Release and Gas-Particle Partitioning Behaviors of Short-Chain

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Release and Gas-Particle Partitioning Behaviors of Short-Chain Chlorinated Paraffins (SCCPs) During the Thermal Treatment of Polyvinyl Chloride Flooring Faqiang Zhan, Haijun Zhang, Jing Wang, Jiazhi Xu, Heping Yuan, Yuan Gao, Fan Su, and Jiping Chen Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b01965 • Publication Date (Web): 11 Jul 2017 Downloaded from http://pubs.acs.org on July 11, 2017

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Environmental Science & Technology

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Release and Gas-Particle Partitioning Behaviors of

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Short-Chain Chlorinated Paraffins (SCCPs) During the

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Thermal Treatment of Polyvinyl Chloride Flooring

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Faqiang Zhan,†,‡ Haijun Zhang, *,† Jing Wang,§,║ Jiazhi Xu,†,‡ Heping Yuan,†

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Yuan Gao,† Fan Su,† and Jiping Chen†

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†

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Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, China

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‡

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§

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║

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CH-8600, Switzerland

CAS Key Laboratory of Separation Science for Analytical Chemistry, Dalian Institute of

University of Chinese Academy of Sciences, Beijing 100049, China Institute of Environmental Engineering, ETH Zurich, Zurich CH-8093, Switzerland Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf

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TOC/Abstract Art

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*Corresponding Authors

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Phone: +86-411-8437-9972, fax: +86-411-8437-9562; e-mail: [email protected].

ACS Paragon Plus Environment


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ABSTRACT

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Chlorinated paraffin (CP) mixture is a common additive in polyvinyl chloride (PVC)

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products as a plasticizer and flame retardant. During the PVC plastic life cycle, intentional

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or incidental thermal processes inevitably cause an abrupt release of short-chain CPs

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(SCCPs). In this study, the thermal processing of PVC plastics was simulated by heating

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PVC flooring at 100–200 °C in a chamber. The 1-h thermal treatment caused the release of

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1.9%–10.7% of the embedded SCCPs. A developed emission model indicated that SCCP

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release was mainly controlled by material–gas partitioning at 100 °C. However, release

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control tended to be subjected to material-phase diffusion above 150 °C, especially for

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SCCP congeners with shorter carbon-chain lengths. A cascade impactor (NanoMoudi) was

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used to collect particles of different sizes and gas-phase SCCPs. The elevated temperature

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resulted in a higher partition of SCCPs from the gas-phase to particle-phase. SCCPs were

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not strongly inclined to form aerosol particles by nucleation, and less present in the Aitken

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mode particles. Junge-Pankow adsorption model well fitted the partitioning of SCCPs

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between the gas-phase and accumulation mode particles. Inhalation exposure estimation

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indicated that PVC processing and recycling workers could face a considerably high risk

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for exposure to SCCPs.

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INTRODUCTION

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Polyvinyl chloride (PVC) is one of the highest-volume plastics produced, and it is

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widely used in packaging, electronic devices, the automobile industry and building

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materials.1 To enable PVC processing and improve its physical and mechanical properties,

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PVC is always mixed with additives, such as stabilizers, plasticizers, lubricants, flame

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retardants and other agents. Chlorinated paraffins (CPs) are common additives in PVC

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plastics as both plasticizers and flame retardants.2 They are extremely complex mixtures

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that consist of thousands of congeners and isomers, which can be subdivided into

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short-chain (SCCPs, C10−13), medium-chain (MCCPs, C14−17) and long-chain CPs (LCCPs, ACS Paragon Plus Environment

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C>17) according to their carbon chain length. Among them, SCCPs has been proposed as a

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group of new persistent organic pollutants (POPs) by the Stockholm Convention (UNEP,

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2017),3 due to their environmental persistence, long-range transport potential, tendency to

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bioaccumulate and high toxicity.4–9

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SCCPs have been subjected to regulation in Europe, the U.S. and Canada due to their

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physical-chemical properties and adverse effects.8 In the European Union, articles

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containing SCCPs in concentrations equal to or greater than 0.15% by weight are

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prohibited.10 However, the use and production of SCCPs in most developing countries is

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not yet restricted. In China, a larger quantity of commercial CP mixtures were produced

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without being classified by carbon chain length, and approximately 70% of produced CP

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mixtures were consumed by the PVC processing industry.11 It was estimated that the

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consumption of SCCPs in the Chinese PVC processing industry was as high as 58,700

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tons in 2011, and could reach 75,500 tons in 2016.11 Therefore, serious concerns should be

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raised for the release of SCCPs from the PVC life cycle to the ambient environment.

