 Cl7 Cl8 Cl9 Cl10

Congeners

A 0 A1 0 A2 03 A 0 A4 05 A 0 A6 07 A 0 A8 09 A 10

Diffusion flux (ng m-2 day-1)

Page 17 of 23

-26000

August

435 436

Figure 5. Average values of air-sea gas exchange fluxes and dry deposition fluxes for

437

CP formula group congeners. Minus value means net deposition, and plus value

438

means volatilization.

439 440

In this work, the concentrations and profiles of SCCPs and MCCPs in air samples

441

and seawater samples from a typical coastal area of China were investigated. The

442

fugacity ratios (logfa/fw) between air and seawater indicate a net deposition process for

443

most CP formula groups. The flux evaluation of air-seawater diffusion and dry

444

deposition indicated that air-seawater gas exchange of CPs was significantly higher

445

than dry deposition in this area. Since the temperature might be an important factor in

446

affecting the occurrence of CPs in both air and seawater, distributions and

447

air-seawater gas exchange in winter might present some difference from the results of

448

spring and summer. To comprehensively understand the occurrence and air-seawater

449

exchange process of CPs, also including other semi-volatile organic pollutants, further

450

studies covered the data of full seasons should be needed.

451 452

Corresponding Author

453

*Address: Research Center for Eco-Environmental Sciences, Chinese Academy of -17-



454

Sciences, Beijing 100085, China;

455

Tel: 8610-6284-9124; e-mail: [email protected].

456 457

Notes

458 459

The authors declare no competing financial interest.

460

ACKNOWLEDGEMENTS

461

This study was supported by the National Natural Science Foundation of China

462

(21577028, 21625702, and 21337002), the National Basic Research Program of China

463

(2015CB453102), and the Strategic Priority Research Program of the Chinese

464

Academy of Science (XDB14010400). We also express our sincere gratitude to the

465

crew of R/V Yixing and the Shared Voyage of the National Nature Science Foundation.

466 467

ASSOCIATED CONTENT

468

Supporting Information

469

Detailed information in SI are Materials, standards, and regents (Text 01); Calculation

470

of the fugacity ratios and uncertainty analysis (Text 02); Calculation of the air–

471

seawater gas exchange flux and uncertainty analysis (Text 03); Parameters and CPs

472

concentrations in air samples from Liaodong Bay (Table S01); Parameters and CPs

473

concentrations in seawater samples from Liaodong Bay (Table S02); Pearson

474

correlation analysis of CP formula group abundance between different matrixes (Table

475

S3); The sampling sites in the Bohai sea (Figure S1); Box-plots of SCCPs and

476

MCCPs in air and seawater samples (Figure S2); Spatial distribution of atmospheric

477

CPs (Figure S3); Correlation analyses (Figure S3, S4, S7, S9-S11, S13, S14, S16); Air

478

mass backward trajectories (Figure S4); Spatial distribution of particulate CPs

479

normalized by SPM in seawater (Figure S7); Correspondence analysis of congener

480

group abundance in different matrices (Figure S12); Concentration ratios of gaseous

481

air, dissolved seawater, and logarithmic fa/fw between May and August for different CP

482

congeners (Figure S115). This material is available free of charge via the Internet at -18-


Page 18 of 23

Page 19 of 23


483

http://pubs.acs.org.

484 485

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