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Asian Journal of Atmospheric Environment - Vol. 8 , No. 4

[ Research Article ]
Asian Journal of Atmospheric Environment - Vol. 8, No. 4, pp.192-201
Abbreviation: Asian J. Atmos. Environ
ISSN: 1976-6912 (Print) 2287-1160 (Online)
Print publication date 31 Dec 2014
Received 17 Apr 2014 Revised 04 Nov 2014 Accepted 07 Nov 2014
DOI: https://doi.org/10.5572/ajae.2014.8.4.192

Identification of Volatile Organic Compounds in Several Indoor Public Places in Korea
Sooyun Seo1), 2) ; Soogil Lim1) ; Kiyoung Lee1), * ; Young-Kyo Seo3) ; Sung-Ok Baek3)
1)Graduate School of Public Health and Institute of Health and Environment, Seoul National University, Seoul 151-742, Korea
2)Korea Institute of Environmental Research, Incheon 404-708, Korea
3)Department of Environmental Engineering, Yeungnam University, Gyeongsan 712-749, Korea

Correspondence to : *Tel:+82-2-880-2735, Email:cleanair@snu.ac.kr

Funding Information ▼

Abstract

A comprehensive profile of volatile organic compounds (VOCs) in public spaces is needed for interpreting indoor air measurements. Seasonal differences in profiles are critical for epidemiological study and risk assessment. The purposes of this study were to establish profiles for individual VOCs in 50 indoor public places in Korea and to determine seasonal variations in their concentrations. Air samples were taken during working hours. Seventy-two of the 91 targeted VOCs were identified using multiple standards. Six VOCs detected in all summer and winter samples were toluene, acetone, m,p-xylenes, ethylbenzene, benzene, and styrene. In summer, methyl ethyl ketone and 1-butanol were also found in all samples. In both seasons, the dominant indoor VOCs were toluene, m,p-xylenes, ethylbenzene, acetone, and isopropyl alcohol. Other chemicals associated with gasoline emissions were dominant in summer. Limonene was dominant only in winter due to the consumption of tangerines. The nine VOCs with the highest concentrations comprised 64.8% and 49.6% of the TVOC in summer and winter, respectively. Comparing two types of adsorbent tube, a single adsorbent tube with Tenax-TA had similar detection performance as a double adsorbent tube with Tenax and Carbotrap.


Keywords: Individual VOC, Indoor air, Adsorbent tube, Seasonal variation, Source

1. INTRODUCTION

Volatile organic compounds (VOCs) are all organic compounds with a boiling point between 50°C and 250°C (WHO, 1989), although there is no clear and widely accepted definition. Although more than 900 VOCs have been identified at detectable levels in indoor air, about 250 chemicals have been recorded at concentrations higher than 1 ppb (Nathanson, 1993). The presence and magnitude of a wide variety of VOCs can be affected by different factors, which increase the complexity of indoor air quality. The VOCs most commonly detected in indoor air are benzene, ethylbenzene, tetrachloroethylene, trichloroethylene, toluene, o-xylene, and m,p-xylenes (Etkin, 1996).

Many researchers are currently using the concept of total volatile organic compounds (TVOC), since the identification and measurement of individual VOCs are expensive and time-consuming and some compounds are difficult to identify or measure because of their very low concentrations. Indoor TVOC and VO Cs concentrations are often significantly higher than those outdoors (Salonen et al., 2009; Brown et al., 1994; Wallace et al., 1991). Many indoor VOC sources exist, including outdoor sources, human activities, building materials, furniture, and other indoor products (Nazaroff and Weschler, 2004; Ekberg, 2003; Edwards et al., 2001; Hodgson et al., 2000; Wolkoff, 1995). Due to various source strengths and ventilation conditions, estimation of indoor VOC concentrations is difficult.

TVOC levels are generally associated with general indoor air quality (Molhave et al., 1997). VOCs are frequently investigated when bad indoor air quality is suspected. Many VOCs are known to have acute and chronic adverse effects on human health and comfort (Molhave, 1991). Some VOCs are associated with the perception of odors. Adverse health impacts include the irritation of mucous membranes, mostly of the eyes, nose, and throat, and long-term toxic reactions of various kinds (ECA-IAQ, 1991). However, it is difficult to conclude that TVOC is a predictor of health risks as they represent only the sum of the mass concentrations of VOCs at the low exposure levels typically encountered in nonindustrial indoor air (Wolkoff and Nielson, 2001; Andersson et al., 1997; Molhave et al., 1997). The results of the few reported controlled human exposure studies and epidemiological studies have confirmed that health effects and outcomes were often inconsistent (Molhave et al., 1997).

Although the TVOC concept is widely used, information on the individual VOCs concentrations typically present in public spaces is needed for the interpretation of indoor air measurements. The purposes of our study were to establish profiles for 91 individual VOCs in indoor public places in Korea and to determine seasonal variations in their concentrations. In addition, statistical analyses were conducted to determine correlations between individual VOCs.


2. MATERIALS AND METHODS
2. 1 Sampling Locations

VOC concentrations were measured in a total of 50 indoor public spaces, which consisted of 17 types of public space, as classified by Korean regulation. The 17 types were underground station (n=2), underground market (n=2), department store (n=7), public bath (n=5), funeral home (n=2), waiting room of a bus terminal (n=2), airport (n=1), waiting room of a port facility (n=1), waiting room of a train station (n=2), library (n=2), museum (n=2), art gallery (n=1), health care facility (n=5), preschool (n=6), elderly welfare facility (n=2), postpartum care facility (n=3), and indoor parking lot (n=5). VOCs were measured in all 50 locations between July and August 2008, and 49 locations were measured between January and February 2009. One preschool was not measured in winter.