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Thermal treatment is an essential process for the processing and recycling of PVC

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plastics, during which organic additives can be abruptly and prominently released to the

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ambient environment under thermal stress. PVC processing techniques, including

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extrusion, calendaring and injection molding, usually operate at 100−210 °C. Meanwhile,

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the abruptly elevated temperature of PVC plastics usually occurs during open burning of

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municipal solid waste, melting for PVC recycling, building fire accidents and short circuit

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current of PVC cables. A previous study found that the emission of di-(2-ethylhexyl)

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phthalate (DEHP) from PVC plastics increased 100 folds when temperature increased

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from 20 °C to 80 °C.12 The evaporation rate of DEHP would be independent of DEHP

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concentration in PVC plastics at ≥ 80 °C, and the transport of DEHP from PVC plastics to

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the surrounding air was controlled by diffusion at ≥ 120 °C.13 An emission inventory

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prediction assumed that the emission of SCCPs from PVC processing to air was 4-fold ACS Paragon Plus Environment


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higher than from the routine use of PVC plastics in China,11 according to the default

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emission factors for the release of additives from polymer processing to air.14 Thus, an

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investigation of the actual release characteristics of SCCPs from thermally treated PVC

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plastics should be conducted.

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During the thermal treatment of PVC plastics, released SCCPs can be rapidly associated

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with aerosol particles formed from volatile compounds through nucleation and

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coagulation.15, 16 Gas–particle partitioning, on the one hand, can reduce the gas-phase

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concentration of SCCPs and thus increase the release rate.17 On the other hand, it can

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significantly affect the transport and environmental fate of the released SCCPs.18 In

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addition, the distribution of SCCPs in particle fractions of different sizes will also

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determine the occupational exposure levels for PVC processing workers or firefighters to

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SCCPs through inhalation. The primary objective of this study was to investigate the

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release characteristics of SCCPs from thermally treated PVC plastics and gas–particle

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partitioning behaviors of the released SCCPs. The obtained results will provide missing

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information on the source characteristics of SCCPs from PVC processing and other

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heating processes, and help estimate the health risk of inhalation exposure to SCCPs

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released from the thermal treatment of plastics.

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EXPERIMENTAL SECTION

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Experimental Setup and Sampling. A resilient type of PVC flooring, purchased

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from a building material market in China, was adopted as the model PVC material. The

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PVC flooring was composed of a wear layer (pure PVC, thickness: 0.1 mm), a patterned

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layer (thickness: 0.65 mm) and a foamed layer (thickness: 0.85 mm). The patterned layer

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and foamed layer contained 60–70% PVC and 30–40% additives (mainly CaO and TiO2)

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by weight. CPs with chlorine content of 52% by mass (CP-52) were added, and the total

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content of SCCPs in raw PVC was determined to be 2.36 mg/g. Elemental abundance in

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PVC flooring was analyzed by X ray fluorescence, and the results are listed in Table S1 of ACS Paragon Plus Environment

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the Supporting Information (SI).

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The thermal treatment experiments were performed in a stainless steel chamber (length

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1200 mm × width 900 mm × height 1200 mm) constructed in our lab and equipped with a

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vent hole on the top and an electric heating plate on the bottom (SI Figure S1). The surface

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temperature of the electric heating plate was precisely adjusted using a digital temperature

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controller, and further verified by an infrared radiation thermometer. PVC flooring was

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chopped into small discs with the same size (diameter: 123 mm, mass: approximately 17 g)

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for each run. The chopped PVC flooring was placed on the center of the electric heating

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plate after desired temperature (100 °C, 150 °C and 200 °C) was reached.

