Cm-History Method, a Novel Approach to ... - ACS Publications

Subscriber access provided by UNIV OF NEBRASKA - LINCOLN

Article

Cm-history method, a novel approach to simultaneously measure source and sink parameters important for estimating indoor exposures to phthalates Jianping Cao, Charles J. Weschler, Jiajun Luo, and Yinping Zhang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b04404 • Publication Date (Web): 17 Dec 2015 Downloaded from http://pubs.acs.org on December 17, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30

Environmental Science & Technology

1

Cm-history method, a novel approach to simultaneously measure source

2

and sink parameters important for estimating indoor exposures to

3

phthalates

4

Jianping Cao1, 2, Charles J. Weschler1, 2, 3, Jiajun Luo1, 2, Yinping Zhang1, 2, *

5 6

1

Department of Building Science, Tsinghua University, 100084, Beijing, China

7

2

Beijing Key Laboratory of Indoor Air Quality Evaluation and Control, 100084, Beijing,

8

China

9

3

10

Environmental and Occupational Health Sciences Institute, Rutgers University,

Piscataway, 08854, New Jersey, United States

11 12

Abstract:

13

The concentration of a gas-phase SVOC in equilibrium with its mass-fraction in the

14

source material, y0, and the coefficient for partitioning of an SVOC between clothing and

15

air, K, are key parameters for estimating emission and subsequent dermal exposure to

16

SVOCs. Most of the available methods for their determination depend on achieving

17

steady-state in ventilated chambers. This can be time consuming and of variable

18

accuracy. Additionally, no existing method simultaneously determines y0 and K in a

19

single experiment. In this paper we present a sealed-chamber method, using early stage

20

concentration measurements, to simultaneously determine y0 and K. The measurement

21

error for the method is analyzed and optimization of experimental parameters is explored.

22

Using this method, y0 for phthalates (DiBP, DnBP and DEHP) emitted by two types of

23

PVC flooring, coupled with K’s for these phthalates partitioning between a cotton T-shirt

24

and air, were measured at 25 °C and 32 °C -- room and skin temperatures respectively.

25

The measured y0’s agree well with results obtained by alternate methods. The changes of

26

y0 and K with temperature were used to approximate the changes in enthalpy, ∆H,

27

associated with the relevant phase changes. We conclude with suggestions for further

28

related research.

1

ACS Paragon Plus Environment


29

Page 2 of 30

1. Introduction

30

Semi-volatile organic compounds (SVOCs), ubiquitous in indoor environments1, 2,

31

tend to redistribute from their original source to air3, room and indoor material surfaces4-

32

6

33

to SVOCs via inhalation, ingestion and dermal absorption.10, 14, 15 Such exposures have

34

been associated with multiple adverse health effects (e.g., endocrine disruption, asthma,

35

altered sperm quality, cancer and birth defects1, 2, 4).

, dust7, suspended particles8, 9, human skin10, 11 and clothing12, 13. Occupants are exposed

36

Among the SVOC exposure pathways, dermal exposure to gas-phase SVOCs has

37

often been overlooked. In fact, for certain compounds it may be comparable or larger

38

than inhalation intake.10, 11, 15-19 Furthermore, health impacts may differ from ingestion or

39

inhalation, since metabolism is different (enzymes in the stomach and intestines are

40

avoided, respiratory defense functions are not activated, and some metabolism may occur

41

in the skin).10 Recently, efforts have been made to better estimate dermal exposure to gas-

42

phase SVOCs.10,

43

clothing on dermal exposure to indoor gas-phase SVOCs.12,

44

Morrison et al.21 measured dermal uptake of gas-phase diethyl phthalate (DEP) and di-n-

45

butyl phthalate (DnBP) by an individual wearing clean clothes or DEP- and DnBP-

46

contaminated clothes. Based on comparisons with dermal uptake for bare-skinned

47

individuals under the same experimental conditions11, they concluded that the clean

48

clothes acted as a barrier to dermal exposure, while contaminated clothes increased

49

dermal uptake for DEP and DnBP by factors of 3.3 and 6.5, respectively.21

15, 16, 20

However, only a few studies have considered the effect of 13, 21

In the last of these

50

Figure 1 presents a schematic illustrating migration of SVOCs from their source to

51

clothing to human skin (transport via particle deposition has been omitted, since its

52

modeled contribution to total dermal exposure has been estimated to be < 15% for PAHs

53

and DEHP20). As shown in Figure 1, to quantitatively estimate an SVOC emission

54

indoors, it is necessary to know its gas-phase concentration in equilibrium with its source

55

material (y0)22; and to estimate the role of clothing in dermal exposure, it is necessary to

56

know the SVOC’s equilibrium coefficient for partitioning between clothing and air (K)

57

and its diffusion coefficient in the clothing (D)

58

neglected (see Section S6, section, table and figure numbers preceded by an “S” are in the

59

Supporting Information). Hence, the key parameters are y0 and K.

12, 13, 21

. In some instances D can be

2


Page 3 of 30


60 While earlier studies have investigated emissions of SVOCs from indoor materials23-

61 62

31

, only a few have measured y0

32, 33

. These have used different types of ventilated

34

63

chambers (e.g., the CLIMPAQ , FLEC34, 35 and a sandwich-like chamber36, 37); selected

64

details are listed in Table 1. Through mass transfer analysis, Liu et al.32 proposed several

65

practical ways to improve the measurement accuracy of y0 or simplify the procedure.

66

Based on these, Cao et al.38 recently developed an SPME-based method to determine y0.

67

Collectively, the existing experimental results indicate that y0 (1) is approximately

68

constant for long periods (e.g., a year)22, 39, (2) increases with increasing temperature35, 40,

69

41

and (3) is little affected by relative humidity42.

70

In contrast to the situation for y0, few studies have determined K for different

71

combinations of SVOCs and clothing material. Guerrero43 measured clothing/air partition

72

coefficients of p-dichlorobenzene (p-DCB) and naphthalene for wool by keeping cloth

73

specimens in a chamber ventilated with air containing p-DCB or naphthalene for one

74

month. Using the same experimental approach, K’s for methamphetamine on cotton and

75

polyester fabrics12, and for DEP and DnBP on cotton fabrics13 were measured with

76

experiments lasting 60 and 10 days, respectively. Bi et al.41 measured K’s for butyl benzyl

77

phthalate (BBzP) and di(2-ethylhexyl) phthalate (DEHP) on cotton and polyester fabrics

78

by hanging clothes in a bedroom wardrobe whose air contained elevated concentrations

79

of these two species. Given that these methods require the adsorption of clothing to reach

80

equilibrium, it can take a very long time to measure K’s for SVOCs that have large values

81

for the clothing/air partition coefficient (see eq (4) in Morrison et al.13; as an example, the

82

time would be longer than 85 days if K > 7 × 107 for the undershirt in their experiment).

83

Additionally, clothing is often stored at a temperature (roughly 20 to 25 °C), which is

84

lower than the temperature encountered when it is worn (roughly 32 °C10, 44, 45). This

85

necessitates measurements of K at these two temperatures to accurately estimate dermal

86

exposure from stored clothing.

