Environ. Sci. Technol. 2001, 35, 997-1004
Concentrations and Sources of VOCs in Urban Domestic and Public Microenvironments YOUNG MIN KIM, STUART HARRAD,* AND ROY M. HARRISON Division of Environmental Health & Risk Management, University of Birmingham, Birmingham, B15 2TT United Kingdom
Concentrations of 15 VOCs including 1,3-butadiene, benzene, and styrene were measured in a wide range of urban microenvironments, viz: homes, offices, restaurants, pubs, department stores, coach and train stations, cinemas, libraries, laboratories, perfume shops, heavily trafficked roadside locations, buses, trains, and automobiles. For most target VOCssincluding 1,3-butadiene and benzenesmean concentrations at heavily trafficked roadside locations were exceeded by those in automobiles and were comparable to those in pubs and train stations. With regard to indoor-outdoor relationships in homes, this study revealed higher mean indoor concentrations, no correlation between simultaneously measured indoor and outdoor concentrations, and significantly different patterns of diurnal variation. Thussin poorly ventilated buildingssindoor emission source strength is considered a more significant influence on VOC concentrations than infiltration of outdoor air. In the six smoking homes studied, environmental tobacco smoke (ETS) was found to make a substantial contribution to concentrations of 1,3butadiene. This finding was based on the significantly higher concentrations detected in smoking compared to nonsmoking homes, the significant correlation between 1,3butadiene concentrations and those of 3-ethenylpyridine (an ETS marker), factor analysis, and the results of a source apportionment exercise based on ratios of 1,3-butadiene to 3-ethenylpyridine.
Introduction Studies of indoor airborne concentrations of volatile organic compounds (VOCs) are urgently required, due to their adverse human health effects, the existence of a large number of indoor emission sources, and the fact that in modern urban areas, people spend more than 70% of their time indoors (1). The situation is complicated by the existence of a wide range of indoor microenvironments, such as homes, offices, restaurants, pubs, stores, cinemas, libraries, coach and train stations, etc. Each of these microenvironments are impacted by one or more potential sources of VOCs, including the following: the use of solvents and petroleum related consumer products, building or furnishing materials, heating and cooking equipment such as gas stoves and kerosene or oil heaters, infiltration of outdoor VOCs, and Environmental Tobacco Smoke (ETS) (1-5). Most previous studies have * Corresponding author phone: +44 121 414 7298; fax: +44 121 414 3078; e-mail: S.
[email protected]. 10.1021/es000192y CCC: $20.00 Published on Web 02/06/2001
2001 American Chemical Society
focused on a limited range of indoor environments, specifically homes and offices (6-10), with the result that few data exist on VOC concentrations in public microenvironments. This is potentially significant, as densely populated public microenvironments such as pubs, restaurants, and coach stations are likely to be strongly influenced by significant VOC sources such as ETS and vehicular emissions. Previous studies of VOCs in indoor environments have also been restricted with respect to the VOCs monitored. In particular, 1,3-butadiene has been omitted from most previous studies, due to a lack of validated methods for its sampling and analysis at ambient concentrations. Given that it has been identified as a genotoxic carcinogen for which no absolutely safe level of human exposure may be determined (11) and that the United States Environmental Protection Agency (USEPA) has classified it as a probable carcinogen with an estimated unit risk factor almost 30 times higher than that of benzene (12), this is a potentially serious omission from current assessments of the human health risks arising from indoor air quality. This study reports the concentrations of 15 VOCs including 1,3-butadiene, benzene and styrene, in a wide range of microenvironments, viz homes, offices, restaurants, pubs, department stores, coach and train stations, cinemas, libraries, laboratories, perfume shops, heavily trafficked roadside locations, buses, trains, and automobiles. Indooroutdoor concentration ratios for homes are measured via simultaneous indoor:outdoor sampling, and the contribution of ETS to VOC concentrations in six smoking homes (i.e. those inhabited by smokers) is assessed.