2. 2 Sampling Method

At each location, indoor air samples were collected at flow rate of 100 mL/min for 30 min. Two types of adsorbent tubes were used. VOCs at all 50 locations were measured using a Tenax-TA 300 mg with a stainless steel tube (6.35 mm×9 cm, PerkinElmer, Cambridge, Cambridgeshire, UK). The tubes were treated by thermal conditioner (Markes Inc., Llantrisant, Rhondda Cynon Taff, UK) with ultrapure helium at 80 mL/min. Conditioned tubes were blocked by 6.35 mm Swage-lok-type lids with PTFE ferrules and were stored in 50-mL glass vials with a septum.

2. 3 Analysis

The samples were analyzed using a GC/MS (HP 6890/5973) with thermal desorption system (UNITY/ ULTRA, Markes Inc.). The GC column was an Rtx-1 (0.32mm×105m×1.50 μm). In this study, 91 VOCs were identified using four different standards. The standards were 52 Component Indoor Air Standards (Supelco, Bellefonte, PA, USA), EPA VOC Mix 1 containing 12 chemicals (Supelco), EPA VOC Mix 2 containing 13 chemicals (Supelco), and EPA TO-15 Calibration Mix containing 62 chemicals (Supelco). The 91 chemicals are shown in Table 1. All standards were liquid-based, except the EPA TO-15, which was gas-based. Concentrations of individual compounds were determined according to calibration curves. The samples below LOD was estimated as a half of the LOD for the chemicals.

Table 1. 
Physical and chemical characteristics of 91 targeted VOCs.
No. VOCs CAS No. STD①1) STD②2) STD③3) Molecular form MW BP(°C)
1 Difluorodichloromethane 75-71-8 O Cl2CF2 120.91 -30
2 Dichlorotetrafluoroethane 76-14-2 O F2CClCClF2 170.92 4
3 1,3-Butadiene 106-99-0 O CH2CHCHCH2 54.09 -5
4 Ethyl chloride 75-00-3 O C2H5Cl 64.52 12
5 Acetone 67-64-1 O O CH3C(O)CH3 58.08 56
6 Isopropyl alcohol 67-63-0 O O CH3CH(OH)CH3 60.10 80-83
7 Trichlorofluoromethane 75-69-4 O CCl3F 137.37 24
8 1,1-Dichloroethene 75-35-4 O C2H2Cl2 96.94 57
9 Methylene chloride 75-09-2 O O CH2Cl2 84.93 40
10 1,1,2-Trichlorotrifluoroethane 76-13-1 O CF2ClCCl2F 187.38 48
11 Carbon disulfide 75-15-0 O CS2 76.13 46
12 1-Propanol 71-23-8 O C3H8O 60.10 97.2
13 trans-1,2-Dichloroethylene 156-60-5 O C2H2Cl2 96.94 48
14 Methyl tert-butyl ether 1634-04-4 O (CH3)3COCH3 88.15 55
15 1,1-Dichloroethane 75-34-3 O CH3CHCl2 98.96 57
16 Vinyl acetate 108-05-4 O CH3CO2CHCH2 86.09 72
17 Methyl ethyl ketone 78-93-3 O O CH3CH2COCH3 72.12 80
18 cis-1,2-Dichloroethylene 156-59-2 O C2H2Cl2 96.94 60
19 Ethyl acetate 141-78-6 O O CH3CO2C2H5 88.11 77
20 Hexane 110-54-3 O O CH3(CH2)4CH3 86.18 69
21 Chloroform 67-66-3 O O CHCl3 119.38 62
22 Tetrahydrofuran 109-99-9 O C4H8O 72.10 67
23 2,4-Dimethylpentane 108-08-7 O C7H16 100.20 81
24 1,2-Dichloroethane 107-06-2 O O ClCH2CH2Cl 98.96 84
25 1,1,1-Trichloroethane 71-55-6 O O CH3CCl3 133.40 74
26 1-Butanol 71-36-3 O C4H10O 74.12 117.6
27 Benzene 71-43-2 O O O C6H6 78.11 80
28 Carbon tetrachloride 56-23-5 O O CCl4 153.82 77
29 Cyclohexane 110-82-7 O C6H12 84.18 81
30 1,2-Dichloropropane 78-87-5 O O CH3CH2ClCH2Cl 112.99 96
31 1,4-Dioxane 123-91-1 O OCH2CH2OCH2CH2 88.11 101
32 Bromodichloromethane 75-27-4 O O CHBrCl2 163.83 90