87

The features and disadvantages of the various methods that have been used to

88

measure y0 or K are summarized in Table 1. The common practice of using a ventilated

89

chamber requires systems to maintain supply air, control the airflow and sample the air

90

concentration, increasing costs. Furthermore, calculating y0 from an equilibrium

3



Page 4 of 30

91

concentration (yequ, µg/m3) can be quite time-consuming, while uncertainty in the

92

convective mass transfer coefficient (hm, m/s) in ventilated chambers46 will reduce the

93

accuracy of the measured results.33 Finally, no method in the literature can

94

simultaneously determine y0 and K in a single test run.

95

The objective of the present study is to develop a more rapid, accurate and

96

convenient method to simultaneously determine y0 and K for selected indoor SVOC

97

sources and clothing pairs. The method has been applied to two different types of PVC

98

flooring, each a source of phthalates, and a cotton T-shirt.

99

2. Method principle and development

100

To simultaneously measure y0 and K in an experiment, the SVOC source material

101

and a sample of clothing are placed together in a chamber. Figure 2 (a) is a schematic of

102

SVOC mass transfer if the chamber resembles those used in traditional methods (i.e.,

103

those listed in Table 1 excepting the SPME-based method), and a sample of the clothing

104

is hung in the chamber. To simplify the analysis, the following assumptions are often

105

made: (1) air in the chamber is well-mixed except in the boundary layers; (2) the

106

materials in the experiment are homogenous; (3) K for the clothing and y0 for the source

107

material are constant at a given temperature. Given these assumptions, a mass transfer

108

model describing the process shown in Figure 2 (a) is expressed as eqs (S5)-(S11) in

109

Section S4. Measuring the gas-phase SVOC concentration in the chamber air and

110

clothing-sorbed SVOC concentration at equilibrium, y0 and K can be obtained by eqs

111

(S12) and (S13). However, even for moderate values of K, weeks are needed to reach

112

equilibrium (e.g., 15 days for a compound with log (K) = 5.6 in measurements by

113

Morrison et al.12).

114

A transient method (e.g., C-history method5, 47), which only uses the early stage

115

concentrations of an SVOC in the gas-phase (Ca, µg/m3) and sorbed to clothing (Cm,

116

µg/m3) can shorten the time required for measurements. It is seen from eqs (S14) and

117

(S15) that, if the history of Ca and Cm is measured, y0 and K are of the functional forms:

118

y 0 = f1 ( hm , e , hm , c , hm , w , K w , Q , K )

(1)

119

K = f 2 ( hm , e , hm , c , hm , w , K w , Q , y 0 )

(2)

120

Here, hm,e, hm,c and hm,w are convective mass transfer coefficients to the source 4


Page 5 of 30


121

material, clothing material and chamber wall surface, respectively, m/s; Kw is the SVOC

122

partition coefficient between chamber wall and air, m; and Q is the air flow rate through

123

the chamber, m3/s. hm,e, hm,c, hm,w and Kw are commonly estimated by empirical

124

correlations or additional measurements.22, 36, 37 If hm,e, hm,c, hm,w, Kw and Q are known, y0

125

and K can be obtained because the equations for both parameters are closed. It is

126

desirable to eliminate the effects of uncertainty in hm,e, hm,c, hm,w and Kw on the measured

127

values of K and y0. In addition, if Q is zero (a sealed chamber is used) the complexity and

128

cost of the experiment would be substantially decreased.

129

With these considerations in mind, Fujii et al.23 developed a small chamber, referred

130

to as a passive flux sampler (PFS), to measure the flux of SVOCs emitted from indoor

131

sources of SVOCs. The PFS was a very short cylinder whose diameter was far larger than

132

its height (i.e., height/diameter < 0.025). The SVOC source material and sorption

133

material (activated carbon) were placed on the top and bottom surfaces, respectively. In

134

this way, the sorption area of the chamber wall was far less than the emission area of the

135

SVOC source material or sorption area of the sorbing material (i.e., wall sorption

136

area/emission area < 0.1). Consequently, the sorption of SVOC on the chamber wall was

137

negligible and the impact of Kw could be ignored. Since the chamber was sealed and the

138

chamber air was still during experiments, the transport of SVOCs from the source

139

material to the sorption material was assumed to be governed by molecular diffusion and

140

follow Fick’s Law. In this way, the requirement to accurately know hm,e, hm,c, hm,w and Q

141

was also eliminated. However, Fujii et al.23 did not consider the transient behavior of the

142

mass transfer process and assumed that the concentration of the SVOC in the sink

143

material (Cm) was zero. Hence, their method was a useful approach but cannot be directly

144

used for the simultaneous measurement of y0 for an SVOC source material and K for a

145

clothing sample.

146

To develop a new method which overcomes the aforementioned limitation, we

147

present the following mass transfer analysis. A piece of clothing and the SVOC source

148

material are placed in a sealed chamber (similar to the PFS) as shown in Figure 2 (b).

149

SVOCs emitted from the source material diffuse to the clothing sample where they are

150

absorbed onto its exposed surface. With reference to eqs (S1)-(S3), the governing

151

equation describing SVOC diffusion in the clothing is expressed as:

5



∂Cm ∂2Cm =D 2 ∂t ∂x

152

Page 6 of 30

(3)

153

where t is time, s; x is the distance to the surface of the clothing sample, m; and D is the

154

effective diffusion coefficient of the SVOC in the clothing material (see eq (S3)), m2/s.

155 156

The SVOC sorption rate on clothing equals the SVOC emission flux from the source material:

−D

157

∂Cm ∂x

= Da x =δ

y − Cm ( x = δ ) K y0 − Cs = Da 0 L L

(4)

158

where δ is the thickness of clothing material, m; L is the thickness of circular chamber, m;

159

Cs is the concentration of the SVOC in the air immediately adjacent to the clothing

160

surface, µg/m3; and Da is the SVOC’s diffusion coefficient in air, m2/s (which can be

161

estimated using empirical correlations48).

162 163

At x=0, since the clothing is resting on a SVOC-impermeable surface, the boundary condition is:

∂Cm ∂x

164

=0

(5)

x =0

165

The lumped parameter method can be employed to simplify the mass transfer

166

problem described by eqs (3)-(5), provided that the ratio of the resistance to diffusion

167

within the clothing to across the air gap between the source’s surface and the clothing’s

168

surface is less than 0.1.49, 50 This ratio has been defined by Xu and Zhang50 and named the

169

“Little number”51:

Lt =

170

D aδ DLK

(6)

171

It should be noted that Da/L in eq (6) is replaced by hm (convective mass transfer

172

coefficient) in Zhang et al.51 Under this condition, the concentration in the clothing is

173

considered to be uniform and eqs (3)-(5) can be simplified as:

174

V

dC m y − Cm K dC m Da y0 − C m K = ADa 0 or = dt L dt δ L

(7)

175

where A is the exposed area of clothing or emission area of the SVOC source material

176

(which are the same in the chamber), m2; V is the volume of the clothing, m3; and V=Aδ.