Experimental Methodology Selection of Microenvironments. In modern societies, urban dwellers frequent four principal groups of microenvironments, specifically homes, public microenvironments, transportation microenvironments, and occupational microenvironments. In all, 15 microenvironment categories covering these four groups were selected. All were located within a 3 km radius of central Birmingham, with full details given in Table 1. Public microenvironments selected consisted of department stores, libraries, restaurants, pubs, coach and train stations, cinemas, and perfume shops, while the transportation microenvironments chosen were heavily trafficked roadside locations and the interiors of buses, trains, and automobiles. To facilitate evaluation of the contribution of ETS to VOC concentrations, six smoking and six nonsmoking homes were selected. Smoking homes were defined as those in which at least one smoker was residing, and in which smoking occurred during sampling. In all bar one home, electricity was used for cooking and gas heaters were not used during sampling. Three homes were located within 10 m of a heavily trafficked road. The diurnal variation of VOC concentrations was measured in one smoking and one nonsmoking home. In the remaining 10 homes, sampling was conducted between the following periods: 12:00 to 14:00, 18:00 to 22:00, and 24:00 to 02:00, representing concentrations during the day, evening, and night, respectively. Sampling and Analytical Methods. Analyte Selection Criteria. VOCs monitored in this study were selected according to the following criteria: (a) adverse human health effects, in particular carcinogenicity (1,3-butadiene, benzene, and styrene), (b) the extent of previous monitoring, and (c) potential utility as a tracer of a specific emission sourcese.g. 3-ethenylpyridine for ETS. VOL. 35, NO. 6, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
997
TABLE 1. Description of Microenvironments Monitored microenvironment
location
sampling conditions
homes (12b)
around University of Birmingham
offices (6)
in University of Birmingham
laboratories (4)
in University of Birmingham
cinemas (2) in City center department stores (2) in City center perfume shops (3) libraries (3)
in City center (2 places) in University of Birmingham
pubs (6) restaurants (6) train stations (2)
around University of Birmingham (3 pubs); in City center (3 pubs) in City center in City center
coach stations (1)
in City center
trafficked roadside locations (4)
in City center (1 road); around University of Birmingham (3 roads) cars driven inside Birmingham city
automobiles (12) buses (18) trains (18) a
smoking status
3 times per home per day simultaneous sampling indoors and outdoors (12:00-14:00; 18:00-22:00; 24:00-02:00) twice per office per day (09:30-11:30; 14:00-16:00) twice per laboratory per day (09:30-11:30; 14:00-16:00) 3 times per cinema (during movie time) twice per department store per day on 2 days (09:30-11:30; 14:00-16:00) once per shop twice per library per day (09:30-11:30; 14:00-16:00) once per pub once per restaurant 3 times per train station per day on 2 days sampling at waiting area and platform (07:30-09:30; 12:00-14:00; 17:00-19:00) 6 times per coach station per day on 2 days sampling at waiting area and platform (07:30-09:30; 12:00-14:00; 17:00-19:00) 3 times per road (07:30-09:30; 12:00-14:00; 17:00-19:00)
3 times per automobile per day (08:00-09:00; 12:00-13:00; 18:00-19:00) bus services inside Birmingham city once per bus per day train services inside Birmingham city once per train per day
yes (6 homes) no (6 homes)
Na 128
no
12
no
8
no no
6 8
no no
3 6
yes
6
yes no
6 12
no (in waiting area); yes (on coach platform) no
12
yes (6 cars) no (6 cars) no no
36
12
18 18
N is the number of samples collected in the microenvironment. b The number of places selected.
TABLE 2. TD/GC/MS Operating Conditions for VOCs Other Than 1,3-Butadiene TD (Tekmar 6000)
a
GC (HP 5890 series II) value
parameter
value
parameter
value
desorb temp. desorb time valve temp. trap high trap low trap hold line temp.
250 °C 20 min 200 °C 375 °C -30 °C 5 min 200 °C
initial temp. final temp. initial time final time oven ramp rate carrier pressure carrier gas
40 °C 180 °C 5 min 1 min 5 °C/min 14.5 psi helium
interface temp. EMVa mode tune masses interface type
250 °C 2494 SIM 69, 131, 219 capillary D.b
Electron multiplier voltage.
b
Capillary direct.
