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Influence of basements, garages, and common hallways on indoor residential volatile organic compound concentrations
ARTICLE IN PRESS
Atmospheric Environment 42 (2008) 1569–1581 www.elsevier.com/locate/atmosenv
Influence of basements, garages, and common hallways on indoor residential volatile organic compound concentrations Robin E. Dodsona,, Jonathan I. Levya, John D. Spenglera, James P. Shinea, Deborah H. Bennetta,b a
Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA b Department of Public Health Sciences, University of California, Davis, CA, USA
Received 6 June 2007; received in revised form 26 October 2007; accepted 31 October 2007
Abstract Concentrations of many volatile organic compounds (VOCs) are often higher inside residences than outdoors as a result of sources or activities within the residences. These sources can be located directly in the living space of the home or in areas associated with the home such as an attached garage, basement, or common apartment hallway. To characterize the contributions from these areas to indoor residential concentrations, VOC concentrations were measured inside, outside, and, if present, in the attached garage, basement, or common hallway of an apartment of 55 residences in the Boston area, most over two seasons, as part of the Boston Exposure Assessment in Microenvironments (BEAM) Study. Of the 55 residences in the study, 11 had attached garages and basements, 24 had only basements, 10 other residences had common apartment hallways, and the remaining 10 were treated as single compartment residences. Concentrations in the garage were up to 5–10 times higher at the median than indoor concentrations for mobile source pollutants including benzene, toluene, ethylbenzene, and xylenes. Basement/indoor concentration ratios were significantly 41 for methylene chloride, ethylbenzene, m,p-xylene, and o-xylene, and summer ratios tended to be higher than winter ratios. Approximately, 20–40% of the indoor concentration for compounds associated with gasoline sources, such as methyl t-butyl ether (MTBE), benzene, toluene, ethylbenzene, and xylenes, can be attributed to an attached garage at the residence, with garages laterally attached to the first floor of the home having a larger impact. At the median, basements contributed to approximately 10–20% of the estimated indoor concentrations. For apartments, approximately 5–10% of the estimated indoor concentrations confer with air from the hallway. Contributions of these secondary zones to concentrations in the living area of a home were calculated using concentration and airflow estimates. Our findings illustrate the potential significance of these non-living spaces from an exposure perspective and suggest potentially effective mitigation measures. r 2007 Elsevier Ltd. All rights reserved. Keywords: Attached garages; Basements; Apartment; Mass-balance model
1. Introduction Corresponding author. Tel.: +1 617 384 8815; fax: +1 617 384 8859. E-mail address: [email protected] (R.E. Dodson).
1352-2310/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2007.10.088
For several volatile organic compounds (VOCs), past studies have found that indoor concentrations constitute a significant portion of overall exposure
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due both to the amount of time spent indoors and elevated concentrations indoors (Adgate et al., 2004a, b; Hodgson, 2003; Sax et al., 2006; Sexton et al., 2004). Increased indoor concentration levels result from sources of VOCs present directly within the occupied area of the residence as well as in areas such as attached garages, basements, or common apartment hallways. The impact of sources of VOCs in these regions of the residence and the resulting transport into the occupied area are not well understood for US residences. In addition to automobiles, people often store gasoline, oil, paints, lacquers, and yard and garden supplies in garages, which can be a source of VOCs such as benzene, toluene, ethylbenzene, m,p-xylene and o-xylene (BTEX), both from evaporative emissions and start-up/shut-down emissions (Batterman et al., 2006a). As a result, some studies have found elevated indoor VOC concentrations in residences with attached garages compared to those without attached garages (Adgate et al., 2004b; Gordon et al., 1999; Graham et al., 1999; Lansari et al., 1996; Thomas et al., 1993; Wallace, 1991). While previous studies have shown elevated concentration levels, limited studies have attempted to quantify the contribution of the attached garage. For example, available studies estimated that over 50% of benzene concentrations in a home may be attributable to the garage (Batterman et al., 2007; Furtaw et al., 1993; Noseworthy and Graham, 1999). Another potential area associated with the home that may influence residential exposures is a basement. Approximately, 45% of all residences in the US have a basement, with the New England area having approximately 93% of residences with basements (US EPA, 1997). Basement air can be exchanged with upstairs air (Dodson et al., 2007; McGrath and McManus, 1996; Olson and Corsi, 2001), and transport of radon and VOCs from contaminated soils to homes has been well documented (Nazaroff et al., 1985; Wang and Ward, 2002). In addition, many residents may store products such as solvents, paints, and some gasoline products in basements. These sources of VOCs may result in elevated concentrations within the basement area, which can be potentially transported into the occupied area of the residence. However, this process has not been quantified. In addition, airflows within an apartment building may transport concentrations into an apartment unit via the common apartment hallway. Sax et al.
(2004) suggested concentrations of some VOCs within apartment units unaccounted for by known activities within the apartment are from pathways within the building. Although airflows within apartment buildings have been investigated, little research has been conducted to quantify the impact of interior corridors on concentrations observed in an apartment unit (Diamond et al., 1996). The objective of this study was to estimate the potential contribution of attached garages, basements, and common apartment hallways to occupied area concentrations. While single family homes are quite different from apartment units, both types are common in the US housing stock and exposure to VOCs in all types of residences need to be better characterized. Specifically, we measured the concentrations in attached garages, basements, common apartment hallways, and occupied areas of residences during 89 sampling visits to 55 residences in the Boston, Massachusetts area to quantify the percent contribution of these areas to the occupied area’s concentrations of 17 different VOCs. Concentrations were then combined with previously estimated airflow rates to investigate the impact on concentrations in the occupied area. 2. Methods 2.1. Study design The Boston Exposure Assessment in Microenvironments (BEAM) Study enrolled a total of 55 nonsmoking participants from sub-urban and urban locations throughout the Boston, Massachusetts area as a convenience sample, including through the Harvard School of Public Health alumni network, local boards of health, and environmental organizations. A total of 89 sampling visits were conducted across two seasons (summer 2004 and winter 2005), with 34 repeat visits and 8 and 13 visits in the summer and winter seasons only, respectively, due to participant availability. Of the 55 residences involved, 11 had an attached garage and basement, 24 had a basement only and 10 were apartment units with an interior common hallway. All of the residences with an attached garage also had a basement. The remaining 10 residences did not have a secondary zone of potential interest but are included with indoor concentrations for comparison purposes. Additional details regarding the residences in this study can be found in Dodson et al. (2007).
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Tracer gas measurements used to estimate air flows and integrated VOC measurements for 17 compounds (2 aldehydes, 13 other VOCs, a-pinene, and d-limonene) were collected over a 48 h period, generally Tuesday evening to Thursday evening. Samples were collected at breathing height outdoors, in the occupied area of the home, typically the living room, and when applicable, in the garage, basement, and/or common apartment hallway. Compounds selected were found at elevated levels in previous studies and/or pose a health risk at observable levels. a-Pinene and d-limonene, two reactive compounds frequently found in air fresheners and cleaning products, were specifically included because as unsaturated hydrocarbons they can react with ozone to form particles, aldehydes and organic acids (Fan et al., 2003). Simultaneous airflow rates over the same time period were quantified between zones in the residence and with the outdoors as discussed in Dodson et al. (2007). In short, the garage airflow rates were estimated continuously while the estimates for the occupied area, basement, and common apartment hallways were integrated measures. Due to the potential rapid changes in airflow within the garage resulting from garage door use, sulfur hexafluoride was continuously released in the garage and then continuously measured both in the garage and in the adjacent zone to the garage over the sampling period. This allowed for continuous estimation of the airflow rates associated with the garage over the entire 48 h sampling period. To quantify the remaining airflow rates within a residence, one type of perflourocarbon tracer was continuously released in the occupied area of the residence and a second type was continuously released in either the basement or common apartment hallway. Each tracer type was then sampled for in each zone over the 48 h sampling period.