177

The initial condition of eq (7) is:

6


Page 7 of 30


Cm = Cm,0

178 179 180

where Cm,0 is the initial concentration of the target SVOC in the clothing sample. We derived the analytical solution to eqs (7) and (8) as follows:

C m = C m ,0

181 182

− Da t   δ LK + ( Ky 0 − C m ,0 )  1 − e   

(9)

If Cm,0 in eq (9) is zero, we have: − Da t   C m = Ky0  1 − e δ LK  = C equ (1 − e − Nt )  

183 184

(8)

(10)

where Cequ = Ky0 and N = Da/δLK.

185

If the clothing-sorbed concentration (Cm) of a target SVOC is measured at a series of

186

times early in the process, N and Cequ can be obtained by fitting eq (10) to these measured

187

points. Then K and y0 are calculated by the following equations:

K =

188

Da δ LN

y0 =

189

Cequ K

(11) (12)

190

Eqs. (9)-(12) describe the principle of the present method. Since this method

191

involves simultaneously determining y0 and K based on measurements of Cm in a time

192

series (a “Cm-history”) via extraction of clothing samples, we call this the “Cm-history

193

method”. In contrast to the methods outlined in Table 1, which generally need to measure

194

a series of Ca and Cm until equilibrium is reached, the present method only measures Cm

195

at the early stage of the process. Therefore, it has the following salient features: (1) less

196

time-consuming, (2) more accurate, and (3) easier to implement. These benefits will be

197

examined in greater detail in the following sections.

198

3. Experiments

199

3.1 Experimental system

200

Based on the above analysis, we designed a sealed test chamber as illustrated in

201

Figures 3a (schematic) and 3b (photo). From eq (10), it is seen that the time required for

202

an experiment decreases with increasing N. Towards this end, two pieces of the SVOC

203

source material are placed on circular rings symmetrically arranged on each side of the 7



204

clothing sample. On either side, the distance between the surface of the source and

205

surface of the clothing (L in eq (10)) is very small. In this way, both surfaces of the

206

clothing sample are exposed to SVOCs with the same sorption rate. We can treat the

207

sorption process as single-side sorption on half of the clothing material. For this scenario,

208

δ in eqs (10) and (11) is replaced by δ/2 (δ/2 is expressed as d in the following analysis).

209

The circular rings were made of FR4 glass fiber; each had an internal diameter of 80

210

mm, an external diameter of 110 mm and a thickness, L, of 2 mm. The thickness defines

211

the distance between the surface of the source and surface of the clothing and was chosen

212

based on the precision with which the circular ring could be machined (±0.05 mm). The

213

interior surface area (exposed wall) of the circular ring has a surface area (As) that is far

214

less than the area of a single-side of the clothing sample (A), i.e., As/A < 0.1, and sorption

215

of SVOCs on the chamber wall can be neglected. Other elements of the new chamber are

216

two flat plates, also made of FR4 glass fiber, each with a diameter of 110 mm and a

217

thickness of 2 mm, as well as several bolts and nuts. The flat plates are arranged on top of

218

each piece of SVOC source material, sealing the chamber and maintaining the flatness of

219

the source material. Bolts and nuts are used for sealing the chamber by tightening the two

220

flat plates. Given that the chamber is symmetrical, thin and based on transport via

221

diffusion, the chamber is referred to as the Symmetrical Thin Diffusion Chamber

222

(STDC).

223

No SVOCs were detected in samples of the FR4 glass fiber. In order to control the

224

temperature of the STDC, it was placed in a 30 L chamber immediately after installing

225

the pieces of source material, clothing sample and sealing. The temperature of the air

226

within the 30 L chamber was controlled using a water bath (32 ± 0.5 °C and 25 ± 0.5 °C),

227

and the measured temperature of the STDC was close to this temperature within

228

approximately 0.5 hours.

229

3.2 Source material and clothing

230

Two types of 5 mm thick homogeneous polyvinyl chloride (PVC) flooring,

231

purchased from a local building materials store and designated as PVC 1 and PVC 2,

232

were used as sources of SVOCs. A few days before an experiment, pieces were cut from

233

the targeted PVC flooring material (90 mm in diameter), wiped on both sides using

234

medical gauze soaked with deionized water and stored at room temperature. The 8


Page 8 of 30

Page 9 of 30


235

phthalate contents of PVC 1 and PVC 2 were quantified by GC/MS analysis (extracts

236

were obtained using a Soxhlet apparatus, see Section S2). The analysis indicated that

237

PVC 1 contained only DEHP at a mass fraction of 18.2%, while PVC 2 contained three

238

phthalates: DEHP, DiBP and DnBP at respective mass fractions of 5.1%, 4.3% and 4.4%.

239

Pure cotton shirts (> 95% cotton) were chosen for the test material, since cotton is a 52

240

frequently used clothing fabric. These were purchased from a local online shop

,

241

selecting the most popular product. The shirts were cut into circles (110 mm diameter)

242

immediately after purchase, wrapped in tinfoil and stored at room temperature. The

243

thickness of the cotton shirts was measured to be 0.58 mm by GB/T 3820-1997.53

244

3.3 Experimental procedure

245

An experiment began (time zero) when the STDCs were placed in the 30 L chamber.

246

Twelve hours after the experiment began, three STDCs containing PVC 1 and three

247

containing PVC 2 were taken from the chamber; the cloth samples they contained were

248

immediately removed. A piece 80 mm in diameter was cut from the middle of each cloth

249

piece and placed in a Soxhlet flask for extraction and analysis (see Section S2). This

250

procedure was repeated at 24, 48, 120, 240, 360, 480, 600 and 720 hours. Given that

251

sorption of DiBP and DnBP on clothing reaches equilibrium in about 20 to 120 hours (as

252

observed in this study), in the case of PVC 2 the same procedure was repeated 1, 2, 3, 6

253

and 9 hours after an experiment began. Additionally, for the experiment at 25 °C, to

254

provide results suitable for fitting eq (10) to the experimental data, the procedure was

255

also repeated for STDCs containing PVC 1 and PVC 2 at 960, 1200, and 1680 hours.

256

Given this experimental procedure, 27 (3 ×9) STDCs containing PVC 1 and 42 (3 ×14)

257

containing PVC 2 were placed in the 30 L chamber at 32 °C; at 25 °C, the numbers were

258

36 (3 ×12) STDCs containing PVC 1 and 51 (3 ×17) containing PVC 2. In addition, three

259

STDCs without PVC were placed in the 30 L chamber at 32 °C (field blanks); the same

260

was done at 25 °C.