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For the SCCP release experiment, seven sampling time points were established for each

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temperature condition. At each sampling time point, the thermally treated PVC flooring

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disc was taken out from the box and immediately weighed, and one seventh of the test

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PVC flooring piece was cut down for SCCPs analysis. The remaining part of the test PVC

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flooring piece was immediately placed back in the center of electric heating plate. The

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weighing and sampling operation was completed within 2 min, and the operation time was

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not counted as heating time.

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For the gas–particle partitioning study, a cascade impactor (Mode 122-NR NanoMoudi,

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MSP Corporation) was applied to collect particles with different diameter at the flow rate

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of 30 L/min. The sampling nozzle was fixed at the center of the chamber, and the distance

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from the heating plate was 0.5 m. Sampling was conducted for 8 h at 100 °C and 4 h at

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150 °C and 200 °C. The average relative humidity in the chamber was 48%, 49% and 47%

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for the thermal treatment at 100 °C, 150 °C and 200 °C, respectively.

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There are 13 stages in the cascade impactor, and the 50% cutoff diameters ranged from

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10 nm to 18000 nm. Uncoated aluminum foil was used as the impaction substrate to

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collect the particles on impactor plates, followed by a back-up filter (Quartz Microfiber

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Filters, WhatmanTM, 90 mm) to collect uncaptured particles. Polyurethane foam (PUF) ACS Paragon Plus Environment


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was placed under the back-up filter to collect SCCPs in the gas phase. Aluminum foil was

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baked at 500 °C for 12 h in a muffle oven to remove organic substances. PUF was washed

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with n-hexane and dichloromethane (DCM) three times using accelerated solvent

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extraction (ASE 350, Dionex, USA). The impaction substrate was taken from the cascade

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impactor and kept in an incubator for 24 h to reach equilibrium after sampling. The mass

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of aluminum foil at each stage was measured on a microbalance (Mettler Greifensee,

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Switzerland; precision: ± 1 µg) before and after the experiment, repeated three times and

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averaged.

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Sample Extraction and Cleanup. Raw PVC flooring samples and thermally treated

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PVC flooring samples were cut and ground into small pieces (through 24 mesh sieve) with

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liquid nitrogen, and 0.3 g of PVC samples were ultrasonically extracted with 20 mL

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n-hexane/DCM (1: 1, v/v) three times (15 min for each run). Extraction of particles on

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aluminum foils followed the same procedure as PVC samples. PUF and quartz microfiber

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filters were Soxhlet-extracted for 24 h with 250 mL n-hexane/DCM (1: 1, v/v). Prior to

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extraction, 2 ng of

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samples, as the extraction internal standard. For PVC flooring samples, 2 µg of chlorinated

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2-methyl undecane (branched C12-CPs, chlorine content: 55.4% by mass) was spiked as

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the extraction internal standard.

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C6-δ-hexachlorocyclohexane was spiked into particle and PUF

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A silica gel column was used to clean up samples. The column was packed with 5.0 g

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anhydrous Na2SO4, 3.5 g silica gel (activated at 650 °C for 12 h) and 6.0 g anhydrous

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Na2SO4 from bottom to top. The extract was transferred to the column after concentration

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to approximately 1 mL. The fraction was received by eluting with 40 mL n-hexane/DCM

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(2: 1, v/v). The target solution was concentrated to approximately 0.5 mL, transferred to a

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vial, evaporated to near dryness with a gentle stream of N2, and re-dissolved in 40 µL of

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injection internal standard solution for instrumental analysis. Chlorinated 2-methyl nonane

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(branched C10-CPs) and

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C10-trans-CD were adopted as injection internal standards for ACS Paragon Plus Environment

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extracts of PVC flooring samples and extracts of particle and PUF samples, respectively.

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Detailed information about chemicals and reagents is shown in the SI.

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Instrumental Analysis and Quantification. In this study, the release of SCCPs

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from the heating of PVC flooring was calculated according to the concentration loss of

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SCCPs in the flooring before and after thermal treatment. In the tested PVC flooring

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material, medium-chain CPs (MCCPs) were detected at high concentrations (SI Figure S2).