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collected using a custom-made triple-bed thermal desorption tube with 200 mg of Carbopack B, 230 mg of Carbopack X, and 170 mg of Carboxen 1001 (Supelco/Perkin-Elmer; Bellefonte, PA), with a target sampling volume of 15 L. Stainless steel diffusion barriers were used on all samples. Tubes were thermally desorbed in the laboratory using an automated thermal desorber (ATD) (Perkin-Elmer, Model 400; Waltham, MA) and analyzed via GC–MS following US EPA Compendium Method TO-17 (Woolfenden and McClenny, 1997). Housing characteristics and activities such as home design and product storage during the sampling period were collected using standardized questionnaires. Field staff also conducted a home walkthrough at the beginning of each sampling period and noted general characteristics about the residence, including ventilation systems and occupant use. 2.3. Data treatment All samples were blank corrected by subtracting the mean value, if it differed significantly from zero, of either the lab or field blanks, whichever is greater. A value equal to one-half the detection limit was used for compounds that were negative after blank correction. Limits of detection (LODs) were calculated as three times the standard deviation of the field blanks or analytical method LOD, whichever is greater, for each season. The median relative precision across all analytical samples by compound was 65% (range 7–96%). Additional quality assurance and quality control information is provided in the Supplemental material. Due to moisture issues in some of the summer samples, some samples were lost and are not included in the analyses. For this reason, sample sizes are specified for each analysis since a lost sample differentially impacted sample sizes needed for ratio and contribution analyses.
2.2. Sampling and analytical methods 2.4. Concentrations and ratios Formaldehyde and acetaldehyde were actively collected using acidified 2,4-dinitrophenylhydrazine (DNPH)-coated silica cartridges (Waters Corp.; Milford, MA), with a target sampling volume of 300 L, and analyzed via HPLC following US EPA Compendium Method TO-11A (Willbury et al., 1999). Ozone scrubbers containing potassium iodide were used with all summer outdoor aldehyde samplers (Arnts and Tejada, 1989; Sirju and Shepson, 1995). All other VOCs were actively
Measured concentrations in the occupied area (indoor), outdoors, attached garage, basement, and common apartment hallway are summarized and potential relationships or predictors, including season, were explored using Wilcoxon rank sum tests (unpaired) and Wilcoxon sign rank tests (paired), if appropriate. Measured garage, basement, and common hallway concentrations were divided by the concentration measured in the
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occupied area for each residence. Ratios 41 indicate that the garage, basement, or apartment hallway may be a potential source to the occupied area if air also flows from these areas to the occupied area. Ratios significantly different from one were tested for using a Wilcoxon sign rank test. 2.5. Contribution to indoor concentrations Concentrations in the occupied area can be apportioned between infiltration of outdoor air, sources in the occupied area, and where applicable, sources in the garages or basements, and infiltration of air from the apartment hallways. We note that quantified sources within the apartment hallway may be a result of sources in the hallway or from other units connected to the hallway. Steady state multi-zonal mass-balance models assuming wellmixed compartments were used, depending on the home configuration (e.g., a two compartment model was used if there was only an occupied area and a basement and a three compartment model was used if there was also an attached garage). Airflow estimates previously calculated from multi-zonal mass-balance models of tracer gases were used in the model (see Dodson et al., 2007 for airflow
estimates). Airflow estimates were concurrent with concentration measurements. Airflow estimates were removed from the analysis if the total flow within the compartment is extreme in either direction and thus considered an outlier, defined as values 4 or o 1.5 times the 75th or 25th percentile, respectively, on a log scale. These airflow estimates were combined with the concentration of the compound in each compartment to determine the source rate within each compartment. The source rate for each compartment was then used to determine the concentration in that compartment resulting only from sources in that compartment. This concentration was then multiplied by the airflow rate into the occupied area to determine the resulting mass flow to the occupied area resulting from that adjacent area. Mass flows to the occupied area also come from infiltration of outdoor air and sources in the occupied area, which were also quantified. The percent contribution of mass flows from the garages, basements, hallways, outdoors, and occupied area to the total mass flow to the occupied area were then calculated for each home, with the distributions across homes for the first three contributions presented in this paper. For additional details, see equations in Supplemental material.
Table 1 Arithmetic means and S.D. (in parentheses) of measured concentrations (in mg m3)
Methylene chloride Chloroform Trichloroethene Tetrachloroethene 1,4-Dichlorobenzene 1,3-Butadiene MTBE Benzene Toluene Ethylbenzene m,p-Xylene o-Xylene Styrene a-Pinene d-Limonene Formaldehyde Acetaldehyde
LODa,b Summer
LOD Winter
Indoor (n ¼ 83)
Outdoor (n ¼ 80)
Garage (n ¼ 16)
Basement (n ¼ 52)
Hallway (n ¼ 10)
0.39 0.08 0.04 0.17 0.34 0.36 0.12 0.30 0.24 0.06 0.13 0.06 0.19 0.03 0.19 0.4 0.7
1.25 0.06 0.04 0.07 0.13 0.87 0.04 1.51 0.15 0.04 0.12 0.06 0.16 0.03 0.03 0.4 0.7
2.5 (8.7) 1.2 (1.2) 0.61 (1.7) 1.9 (3.1) 3.1 (16) 0.54 (1.1) 7.6 (16) 2.6 (3.1) 13 (15) 2.4 (3.1) 7.3 (9.7) 2.6 (3.5) 1.1 (1.9) 11 (32) 17 (26) 21 (16) 13 (13)
0.28 (0.24) 0.07 (0.13) 0.13 (0.49) 0.46 (0.92) 0.26 (0.47) 0.27 (0.36) 1.2 (0.96) 0.88 (0.66) 2.3 (1.4) 0.42 (0.29) 1.3 (0.99) 0.47 (0.35) 0.1 (0.07) 0.42 (0.85) 0.23 (0.4) 1.2 (1.6) 5.6 (8.3)
9.8 (36) 0.08 (0.08) 3.3 (10) 2.8 (7.8) 2.3 (8.4) 7.4 (18) 131 (338) 58 (145) 102 (69) 35 (39) 90 (64) 35 (36) 3.4 (5.3) 38 (110) 7.3 (13) 6.7 (6.4) 8.9 (8.6)
9.5 (28) 0.57 (1) 0.43 (1.1) 1.7 (6.4) 1.3 (3.4) 0.5 (1) 8.8 (13) 3.2 (5) 21 (24) 4.1 (5.7) 12 (16) 4.2 (5.7) 1.7 (4.5) 11 (23) 8.8 (12) 12 (12) 8.5 (11)
2.6 (4.6) 1.3 (1) 3.7 (7.3) 1.9 (3.4) 0.78 (0.92) 0.68 (0.51) 3.2 (4.1) 2.8 (4.3) 9.9 (13) 2.1 (3.4) 6.2 (9.7) 2.2 (3.5) 1.1 (1.6) 10 (28) 10 (20) 12 (7.8) 7.3 (5.2)
Additional measured concentration summary statistics provided in the supplemental material. a Season-specific limits of detection (LODs) were calculated. b LODs converted to concentrations assuming 48 sampling period and sampling rates of 5.21 and 104 cm3 min1 for VOCs and aldehydes, respectively.