261

3.4 Quality assurance and control (QA/QC)

262

A nine point calibration was prepared based on 1 µL injections of standard solutions

263

containing 0.05, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10 and 20 µg/mL of DiBP, DnBP and DEHP. 1

264

µg of benzyl benzoate (BB) was added as an internal standard to 100 µL phthalate 9



265

solutions. DiBP-d4 and DEHP-d4 (1 µg each) were also added to 100 µL phthalate

266

solutions as recovery standards. The phthalate solutions were analyzed using the GC-MS

267

analysis procedures described in Section S2. The ratio of each phthalate’s peak area (Aph)

268

to the BB peak area (ABB) was linearly related (r2 > 0.99) to the ratio of each phthalate’s

269

amount (mph) to the BB amount (mBB). The slope, k, of the linear relationship (i.e.,

270

Aph/ABB = k·mph/mBB) was used to determine the amount of each phthalate extracted from

271

the samples. In instances when the measured Aph/ABB in the extracts was higher than 2k,

272

the extract was diluted and reanalyzed. The method detection limit (MDL) was calculated

273

using the GC-MS’s detection limit (i.e., signal-to-noise ratio of 3). The limit of

274

quantitation (LOQ) was 0.05 µg/mL for a 1 µL injection (i.e., 0.05 ng); below this level

275

the calibration line was no longer linear.

276

Before assembling the STDCs, their circular rings were soaked three times (2 hours

277

each time) in pure CH2Cl2. Small amounts of DnBP, DiBP, and DEHP were detected in

278

the lab blanks (Soxhlet extraction but without cloth pieces in the extraction flask), field

279

blanks (cloth samples from STDCs without PVC flooring) and just-purchased samples of

280

clothing. These were lower than the LOQ and treated as negligible since the amount of

281

phthalates in exposed samples was at least 3 times higher than the LOQ (at least 10 times

282

higher than the LOQ for most samples). Note: this supports the assumption used to derive

283

eq (10).

284

Recoveries from cloth samples were determined by spiking clothing with DiBP-d4

285

and DEHP-d4 (250 µg each) prior to Soxhlet extraction. The recovery of DiBP-d4 (74% -

286

127 %, averaging 85%) was used to adjust the DiBP and DnBP results; that of DEHP-d4

287

(75% - 123%, averaging 83%) was used to adjust the DEHP results. The precision for the

288

triplicate samples was within 20% of the mean.

289

Detailed information regarding chemicals used in the analysis and mathematical

290

tools are provided in Sections S1 and S3.

291

4. Results

292

4.1 K and y0

293

Figure 4 displays the measured concentrations of the targeted phthalates in the

294

clothing at different sampling times. More specifically, the measured values are plotted

10


Page 10 of 30

Page 11 of 30


295

for DiBP and DnBP at 32 °C (Figure 4a); DiBP and DnBP at 25 °C (Figure 4b); DEHP at

296

32 °C (Figure 4c); and DEHP at 25 °C (Figure 4d). Each point represents the average

297

value of three samples, and the error bar represents the upper or lower bound of each

298

point. The nonlinear curves that have been fit to these sets of measured values are also

299

displayed in Figure 4, as well as the fitting equation (applying eq (10)). To facilitate an

300

evaluation of the goodness of fit, Figures 4 (a) and (b) contain only a subset of the results

301

for DiBP and DnBP; the full results can be found in Figures S3 (a) and (b). There is very

302

good agreement between the experimental results and fitted curves (r2>0.90) for all cases.

303

Results from the nonlinear curve fitting are listed in Table S1. Having obtained a best-fit

304

curve, the two targeted parameters, K and y0, were estimated using eqs (11) and (12).

305

When calculating K at 25 °C, the value used for the gas-phase diffusion coefficient Da of

306

DiBP and DnBP was 4.21×10-6 m2/s, while for DEHP the value used was 3.37×10-6

307

m2/s.54 The relative deviations of Da between these values and the values estimated by

308

empirical correlations (4.50 × 10-6 m2/s for DiBP and DnBP, 3.65 × 10-6 m2/s for DEHP at

309

25 °C) are less than 10%.48, 55, 56 When calculating K at 32 °C, the value used for Da was

310

estimated using the following empirical relationship:48 1.75

311

Da  T  =  Da,0  T0 

(13)

312

where Da,0 is the gas-phase diffusion coefficient at 25 °C; T is the temperature, K; and

313

T0=298 K (i.e., 25 °C). Table 2 lists the values of K and y0 determined in this manner for

314

DEHP, DiBP and DnBP at 25 °C and 32 °C.

315

It should be noted that the value of K determines the time required to reach

316

equilibrium for the sorption process (tequ). If we assume that the sorption process is close

317

to equilibrium when Cm reaches 95% of its equilibrium concentration (Cequ), tequ can be

318

approximated as 3N-1 (i.e., 3δLK/Da) according to eq (10) -- tequ increases linearly with

319

increasing K. Based on the measured values of K listed in Table 2: for DEHP, tequ values

320

were calculated to be about 9400 hours at 25 °C and 3880 hours at 32 °C; for DiBP, tequ

321

values were calculated to be about 58 hours at 25 °C and 22 hours at 32 °C; and for

322

DnBP, tequ values were calculated to be about 41 hours at 25 °C and 122 hours at 32 °C.

323

This is consistent with the measurements shown in Figure 4, which indicates that for

324

DEHP equilibrium is not reached after more than 720 hours, while for DiBP and DnBP 11



325

equilibrium is reached in 20 hours to 120 hours.

326

4.2 Assessment of accuracy

Page 12 of 30

327

Based on error propagation theory, δCequ and δN (directly obtained in the process of

328

nonlinear curve fitting) can be used to calculate the standard deviations of K and y0.

329

Specifically, δK and δy0 can be calculated as:

δK

2

2

δN  δL =   +  K  N   L

330

δ y0

331

y0

2  δ K   δ C equ =   +  K   C equ

(14)

  

2

(15)

332

where δL is the error of the thickness of the circular rings (L) (δL is equal to 0.05 mm as

333

aforementioned).

334

The relative deviations for K and y0 (RDK = δK/K × 100%, RDy = δy0/y0 × 100%)

335

obtained in this fashion are listed in Table 2. For all cases, the relative deviations of K and

336

y0 are less than 20% and 25%, respectively. Also noteworthy in Table 2 are the values of

337

K for DEHP partitioning between cotton and air measured using samples from either

338

PVC 1 or PVC 2. At 25 °C the value obtained by the present method is 6.6 × 107 in the

339

case of PVC 1 and 6.9 × 107 in the case of PVC 2; at 32 °C, the values for K are 2.8 × 107

340

(PVC 1) and 2.9 × 107 (PVC 2). The close agreement, at a given temperature, between K

341

measured using PVC samples with quite different concentrations of DEHP gives

342

confidence in the method.

343

Table S2 compares results for y0 obtained by the present method with results

344

obtained by the passive flux sampler method (PFS)23 and the newly developed SPME-

345

based method38. The difference between the present method and the PFS method is less

346

than 10% in all cases (see Section S5).The measurements of y0 using the SPME-based

347

method38 were limited to DEHP in PVC 1 and PVC 2 at 25 °C. For both types of PVC,

348

the difference between the present method and SPME method is less than 10% (see Table

349

S2), further supporting the accuracy of the present method.

350

4.3 Validation of assumption for model simplification

351

In Section 2, we assumed that resistance to diffusion within the clothing was

12


Page 13 of 30


352

negligible (i.e., Lt < 0.1), which allowed the mass transfer problem (eqs (3)-(5)) to be

353

simplified (eq (9)). To check this assumption, a non-simplified model that includes

354

resistance to diffusion within the clothing is presented in Section S6 (see eqs (S21)-

355

(S25)). The results (see details in Table S3) using this non-simplified model indicate that

356

the initial assumption (Lt = Daδ/DLK < 0.1) was valid.