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To avoid strong interferences of MCCPs with SCCP analysis on mass spectrometry,19 the

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carbon skeleton reaction gas chromatography (GC) method was adopted for the analysis

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of SCCPs in PVC flooring. The analysis was conducted on a Hewlett-Packard GC (HP

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5890 Series II) equipped with a capillary DB-5 column (30 m × 0.32 mm i.d. × 0.25 µm

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film thickness, J&W Scientific, USA) and FID detector. The concentrations of n-alkanes

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(C10−13), produced from the dechlorination reaction were calibrated using n-alkane

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standards (purity: > 99.9%); thereafter the concentrations of SCCPs with different carbon

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chain lengths were quantified with corrections of the internal standard recovery rate and

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average chlorine content (52% by mass). Detailed information about carbon skeleton

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reaction GC method is shown in the SI.

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In particle and PUF samples, SCCPs were the predominant CP components due to less

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volatilization of MCCPs from the heating of PVC flooring (SI Figure S3), and thus the

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interference of MCCPs in SCCP analysis on mass spectrometry could be ignored. In this

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study, the SCCPs in particle and PUF samples were analyzed using a high-resolution gas

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chromatography/electron capture negative ion−low resolution mass spectrometry

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(HRGC/ECNI−LRMS) method, in which information about both the carbon chain lengths

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and chlorine distribution of SCCPs could be obtained. The analysis was conducted on a

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GCMS-QP2010 (Shimadzu, Japan) coupled with a capillary DB-5 column (15 m × 0.25

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mm i.d. × 0.25 µm film thickness, J&W Scientific, U.S.). The quantification of SCCPs

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followed the procedure described by Reth et al.20 Detailed information about ACS Paragon Plus Environment


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HRGC/ECNI−LRMS method and SCCP quantification is shown in the SI.

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Quality Assurance and Quality Control. During particle sampling, the measured

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gas flow rates and pressure drops of the cascade impactor all met the specified values. The

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relative deviation in particle mass at each stage, measured by microbalance three times,

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was less than 10%. For the analysis of SCCPs, procedural blanks were first performed for

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each batch of solvents and adsorbents. No SCCPs were detected in the procedural blanks.

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The procedural blanks spiked with a small quantity of SCCP mixture standards were used

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to determine the method detection limit (MDL) of HRGC/ECNI−LRMS analysis, which

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was calculated as three times the standard deviation at 4 time measurements. The MDL

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value for the total SCCPs (∑SCCPs) in particle and PUF samples was estimated to be 0.49

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ng/m3. In the gas–particle partitioning study, the field blank samples were obtained by

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sampling ambient air through the cascade impactor. The concentrations of SCCPs in field

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blank samples of back-up filter and aluminum foil were below MDL. SCCP level in field

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PUF blank was determined to be 79.3 ng, which was 3−4 orders of magnitude lower than

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those (54.3−815.8 µg) of field samples.

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For the HRGC/ECNI−LRMS analysis of SCCPs, the recoveries of internal standard

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13C6-δ- hexachlorocyclohexane in all particle and PUF samples were in the range of

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51.4%−135.8%. The reported concentrations of SCCPs in particle and PUF samples were

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not corrected by the recovery rates of extraction internal standard and field blanks. For the

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carbon skeleton reaction GC analysis of SCCPs, the internal standard chlorinated 2-methyl

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undecane in all PVC flooring samples ranged from 70.5% to 140.3%.

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RESULTS AND DISCUSSION

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Release Kinetics of SCCPs. An abrupt and prominent release of SCCPs was

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observed during the initial stage of thermal treatment of PVC flooring. Within the initial

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1-h, the overall loss of ∑SCCPs from PVC flooring mass was 1.9%, 7.4% and 10.7% at

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heating temperatures of 100 °C, 150 °C and 200 °C, respectively (SI Table S3). SCCP ACS Paragon Plus Environment

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release rates gradually decreased with increased heating time, and SCCP congener groups

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with shorter carbon chain lengths exhibited higher release rates (Figure 1 and SI Figure

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S4).