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compounds and zones; however, both methylene chloride and 1,3-butadiene were detected the least frequently in all zones. Due to this measurement misclassification, the contribution estimates may be biased towards the null. Nevertheless, 1,3-butadiene and methylene chloride were included in subsequent analyses because of their potential health effects. Residences with attached garages had significantly higher measured indoor benzene (p ¼ 0.0072), toluene (p ¼ 0.00080), ethylbenzene (p ¼ 0.00027), m,p-xylene (p ¼ 0.00019), o-xylene (p ¼ 0.00010) (BTEX), and methyl t-butyl ether (MTBE) (p ¼ 0.000048) concentrations than residences without attached garages while other compounds were not significantly different in homes with attached garages (Fig. 1). On average, the indoor BTEX concentrations in residences with attached garages were two to six times higher than those in those without attached garages. These results are consistent with findings from other studies (Batterman et al., 2007; Isbell et al., 2005; Thomas et al., 1993). The concentrations measured
3. Results and discussion 3.1. Concentrations Table 1 presents the arithmetic means and standard deviations (S.D.) of the concentrations measured in the occupied areas of the residence, basements, hallways, and attached garages across both seasons. The indoor concentrations were lower than those observed in a New York City and Los Angeles-based study (Sax et al., 2006) but were comparable to recent studies in Minnesota (Adgate et al., 2004a, b) while the measured outdoor concentrations were lower than those observed in these studies, possibly a result of including both suburban and urban residences in this study. Comparison of measured concentrations in the basement and hallway are not available as this is one of the few studies to study these zones. Additional summary statistics, including the percent to samples above the LOD are provided in the Supplemental material. The detection frequency varied across
Measured Indoor Concentration (µg/m3)
100
10
1
MTBE
Benzene
Toluene
Ethylbenzene
m,p-Xylene
no Garage
Garage
no Garage
Garage
no Garage
Garage
no Garage
Garage
no Garage
Garage
no Garage
Garage
0.1
o-Xylene
Fig. 1. Measured indoor concentrations for residences with (n ¼ 15) and without (n ¼ 68) an attached garage. Only compounds with significant differences shown. Note: log scale on concentration axis and box plots represent 5th, 25th, 50th, 75th, and 95th percentiles.
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(p ¼ 0.045), tetrachloroethene (p ¼ 0.0015), styrene (p ¼ 0.00020), o-xylene (p ¼ 0.047), 1,4-DCB (p ¼ 0.0084), a-pinene (p ¼ 0.0012), d-limonene (p ¼ 0.019), formaldehyde (p ¼ 0.00043), and acetaldehyde (p ¼ 0.0048). Those residences with basements associated with attached garages had significantly higher basement concentrations for 1,3-butadiene, benzene, carbon tetrachloride, toluene, ethylbenzene, m,p-xylene, o-xylene, and 1,4-DCB (po0.05) than those residences with basements but without a garage or with the garage attached to the occupied area. While many of these compounds may be a result of gasoline-related sources within the garage, the association with carbon tetrachloride and 1,4DCB is less clear. In 8 of the 52 basements visits, at least one type of gasoline powered equipment (including motorcycle, lawnmower, trimmers, leaf or snow blower, or boat engine) or gasoline containers was being stored in the basement. These basements had significantly higher concentrations of MTBE, tetrachloroethene, ethylbenzene, m,pxylene, o-xylene, styrene, and a-pinene (po0.05). While some of these compounds do not result from
in the attached garage tend to be higher in the summer than in the winter for most compounds except 1,3-butadiene and a-pinene. This may be due to the higher airflow rates out of the garage or lower temperatures in the winter. Residences with basements had significantly lower occupied area concentrations of trichloroethene (p ¼ 0.0071), chloroform (p ¼ 0.025), tetrachloroethene (p ¼ 0.0053), and 1,4-dichlorobenzene (1,4-DCB) (p ¼ 0.018) compared to those residences without basements. Overall, the measured concentrations in the basement tend to be higher, on average, for most compounds, in the summer than in the winter, likely the result of dilution from increased airflows in the winter. Paired tests revealed significantly higher summer concentrations for 14 out of the 17 compounds investigated (n ¼ 18, po0.05), with the exceptions being 1,3butadiene, methylene chloride, chloroform, and benzene. Using unpaired tests with all of the data, the summer concentrations (n ¼ 21) are significantly higher than winter concentrations (n ¼ 31) for 9 out of the 17 compounds, specifically trichloroethene
*
*
*
o-Xylene
*
m,p-Xylene
*
*
Ethylbenzene
Measured Garage/Measured Indoor Concentrations
100
* 10
1
0.1
Acetaldehyde
Formaldehyde
d-Limonene
a-Pinene
Styrene
Toluene
Benzene
MTBE
1,3-Butadiene
1,4-DCB
Tetrachloroethene
Trichloroethene
Chloroform
Methylene Chloride
0.01
Fig. 2. Garage/indoor concentration ratios across seasons (n ¼ 15). Indoor indicates occupied area of the home. Note: 5th, 25th, 50th, 75th, and 95th percentiles shown in box plots and log scale. Ratios that are significantly 41 are shown with asterisk (*po0.05).
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indoor concentrations. The observed differences for BTEX compounds between garage and indoor concentrations are similar to those found in other studies (Batterman et al., 2006a, b, 2007; Tsai and Weisel, 2000). For the basement ratios, we present ratios by season to highlight the differences. The basement/ indoor ratios across seasons for methylene chloride (p ¼ 0.016), ethylbenzene (p ¼ 0.0049), m,p-xylene (p ¼ 0.0013), and o-xylene (p ¼ 0.0061) were significantly 41 while ratios for chloroform (p ¼ 0.00029), formaldehyde (p ¼ 0.00023), and acetaldehyde (p ¼ 0.0027) were significantly o1. The majority of the compounds (12 out of 17) had basement/indoor ratios that were significantly higher in the summer than in the winter (po0.05), when using all available data. As not all homes were sampled in both seasons, we also looked just at paired samples, finding virtually the same results, with MTBE being added to the list of compounds with significant seasonal differences and 1,4-DCB being dropped. Higher summer ratios are likely due
gasoline powered equipment, gasoline powered equipment may be a proxy for having more intensive storage of other products as well. 3.2. Ratios The distribution of the ratios of concentrations measured within the attached garages, basements, and hallways compared to the concentrations measured in the occupied area are presented in Figs. 2–4. Compounds associated with gasoline and vehicle exhaust, such as 1,3-butadiene (p ¼ 0.0016), MTBE (p ¼ 0.00006), benzene (p ¼ 0.00006), toluene (p ¼ 0.00006), ethylbenzene (p ¼ 0.00006), and xylenes (p ¼ 0.00006) had median garage/ indoor concentration ratios significantly 41, while chloroform (p ¼ 0.00006), tetrachloroethene (p ¼ 0.022), d-limonene (p ¼ 0.022), formaldehyde (p ¼ 0.00012), and acetaldehyde (p ¼ 0.018) had ratios significantly o1. In fact, the mobile source compounds had measured garage concentrations 5–10 times higher at the median than the measured 1000
# *
* 100
*
#
#
*
#
#
#
# #
#
10
# #
#
1
0.1
Acetaldehyde (S)
Acetaldehyde (W)
Formaldehyde (W)
d-Limonene (W)
Formaldehyde (S)
a-Pinene (W)
d-Limonene (S)
Styrene (W)
a-Pinene (S)
Styrene (S)
o-Xylene (S)
o-Xylene (W)
m,p-Xylene (S)
m,p-Xylene (W)
Ethylbenzene (W)
Toluene (W)
Ethylbenzene (S)
Toluene (S)
Benzene (S)
Benzene (W)
MTBE (S)
MTBE (W)
1,3-Butadiene (S)
1,3-Butadiene (W)
1,4-DCB (S)
1,4-DCB (W)
Tetrachloroethene (S)
Tetrachloroethene (W)
Trichloroethene (S)
Trichloroethene (W)
Chloroform (S)
Chloroform (W)
Methylene Chloride (S)
0.01 Methylene Chloride (W)
Measured Basement/Measured Indoor Concentrations
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Fig. 3. Basement/indoor concentration ratios in summer (S) (n ¼ 19) and winter (W) (n ¼ 31). Indoor indicates occupied area of the home. Note: 5th, 25th, 50th, 75th, and 95th percentiles shown in box plots and log scale. Ratios that are significantly 41 are shown with asterisk (*po0.05). Summer ratios that are significantly greater than winter ratios are shown with a pound sign (#po0.05).