Since 1,3-butadiene differs considerably from the other VOCs monitored with respect to adsorption/desorption characteristics and susceptibility to decomposition/artifact formation, it was monitored using a different protocol to that employed for the other 14 targeted VOCs (benzene, toluene, ethylbenzene, m-xylene, p-xylene, o-xylene, 1,3,5trimethylbenzene, styrene, p-isopropyltoluene, 1,2,4-trimethylbenzene, 1,4-dichlorobenzene, naphthalene, pyridine, and 3-ethenylpyridine). Sampling Method. Sampling was conducted between November 1999 and February 2000 using adsorbent tubes fitted to a personal pump operated at a flow rate of ca. 40 mL min-1. For 1,3-butadiene, the adsorbent tube was packed with 1000 mg of Carbopack B (60/80 mesh, Supelco) followed by 150 mg of Carbosieve SIII (60/80 mesh, Supelco) (13), while the other VOCs were trapped on an adsorbent tube packed with 300 mg of Tenax GR (60/80 mesh, Chrompack) followed by 600 mg of Carbotrap (20/40 mesh, Supelco). The duration of sampling time varied according to the microenvironment, with details given in Table 1. Each adsorbent tube was capped with swagelok fittings before and after sampling. Analytical Method. Analysis of all VOCs was conducted using a thermal desorber (Tekmar 6000/6016) interfaced with 998
MSD (HP 5971A)
parameter
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 6, 2001
a gas chromatograph (HP 5890 series II) and mass selective detector (HP 5971A). Chromatographic separation was achieved using a PLOT capillary column (50 m, 0.32 mm i.d., 5 µm film thickness, Chrompack) for 1,3-butadiene and a Stabil-wax capillary column (50 m, 0.25 mm i.d., Restek) for the other VOCs. The analytical conditions for 1,3-butadiene are described elsewhere (13), but those for the other VOCs are given in Table 2. For 1,3-butadiene, calibration was achieved via introduction of an appropriate aliquot of 1,3butadiene standard gas (10 ppm, BOC speciality gases) onto an adsorbent tube, via a gas valve and sample loop. For other VOCs, calibration was conducted using a standard liquid mixture spiked onto an adsorbent tube. In each case, calibration standards were analyzed before and after analysis of each batch of samples. Note that in this study, 4-ethenylpyridine was used for the calibration of 3-ethenylpyridine. This was considered justified, given that reference standards of 3-ethenylpyridine were not commercially available during this work, and because the mass fragmentation patterns of the two isomers are similar (14). Method Validation. Extensive validation was conducted of our sampling and analytical methodology. A detailed description of our method validation techniques for VOC analysis as applied to 1,3-butadiene is given elsewhere (13).
a Number of samples collected. b Mean concentration. c Standard deviation. d rest. (restaurant), dep. st. (department store), p.f. shop (perfume shop), t. sta. (train station), c. sta. (coach station), t. roads (trafficked roads); 1,3,5-TMB (1,3,5-trimethylbenzene), p-IPT (p-isopropyltoluene), 1,2,4-TMB (1,2,4-trimethylbenzene), 1,4-DCB (1,4-dichlorobenzene). e nd ) not detected.