357

The sorption of SVOCs onto the surface of the chamber walls (i.e., interior surfaces

358

of circular rings) was also assumed to be negligible. A mass transfer model that includes

359

the sorption to the chamber walls is presented in Section S7. The results show that the

360

relative difference between Cm obtained by the non-simplified model and Cm obtained by

361

the simplified model (i.e., eq (10)) is less than 5% (less than 1% for most time).

362

Therefore, neglecting sorption to the chamber walls was a reasonable assumption.

363

5 Discussion

364

5.1 Comparisons with K measured by other methods

365

Bi et al.41 attempted to measure K for DEHP partitioning between cotton and air at

366

21 °C and 30 °C. However, as noted by the authors, there was likely insufficient time for

367

the fabric samples to reach equilibrium. Their estimated values were about 15 times

368

lower than K measured for DEHP (32 °C) in the present study. Morrison et al.13 measured

369

K for DnBP in three samples of cotton clothing at 25 °C. The reported results were 3.6 ×

370

106, 3.7 × 106 and 4.4 × 106 for an undershirt, an outershirt and jeans. These values are

371

about three times higher than the value of K (1.1 × 106 at 25 °C) obtained in the present

372

study. The densities of the undershirt, outershirt and jeans were 0.45 g/cm3, 0.47 g/cm3

373

and 0.71g/cm3, respectively, while that of the T-shirt in the present study was 0.29 g/cm3.

374

Adjusting for clothing mass when calculating the clothing partition coefficient

375

(designated Kmass; see eq 2 in Morrison et al.13) yields values that are in good agreement;

376

at 25 °C, Kmass values in Morrison et al.13 were 8.0 m3/g (undershirt), 7.7 m3/g (outershirt)

377

and 6.2 m3/g (jeans) compared to a Kmass of 3.8 m3/g (T-shirts) in the present study.

378

5.2 Temperature dependence of K and y0

379

Table 2 shows that temperature has a strong influence on K and y0. The van’t Hoff

380

equation is often used to describe the temperature dependence of partition coefficients.48

381

Table S4 presents van’t Hoff constants for K and y0 (which can also be viewed as a 13



382

partition coefficient) for DiBP, DnBP and DEHP. In this table ∆H12 is the change in

383

enthalpy associated with the phase change from clothing to air; ∆H23 is the change in

384

enthalpy associated with the phase change from the PVC source to air (eqs (S36) and

385

(S37)). ∆H12 and ∆H23 are helpful in understanding the energies of the target SVOCs

386

interacting with the sorbing and source materials.48,

387

comparisons with other studies are presented in Section S8 and Table S4. Reassuringly,

388

the results obtained for DEHP using two different flooring materials (PVC 1 and PVC 2)

389

are reasonably close. Nonetheless, these results should be interpreted with caution.

390

Measurements over a wider range of temperatures are necessary to accurately assess the

391

temperature dependence of these parameters.

392

5.3 Minimum length of time and number of samples to reliably measure K and y0

57

Details of this analysis and

393

A salient feature of the present method is that it is more rapid than traditional

394

methods since it can be terminated before the sorption process reaches equilibrium.

395

Utilizing the measured data, Section S9 provides a rough analysis of the minimum length

396

of time (tmin) required for reliable measurements of K and y0. As shown there, a criterion

397

for reliable measurements using the present method is that the product of “tmin” and N, as

398

defined in eq (10), is larger than 0.5 (see eq (S38)). A further criterion for accurate

399

measurements is a sufficiently large number of sampling points (nsamples). An analysis of

400

the sensitivity of K to the parameters tmin and nsamples is briefly presented in Section S10.

401

The results (detailed in Table S5) show that N·tmin > 1, nsamples=24, and three replicates for

402

each point are sufficient to insure a deviation in K of less than 10% from its “true” value.

403

Further studies are required to determine the optimal values for tmin, nsamples, and the time

404

interval between contiguous measurements.

405

As mentioned in the Section 1, traditional methods for measuring K require the

406

SVOC absorption by clothing to reach equilibrium. With reference of eq (10), the time

407

required to reach equilibrium, tequ, is approximately 3/N = 3dLK/Da or 3dK/hm (based on

408

Cm > 0.95 Cequ). Using the present method, the minimum time required for measurements

409

is 1/6 of that for traditional methods (i.e., (0.5/N)/(3/N)). Even for the case in which hm in

410

a ventilated chamber is fairly large (e.g., an hm of 7.50 mm/s in the chamber used by

411

Morrison et al.13), the time required for measurements is still longer than the minimum

412

time for the present method (tequ = 400 dK when hm = 7.50 mm/s, while ts < 297 dK given 14


Page 14 of 30

Page 15 of 30


413

that Da/L > 1.69 mm/s).

414

5.4 Limitations

415

As presently designed, the STDC has some inherent limitations. First, it is difficult

416

to control RH inside the device. Although relative humidity (RH) is not anticipated to

417

have a significant effect on SVOC emissions from PVC floorings42, it may influence

418

sorption of SVOCs in clothing material. Second, it is only suitable for flat, homogeneous

419

sources of SVOCs. Third, the accuracy of the method is dependent on the accuracy with

420

which L, the distance between the surface of the cloth and the surface of the PVC

421

flooring, is known. This, in turn, depends on how much the two rings “compress” the

422

cloth that is held between them, as well as the roughness of the cloth. We estimate that

423

compression reduces the thickness of the cloth in the present study by about 0.03 mm,

424

resulting in about a 2% decrease in L. The roughness of the cloth used in this study is on

425

the order of 0.1 mm and therefore appears to have a larger impact on L.

426

Regarding the method itself, an estimation of K is necessary to estimate tmin. Hence,

427

the optimal sampling period is unknown until after the fact. Additionally, for compounds

428

with large values of K, the requisite time to make reliable measurements (tmin) can be

429

long (e.g., for DEHP more than 1680 hours at 25 °C and 720 hours at 32 °C). However,

430

this is still significantly shorter than waiting until equilibrium is achieved (for DEHP

431

more than 9400 hours at 25 °C and 3880 hours at 32 °C). Moreover, even though the

432

effects of hm,e, hm,c, hm,w and Kw are eliminated by employing the STDC, the parameter Da

433

is still required. Based on eq (11), K is linearly dependent on Da. The uncertainty of Da

434

estimated by empirical correlations48 is anticipated to be less than 10%.