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Measured Hallway/Measured Indoor Concetrations
100
10
*
1
0.1
Acetaldehyde
Formaldehyde
d-Limonene
a-Pinene
Styrene
o-Xylene
m,p-Xylene
Ethylbenzene
Toluene
Benzene
MTBE
1,3-Butadiene
1,4-DCB
Tetrachloroethene
Trichloroethene
Chloroform
Methylene Chloride
0.01
Fig. 4. Hallway/indoor concentration ratios across seasons (n ¼ 10). Indoor indicates occupied area of the home. Note: 5th, 25th, 50th, 75th, and 95th percentiles shown in box plots and log scale. Ratios that are significantly 41 are shown with asterisk (*po0.05).
3.3. Contribution to indoor concentrations
dominant source to the occupied area while in others the outdoor or sources within the occupied area are dominant. Each home-compound combination can be represented by a pie chart, for example, see inset in Fig. 5. To summarize the contributions across residences, therefore, for a given compound, we present the distribution across residences of the percent contribution from sources within the attached garage, basement, and common apartment hallway to the occupied area’s estimated concentrations (Figs. 5–7), with contributions from sources within the occupied area and outdoors presented in the Supplemental material. We note that the distributions will not sum to 100% due to variability across homes.
For each residence, treated independently across seasons, we can determine the percent contribution to the indoor concentration from the outside and each compartment within the home. The contributions from each region are highly variable across participants’ residences. Using toluene as an example, in some residences, the basement is the
3.3.1. Garages At the median, approximately 40% of the indoor concentrations of benzene, toluene, ethylbenzene, and xylenes are attributable to the attached garage. Graham et al. (2004) found that between 10% and 85% of the concentrations measured in the one residence during the study can be attributable to the
to lower airflow rates in the basements and higher airflow rates in the occupied area. The median hallway/indoor concentration ratios were near one for almost all compounds; however, the distribution of ratios spanned at least an order of magnitude. Only 1,3-butadiene (p ¼ 0.0059) had a median ratio significantly 41 while only formaldehyde (p ¼ 0.037) had a median ratio significantly o1. Over 75% of the ratios for 1,4-DCB were above one; however, the median was not statistically different than one (p ¼ 0.11). The lack of statistical significance may be due to the small sample number (n ¼ 10).
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100
Percent Contribution from Garage (%)
outdoor
indoor
80
basement
garage
60
40
20
Acetaldehyde
Formaldehyde
d-Limonene
a-Pinene
Styrene
o-Xylene
m,p-Xylene
Ethylbenzene
Toluene
Benzene
MTBE
1,3-Butadiene
1,4-DCB
Tetrachloroethene
Trichloroethene
Chloroform
Methylene Chloride
0
Fig. 5. Garage contribution to estimated indoor concentration (n ¼ 9) across seasons and garage type. Inset: hypothetical pie graph for one residence showing the contribution of the various areas on indoor concentration. Contribution of the attached garage is solid and represents just one of the data points included in the distributions presented in the box plots. Note: box plots include the median and 5th, 25th, 75th, and 95th percentiles.
attached garage. In a recent study by Batterman et al. (2007) approximately 50–60% of the indoor BTEX concentrations were attributable to the garage, which substantiates our findings. The impact of other similarly measured compounds on the indoor concentrations is not remarkable. Due to the small sample size, the contribution box plot for the attached garages contains both the sub-terranean (sub) and lateral garages; however, in general, the lateral garages had a larger median percent contribution than the sub-garages. All of the sub-garages in this analysis were connected to the basement of the residence and so the contributions reflect the transport through an intermediate zone, through which it was assumed that all air traveled from the garage to the occupied area. We should note, however, that the airflow rate between the sub-garage and the basement was higher than the airflow rate between the lateral garage and the occupied area and the lower percent contributions are a result of the transport through the inter-
mediate zone (i.e., the basement). The results of this study highlight a potentially important issue in home design; establishing living areas in zones immediately adjacent to the sub-garages can result in higher exposures. 3.3.2. Basements The median percent contributions from the basement range from effectively 0% for 1,3-butadiene to 22% for m,p-xylene, although significant variability exists in contribution estimates for most compounds. While we saw higher concentration ratios in summer than winter, this effect was not consistently seen in the source contributions because, in part, the airflow rates were shown to be lower in the summer than in the winter in a previous paper (Dodson et al., 2007). As a result, the contribution from the basement of 1,4-DCB (p ¼ 0.0016) and acetaldehyde (p ¼ 0.013) is significantly less in the summer season. In general, 1,3-butadiene, tetrachloroethene, styrene, o-xylene, a-pinene, and
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Percent Contribution from Basement (%)
100
80
60
40
20
Acetaldehyde
Formaldehyde
d-Limonene
a-Pinene
Styrene
o-Xylene
m,p-Xylene
Ethylbenzene
Toluene
Benzene
MTBE
1,3-Butadiene
1,4-DCB
Tetrachloroethene
Trichloroethene
Chloroform
Methylene Chloride
0
Fig. 6. Basement contribution to estimated indoor concentration (n ¼ 42) across seasons. Note: box plots include the median and 5th, 25th, 75th, and 95th percentiles.
d-limonene contributed to occupied area concentrations to a slightly greater extent in the summer than in the winter season. All other compounds had higher contributions, on a mass basis, in the winter. 3.3.3. Hallways The median percent contribution from the hallway ranges from o1% for tetrachloroethylene to 18% for 1,4-DCB. As an example, very few participants reported using products containing 1,4-DCB, indicating the potential impact of other units on hallway concentrations and ultimately exposures within individual units. 3.4. Potential limitations Potential limitations to this work include elevated LODs for some compounds and uncertainty in the air exchange, measured chemical concentrations, and estimated concentration contributions. A standard approach of using one-half the detection limit for undetected compounds was used; however, we
note that the results for methylene chloride, the outdoor and garage results for 1,4-DCB, 1,3butadiene, outdoor results for styrene, and the hallway and outdoor results for benzene should be interpreted with caution given the small fraction of samples above the LOD. There are uncertainties in the airflow estimates as a result of the mass-balance model assumptions; however, the range of uncertainty is less than the range of variability, as discussed in a previous paper (see Dodson et al., 2007). Uncertainties related to measurement error (i.e., precision) and its impact on the chemical concentrations, since they are non-differential, will only bias the results towards a null finding due to increased variability. Another potential limitation is that we were unable to account specifically for any soil vapor intrusion contribution into the basement and thereby into the home. We believe the influence of soil vapor as a source of VOCs to the basement to be small, if not negligible, as none of our homes were reported to be above or in close proximity to
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Percent Contribution from Hallway (%)
100
80
60
40
20
Acetaldehyde
Formaldehyde
d-Limonene
a-Pinene
Styrene
o-Xylene
m,p-Xylene
Ethylbenzene
Toluene
Benzene
MTBE
1,3-Butadiene
1,4-DCB
Tetrachloroethene
Trichloroethene
Chloroform
Methylene Chloride
0
Fig. 7. Hallway contribution to estimated indoor concentration (n ¼ 9) across seasons. Note: box plots include the median and 5th, 25th, 75th, and 95th percentiles.