33 2,2,4-Trimethylpentane 540-84-1 O C8H18 114.23 99.2
34 Trichloroethylene 79-01-6 O O ClCHCCl2 131.39 87
35 Heptane 142-82-5 O O CH3(CH2)5CH3 100.21 98
36 Methyl isobutyl ketone 108-10-1 O O (CH3)2CHCH2C(O)CH3 100.16 117
37 cis-1,3-Dichloropropene 10061-01-5 O ClCH2CHCHCl 110.97 104
38 trans-1,3-Dichloropropene 10061-02-6 O ClCH2CHCHCl 110.97 112
39 1,1,2-Trichloroethane 79-00-5 O CH2ClCHCl2 133.40 113-114
40 Toluene 108-88-3 O O O C6H5CH3 92.14 111
41 2-Hexanone 591-78-6 O C6H12O 100.18 128
42 Dibromochloromethane 124-48-1 O O ClCHBr2 208.28 119-120
43 Butyl acetate 123-86-4 O C6H12O2 116.16 126.1
44 1,2-Dibromoethane 106-93-4 O BrCH2CH2Br 187.86 131
45 Octane 111-65-9 O C8H18 114.23 126
46 Tetrachloroethylene 127-18-4 O O Cl2CCCl2 165.83 121
47 Chlorobenzene 108-90-7 O O C6H5Cl 112.56 132
48 Ethylbenzene 100-41-4 O O O CH3CH2C6H5 106.17 136
49 m-Xylene 108-38-3 O O O C8H10 106.17 138-139
50 p-Xylene 106-42-3 O O O C8H10 106.17 138-139
51 Bromoform 75-25-2 O CHBr3 252.73 150
52 Styrene 100-42-5 O O O C8H8 104.14 146
53 1,1,2,2-Tetrachloroethane 79-34-5 O CHCl2CHCl2 167.85 146
54 o-Xylene 95-47-6 O O O C8H10 106.17 144
55 Nonane 111-84-2 O C9H20 128.26 150.8
56 Isopropylbenzene 98-82-8 O C9H12 120.19 151
57 Bromobenzene 108-86-1 O C6H5Br 157.01 155
58 α-Pinene 7785-26-4 O C10H16 136.24 155-156
59 n-Propylbenzene 103-65-1 O C9H12 120.19 159
60 4-Chlorotoluene 106-43-4 O C7H7Cl 126.59 158.97
61 2-Chlorotoluene 95-49-8 O C7H7Cl 126.59 161.9
62 3-Ethyltoluene 620-14-4 O C9H12 120.19 158-159
63 4-Ethyltoluene 622-96-8 O O CH3C6H4C2H5 120.19 160-163
64 1,3,5-Trimethylbenzene 108-67-8 O O O C9H12 120.21 165
65 2-Ethyltoluene 611-14-3 O C9H12 120.19 164-165
66 β-Pinene 18172-67-3 O C10H16 136.24 165-167
67 Decane 124-18-5 O C10H22 142.28 174.1
68 1,2,4-Trimethylbenzene 95-63-6 O O O (CH3)3C6H3 120.19 169
69 tert-Butylbenzene 98-06-6 O C10H14 134.22 169
70 Benzyl chlororide 100-44-7 O C6H5CH2Cl 126.59 179
71 1,3-Dichlorobenzene 541-73-1 O O C6H4Cl2 147.00 173
72 1,4-Dichlorobenzene 106-46-7 O O O C6H4Cl2 147.00 174
73 sec-Butylbenzene 135-98-8 O C10H14 134.22 173
74 p-Isopropyltoluene 99-87-6 O C10H14 134.22 176-178
75 1,2,3-Trimethylbenzene 526-73-8 O C9H12 120.19 175
76 Limonene 5989-27-5 O C10H16 136.24 175.5
77 1,2-Dichlorobenzene 95-50-1 O O C6H4Cl2 147.00 181
78 n-Butylbenzene 104-51-8 O C10H14 134.22 183
79 Nonanal 124-19-6 O C9H18O 142.24 93
80 Undecane 1120-21-4 O C11H24 156.31 195.9
81 1,2,4,5-Tetramethylbenzene 95-93-2 O C10H14 134.22 196.8
82 Decanal 112-31-2 O C10H20O 156.27 207-209
83 Dodecane 112-40-3 O C12H26 170.34 216.3
84 1,2,4-Trichlorobenzene 120-82-1 O O C6H3Cl3 181.44 214
85 Naphthalene 91-20-3 O C10H8 128.17 218
86 1,2,3-Trichlorobenzene 87-61-6 O C6H3Cl3 181.45 219
87 Hexachloro-1,3-butadiene 87-68-3 O Cl2CCClCClCCl2 260.74 210-220
88 Tridecane 629-50-5 O C13H28 184.36 235.4
89 Tetradecane 629-59-4 O C14H30 198.39 253.7
90 Pentadecane 629-62-9 O C15H32 212.42 270.63
91 Hexadecane 544-76-3 O C16H34 226.44 287
1)STD① : 52mix component indoor air standard
2)STD② : 62mix EPA TO-15 calibration mix
3)STD③ : EPA VOC mix 1 (12mix)+EPA VOC mix 2 (13mix)