435

There are a number of issues that warrant further study. The T-shirt sample tested in

436

this study had never been worn. The measured K is likely to be altered if the clothing

437

were worn and soiled with skin oils.12 Additionally, applying the Cm-history method to

438

other clothing materials (e.g., silk, wool, linen, polyester) would broaden understanding

439

of how K varies with the nature of the cloth. Further examination of K and y0, over a

440

wider range of temperatures, source materials and clothing fabrics would test the

441

applicability of the van’t Hoff expression to other SVOC source materials and other types

442

of fabrics. This, in turn, would improve understanding of how temperature, humidity, the

443

nature of the material and the SVOC concentration in the material influence the enthalpy 15



444

and entropy associated with phase change from source material to air (or from air to the

445

clothing material). Design changes in the STDC may lead to improved control of RH

446

within the device and increased ease of use, facilitating routine measurements. The

447

present method has been applied to measurements of only three phthalates; its general

448

applicability to other SVOCs requires further study. Finally, additional measurements are

449

required to more fully evaluate the accuracy of the Cm-history method, especially in the

450

case K. Inter-lab comparisons using the present method in combination with other

451

methods would be valuable in this regard.

452 453

Associated content

454

Supporting Information

455 456

Additional information as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.

457 458

Author information

459

Corresponding Author *

460

E-mail: [email protected]; Phone: +86 10 62772518; Fax: +86 10

461

62773461; Address: Department of Building Science, Tsinghua University, 100084,

462

Beijing, China

463

Note

464

The authors declare no competing financial interest.

465 466

Acknowledgments

467

This work was supported by the Natural Science Foundation of China (Grant Nos.

468

51136002 and 51420105010), Tsinghua University’s Initiative for Scientific Research

469

(Grant No. 20121088010) and the 12th Five-year National Key Technology R&D

470

Program of China (Grant No. 2012BAJ02B03). We thank Prof. John C. Little of Virginia

471

Tech, USA and Dr. Mengyan Gong of National Institute of Standards and Technology 16


Page 16 of 30

Page 17 of 30

472


(NIST), USA for helpful discussions.

473 474

References

475

(1)

476

alkylphenols, pesticides, polybrominated diphenyl ethers, and other endocrine-disrupting

477

compounds in indoor air and dust. Environ. Sci. Technol. 2003, 37 (20), 4543-4553.

478

(2)

479

Semivolatile organic compounds in homes: strategies for efficient and systematic

480

exposure measurement based on empirical and theoretical factors. Environ. Sci. Technol.

481

2014, 49 (1), 113-122.

482

(3)

483

indoor exposure to semivolatile organic compounds. Indoor Air 2015, 25 (3), 285-296.

484

(4)

485

environments. Atmos. Environ. 2008, 42 (40), 9018-9040.

486

(5)

487

estimating solid-phase diffusion coefficients and material/air partition coefficients of

488

SVOCs. Atmos. Environ. 2014, 89, 76-84.

489

(6)

490

2009, 43 (1), 153-169.

491

(7)

492

settled dust indoors. Atmos. Environ. 2010, 44 (30), 3609-3620.

493

(8)

494

between air and indoor surfaces and its influence on exposure. Atmos. Environ. 2012, 55,

495

347-356.

496

(9)

497

tnteraction between SVOCs and airborne particles. Aerosol Sci. Techol. 2013, 47 (2),

498

125-136.

499

(10)

500

pathways. Indoor Air 2012, 22 (5), 356-77.

501

(11)

Rudel, R. A.; Camann, D. E.; Spengler, J. D.; Korn, L. R.; Brody, J. G. Phthalates,

Dodson, R. E.; Camann, D. E.; Morello-Frosch, R.; Brody, J. G.; Rudel, R. A.

Liu, C.; Zhang, Y. P.; Benning, J. L.; Little, J. C. The effect of ventilation on

Weschler, C. J.; Nazaroff, W. W. Semivolatile organic compounds in indoor

Liu, X. Y.; Guo, Z. S.; Roache, N. F. Experimental method development for

Weschler, C. J. Changes in indoor pollutants since the 1950s. Atmos. Environ.

Weschler, C. J.; Nazaroff, W. W. SVOC partitioning between the gas phase and

Liu, C.; Morrison, G. C.; Zhang, Y. P. Role of aerosols in enhancing SVOC flux

Liu, C.; Shi, S. S.; Weschler, C. J.; Zhao, B.; Zhang, Y. P. Analysis of the dynamic

Weschler, C. J.; Nazaroff, W. W. SVOC exposure indoors: fresh look at dermal

Weschler, C. J.; Bekö, G.; Koch, H. M.; Salthammer, T.; Schripp, T.; Toftum, J.;

17



502

Clausen, G. Transdermal uptake of diethyl phthalate and di(n-butyl) phthalate directly

503

from air: experimental verification. Environ. Health Perspect. 2015, 123 (10), 928-934.

504

(12)

505

methamphetamine on clothing, toy fabrics, and skin oil. Indoor Air 2015, 25 (4), 405-

506

414.

507

(13)

508

to cotton clothing. Atmos. Environ. 2015, 115, 149-152.

509

(14)

510

pollution in China: a review. Chinese Sci. Bull. 2010, 55 (15), 1469-1478.

511

(15)

512

methods to estimate potential exposure to semivolatile organic compounds in the indoor

513

environment. Environ. Sci. Technol. 2012, 46 (20), 11171-11178.

514

(16)

515

phase chemicals: transient model development, evaluation, and application. Indoor Air

516

2014, 24 (3), 292-306.

517

(17)

518

wipes: estimating exposure from dermal absorption. Environ. Sci. Technol. 2014, 48 (13),

519

7428-7435.

520

(18)

521

Zhang, Y. P. Phthalate metabolites in urine samples from Beijing children and

522

correlations with phthalate levels in their handwipes. Indoor Air 2015, 25 (6), 572-581.

523

(19)

524

found in indoor air. Environ. Sci. Technol. 2014, 48 (2), 1230-1237.

525

(20)

526

pathways to airborne semivolatile organic compounds (SVOCs) in residences. Environ.

527

Sci. Technol. 2014, 48 (10), 5691-5699.

528

(21)

529

T.; Toftum, J.; Clausen, G. Role of clothing in both accelerating and impeding dermal

530

absorption of airborne SVOCs. J. Exposure Sci. Environ. Epidemiol. 2015,

531

DOI:10.1038/jes.2015.42.

532

(22)

Morrison, G.; Shakila, N. V.; Parker, K. Accumulation of gas-phase

Morrison, G.; Li, H. W.; Mishra, S.; Buechlein, M. Airborne phthalate partitioning

Wang, L. X.; Zhao, B.; Liu, C.; Lin, H.; Yang, X.; Zhang, Y. P. Indoor SVOC

Little, J. C.; Weschler, C. J.; Nazaroff, W. W.; Liu, Z.; Cohen Hubal, E. A. Rapid

Gong, M. Y.; Zhang, Y. P.; Weschler, C. J. Predicting dermal absorption of gas-

Gong, M. Y.; Zhang, Y. P.; Weschler, C. J. Measurement of phthalates in skin

Gong, M. Y.; Weschler, C. J.; Liu, L. P.; Shen, H. Q.; Huang, L. H.; Sundell, J.;

Weschler, C. J.; Nazaroff, W. W. Dermal uptake of organic vapors commonly

Shi, S. S.; Zhao, B. Modeled exposure assessment via inhalation and dermal

Morrison, G. C.; Weschler, C. J.; Bekö, G.; Koch, H. M.; Salthammer, T.; Schripp,

Xu, Y.; Little, J. C. Predicting emissions of SVOCs from polymeric materials and

18


Page 18 of 30

Page 19 of 30


533

their interaction with airborne particles. Environ. Sci. Technol. 2006, 40 (2), 456-461.