a major contaminated groundwater plume (Hers et al., 2001). 3.5. Conclusions This work adds substantially to the literature on the impact of attached garages, basements, and common apartment hallways on occupied area concentrations. Residences with attached garage, basements, or common apartment hallways areas are associated with different residence types; however, it is apparent that occupied areas may be affected by sources within associated areas. While the outdoor air and sources in the occupied area generally make up the majority of the observed concentration in the occupied area, mass flows from other regions do represent a potentially substantial contribution in some of the homes studied. Understanding the potential impact of attached garages, basements, and common apartment hallways on exposures experienced within the home is important for both future modeling efforts characterizing the
impact of indoor residential exposures on personal concentrations as well as exposure reduction. These results suggest that proper storage of products containing solvents within basements or attached garages as well as increased ventilation within these areas is important to mitigate exposures within the home. It also verifies our hypothesis that activities within an apartment building but outside of the individual units may impact the residents within the individual units. Acknowledgments This work is funded by a grant from the American Chemistry Council. Laboratory analyses were partially funded by the Harvard NIEHS Center for Environmental Health (Grant no. P30ES00002). We would like to thank the study participants for letting us study their residences. We would also like to acknowledge the field staff (J. Allen, S. Sax, M. Loh, M. Anand, M. Anand, K. Kopko, T. Goldberg, and M. Penterson),
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sampler design engineer (M. Davey), the laboratory staff (B. LaBrecque, S. Forsberg, and R. Weker), database manager (S. Melly), and QA/QC supervisor (J. Vallarino) for their help with this study. Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at doi:10.1016/ j.atmosenv.2007.10.088.
References Adgate, J.L., Eberly, L.E., Stroebel, C., Pellizzari, E.D., Sexton, K., 2004a. Personal, indoor, and outdoor VOC exposures in a probability sample of children. Journal of Exposure Analysis and Environmental Epidemiology 14, S4–S13. Adgate, J.L., Church, T.R., Ryan, A.D., Ramachandran, G., Fredrickson, A.L., Stock, T.H., Morandi, M.T., Sexton, K., 2004b. Outdoor, indoor, and personal exposure to VOCs in children. Environmental Health Perspectives 112, 1386–1392. Arnts, R.R., Tejada, S.B., 1989. 2,4-Dinitrophenylhydrazinecoated silica-gel cartridge method for determination of formaldehyde in air—identification of an ozone interference. Environmental Science and Technology 23, 1428–1430. Batterman, S., Hatzvasilis, G., Jia, C.R., 2006a. Concentrations and emissions of gasoline and other vapors from residential vehicle garages. Atmospheric Environment 40, 1828–1844. Batterman, S., Jia, C.R., Hatzivasilis, G., Godwin, C., 2006b. Simultaneous measurement of ventilation using tracer gas techniques and VOC concentrations in homes, garages and vehicles. Journal of Environmental Monitoring 8, 249–256. Batterman, S., Jia, C.R., Hatzivasilis, G., 2007. Migration of volatile organic compounds from attached garages to residences: a major exposure source. Environmental Research 104, 224–240. Diamond, R.C., Feustel, H.E., Dickeroff, D.J., 1996. Ventilation and Infiltration in High-Rise Apartment Buildings. Lawrence Berkeley Laboratory. Dodson, R.E., Levy, J.I., Shine, J.P., Spengler, J.D., Bennett, D.H., 2007. Multi-zonal air flow rates in residences in Boston, Massachusetts. Atmospheric Environment 41, 3722–3727. Fan, Z., Lioy, P.J., Weschler, C.J., Fiedler, N., Kipen, H., Zhang, J., 2003. Ozone-initiated reactions with mixtures of volatile organic compounds under simulated indoor conditions. Environmental Science and Technology 37, 1811–1821. Furtaw, E.J., Pandian, M.D., Behar, J.V., 1993. Human exposure in residences to benzene vapors from attached garages. In: Proceedings of International Conference on Indoor Air Quality and Climate, Indoor Air ‘93, Vol 5. Gordon, S., Callahan, P., Nishioka, M., Brinkman, M., O’Rourke, M., Lebowitz, M., Moschandreas, D., 1999. Residential environmental measures in the National Human Exposure Assessment Survey (NHEXAS) pilot study in Arizona: preliminary results for pesticides and VOCs. Journal of Exposure Analysis and Environmental Epidemiology 9, 456–470.
Graham, L., O’Leary, K. Noseworthy, L., 1999. Indoor air sampling for infiltration of vehicle emissions to the house from the attached garage. ERMD Report No. 99-26768-2, Environment Canada. Graham, L.A., Noseworthy, L., Fugler, D., O’Leary, K., Karman, D., Grande, C., 2004. Contribution of vehicle emissions from an attached garage to residential indoor air pollution levels. Journal of the Air and Waste Management Association 54, 563–584. Hers, I., Zapf-Gilje, R., Li, L., Atwater, J., 2001. The use of indoor air measurements to evaluate intrusion of subsurface VOC vapors into buildings. Journal of the Air and Waste Management Association 51, 1318–1331. Hodgson, A.T., 2003. Volatile Organic Compounds in Indoor air: A Review of Concentrations Measured in North America Since 1990. E.O. Lawrence Berkeley National Laboratory, LBNL-51715. Isbell, M.A., Stolzberg, R.J., Duffy, L.K., 2005. Indoor climate in interior Alaska: simultaneous measurement of ventilation, benzene and toluene in residential indoor air of two homes. Science of the Total Environment 345, 31–40. Lansari, A., Streicher, J.J., Huber, A.H., Crescenti, G.H., Zweidinger, R.B., Duncan, J.W., Weisel, C.P., Burton, R.M., 1996. Dispersion of automotive alternative fuel vapors within a residence and its attached garage. Indoor AirInternational Journal of Indoor Air Quality and Climate 6, 118–126. McGrath, P., McManus, J., 1996. Air infiltration from basements and sub-floors to the living space. Building Services Engineering Research and Technology 17. Nazaroff, W.W., Feustel, H., Nero, A.V., Revzan, K.L., Grimsrud, D.T., Essling, M.A., Toohey, R.E., 1985. Radon transport into a detached one-story house with a basement. Atmospheric Environment 19, 31–46. Noseworthy, L., Graham, L., 1999. Chemical mass balance analysis of vehicle emissions in residential houses from attached garages. ERMD Report No. 99-26768-3, Environment Canada. Olson, D.A., Corsi, R.L., 2001. Characterizing exposure to chemicals from soil vapor intrusion using a two-compartment model. Atmospheric Environment 35, 4201–4209. Sax, S.N., Bennett, D.H., Chillrud, S.N., Kinney, P.L., Spengler, J.D., 2004. Differences in source emission rates of volatile organic compounds in inner-city residences of New York City and Los Angeles. Journal of Exposure Analysis and Environmental Epidemiology 14 (Suppl. 1), S95–S109. Sax, S.N., Bennett, D.H., Chillrud, S.N., Ross, J., Kinney, P.L., Spengler, J.D., 2006. A cancer risk assessment of inner-city teenagers living in New York City and Los Angeles. Environmental Health Perspectives 114, 1558–1566. Sexton, K., Adgate, J.L., Ramachandran, G., Pratt, G.C., Mongin, S.J., Stock, T.H., Morandi, M.T., 2004. Comparison of personal, indoor, and outdoor exposures to hazardous air pollutants in three urban communities. Environmental Science and Technology 38, 423–430. Sirju, A.P., Shepson, P.B., 1995. Laboratory and field investigation of the DNPH cartridge technique for the measurement of atmospheric carbonyl-compounds. Environmental Science and Technology 29, 384–392. Thomas, K.W., Pellizzari, E.D., Clayton, C.A., Perritt, R.L., Dietz, R.N., Goodrich, R.W., Nelson, W.C., Wallace, L.A., 1993. Temporal variability of benzene exposures for residents
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Wang, F., Ward, I., 2002. Radon entry, migration and reduction in houses with cellars. Building and Environment 37, 1153–1165. Willbury, W.T., Tejada, S., Lonneman, W., Kleindienst, E., 1999. Compendium Method TO-11A: Determination of Formaldehyde in Ambient Air Using Adsorbent Followed by High Performance Liquid Chromotography (HPLC) (Active Sampling Methodology). US Environmental Protection Agency. EPA/625/R-96/010b. Woolfenden, E., McClenny, W., 1997. Compendium Method TO-17: Determination of Volatile Organic Compounds in Ambient Air Using Active Sampling onto Sorbent Tubes. US Environmental Protection Agency. EPA/625/R-96/010b.