2. 4 Statistical Analysis

Correlation analyses were used to evaluate the sources of compounds measured in the public spaces (SAS version 9.1, SAS Institute, Cary, NC, USA). For correlation analyses, compounds with frequencies of detection greater than 50% were included. Since the concentration data were consistent with lognormal distribution, a Spearman correlation matrix was calculated.


3. RESULTS

The mean TVOC concentrations in public spaces were 782±1084 μg/m3 in summer and 540±380 μg /m3 in winter. The mean TVOC concentrations were slightly higher in summer than in winter, although they were not significantly different (Paired t-test, p=0.14). Cumulative distributions of TVOC in summer and winter are shown in Fig. 1. In summer, the highest concentrations were observed in the preschool (1718 μg/m3), health care facility (1709 μg/m3), art gallery (1667 μg/m3), and elderly welfare facility (1046 μg/m3). In winter, the highest concentrations were observed in the airport (2096 μg/m3), underground market (854 μg/m3), and health care facility (839 μg/m3).


Fig. 1. 
Cumulative distribution of TVOC in public places in summer and winter.

In summer, acetone, methylethylketone, benzene, toluene, ethylbenzene, m,p-xylenes, styrene, and naphthalene were detected in all samples from the 50 locations. Another 33 chemicals were detected in more than 80% of samples, 11 chemicals were detected in less than 20% of the samples, and 21 chemicals were not detected in any samples. The individual VOC concentrations of 10 μg/m3 or more were toluene (316.7 μg/m3), acetone (44.1 μg/m3), hexane (41.5 μg/m3), isopropyl alcohol (36.6 μg/m3), m,p-xylenes (19.2 μg/m3), ethyl acetate (14.5 μg/m3), ethylbenzene (13.6 μg/m3), methyl ethyl ketone (13.6 μg/m3), and nonanal (10.1 μg/m3). These nine compounds comprised 64.8% of TVOCs. The individual VOC levels in summer are shown in Table 2.