534

(23)

535

on emission of phthalate esters from plastic materials using a passive flux sampler.

536

Atmos. Environ. 2003, 37 (39-40), 5495-5504.

537

(24)

538

from PVC and other materials. Indoor Air 2004, 14 (2), 120-128.

539

(25)

540

floor coverings and complete floor structures. Indoor Air 2004, 14 (s8), 98-107.

541

(26)

542

flame retardants using a passive flux sampler. Atmos. Environ. 2007, 41 (15), 3235-3240.

543

(27)

544

ethylhexyl)phthalate (DEHP) from pristine DEHP and plasticized PVC. Polym. Degrad.

545

Stabil. 2010, 95 (9), 1789-1793.

546

(28)

547

and BDE 209 to indoor air and their impact on urban air quality. Sci. Total Environ. 2014,

548

470-471, 527-535.

549

(29)

550

delivery vehicle for diethylphthalate and di-n-butylphthalate: predictable boundary layer

551

concentrations and emission rates. Sci. Total Environ. 2014, 494-495, 299-305.

552

(30)

553

in PVC flooring and air using a closed-chamber SPME method. Build. Environ. 2016, 95,

554

283-290.

555

(31)

556

PCBs under low volume conditions. Chemosphere 2015, 118, 65-71.

557

(32)

558

measurement of SVOC emission characteristics in experimental chambers. PloS One

559

2013, 8 (8), e72445.

560

(33)

561

accurate determination of the key SVOC emission or sorption parameters of indoor

562

materials. Build. Environ., 2016, 95, 314-321.

563

(34)

Fujii, M.; Shinohara, N.; Lim, A.; Otake, T.; Kumagai, K.; Yanagisawa, Y. A study

Afshari, A.; Gunnarsen, L.; Clausen, P. A.; Hansen, V. Emission of phthalates Wilke, O.; Jann, O.; Brödner, D. VOC‐and SVOC‐emissions from adhesives,

Ni, Y.; Kumagai, K.; Yanagisawa, Y. Measuring emissions of organophosphate

Ekelund, M.; Azhdar, B.; Gedde, U. W. Evaporative loss kinetics of di(2-

Cousins, A. P.; Holmgren, T.; Remberger, M. Emissions of two phthalate esters

Schripp, T.; Salthammer, T.; Fauck, C.; Beko, G.; Weschler, C. J. Latex paint as a

Liu, C.; Zhang, Y. P. Characterizing the equilibrium relationship between DEHP

Mull, B.; Horn, W.; Jann, O., Investigations on the emissions of biocides and

Liu, C.; Liu, Z.; Little, J. C.; Zhang, Y. P. Convenient, rapid and accurate

Xiong, J. Y.; Cao, J. P.; Zhang, Y. P. Early stage C-history method: Rapid and

Clausen, P. A.; Hansen, V.; Gunnarsen, L.; Afshari, A.; Wolkoff, P. Emission of di-

19



564

2-ethylhexyl phthalate from PVC flooring into air and uptake in dust: emission and

565

sorption experiments in FLEC and CLIMPAQ. Environ. Sci. Technol. 2004, 38 (9), 2531-

566

2537.

567

(35)

568

temperature on the emission of di-(2-ethylhexyl)phthalate (DEHP) from PVC flooring in

569

the emission cell FLEC. Environ. Sci. Technol. 2012, 46 (2), 909-915.

570

(36)

571

predicting the emission rate of phthalate plasticizer from vinyl flooring in a specially-

572

designed chamber. Environ. Sci. Technol. 2012, 46 (22), 12534-12541.

573

(37)

574

emissions from building materials and its application to exposure assessment. Environ.

575

Sci. Technol. 2014, 48 (8), 4475-4484.

576

(38)

577

and accurately measuring the emission parameter from SVOC source materials.

578

Submitted to Environ. Sci. Technol., 2015.

579

(39)

580

exposure to phthalate plasticizer emitted from vinyl flooring: a mechanistic analysis.

581

Environ. Sci. Technol. 2009, 43 (7), 2374-2380.

582

(40)

583

flooring and crib mattress covers: the influence of temperature. Environ. Sci. Technol.

584

2014, 48 (24), 14228-14237.

585

(41)

586

environments and the influence of temperature: A case study in a test house. Environ. Sci.

587

Technol. 2015, 49 (16), 9674–9681.

588

(42)

589

influence of humidity on the emission of di-(2-ethylhexyl) phthalate (DEHP) from vinyl

590

flooring in the emission cell “FLEC”. Atmos. Environ. 2007, 41 (15), 3217-3224.

591

(43)

592

Primary and Secondary Exposures in Residential Buildings. Ph.D. Dissertation,

593

University of Texas, Austin, US, 2013.

594

(44)

Clausen, P. A.; Liu, Z.; Kofoed-Sorensen, V.; Little, J.; Wolkoff, P. Influence of

Xu, Y.; Liu, Z.; Park, J.; Clausen, P. A.; Benning, J. L.; Little, J. C. Measuring and

Liang, Y. R.; Xu, Y. Improved method for measuring and characterizing phthalate

Cao, J. P.; Zhang, X.; Little, J. C.; Zhang, Y. P. A SPME-based method for rapidly

Xu, Y.; Cohen Hubal, E. A.; Clausen, P. A.; Little, J. C. Predicting residential

Liang, Y. R.; Xu, Y. Emission of phthalates and phthalate alternatives from vinyl

Bi, C. Y.; Liang, Y. R.; Xu, Y. Fate and transfport of phthalates in indoor

Clausen, P. A.; Xu, Y.; Kofoed-Sørensen, V.; Little, J. C.; Wolkoff, P. The

Guerrero, P. A. p-Dichlorobenzene and Naphthalene: Emissions and Related

Lachke, S. A.; Lockhart, S. R.; Daniels, K. J.; Soll, D. R. Skin facilitates Candida

20


Page 20 of 30

Page 21 of 30


595

albicans mating. Infect. Immun. 2003, 71 (9), 4970-4976.

596

(45)

597

under Cold Conditions Two Figures. J. Nutr. 1938, 15 (6), 597-606.

598

(46)

Holman, J. P. Heat Transfer 9th ed.; McGraw-Hill: New York, 2002.

599

(47)

Xiong, J. Y.; Yao, Y.; Zhang, Y. P. C-history method: rapid measurement of the

600

initial emittable concentration, diffusion and partition coefficients for formaldehyde and

601

VOCs in building materials. Environ. Sci. Technol. 2011, 45 (8), 3584-90.

602

(48)

603

Chemistry; John Wiley & Sons Press: New York, 2005.

604

(49)

605

Press: New York, 2011.

606

(50)

607

emissions from building materials. Atmos. Environ. 2003, 37 (18), 2497-2505.