Atmospheric Environment 42 (2008) 1569–1581 www.elsevier.com/locate/atmosenv
Influence of basements, garages, and common hallways on indoor residential volatile organic compound concentrations Robin E. Dodsona,, Jonathan I. Levya, John D. Spenglera, James P. Shinea, Deborah H. Bennetta,b a
Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA b Department of Public Health Sciences, University of California, Davis, CA, USA
Received 6 June 2007; received in revised form 26 October 2007; accepted 31 October 2007
Abstract Concentrations of many volatile organic compounds (VOCs) are often higher inside residences than outdoors as a result of sources or activities within the residences. These sources can be located directly in the living space of the home or in areas associated with the home such as an attached garage, basement, or common apartment hallway. To characterize the contributions from these areas to indoor residential concentrations, VOC concentrations were measured inside, outside, and, if present, in the attached garage, basement, or common hallway of an apartment of 55 residences in the Boston area, most over two seasons, as part of the Boston Exposure Assessment in Microenvironments (BEAM) Study. Of the 55 residences in the study, 11 had attached garages and basements, 24 had only basements, 10 other residences had common apartment hallways, and the remaining 10 were treated as single compartment residences. Concentrations in the garage were up to 5–10 times higher at the median than indoor concentrations for mobile source pollutants including benzene, toluene, ethylbenzene, and xylenes. Basement/indoor concentration ratios were significantly 41 for methylene chloride, ethylbenzene, m,p-xylene, and o-xylene, and summer ratios tended to be higher than winter ratios. Approximately, 20–40% of the indoor concentration for compounds associated with gasoline sources, such as methyl t-butyl ether (MTBE), benzene, toluene, ethylbenzene, and xylenes, can be attributed to an attached garage at the residence, with garages laterally attached to the first floor of the home having a larger impact. At the median, basements contributed to approximately 10–20% of the estimated indoor concentrations. For apartments, approximately 5–10% of the estimated indoor concentrations confer with air from the hallway. Contributions of these secondary zones to concentrations in the living area of a home were calculated using concentration and airflow estimates. Our findings illustrate the potential significance of these non-living spaces from an exposure perspective and suggest potentially effective mitigation measures. r 2007 Elsevier Ltd. All rights reserved. Keywords: Attached garages; Basements; Apartment; Mass-balance model
1. Introduction Corresponding author. Tel.: +1 617 384 8815; fax: +1 617 384 8859. E-mail address: [email protected] (R.E. Dodson).
1352-2310/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2007.10.088
For several volatile organic compounds (VOCs), past studies have found that indoor concentrations constitute a significant portion of overall exposure
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due both to the amount of time spent indoors and elevated concentrations indoors (Adgate et al., 2004a, b; Hodgson, 2003; Sax et al., 2006; Sexton et al., 2004). Increased indoor concentration levels result from sources of VOCs present directly within the occupied area of the residence as well as in areas such as attached garages, basements, or common apartment hallways. The impact of sources of VOCs in these regions of the residence and the resulting transport into the occupied area are not well understood for US residences. In addition to automobiles, people often store gasoline, oil, paints, lacquers, and yard and garden supplies in garages, which can be a source of VOCs such as benzene, toluene, ethylbenzene, m,p-xylene and o-xylene (BTEX), both from evaporative emissions and start-up/shut-down emissions (Batterman et al., 2006a). As a result, some studies have found elevated indoor VOC concentrations in residences with attached garages compared to those without attached garages (Adgate et al., 2004b; Gordon et al., 1999; Graham et al., 1999; Lansari et al., 1996; Thomas et al., 1993; Wallace, 1991). While previous studies have shown elevated concentration levels, limited studies have attempted to quantify the contribution of the attached garage. For example, available studies estimated that over 50% of benzene concentrations in a home may be attributable to the garage (Batterman et al., 2007; Furtaw et al., 1993; Noseworthy and Graham, 1999). Another potential area associated with the home that may influence residential exposures is a basement. Approximately, 45% of all residences in the US have a basement, with the New England area having approximately 93% of residences with basements (US EPA, 1997). Basement air can be exchanged with upstairs air (Dodson et al., 2007; McGrath and McManus, 1996; Olson and Corsi, 2001), and transport of radon and VOCs from contaminated soils to homes has been well documented (Nazaroff et al., 1985; Wang and Ward, 2002). In addition, many residents may store products such as solvents, paints, and some gasoline products in basements. These sources of VOCs may result in elevated concentrations within the basement area, which can be potentially transported into the occupied area of the residence. However, this process has not been quantified. In addition, airflows within an apartment building may transport concentrations into an apartment unit via the common apartment hallway. Sax et al.
(2004) suggested concentrations of some VOCs within apartment units unaccounted for by known activities within the apartment are from pathways within the building. Although airflows within apartment buildings have been investigated, little research has been conducted to quantify the impact of interior corridors on concentrations observed in an apartment unit (Diamond et al., 1996). The objective of this study was to estimate the potential contribution of attached garages, basements, and common apartment hallways to occupied area concentrations. While single family homes are quite different from apartment units, both types are common in the US housing stock and exposure to VOCs in all types of residences need to be better characterized. Specifically, we measured the concentrations in attached garages, basements, common apartment hallways, and occupied areas of residences during 89 sampling visits to 55 residences in the Boston, Massachusetts area to quantify the percent contribution of these areas to the occupied area’s concentrations of 17 different VOCs. Concentrations were then combined with previously estimated airflow rates to investigate the impact on concentrations in the occupied area. 2. Methods 2.1. Study design The Boston Exposure Assessment in Microenvironments (BEAM) Study enrolled a total of 55 nonsmoking participants from sub-urban and urban locations throughout the Boston, Massachusetts area as a convenience sample, including through the Harvard School of Public Health alumni network, local boards of health, and environmental organizations. A total of 89 sampling visits were conducted across two seasons (summer 2004 and winter 2005), with 34 repeat visits and 8 and 13 visits in the summer and winter seasons only, respectively, due to participant availability. Of the 55 residences involved, 11 had an attached garage and basement, 24 had a basement only and 10 were apartment units with an interior common hallway. All of the residences with an attached garage also had a basement. The remaining 10 residences did not have a secondary zone of potential interest but are included with indoor concentrations for comparison purposes. Additional details regarding the residences in this study can be found in Dodson et al. (2007).