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Figure 1. Comparison of fitted and measured accumulative release of SCCP congener groups

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from thermal treatment of PVC flooring.

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A simplified schematic representation for the release of SCCPs from thermally treated

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PVC flooring in the stainless steel chamber is shown in SI Figure S5. The release of

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SCCPs from plastic materials can generally be described with three physical processes: (1)

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material-phase mass-transfer (internal diffusion), (2) material−gas partitioning (boundary

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condition) and (3) gas-phase mass-transfer (external diffusion).17,

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diffusion coefficient D, material−gas partition coefficient K and convective mass-transfer

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coefficient hm are the corresponding parameters governing the three processes. Based on

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emission model of VOCs from building materials,22−24 a model that integrates these three

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physical processes governing release of SCCPs from the thermally treated PVC flooring

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was developed in this study, and model details are shown in the SI. When the key

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coefficients K, D and hm were known, the model could be numerically solved by using the

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finite difference method.24 ACS Paragon Plus Environment

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Material-phase


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In this emission model, the coefficient hm for the laminar flow of ∑SCCPs was

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evaluated according to the relationship of Sherwood number (Sh) with Reynolds number

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(Re) and Schmidt number (Sc).23, 25 The calculated hm values were 0.017 m/s, 0.019 m/s

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and 0.021 m/s at heating temperatures of 100 °C, 150 °C and 200 °C, respectively. The

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coefficients K and D were obtained by fitting the variation of measured residual

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concentrations of SCCPs in PVC flooring with heating time, based on the

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Levenberg–Marquardt algorithm (details in SI). Before optimizing, a careful check for the

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relative sensitivity of coefficients D and K was conducted. The result showed that no

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linear dependence existed between D and K values (SI Figure S6), and thus these two

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coefficients could be independently estimated by the inverse method. The fitted values for

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the accumulative release of various SCCP congener groups were all significantly (P < 0.01)

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correlated with the measured values (Figure 1 and SI Table S4), validating the developed

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model. As shown in SI Table S5, the obtained K and D values both depended strongly on

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the heating temperature. In addition, SCCP congener groups with shorter carbon chain

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lengths showed larger D values and smaller K values.

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The time-dependent release rates of SCCPs were predicted by the developed model

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with estimated parameters (Figure 2). During the initial 1-h of thermal treatments at

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150 °C and 200 °C, SCCP release rates declined dramatically. The rapid decreases resulted

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from fast surface volatilization during thermal stress, which was controlled by the

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material–gas partition coefficient K and convective mass-transfer coefficient hm.

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Subsequently, SCCP release rates fell, suggesting that the release control was gradually

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subjected to the material-phase diffusion. SCCP congener groups with shorter carbon

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chain lengths were more easily volatilized from the surface of thermally treated PVC

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flooring, and thus their release was more inclined to be limited by material-phase diffusion.

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At the heating temperature of 100 °C, SCCP release rate did not present an obviously

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sharp drop during the initial 1-h of thermal treatment, indicating that the material–gas ACS Paragon Plus Environment

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partition decisively affected the release rate of SCCPs from thermal treatment of PVC

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flooring at 100 °C.

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Figure 2. Predicted release rate of SCCP congener groups from thermal treatment of PVC

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flooring.

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Mass Size Distribution of the Emitted Particles. During the 4-h thermal

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treatment of PVC flooring, the total mass of particles captured by the NanoMoudi stages

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was 85.3 mg at heating temperature of 200 °C, which was 4.4-fold higher than that at

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150 °C. Only 4.1 mg of particles was captured during 8-h thermal treatment at 100 °C.

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The emitted particles generally exhibited a unimodal mass size distribution (SI Figure S7).