Table 2. 
Individual VOCs levels (μg/m3) in summer.
Detection frequency (%) Mean SD 25th percentile 50th percentile 75th percentile 90th percentile Min Max GM
Toluene 100 316.8 955.2 41.3 74.2 151.2 151.2 2.1 5774.5 81.2
Acetone 100 44.1 58.7 13.8 25.1 51.5 51.5 4.9 382.8 27.2
m,p-Xylenes 100 19.2 32.8 5.9 11.4 16.6 16.6 0.5 184.1 10.6
Ethylbenzene 100 13.6 30.2 4.2 6.8 11.5 11.5 0.2 160.9 6.6
Methyl ethyl ketone 100 10.2 7.2 4.7 8.1 14.9 14.9 0.4 33.7 7.8
1-Butanol 100 8.3 6.3 4.2 6.7 9.8 9.8 0.7 31.4 6.3
Benzene 100 6.5 8.9 3.2 4.1 5.6 5.6 1.8 49.2 4.6
Styrene 100 2.1 1.6 1.0 1.5 2.8 2.8 0.5 8.1 1.7
Naphthalene 98 7.6 15.5 1.5 2.3 7.2 7.2 0.3 102.4 3.1
o-Xylene 98 7.1 12.7 1.9 4.5 6.1 6.1 0.2 75.3 3.9
1,2,4-Trimethylbenzene 98 4.2 8.2 1.2 1.8 3.2 3.2 0.2 46.8 2.1
3-Ethyltoluene 98 3.7 6.8 0.7 1.4 2.9 2.9 0.2 31.6 1.6
1,3,5-Trimethylbenzene 98 2.3 4.4 0.5 0.8 1.8 1.8 0.3 23.0 1.0
4-Ethyltoluene 98 2.1 3.7 0.5 0.8 1.6 1.6 0.2 16.5 0.9
Trichlorofluoromethane 96 5.5 16.8 0.5 0.9 2.2 2.2 0.3 115.0 1.4
Cyclohexane 96 3.8 4.1 1.0 1.9 5.8 5.8 0.2 17.5 2.2
Chloroform 96 3.8 8.0 0.7 1.2 2.7 2.7 0.2 49.4 1.5
Isopropyl alcohol 94 36.6 188.5 1.7 3.6 10.4 10.4 0.1 1335.5 4.0
Butyl acetate 94 4.9 6.8 1.3 2.9 5.3 5.3 0.2 36.2 2.7
Ethyl acetate 92 14.5 25.8 4.0 7.0 13.4 13.4 0.2 153.7 6.2
Decane 92 2.9 2.3 1.5 2.4 3.5 3.5 0.3 10.8 2.1
2-Ethyltoluene 92 1.7 3.1 0.3 0.7 1.3 1.3 0.2 15.5 0.8
Carbon tetrachloride 92 0.8 1.5 0.5 0.6 0.7 0.7 0.3 11.4 0.6
Hexane 90 41.5 114.2 3.3 5.9 27.3 27.3 0.2 768.3 8.3
Nonanal 90 10.2 11.0 4.2 7.5 11.1 11.1 0.3 53.2 6.0
Tetradecane 90 6.5 11.7 2.0 4.3 6.2 6.2 0.4 79.3 3.5
Tridecane 90 5.9 12.0 1.5 2.5 5.7 5.7 0.4 83.8 2.9
Limonene 90 4.4 3.7 1.3 3.8 6.8 6.8 0.3 13.1 2.6
Heptane 90 4.3 6.8 1.6 2.3 4.4 4.4 0.2 42.8 2.3
Methyl isobutyl ketone 90 2.5 2.1 0.9 1.9 3.3 3.3 0.2 9.8 1.6
Dodecane 88 3.3 4.1 1.1 2.6 3.9 3.9 0.4 27.0 2.1
Methylene chloride 86 4.0 4.5 0.6 2.4 5.6 5.6 0.2 20.2 1.9
Trichloroethylene 86 3.0 3.1 0.7 1.9 4.4 4.4 0.3 13.1 1.7
Nonane 86 2.4 2.1 1.1 1.9 3.3 3.3 0.3 10.6 1.6
Octane 84 2.7 3.2 1.1 1.8 3.1 3.1 0.2 15.0 1.6
Pentadecane 82 2.6 4.0 0.8 1.7 2.5 2.5 0.4 18.9 1.5
Methyl tert-butyl ether 82 2.1 5.1 0.5 0.7 1.4 1.4 0.2 33.7 0.8
1,2,3-Trimethylbenzene 82 1.1 1.9 0.3 0.5 0.9 0.9 0.2 11.0 0.6
Hexadecane 80 5.8 10.7 1.1 1.9 4.0 4.0 0.5 58.6 2.4
Vinyl acetate 80 2.6 2.8 1.2 2.2 2.9 2.9 0.2 18.4 1.5
n-Propylbenzene +4-Chlorotoluene 80 0.8 1.0 0.3 0.4 0.8 0.8 0.2 6.7 0.5
α-Pinene 74 2.0 4.4 0.3 1.0 1.5 1.5 0.3 30.7 1.0
Undecane 74 1.9 1.8 0.4 1.4 2.4 2.4 0.3 8.5 1.2
1,2-Dichloroethane 74 0.7 0.7 0.2 0.5 0.8 0.8 0.2 3.6 0.5
1,1,1-Trichloroethane 74 0.4 0.1 0.3 0.3 0.5 0.5 0.3 0.8 0.4
tert-Butylbenzene 70 0.6 0.9 0.3 0.3 0.5 0.5 0.3 5.4 0.4
Isopropylbenzene 68 0.4 0.5 0.2 0.2 0.3 0.3 0.2 2.7 0.3
Carbon disulfide 64 0.9 1.5 0.2 0.2 0.7 0.7 0.2 6.0 0.4
2,2,4-Trimethylpentane 62 1.0 1.6 0.2 0.4 0.9 0.9 0.2 9.1 0.5
Decanal 60 3.0 4.5 0.3 1.8 3.7 3.7 0.3 27.4 1.4
β-Pinene 60 0.9 0.9 0.3 0.5 1.1 1.1 0.3 5.2 0.6
2-Chlorotoluene 54 0.6 1.0 0.3 0.3 0.4 0.4 0.3 5.7 0.4
Tetrachloroethylene 50 3.9 21.1 0.3 0.4 1.3 1.3 0.3 149.7 0.7
p-Isopropyltoluene 50 0.4 0.2 0.3 0.3 0.4 0.4 0.3 1.1 0.3
Chlorobenzene 44 0.3 0.1 0.2 0.2 0.2 0.2 0.2 0.6 0.3
1,4-Dichlorobenzene 38 1.0 2.5 0.3 0.3 0.3 0.3 0.3 15.0 0.5
Tetrahydrofuran 34 0.5 0.7 0.1 0.1 0.7 0.7 0.1 4.3 0.3
1,4-Dioxane 28 0.4 0.5 0.2 0.2 0.4 0.4 0.2 3.0 0.3
2,4-Dimethylpentane 22 0.8 1.4 0.2 0.2 0.2 0.2 0.2 7.7 0.4
1,2,4,5-Tetra-methylbenzene 20 0.4 0.3 0.3 0.3 0.3 0.3 0.3 1.6 0.3
1,1,2-Trichloro-trifluoroethane 18 0.4 0.1 0.4 0.4 0.4 0.4 0.4 0.9 0.4
2-Hexanone 12 0.4 0.6 0.2 0.2 0.2 0.2 0.2 3.9 0.3
Bromodichloromethane 8 0.4 0.1 0.3 0.3 0.3 0.3 0.3 1.2 0.4
1,2-Dichlorobenzene 6 0.5 1.3 0.3 0.3 0.3 0.3 0.3 8.6 0.3
1,1-Dichloroethane 4 0.5 1.3 0.2 0.2 0.2 0.2 0.2 8.0 0.2
n-Butylbenzene 4 0.3 0.1 0.3 0.3 0.3 0.3 0.3 0.8 0.3
1-Propanol 4 0.3 0.8 0.1 0.1 0.1 0.1 0.1 4.8 0.1
1,2-Dichloropropane 4 0.3 0.1 0.2 0.2 0.2 0.2 0.2 1.2 0.2
sec-Butylbenzene 2 0.3 0.0 0.3 0.3 0.3 0.3 0.3 0.3 0.3
1,3-Butadiene 2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.6 0.1