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Tracer gas measurements used to estimate air flows and integrated VOC measurements for 17 compounds (2 aldehydes, 13 other VOCs, a-pinene, and d-limonene) were collected over a 48 h period, generally Tuesday evening to Thursday evening. Samples were collected at breathing height outdoors, in the occupied area of the home, typically the living room, and when applicable, in the garage, basement, and/or common apartment hallway. Compounds selected were found at elevated levels in previous studies and/or pose a health risk at observable levels. a-Pinene and d-limonene, two reactive compounds frequently found in air fresheners and cleaning products, were specifically included because as unsaturated hydrocarbons they can react with ozone to form particles, aldehydes and organic acids (Fan et al., 2003). Simultaneous airflow rates over the same time period were quantified between zones in the residence and with the outdoors as discussed in Dodson et al. (2007). In short, the garage airflow rates were estimated continuously while the estimates for the occupied area, basement, and common apartment hallways were integrated measures. Due to the potential rapid changes in airflow within the garage resulting from garage door use, sulfur hexafluoride was continuously released in the garage and then continuously measured both in the garage and in the adjacent zone to the garage over the sampling period. This allowed for continuous estimation of the airflow rates associated with the garage over the entire 48 h sampling period. To quantify the remaining airflow rates within a residence, one type of perflourocarbon tracer was continuously released in the occupied area of the residence and a second type was continuously released in either the basement or common apartment hallway. Each tracer type was then sampled for in each zone over the 48 h sampling period.
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collected using a custom-made triple-bed thermal desorption tube with 200 mg of Carbopack B, 230 mg of Carbopack X, and 170 mg of Carboxen 1001 (Supelco/Perkin-Elmer; Bellefonte, PA), with a target sampling volume of 15 L. Stainless steel diffusion barriers were used on all samples. Tubes were thermally desorbed in the laboratory using an automated thermal desorber (ATD) (Perkin-Elmer, Model 400; Waltham, MA) and analyzed via GC–MS following US EPA Compendium Method TO-17 (Woolfenden and McClenny, 1997). Housing characteristics and activities such as home design and product storage during the sampling period were collected using standardized questionnaires. Field staff also conducted a home walkthrough at the beginning of each sampling period and noted general characteristics about the residence, including ventilation systems and occupant use. 2.3. Data treatment All samples were blank corrected by subtracting the mean value, if it differed significantly from zero, of either the lab or field blanks, whichever is greater. A value equal to one-half the detection limit was used for compounds that were negative after blank correction. Limits of detection (LODs) were calculated as three times the standard deviation of the field blanks or analytical method LOD, whichever is greater, for each season. The median relative precision across all analytical samples by compound was 65% (range 7–96%). Additional quality assurance and quality control information is provided in the Supplemental material. Due to moisture issues in some of the summer samples, some samples were lost and are not included in the analyses. For this reason, sample sizes are specified for each analysis since a lost sample differentially impacted sample sizes needed for ratio and contribution analyses.
2.2. Sampling and analytical methods 2.4. Concentrations and ratios Formaldehyde and acetaldehyde were actively collected using acidified 2,4-dinitrophenylhydrazine (DNPH)-coated silica cartridges (Waters Corp.; Milford, MA), with a target sampling volume of 300 L, and analyzed via HPLC following US EPA Compendium Method TO-11A (Willbury et al., 1999). Ozone scrubbers containing potassium iodide were used with all summer outdoor aldehyde samplers (Arnts and Tejada, 1989; Sirju and Shepson, 1995). All other VOCs were actively
Measured concentrations in the occupied area (indoor), outdoors, attached garage, basement, and common apartment hallway are summarized and potential relationships or predictors, including season, were explored using Wilcoxon rank sum tests (unpaired) and Wilcoxon sign rank tests (paired), if appropriate. Measured garage, basement, and common hallway concentrations were divided by the concentration measured in the
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occupied area for each residence. Ratios 41 indicate that the garage, basement, or apartment hallway may be a potential source to the occupied area if air also flows from these areas to the occupied area. Ratios significantly different from one were tested for using a Wilcoxon sign rank test. 2.5. Contribution to indoor concentrations Concentrations in the occupied area can be apportioned between infiltration of outdoor air, sources in the occupied area, and where applicable, sources in the garages or basements, and infiltration of air from the apartment hallways. We note that quantified sources within the apartment hallway may be a result of sources in the hallway or from other units connected to the hallway. Steady state multi-zonal mass-balance models assuming wellmixed compartments were used, depending on the home configuration (e.g., a two compartment model was used if there was only an occupied area and a basement and a three compartment model was used if there was also an attached garage). Airflow estimates previously calculated from multi-zonal mass-balance models of tracer gases were used in the model (see Dodson et al., 2007 for airflow
estimates). Airflow estimates were concurrent with concentration measurements. Airflow estimates were removed from the analysis if the total flow within the compartment is extreme in either direction and thus considered an outlier, defined as values 4 or o 1.5 times the 75th or 25th percentile, respectively, on a log scale. These airflow estimates were combined with the concentration of the compound in each compartment to determine the source rate within each compartment. The source rate for each compartment was then used to determine the concentration in that compartment resulting only from sources in that compartment. This concentration was then multiplied by the airflow rate into the occupied area to determine the resulting mass flow to the occupied area resulting from that adjacent area. Mass flows to the occupied area also come from infiltration of outdoor air and sources in the occupied area, which were also quantified. The percent contribution of mass flows from the garages, basements, hallways, outdoors, and occupied area to the total mass flow to the occupied area were then calculated for each home, with the distributions across homes for the first three contributions presented in this paper. For additional details, see equations in Supplemental material.
Table 1 Arithmetic means and S.D. (in parentheses) of measured concentrations (in mg m3)
Methylene chloride Chloroform Trichloroethene Tetrachloroethene 1,4-Dichlorobenzene 1,3-Butadiene MTBE Benzene Toluene Ethylbenzene m,p-Xylene o-Xylene Styrene a-Pinene d-Limonene Formaldehyde Acetaldehyde
LODa,b Summer
LOD Winter
Indoor (n ¼ 83)
Outdoor (n ¼ 80)
Garage (n ¼ 16)
Basement (n ¼ 52)
Hallway (n ¼ 10)
0.39 0.08 0.04 0.17 0.34 0.36 0.12 0.30 0.24 0.06 0.13 0.06 0.19 0.03 0.19 0.4 0.7
1.25 0.06 0.04 0.07 0.13 0.87 0.04 1.51 0.15 0.04 0.12 0.06 0.16 0.03 0.03 0.4 0.7
2.5 (8.7) 1.2 (1.2) 0.61 (1.7) 1.9 (3.1) 3.1 (16) 0.54 (1.1) 7.6 (16) 2.6 (3.1) 13 (15) 2.4 (3.1) 7.3 (9.7) 2.6 (3.5) 1.1 (1.9) 11 (32) 17 (26) 21 (16) 13 (13)
0.28 (0.24) 0.07 (0.13) 0.13 (0.49) 0.46 (0.92) 0.26 (0.47) 0.27 (0.36) 1.2 (0.96) 0.88 (0.66) 2.3 (1.4) 0.42 (0.29) 1.3 (0.99) 0.47 (0.35) 0.1 (0.07) 0.42 (0.85) 0.23 (0.4) 1.2 (1.6) 5.6 (8.3)
9.8 (36) 0.08 (0.08) 3.3 (10) 2.8 (7.8) 2.3 (8.4) 7.4 (18) 131 (338) 58 (145) 102 (69) 35 (39) 90 (64) 35 (36) 3.4 (5.3) 38 (110) 7.3 (13) 6.7 (6.4) 8.9 (8.6)
9.5 (28) 0.57 (1) 0.43 (1.1) 1.7 (6.4) 1.3 (3.4) 0.5 (1) 8.8 (13) 3.2 (5) 21 (24) 4.1 (5.7) 12 (16) 4.2 (5.7) 1.7 (4.5) 11 (23) 8.8 (12) 12 (12) 8.5 (11)
2.6 (4.6) 1.3 (1) 3.7 (7.3) 1.9 (3.4) 0.78 (0.92) 0.68 (0.51) 3.2 (4.1) 2.8 (4.3) 9.9 (13) 2.1 (3.4) 6.2 (9.7) 2.2 (3.5) 1.1 (1.6) 10 (28) 10 (20) 12 (7.8) 7.3 (5.2)
Additional measured concentration summary statistics provided in the supplemental material. a Season-specific limits of detection (LODs) were calculated. b LODs converted to concentrations assuming 48 sampling period and sampling rates of 5.21 and 104 cm3 min1 for VOCs and aldehydes, respectively.