1.7 (0.9) 20.2 (7.8) 69.3 (30.9) 8.0 (3.9) 7.6 (3.9) 20.3 (10.2) 8.6 (4.1) 2.3 (1.1) 0.7 (0.3) 0.6 (0.3) 11.8 (5.4) 2.4 (2.0) nde (-) 0.9 (0.3) nde (-) 1.0 (0.6) 24.3 (35.8) 64.9 (119.7) 5.6 (8.8) 4.8 (8.5) 13.2 (20.4) 5.0 (8.3) 1.0 (1.6) 1.4 (1.4) 0.4 (0.4) 4.1 (5.4) 0.4 (0.4) nde (-) 1.0 (0.9) nde (-) 7.9 (4.7) 203.7 (152.3) 494.0 (283.6) 51.9 (30.8) 52.5 (31.5) 127.2 (76.8) 54.2 (33.6) 9.4 (5.9) 4.3 (3.1) 1.0 (1.9) 33.9 (21.5) 1.3 (5.5) 1.9 (3.9) 5.0 (3.3) 1.7 (3.5) 1.8 (0.9) 49.6 (22.4) 108.1 (50.3) 12.4 (8.6) 11.6 (8.4) 32.3 (21.2) 13.2 (9.7) 2.8 (3.0) 1.7 (1.5) 0.2 (0.3) 10.9 (10.5) 0.1 (0.1) nde (-) 12.1 (38.0) nde (-) 0.9 (0.7) 20.0 (16.1) 47.3 (33.8) 3.8 (1.3) 3.5 (1.0) 10.1 (3.7) 3.5 (1.3) 0.8 (0.3) 0.6 (0.4) 0.4 (0.6) 3.8 (1.9) 0.7 (0.7) 0.1 (0.4) 1.1 (1.9) 0.1 (0.2) 2.2 (1.7) 46.5 (37.7) 135.3 (117.1) 7.4 (7.6) 6.9 (7.5) 18.8 (18.7) 7.5 (8.1) 1.5 (1.5) 1.4 (0.9) 0.2 (0.1) 6.3 (5.5) 0.2 (0.1) nde (-) 1.6 (0.9) nde (-) 0.2 (0.1) 4.2 (1.6) 8.3 (3.1) 0.7 (0.2) 0.6 (0.2) 1.9 (0.9) 0.8 (0.3) 0.1 (0.0) 0.2 (0.1) 0.2 (0.3) 0.5 (0.2) 0.1 (0.0) nde (-) 0.1 (0.0) nde (-) 0.4 (0.2) 8.8 (2.5) 21.2 (9.7) 3.5 (2.8) 3.1 (2.7) 9.2 (8.2) 3.3 (2.7) 1.1 (0.9) 0.5 (0.4) 0.3 (0.2) 4.8 (3.2) 12.8 (27.7) nde (-) 0.6 (0.3) nde (-) 0.9 (0.1) 6.8 (1.2) 43.8 (26.7) 2.4 (0.1) 2.2 (0.1) 6.0 (0.3) 2.4 (0.3) 0.5 (0.1) 0.7 (0.5) 2.0 (0.8) 2.9 (0.3) 1.7 (0.7) nde (-) 0.4 (0.2) nde (-) 0.6 (0.3) 15.5 (9.1) 43.6 (28.3) 5.9 (5.6) 5.5 (5.3) 15.7 (14.1) 5.9 (5.3) 1.7 (1.3) 0.7 (0.6) 4.9 (10.5) 7.6 (5.4) 0.3 (0.3) nde (-) 0.6 (0.3) nde (-) 0.6 (0.4) 10.5 (5.6) 56.7 (29.2) 3.4 (2.4) 3.1 (2.2) 8.9 (6.4) 3.5 (2.5) 0.8 (0.5) 1.1 (0.5) 0.5 (0.1) 3.4 (2.2) 23.4 (35.4) nde (-) 0.7 (0.4) nde (-) 3.0 (2.0) 31.7 (33.5) 75.4 (79.7) 7.3 (11.4) 6.5 (10.4) 18.3 (28.6) 6.9 (11.2) 1.5 (2.3) 2.1 (2.2) 0.6 (0.7) 6.2 (10.0) 2.3 (4.4) 3.8 (4.4) 1.0 (1.0) 3.3 (3.8)
buses (18) trains (18) cars (35) t. roads (12) c. sta. (12) t. sta. (12) labs (8) cinemas (6) p.f. shop (3) libraries (6) dep. st. (8) pubs (6) rest. (6)
1.5 (0.8) 22.7 (4.0) 57.0 (20.2) 6.2 (3.0) 5.6 (2.8) 16.3 (8.2) 6.0 (2.9) 1.3 (0.7) 1.4 (1.1) 0.6 (0.3) 5.9 (3.5) 2.9 (5.5) 0.6 (1.0) 0.9 (0.4) 0.6 (0.9) 0.3 (0.2) 5.9 (2.3) 22.0 (14.4) 2.4 (1.3) 1.7 (0.7) 6.0 (3.6) 1.8 (0.6) 0.3 (0.1) 0.6 (0.5) 0.3 (0.2) 1.5 (0.5) 0.1 (0.1) nde (-) 1.7 (3.2) nde (-) 1,3-butadiene benzene toluene ethylbenzene p-xylene m-xylene o-xylene 1,3,5-TMB styrene p-IPT 1,2,4-TMB 1,4-DCB 3-ethenylpyridine naphthalene pyridine
13.9 (13.8) 38.4 (21.7) 2.3 (1.3) 1.9 (1.1) 5.3 (3.2) 1.9 (1.3) 0.5 (0.5) 0.8 (0.7) 0.9 (1.2) 1.7 (1.9) 0.1 (0.2) 0.4 (1.1) 0.8 (1.0) 0.4 (1.2)
(1.9)c 1.1b
homes (64)a offices (12)
Concentrations of VOCs in Microenvironments. Concentrations of individual VOCs varied widely according to the microenvironment. Mean concentrations (µg m-3) and standard deviations for each VOC in each microenvironment are shown in Table 3. Mean concentrations of most VOCs were elevated in transportation microenvironments such as automobiles, roadside locations, buses, and trains. Of the public microenvironments monitored, pubs and train stations were shown to have the highest concentrations of most target VOCs. Given the presence of well characterized VOC emission sources such as vehicles and ETS in such microenvironments, the higher concentrations recorded are not unexpected. In all transportation microenvironments, the highest mean concentrations of 1,3-butadiene and benzene of 7.9 µg m-3 and 203.7 µg m-3, respectively, were detected in automobiles. Cars were also shown to have the highest mean concentrations of all other target VOCs, except for pyridine, 3-ethenylpyridine, 1,4-dichlorobenzene, and p-isopropyltoluene. However, all 12 automobiles used in this study were over 10 years old. Furthermore, smoking occurred in six