608

(51)

609

controlling airborne organic compounds in the indoor environment: mass‐transfer

610

analysis and applications. Indoor Air 2015, DOI: 10.1111/ina.12198.

611

(52)

612

2015).

613

(53)

614

textiles products. Chinese National Standard, Beijing, China, 1997.

615

(54)

616

Chem. 1968, 40 (7), 1072-1077.

617

(55)

618

in helium. The effect of structure on collision cross sections. J. Phys. Chem. 1969, 73

619

(11), 3679-3685.

620

(56)

621

evaluation of gas phase diffusion coefficients of reactive trace gases in the atmosphere:

622

Volume 2. Diffusivities of organic compounds, pressure-normalised mean free paths, and

623

average Knudsen numbers for gas uptake calculations. Atmos. Chem. Phys. 2015, 15 (10),

624

5585-5598.

625

(57)

Freeman, H.; Nickerson, R. F. Skin and Body Temperatures of Normal Individuals

Schwarzenbach, R. P.; Gschwend, P. M.; Imboden, D. M. Environmental Organic

Incropera, F. P. Fundamentals of Heat and Mass Transfer; John Wiley & Sons

Xu, Y.; Zhang, Y. P. An improved mass transfer based model for analyzing VOC

Zhang, Y. P.; Xiong, J. Y.; Mo, J. H.; Gong, M. Y.; Cao, J. P. Understanding and

http://item.jd.com/1519692213.html# (in Chinese, accessed on November 28,

GB/T 3820. Standard test methods for determination thickness of textiles and

Lugg, G. Diffusion coefficients of some organic and other vapors in air. Anal.

Fuller, E. N.; Ensley, K.; Giddings, J. C. Diffusion of halogenated hydrocarbons

Tang, M. J.; Shiraiwa, M.; Pöschl, U.; Cox, R. A.; Kalberer, M. Compilation and

Dobruskin, V. K. Effect of chemical composition on enthalpy of evaporation and 21



626

equilibrium vapor pressure. http://arxiv.org/abs/1004.3400v1 (accessed on November 28,

627

2015).

628

22


Page 22 of 30

Page 23 of 30

629


TOC art

630 631

23



632

Figures

633

Figure 1. Schematic showing migration of SVOCs from source material to skin surface.

634

y0 is the gas-phase concentration of a given SVOC in equilibrium with its source

635

material; Ca is its gas-phase concentration; K is its clothing/air partition coefficient; and

636

D is its diffusion coefficient in the clothing.

637 638

24


Page 24 of 30

Page 25 of 30


639

Figure 2. Schematic diagram of SVOCs mass transfer. (a) In a traditional chamber with

640

indoor SVOC source material and clothing material; (b) in a sealed chamber with

641

minimized wall area.

642 643

(a)

(b)

644

25



645

Figure 3. (a) Schematic of the symmetrical, thin diffusion chamber (STDC); (b) photo of

646

STDC.

647 648

(a)

649

650 651

(b)

652

26


Page 26 of 30

Page 27 of 30


653

Figure 4. Comparison between curve fitted using eq (10) and experimental data: (a) for

654

DiBP and DnBP at 32 °C, (b) for DiBP and DnBP at 25 °C, (c) for DEHP at 32 °C, and

655

(d) for DEHP at 25 °C.

656 657

(a)

658 659

(b)

27



660 661

(c)

662 663

(d)

664

28


Page 28 of 30

Page 29 of 30


665

Tables

666

Table 1. Summary of various methods that have been used to measure y0 for SVOCs in source materials or K for SVOC and clothing pairs. Methods

Features Measuring y0 of SVOC source material

Disadvantages or advantages

CLIMPAQ or FLEC34,

Placing SVOC source material in CLIMPAQ or FLEC with constant air flow Measuring SVOC concentration at outlet until equilibrium (yequ) y0 = (1+Q/hmA) yequ, where Q is air flow rate, A is source surface area, hm is convective mass transfer coefficient hm = 0.39 mm/s in CLIMPAQ and 1.39 mm/s in FLEC27

Complicated experimental design requiring systems to supply air, control flow, and collect air samples High cost due to large consumption of clean air Long duration: in case of DEHP, equilibrium reached after about 150 days in CLIMPAQ Uncertainty in hm reduces the accuracy of y0

Sandwich-like chamber36, 37

The same principle of CLIMPAQ method but replacing CLIMPAQ by a specially-designed chamber y0 = (1+Q/hmA) yequ hm = 0.20 mm/s~0.47 mm/s

Complicated experimental design and high cost due to the use of a ventilated chamber Uncertainty in hm reduces the accuracy of y0 Shorter duration: equilibrium reached after 2 to 20 days

Placing SVOC source in the sandwich-like chamber that is sealed Monitoring the mass of SVOC accumulated in the SPME coating Calculating y0 by linear curve fitting

Short experimental time: about 1 day High accuracy: relative deviation of y0 less than 5%

35

SPME-based chamber38

sealed

Measuring K of clothing material Traditional chamber12, 13, 43

Placing clothing samples in a ventilated chamber with a constant gasphase SVOC concentration Measuring SVOC concentration of chamber air at exhaust port (Ca) Measuring SVOC concentration in clothing samples until equilibrium (Cm,equ) K = Cm,equ/Ca With hm as large as 7.50 mm/s

29


Complicated experimental design and high cost due to the use of a ventilated chamber Long duration to form a constant gas-phase SVOC concentration in the chamber. (e.g., for DnBP & cotton, 10 days or more) Impractical for SVOC & clothing pairs with very large K due to equilibrium requirement


Page 30 of 30

667 668

Table 2. Estimated K and y0 for DEHP, DiBP and DnBP at 32 °C and 25 °C. Source

32 °C e

SVOCs K×10-6 (-)

material

RDK c(%)

25 °C f

y0×10-1 (µg/m3)

RDy d(%)

K×10-6 (-)

RDK c(%)

y0 (µg/m3)

RDy d(%)

PVC 1 a

DEHP

28

15

0.60

19

66

16

2.1

21

PVC 2 b

DEHP

29

20

0.21

25

69

15

0.77

19

DiBP

0.20

9.6

27

9.8

0.51

6.8

68

7.0

DnBP

0.38

12

15

13

1.1

6.8

36

6.9

669

a

PVC 1 only contains DEHP; mass fraction = 18%.

670

b

PVC 2 contains DEHP, DiBP and DnBP; mass fractions = 5.1%, 4.3% and 4.4%, respectively.

671

c

RDK represents the relative deviation of K, RDK = δK/K × 100%, where δK is the standard deviation of K calculated by eq (14).

672

d

RDy represents the relative deviation of y0, RDy = δy0/y0 × 100%, where δy0 is the standard deviation of y0 calculated by eq (15).

673

e

For PVC 1, n = 27 (9 sampling times, triplicates each time); for PVC 2, n = 42 (12 sampling times, triplicates each time); n is the number of

674

measurements.

675

f

For PVC 1, n = 36 (12 sampling times, triplicates each time); for PVC 2, n = 51 (17 sampling times, triplicates each time).

676

30


Cm-History Method, a Novel Approach to ... - ACS Publications

Recommend Documents