In winter, toluene, acetone, m,p-xylenes, ethylbenzene, benzene, and styrene were detected in all samples from the 49 locations. Another 18 chemicals were observed in more than 80% of the samples, 14 chemicals were found less than 20% of the samples, and 27 chemicals were not detected in any samples. Compounds with individual VOC concentrations of 10 μg/m3 or more were toluene (109.9 μg/m3), isopropyl alcohol (36.6 μg/m3), acetone (31.0 μg/m3), m,p-xylenes (18.8 μg/m3), tetrachloroethylene (17.6 μg/m3), limonene (16 μg/m3), ethylbenzene (15.9 μg/m3), hexane (11.0 μg/m3), and methyl ethyl ketone (11.2 μg/m3). These nine compounds comprised 49.6% of TVOCs. The individual VOC levels in winter are shown in Table 3.

Table 3. 
Individual VOCs levels (μg/m3) in winter.
Detection frequency (%) Mean SD 25th percentile 50th percentile 75th percentile 90th percentile Min Max GM
Acetone 100 31 65.7 10.3 14.7 19.3 52.6 4.3 442.2 17.0
Benzene 100 8 5.0 5.1 6.7 9.0 12.3 2.4 23.3 6.9
Toluene 100 110 145.0 33.5 59.6 118.1 187.1 7.7 621.9 67.4
Ethylbenzene 100 16 29.7 4.2 6.4 12.1 21.7 1.3 141.5 7.7
m,p-Xylenes 100 19 23.9 7.0 10.7 19.4 38.4 2.0 138.6 11.9
Styrene 100 3 4.5 1.2 1.9 2.6 4.5 0.8 32.3 2.0
Isopropyl alcohol 98 37 194.9 3.0 4.5 8.8 18.0 0.1 1370.4 5.6
3-Ethyltoluene 96 3 4.2 1.0 1.6 2.7 9.3 0.2 17.1 1.9
1,3,5-Trimethylbenzene 96 2 2.0 0.6 0.9 1.4 4.6 0.3 9.1 1.0
2-Ethyltoluene 96 1 1.6 0.6 0.8 1.2 4.1 0.2 6.3 0.9
Trichlorofluoromethane 94 1 2.0 0.6 0.7 1.0 1.7 0.3 13.7 0.8
Methyl ethyl ketone 92 11 12.0 4.9 7.1 12.1 25.8 0.1 52.4 6.3
4-Ethyltoluene 92 2 2.0 0.5 0.9 1.3 4.8 0.2 8.5 1.0
Carbon tetrachloride 90 1 0.4 0.6 0.7 0.8 1.0 0.3 2.7 0.7
o-Xylene 90 6 7.5 2.2 4.1 7.5 16.0 0.2 42.5 3.6
Chloroform 88 1 1.2 0.4 0.8 1.3 2.9 0.2 4.7 0.8
Cyclohexane 88 4 6.5 1.4 2.6 4.8 7.8 0.2 40.0 2.3
1,2,4-Trimethylbenzene 88 6 7.8 1.4 2.8 4.4 16.5 0.2 36.9 2.6
Hexane 86 11 13.2 0.2 7.7 14.3 30.8 0.2 56.5 2.6
Decane 86 8 22.3 1.9 3.9 6.9 12.0 0.3 155.7 3.4
Naphthalene 86 2 3.2 0.9 1.3 2.6 4.4 0.3 20.1 1.4
Methylene chloride 82 4 7.0 1.1 2.0 3.3 5.9 0.2 44.4 1.7
Ethyl acetate 80 9 10.8 1.9 5.6 9.5 17.3 0.2 52.6 3.5
Butyl acetate 80 3 4.4 0.8 2.0 3.9 7.1 0.2 24.7 1.6
Trichloroethylene 78 3 5.6 0.7 2.0 3.3 6.0 0.3 28.1 1.6
Nonane 76 4 5.5 1.2 2.4 5.2 7.8 0.3 32.3 2.0
Limonene 73 16 43.8 0.3 5.9 11.5 32.1 0.3 301.5 3.8
Tetradecane 71 3 3.7 0.4 2.0 4.4 6.8 0.4 21.7 1.7
Tridecane 69 4 5.9 0.4 1.6 3.1 9.6 0.4 32.4 1.6
Undecane 65 3 3.9 0.3 1.3 2.8 6.7 0.3 23.8 1.2
Pentadecane 65 1 1.2 0.4 0.8 1.5 3.0 0.4 6.6 0.9
Heptane 61 5 7.2 0.2 1.9 4.8 15.0 0.2 31.4 1.4
Octane 61 3 3.7 0.2 1.3 3.2 5.1 0.2 19.6 1.1
Nonanal 61 4 4.1 0.3 2.9 7.2 9.9 0.3 15.2 1.8
1,2-Dichloroethane 59 1 0.8 0.2 0.4 0.6 0.8 0.2 5.8 0.4
Methyl isobutyl ketone 59 2 8.5 0.2 0.7 1.1 2.1 0.2 59.9 0.6
n-Propylbenzene +4-Chlorotoluene 57 1 1.5 0.2 0.5 0.9 2.8 0.2 6.8 0.6
1,2,3-Trimethylbenzene 57 1 1.7 0.2 0.5 1.3 3.8 0.2 8.3 0.6
Isopropylbenzene 55 1 0.7 0.2 0.2 0.5 1.6 0.2 4.1 0.4
α-Pinene 55 1 2.1 0.3 0.5 1.4 2.8 0.3 9.9 0.7
Carbon disulfide 54 7 17.9 0.2 0.8 2.9 16.1 0.2 83.6 0.9
1-Butanol 49 3 8.4 0.2 0.2 2.6 5.3 0.2 58.1 0.7
Methyl tert-butyl ether 47 4 8.3 0.2 0.2 2.5 6.9 0.2 36.2 0.7
1,1,1-Trichloroethane 47 1 1.3 0.3 0.3 0.5 0.7 0.3 9.2 0.4
2,2,4-Trimethylpentane 47 3 6.7 0.2 0.2 2.0 7.0 0.2 41.8 0.8
tert-Butylbenzene 47 1 0.8 0.3 0.3 0.5 1.9 0.3 4.2 0.4
Dodecane 47 3 6.2 0.4 0.4 3.6 9.3 0.4 35.4 1.2
p-Isopropyltoluene 41 1 0.5 0.3 0.3 0.6 1.3 0.3 2.6 0.4
Hexadecane 41 1 1.4 0.5 0.5 1.5 3.2 0.5 7.4 0.8
Tetrachloroethylene 22 18 88.6 0.3 0.3 0.3 1.4 0.3 570.5 0.6
1,1,2-Trichloro-trifluoroethane 18 1 1.4 0.4 0.4 0.4 1.6 0.4 7.9 0.5
β-Pinene 18 0 0.4 0.3 0.3 0.3 1.1 0.3 2.2 0.4
Tetrahydrofuran 14 1 6.5 0.1 0.1 0.1 1.0 0.1 45.4 0.2
Vinyl acetate 12 0 0.8 0.2 0.2 0.2 1.5 0.2 3.6 0.2
Chlorobenzene 10 0 0.1 0.2 0.2 0.2 0.2 0.2 0.7 0.3
2,4-Dimethylpentane 8 1 1.5 0.2 0.2 0.2 0.2 0.2 7.0 0.3
Bromodichloromethane 8 0 0.7 0.3 0.3 0.3 0.3 0.3 4.7 0.4
Dibromochloromethane 8 1 0.4 0.4 0.4 0.4 0.4 0.4 3.1 0.5
1,4-Dichlorobenzene 6 1 1.0 0.3 0.3 0.3 0.3 0.3 5.5 0.4
sec-Butylbenzene 4 0 0.0 0.3 0.3 0.3 0.3 0.3 0.3 0.3
n-Butylbenzene 4 0 0.0 0.3 0.3 0.3 0.3 0.3 0.4 0.3
1,3-Dichlorobenzene 2 0 1.2 0.3 0.3 0.3 0.3 0.3 8.8 0.3
1,2-Dichlorobenzene 2 0 0.6 0.3 0.3 0.3 0.3 0.3 4.6 0.3
1,2,4,5-Tetramethylbenzene 2 0 0.0 0.3 0.3 0.3 0.3 0.3 0.3 0.3