VOC
Results and Discussion
TABLE 3. Mean Concentrations (µg m-3) of VOCs in Different Microenvironmentsd
As the same techniques were applied to the validation of our methods for the other target VOCs, only the results of our validation studies will be discussed here. Field Blanks. Ten field blanks (i.e. clean sealed sorbent tubes stored next to a sampler during a sampling event prior to analysis) were tested with no significant contamination found for any of the target VOCs. Storage Stability. Although our sampling protocol permits a maximum delay between sampling and analysis of 48 h, with storage at -18 °C wherever possible, storage stability was evaluated for all target VOCs. When stored at ambient temperature, 1,3-butadiene was stable for at least 2 days, and at least 7 days when stored at -18 °C. All other VOCs including benzene were stable for at least 2 weeks at ambient temperatures. Breakthrough. For 1,3-butadiene, this was evaluated at a concentration of 27.9 µg m-3, compared to the maximum concentration recorded in this study of 20.1 µg m-3. For other VOCs, breakthrough was evaluated for benzene and toluene whichsrespectivelysare the most volatile and abundant of the VOCs monitored. Breakthrough was evaluated at concentrations of 830 and 1480 µg m-3 for benzene and toluene, respectively. By comparison, the highest concentrations recorded in this study were 720 and 1300 µg m-3, respectively. No breakthrough was observed for any VOCs in our tests, and it is not considered to influence our data. Linearity, Precision, and Detection Limits. Linearity of detector response for all VOCs was evaluated using five point calibrations covering the full range of concentrations recorded in this study. The correlation coefficient for all calibration plots exceeded 0.996 (p e 0.05). Analytical precision was found to be less than 7.6% for all target VOCs. In addition, the precision of sampling and analysis combined was evaluated by acquiring six spatially and temporally consistent samples. Subsequent analysis revealed precision to be better than 10% for all target VOCs except 1,3,5trimethylbenzene (11.5%), p-isopropyltoluene (11.7%), and pyridine (14.5%). Method detection limits (MDLs) were calculated according to the method of Glazer et al. (15) and found to be 100 17.7 23.5 24.7 23.3 30.5 17.3 10.9 46.1 92.7
ETS profile of (20) mean 60.6 4.7 4.3 10.8 11.1 10.5 11.0 16.2 31.8 76.3
min 32.5 2.0 1.8 4.1 3.8 3.7 3.1 1.4 14.4 38.8
max
ETS profile of (21) mean NAa
min NAa
max NAa
ETS profile of (19) mean NAa
min NAa
max NAa
99.1 6.7 5.2 2.2 7.4 2.9 1.3 4.2 8.1 4.3 1.8 8.1 2.5 1.0 4.7 19.9 10.1 3.8 18.4 6.0 2.3 11.0 22.0 8.6 2.9 16.9 NAa NAa NAa 21.0 11.2 4.0 22.4 NAa NAa NAa 23.2 7.4 2.1 15.6 5.4 1.5 11.5 32.6 NAa NAa NAa NAa NAa NAa 47.6 30.8 13.9 46.1 21.7 9.8 32.4 89.2 72.0 36.6 84.2 66.4 33.7 77.6
ETS profile of (14) mean
min
NAa
NAa
4.2 NAa NAa NAa NAa NAa NAa NAa NAa
1.8 NAa NAa NAa NAa NAa NAa NAa NAa
max NAa 6.0 NAa NAa NAa NAa NAa NAa NAa NAa
NA ) not available.