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More than 90% of particles were deposited at Stages 6−10 (50% cutoff diameter: 56−1000

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nm) at 100 °C, Stages 5−8 (50% cutoff diameter: 180−1800 nm) at 150 °C and Stages 3−8

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(50% cutoff diameter: 180−5600 nm) at 200 °C, respectively. A continuous mass size

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distribution of emitted particles was reconstructed using the data inversion method

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described by Dong et al.26 The lognormal functions fit the gravimetric NanoMoudi data

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well (significant at 0.01 level) (SI Figure S8), and converged to the following parameters:

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geometric mean diameter (Dg) was 358 nm, 919 nm and 1990 nm for thermal treatment at

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100 °C，150 °C and 200 °C, respectively (SI Table S6). The elevated temperature gave rise



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to an increase in larger particle yield. Scanning electron microscope images showed that

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these larger aerosol particles mainly formed from the coagulation of ultrafine mode

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particles (UFPs, size: < 100 nm) (SI Figure S9). Meanwhile, energy dispersive X-ray

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spectrometer indicated that the main elements in aerosol particles captured by NanoMoudi

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Stages 5−9 (50% cutoff diameter: 100−1000 nm) were C, O, Cl, Ca, Si, Mg and Ti (SI

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Table S7). This suggested that these larger aerosol particles were mainly composed of

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chlorine-containing organic compounds, and plastic additives such as calcium oxide,

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silicon compounds, magnesium oxide and titanium oxide.

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Figure 3. Mass size distribution reconstructed from NanoMoudi impactor data of

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particle-bound SCCPs produced from thermal treatment of PVC flooring. Unit dm is mass of

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SCCPs captured at certain stage when sampling volume is 1 m3, and Dp is the aerodynamic

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diameter of particles deposited at a certain stage.

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Distribution of the Total SCCPs in Gas and Particle Phases. During the 8-h

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thermal treatment of PVC flooring at 100 °C, NanoMoudi captured 909.2 µg of SCCPs,

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89.7% of which was in the gas phase (adsorbed on PUF). However, most emitted SCCPs

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partitioned into the particle phase during the 4-h thermal treatment at 150 °C and 200 °C.


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The total masses of particle-bound SCCPs (captured by different stages and back-up filter)

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were 634.1µg and 1262.0 µg at 150 °C and 200 °C, accounting for 64.5% and 95.9% of

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the total captured SCCPs, respectively. The mass size distribution of SCCPs in the

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particle-phase also featured a unimodal distribution (SI Figure S10). According to the data

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inversion method,26 a continuous mass size distribution of particle-bound SCCPs was

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reconstructed. As shown in Figure 3, the log-normal functions provided a good fit

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(significant at 0.01 level) for the NanoMoudi impactor data of particle-bound SCCPs. The

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fitting results indicated that of SCCP mass peaks occurred at particle sizes of 359 nm, 894

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nm and 1725 nm for thermal treatments at 100 °C, 150 °C and 200 °C, respectively (SI

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Table S8).

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The concentrations of ∑SCCPs in particles showed obvious variation with changes in

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particle size and heating temperature (Figure 4). In the ultrafine particles (UFPs) deposited

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on Stages 10−13 (50% cutoff diameter: 10−56 nm), the ∑SCCPs concentrations were in

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the range of 0.5−13.7 mg/g. Due to the larger deviation in mass measurement, the

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concentrations of ∑SCCPs in the smallest UFPs deposited on the back-up filter (50%

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cutoff diameter: < 10 nm) could not be accurately determined. ∑SCCPs concentrations in

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the accumulation mode particles, consisting of particles deposited on Stages 3−9 (50%

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cutoff diameter: 100−3200 nm), were in the range of 6.9−46.9 mg/g, significantly higher

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than those in UFPs. The accumulation mode particles emitted from thermal treatment at

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150 °C showed higher ∑SCCPs concentrations compared to those at 100 °C and 200 °C.

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However, thermal treatment at 200 °C led to a higher load of SCCPs in coarse mode

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particles deposited on the inlet stage and Stages 1 and 2 (50% cutoff diameter: 5.6−18 µm).

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The average concentration of ∑SCCPs in coarse mode particles emitted from thermal

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treatment at 200 °C was 37.2 mg/g, approximately 49-fold and 20-fold higher than those

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at 100 °C and 150 °C, respectively.