Some compounds had occasional high values. This was apparent for isopropyl alcohol in which the mean was about 8 and 10 times larger than the median. Three compounds with medians greater than 10 μg/m3 were toluene, acetone, and m,p-xylenes. Another six compounds had medians greater than 5 μg/m3 in summer: methyl ethyl ketone (8.1 μg/m3), nonanal (7.5 μg /m3), ethyl acetate (7.0 μg/m3), ethyl benzene (6.8 μg/ m3), 1-butanol (6.7 μg/m3), and hexane (5.9 μg/m3). Four compounds had medians greater than 5 μg/m3 in winter: benzene (6.7 μg/m3), ethylbenzene (6.4 μg/m3), limonene (5.9 μg/m3), and ethyl acetate (5.6 μg/m3).

Several compounds were closely correlated with other compounds. The criteria for determining correlations between individual VOCs were an R>0.9 and a P-value (or significance probability value) <0.001. Based on these criteria, the correlations of different individual VOCs in summer and winter are summarized in Tables 4 and 5, respectively. Among the 91 targeted VOCs in this study, 18 VOCs showed strong cor-relations with other VOCs in summer, including ethylbenzene, m,p-xylenes, o-xylene, isopropylbenzene, tert-butylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, heptane, toluene, 2-ethyltoluene, 3-ethyltoluene, 4-ethyltoluene, ethyl acetate, dodecane, tridecane, naphthalene, and 2-chlorotoluene. In winter, 13 VOCs showed strong correlation with other VOCs, including m,p-xylenes, o-xylene, isopropylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, 2- ethyltoluene, 3-ethyltoluene, 4-ethyltoluene, n-propylbenzene + 4-chlorotoluene, decane, and limonene.

Table 4. 
Correlation of VOCs in summer.
Compounds Correlated compounds Pearson correlation (R)
Ethylbenzene
2-Chlorotoluene 0.980
Isopropylbenzene 0.981
tert-Butylbenzene 0.932
m,p-Xylenes 0.976
o-Xylene 0.973
1,2,3-Trimethylbenzene 0.949
1,2,4-Trimethylbenzene 0.955
m,p-Xylenes
2-Chlorotoluene 0.950
Isopropylbenzene 0.970
tert-Butylbenzene 0.953
o-Xylene 0.995
1,2,3-Trimethylbenzene 0.960
1,2,4-Trimethylbenzene 0.962
o-Xylene
2-Chlorotoluene 0.954
Isopropylbenzene 0.966
tert-Butylbenzene 0.961
1,2,3-Trimethylbenzene 0.972
1,2,4-Trimethylbenzene 0.970
Heptane 0.905
Toluene Ethyl acetate 0.943
1,2,3-Tri-methylbenzene
2-Chlorotoluene 0.943
Isopropylbenzene 0.965
tert-Butylbenzene 0.986
1,2,4-Trimethylbenzene 0.994
Heptane 0.922
1,2,4-Tri-methylbenzene
2-Chlorotoluene 0.943
Isopropylbenzene 0.973
tert-Butylbenzene 0.991
Heptane 0.918
1,3,5-Tri-methylbenzene
2-Ethyltoluene 0.993
3-Ethyltoluene 0.988
4-Ethyltoluene 0.985
2-Ethyltoluene
3-Ethyltoluene 0.986
4-Ethyltoluene 0.983
3-Ethyltoluene 4-Ethyltoluene 0.999
2-Chlorotoluene
Isopropylbenzene 0.964
tert-Butylbenzene 0.915
Isopropylbenzene tert-Butylbenzene 0.963
Tridecane
Dodecane 0.946
Tridecane 0.932
Naphthalene 0.904

Table 5. 
Correlation of VOCs in winter.
Compounds Correlated compounds Pearson correlation (R)
m,p-Xylenes o-Xylene 0.979
1,2,3-Tri-methylbenzene
Isopropylbenzene 0.935
1,2,4-Trimethylbenzene 0.984
1,3,5-Trimethylbenzene 0.975
2-Ethyltoluene 0.957
3-Ethyltoluene 0.962
4-Ethyltoluene 0.965
1,2,4-Tri-methylbenzene
Isopropylbenzene 0.931
1,3,5-Trimethylbenzene 0.987
2-Ethyltoluene 0.969
3-Ethyltoluene 0.978
4-Ethyltoluene 0.980
n-Propylbenzene+4-Chlorotoluene 0.922
1,3,5-Tri-methylbenzene
2-Ethyltoluene 0.995
3-Ethyltoluene 0.992
4-Ethyltoluene 0.990
n-Propylbenzene+4-Chlorotoluene 0.939
2-Ethyltoluene
3-Ethyltoluene 0.991
4-Ethyltoluene 0.989
n-Propylbenzene+4-Chlorotoluene 0.961
3-Ethyltoluene
4-Ethyltoluene 0.992
n-Propylbenzene+4-Chlorotoluene 0.966
4-Ethyltoluene
n-Propylbenzene+4-Chlorotoluene 0.945
Isopropylbenzene 0.911
Decane Limonene 0.940


4. DISCUSSION

In Korea, the indoor air quality of public places is regulated by the Indoor Air Quality Control in Public Use Facilities Act. The recommended TVOC level is 500 μg/m3. VOC levels should be measured once every 2 years and maintained below the guideline. When the VOCs were measured at 50 locations during the summer, 25 locations exceeded the guideline. When the VOCs were measured at 49 locations during the winter, 17 locations exceeded the guideline. Thus, a significant proportion of indoor public places were noncompliant with regulations.