VOL. 35, NO. 6, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
1003
between concentrations of 3-ethenylpyridine (an ETS marker) and 1,3-butadiene in six smoking homes. It is also shown that VOC concentrations in some microenvironments such as automobiles, pubs, and train stations can exceed those at heavily trafficked roadside locations and that in poorly ventilated homes, indoor emission sources are the most significant influence on concentrations of VOCs.
Acknowledgments The authors are grateful to the Department of the Environment, Transport and the Regions for financial support of this research (Contract No. EPG 1/5/72).
Literature Cited (1) Jones, A. P. Atmos. Environ. 1999, 33, 4535-4564. (2) Molhave, L. Environ. Intl. 1982, 8, 117-128. (3) Wallace, L. A.; Pellizzari, E.; Leaderer, B.; Zelon, H.; Sheldon, L. Atmos. Environ. 1987, 21, 385-393. (4) Daisey J. M.; Hodgson, A. T.; Fisk, W. J.; Mendell, M. J.; Ten Brinke, J. Atmos. Environ. 1994, 28, 3557-3562. (5) Perry, R.; Gee, I. Indoor Environ. 1994, 3, 224-236. (6) Fellin, P.; Otson, R. Atmos. Environ. 1994, 28, 3581-3586. (7) Kostiainen, R. Atmos. Environ. 1995, 29, 693-702. (8) Heavner, D. L.; Morgan, W. T.; Ogden, M. W. Environ. Intl. 1995, 21, 3-21. (9) Heavner, D. L.; Morgan, W. T.; Ogden, M. W. Environ. Intl. 1996, 22, 159-183.
1004
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 35, NO. 6, 2001
(10) Bouhamra, W. S.; BuHamra, S. S.; Thomson, M. S. Environ. Intl. 1997, 23, 197-204. (11) EPAQS. Expert Panel on Air Quality Standards: 1,3-Butadiene; HMSO: London, 1994. (12) Duffy, B. L.; Nelson, P. Atmos. Environ. 1996, 30, 2759-2768. (13) Kim, Y. M.; Harrad, S.; Harrison, R. M. Environ. Sci. Technol. 1999, 33, 4342-4345. (14) Heavner, D. L.; Ogden, M. W.; Nelson, P. R. Environ. Sci. Technol. 1992, 26, 1737-1746. (15) Glaser, J. A.; Foerst, D. L.; McKee, G. D.; Quave, S. A.; Budde, W. L. Environ. Sci. Technol. 1981, 15, 1426-1435. (16) Yocom, J. E. J. Air Pollut. Control Ass. 1982, 32, 500-520. (17) Baek, S. O.; Kim, Y. S.; Perry, R. Atmos. Environ. 1997, 31, 529544. (18) Indoor Air Quality - a comprehensive reference book; Maroni, M., Seifert, B., Lindvall, T., Eds.; Elsevier: Amsterdam, 1995. (19) Hodgson, A. T.; Daisey, J. M.; Mahanama, K. R. R.; Ten Brinke, J.; Alevantis, L. E. Environ. Intl. 1996, 22, 295-307. (20) Martin P.; Heavner, D. L.; Nelson, P. R.; Maiolo, K. C.; Risner, C. H.; Simmons, P. S.; Morgan, W. T.; Ogden, M. W. Environ. Intl. 1997, 23, 75-90. (21) Nelson, P. R.; Conrad, F. W.; Kelly, S. P. Proceedings, 5th International Aerosol Conference; Brighton, U.K. Journal of Aerosol Science; 1998; S281-S282.
Received for review August 22, 2000. Revised manuscript received December 12, 2000. Accepted December 19, 2000. ES000192Y