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315 316

Figure 4. SCCP concentrations in size separated particles (collected by NanoMoudi) from

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thermal treatment of PVC.

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The UFPs comprise two sub-modes, i.e. nucleation mode (< 10 nm) and Aitken mode

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particles (10−100 nm).27 During thermal treatment of PVC flooring, nucleation mode

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particles can be formed through nucleation in the ambient air after rapid cooling and

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dilution of emissions when the saturation ratio of gaseous compounds of low volatility (i.e.

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HCl and larger organic molecules) reached a maximum.28−30 Subsequently, Aitken mode

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particles were formed through collision and condensational growth of nucleation mode

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particles.31 In this study, the concentrations of ∑SCCPs in UFPs with a 50% cutoff

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diameter of 10−32 nm were lower, implying that SCCPs were not strongly inclined to

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form aerosol particles by nucleation.

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During the thermal treatment of PVC flooring, accumulation mode particles could be

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produced by coagulation and surface growth of UFPs. Because UFPs had a lower

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concentration of ∑SCCPs, the coagulation of UFPs did not seem to result in a larger

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increase in ∑SCCPs concentration in the formed accumulative mode particles. The

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significantly elevated concentration of ∑SCCPs in accumulation mode particles should

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mainly result from the sorption of gas-phase SCCPs during the surface growth of particles.

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Due to the hydrophobicity, volatilized SCCPs should be partitioned into only the organic ACS Paragon Plus Environment

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phase of particles. Therefore, it could be speculated that the outer layer of accumulation

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mode particles should have higher organic matter content due to the continuous surface

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condensation and adsorption of organic vapors.

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During thermal treatment of PVC flooring at 200 °C, coarse mode particles were

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deposited on the inlet stage and Stages 1 and 2 (50% cutoff diameter: 5.6−18 µm) were

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found to be yellow organic liquid residues, suggesting that these coarse mode particles

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were in an organic liquid state. These organic liquid particles should be formed by the

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rapid condensation of semi-volatile organic compounds that were abruptly emitted from

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the PVC flooring under higher thermal stress. They inevitably exhibited a larger capacity

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to absorb the released SCCPs, and thus resulted in the high accumulation of SCCPs.

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Distribution of SCCP Congener Groups in Gas- and Particle-Phases. To

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understand the dependence of the gas−particle partitioning behavior of SCCPs on their

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physical-chemical properties, SCCP congeners were categorized by both carbon chain

348

length and chlorine atom number into 24 congener groups, and their relative abundances

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were compared (SI Figure S11). Thermal treatments of PVC flooring at three different

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heating temperatures (100 °C, 150 °C and 200 °C) produced similar congener group

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profiles of gas-phase SCCPs, which were characterized by the higher relative abundances

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of C10-CPs (average: 82.6%) groups. In the particle-phases, the proportion of C10-CPs

353

largely decreased, whereas the proportions of C11−13-CPs increased noticeably.

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Principal component analysis (PCA) was applied with unit variance (UV) scaling for

355

data regarding the relative abundances of SCCP congener groups to further investigate

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their similarities and differences with respect to gas−particle partitioning behavior. The

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two dimensions represented the two main factors, which explained most of the original

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variables with a cumulative contribution of 74.0% (Figure 5). The loading factors of the

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SCCP congener groups exhibited an increasing tendency with the increase of log KOA



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values on loadings 1 (SI Figure S12), suggesting that the first factor (Component 1 in the

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score plot) was mainly explained by variables induced by the KOA values.

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Figure 5. PCA score plot for congener group abundances of gas-phase and particle-phase

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SCCPs released from thermal treatments of PVC flooring at three heating temperatures

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(100 °C, 150 °C and 200 °C). The 50% cutoff diameters of nucleation mode particles, Aitken

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mode particles, accumulation mode particles and coarse mode particles, were < 10 nm,

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10−100 nm, 100−3200 nm and > 3200 nm, respectively.

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In the PCA score plot, gas-phase and nucleation mode particles (50% cutoff diameter:

Release and Gas-Particle Partitioning Behaviors of Short-Chain

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