In this study, 72 individual VOCs were identified from indoor air samples. The number of individual VOCs in one indoor air sample can be as many as 250 (Nathanson, 1993). However, 20-30 compounds account for 50-75% of the TVOC in indoor air samples (Molhave et al., 1997). In this study, nine VOCs with more than 10 μg/m3 accounted for 64.8% of the TVOC in summer and 49.6% in winter. Seven VOCs (toluene, acetone, hexane, isopropyl alcohol, m,p-xylenes, ethylbenzene, methyl ethyl ketone) were detected at levels of more than 10 μg/m3 in both seasons. Ethyl acetate and nonanal were included in summer and tetrachloroethylene and limonene were included in winter. In particular, the source of the limonene may have been the high consumption of tangerines in Korea.

Six VOCs (toluene, acetone, m,p-xylenes, ethylbenzene, benzene, styrene) were detected in 100% of the samples in summer and winter. In summer, methylethylketone and 1-butanol were also detected in all samples. Although many VOCs are present in indoor air, the dominant VOCs in indoor air are toluene, m,p-xylenes, ethylbenzene, and benzene, and the dominant VOC profile recorded in this study agreed with those reported for nonresidential spaces (Salonen et al., 2009; Tang et al., 2005; Chao and Chan, 2001; Baek et al., 1997). Based on the location and type of building, some other VOCs may be present. In mechanically ventilated buildings in Hong Kong, chloroform and trichloroethylene were also found in 100% of the samples (Chao and Chan, 2001). When VOCs were measured in problematic buildings, the most abundant VOCs were 2-(2-ethoxyethoxy)ethanol, acetic acid, 1,2-propanediol, and toluene (Salonen et al., 2009).

Several studies have reported on individual VOCs in public spaces. We summarized the indoor concentrations of selected VOC species and compared them with those in other regions, as shown in Table 6 (Eklund et al., 2008; Tang et al., 2005; Chao and Chan, 2001; Kim et al., 2001; Baek et al., 1997). The VOC concentrations showed similar trends. In our study, the toluene concentration during summer was the highest. A shopping mall in Ghangzou reported high concentrations for almost all species (Tang et al., 2005). In Korea, new apartment buildings have guideline levels for benzene (30 μg/m3), toluene (1000 μg/ m3), ethylbenzene (360 μg/m3), xylenes (700 μg/m3), and styrene (300 μg/m3) before occupation. Currently, no specific guidelines have been established for individual VOCs in public spaces in Korea. As BTEX was dominant in both detection frequency and concentration levels, considering the implementation of air quality guidelines may be necessary.

Table 6. 
Comparison of indoor VOCs level in several public places (μg/m3).
Compounds Public spaces, Korea (Current study) Korea Office1) Birmingham, AL Department store2) Hong Kong Public spaces3) Ghuangzou, China Shopping mall4) NJ Shopping center5)
Summer Winter
Benzene 6.5 7.9 12.6 10.5 8.1 78 1.2
Toluene 316.8 109.9 80.4 56.7 52.8 142 144
Ethylbenzene 13.6 15.9 7.6 3.4 7.3 19 0.6
m,p-Xylenes 19.2 18.9 23.4 12 18.9 41.9 3.5
o-Xylene 7.1 6.5 14.5 3.5 5.5 8.9
Styrene 2.1 2.8 5 1.1 5.1 13 0.2
1,2,4-Trimethyl-benzene 4.2 5.5 14.6 3.4 2.2 9.9 1.1
1,3,5-Trimethyl-benzene 2.3 1.7 6.4 0.8 8.8 3.4 0.2

When we determined correlations between individual compounds, 19 and 14 VOCs showed strong correlations with other VOCs in summer and winter, respectively. Many compounds were included in both seasons: m,p-xylenes, o-xylene, isopropylbenzene, 1,2,3- trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, 2-ethyltoluene, 3-ethyltoluene, and 4-ethyltoluene. Alkylbenzenes are well known as anthropogenic chemicals coming from the vehicular emissions of gasoline burning in spark-ignition engines (Chao and Chan, 2001). The main components of these gasoline emissions are benzene, toluene, ethylbenzene, m,p-xylenes, o-xylene, p-ethyltoluene, and 1,2,4-trimethylbenzene (Oelert et al., 1974). Therefore, we suggest that indoor spaces in Korea are being affected by the infiltration of polluted outdoor air.

The sampling of VOCs can be affected by various conditions. One of the critical factors is the adsorbent tube used. When two types of adsorbent tube [a single adsorbent of 300 mg Tenax-TA and a double adsorbent of Tenax-TA in front (100 mg) and Carbotrap (200 mg)] were compared, the recorded TVOC levels were comparable, but the single tube showed slightly higher levels. Relative percent differences between the two methods indicated that the single tube may collect larger amounts of VOCs. A tube with Tenax-TA and Carbotrap was validated in experiments and field study (Kuntasal et al., 2005). The tube showed high recoveries, in the range of 80-100% and MDL from 0.01 to 0.14 ppb. The sampling method also showed good linearity (R2>0.99) and precision (<8%) values (Kuntasal et al., 2005). Two adsorbent tubes showed precisions of 20-30% for most aromatic VOCs (Baek and Moon, 2004).


Acknowledgments

This work was supported by the National Institute of Environmental Research of Korea (NIER) Grant. The investigations were made with the cooperation and support of the Institute’s Indoor Environment and Noise Research Division.


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