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compounds and zones; however, both methylene chloride and 1,3-butadiene were detected the least frequently in all zones. Due to this measurement misclassification, the contribution estimates may be biased towards the null. Nevertheless, 1,3-butadiene and methylene chloride were included in subsequent analyses because of their potential health effects. Residences with attached garages had significantly higher measured indoor benzene (p ¼ 0.0072), toluene (p ¼ 0.00080), ethylbenzene (p ¼ 0.00027), m,p-xylene (p ¼ 0.00019), o-xylene (p ¼ 0.00010) (BTEX), and methyl t-butyl ether (MTBE) (p ¼ 0.000048) concentrations than residences without attached garages while other compounds were not significantly different in homes with attached garages (Fig. 1). On average, the indoor BTEX concentrations in residences with attached garages were two to six times higher than those in those without attached garages. These results are consistent with findings from other studies (Batterman et al., 2007; Isbell et al., 2005; Thomas et al., 1993). The concentrations measured
3. Results and discussion 3.1. Concentrations Table 1 presents the arithmetic means and standard deviations (S.D.) of the concentrations measured in the occupied areas of the residence, basements, hallways, and attached garages across both seasons. The indoor concentrations were lower than those observed in a New York City and Los Angeles-based study (Sax et al., 2006) but were comparable to recent studies in Minnesota (Adgate et al., 2004a, b) while the measured outdoor concentrations were lower than those observed in these studies, possibly a result of including both suburban and urban residences in this study. Comparison of measured concentrations in the basement and hallway are not available as this is one of the few studies to study these zones. Additional summary statistics, including the percent to samples above the LOD are provided in the Supplemental material. The detection frequency varied across
Measured Indoor Concentration (µg/m3)
100
10
1
MTBE
Benzene
Toluene
Ethylbenzene
m,p-Xylene
no Garage
Garage
no Garage
Garage
no Garage
Garage
no Garage
Garage
no Garage
Garage
no Garage
Garage
0.1
o-Xylene
Fig. 1. Measured indoor concentrations for residences with (n ¼ 15) and without (n ¼ 68) an attached garage. Only compounds with significant differences shown. Note: log scale on concentration axis and box plots represent 5th, 25th, 50th, 75th, and 95th percentiles.
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(p ¼ 0.045), tetrachloroethene (p ¼ 0.0015), styrene (p ¼ 0.00020), o-xylene (p ¼ 0.047), 1,4-DCB (p ¼ 0.0084), a-pinene (p ¼ 0.0012), d-limonene (p ¼ 0.019), formaldehyde (p ¼ 0.00043), and acetaldehyde (p ¼ 0.0048). Those residences with basements associated with attached garages had significantly higher basement concentrations for 1,3-butadiene, benzene, carbon tetrachloride, toluene, ethylbenzene, m,p-xylene, o-xylene, and 1,4-DCB (po0.05) than those residences with basements but without a garage or with the garage attached to the occupied area. While many of these compounds may be a result of gasoline-related sources within the garage, the association with carbon tetrachloride and 1,4DCB is less clear. In 8 of the 52 basements visits, at least one type of gasoline powered equipment (including motorcycle, lawnmower, trimmers, leaf or snow blower, or boat engine) or gasoline containers was being stored in the basement. These basements had significantly higher concentrations of MTBE, tetrachloroethene, ethylbenzene, m,pxylene, o-xylene, styrene, and a-pinene (po0.05). While some of these compounds do not result from
in the attached garage tend to be higher in the summer than in the winter for most compounds except 1,3-butadiene and a-pinene. This may be due to the higher airflow rates out of the garage or lower temperatures in the winter. Residences with basements had significantly lower occupied area concentrations of trichloroethene (p ¼ 0.0071), chloroform (p ¼ 0.025), tetrachloroethene (p ¼ 0.0053), and 1,4-dichlorobenzene (1,4-DCB) (p ¼ 0.018) compared to those residences without basements. Overall, the measured concentrations in the basement tend to be higher, on average, for most compounds, in the summer than in the winter, likely the result of dilution from increased airflows in the winter. Paired tests revealed significantly higher summer concentrations for 14 out of the 17 compounds investigated (n ¼ 18, po0.05), with the exceptions being 1,3butadiene, methylene chloride, chloroform, and benzene. Using unpaired tests with all of the data, the summer concentrations (n ¼ 21) are significantly higher than winter concentrations (n ¼ 31) for 9 out of the 17 compounds, specifically trichloroethene
*
*
*
o-Xylene
*
m,p-Xylene
*
*
Ethylbenzene
Measured Garage/Measured Indoor Concentrations
100
* 10
1
0.1
Acetaldehyde
Formaldehyde
d-Limonene
a-Pinene
Styrene
Toluene
Benzene
MTBE
1,3-Butadiene
1,4-DCB
Tetrachloroethene
Trichloroethene
Chloroform
Methylene Chloride
0.01
Fig. 2. Garage/indoor concentration ratios across seasons (n ¼ 15). Indoor indicates occupied area of the home. Note: 5th, 25th, 50th, 75th, and 95th percentiles shown in box plots and log scale. Ratios that are significantly 41 are shown with asterisk (*po0.05).
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indoor concentrations. The observed differences for BTEX compounds between garage and indoor concentrations are similar to those found in other studies (Batterman et al., 2006a, b, 2007; Tsai and Weisel, 2000). For the basement ratios, we present ratios by season to highlight the differences. The basement/ indoor ratios across seasons for methylene chloride (p ¼ 0.016), ethylbenzene (p ¼ 0.0049), m,p-xylene (p ¼ 0.0013), and o-xylene (p ¼ 0.0061) were significantly 41 while ratios for chloroform (p ¼ 0.00029), formaldehyde (p ¼ 0.00023), and acetaldehyde (p ¼ 0.0027) were significantly o1. The majority of the compounds (12 out of 17) had basement/indoor ratios that were significantly higher in the summer than in the winter (po0.05), when using all available data. As not all homes were sampled in both seasons, we also looked just at paired samples, finding virtually the same results, with MTBE being added to the list of compounds with significant seasonal differences and 1,4-DCB being dropped. Higher summer ratios are likely due
gasoline powered equipment, gasoline powered equipment may be a proxy for having more intensive storage of other products as well. 3.2. Ratios The distribution of the ratios of concentrations measured within the attached garages, basements, and hallways compared to the concentrations measured in the occupied area are presented in Figs. 2–4. Compounds associated with gasoline and vehicle exhaust, such as 1,3-butadiene (p ¼ 0.0016), MTBE (p ¼ 0.00006), benzene (p ¼ 0.00006), toluene (p ¼ 0.00006), ethylbenzene (p ¼ 0.00006), and xylenes (p ¼ 0.00006) had median garage/ indoor concentration ratios significantly 41, while chloroform (p ¼ 0.00006), tetrachloroethene (p ¼ 0.022), d-limonene (p ¼ 0.022), formaldehyde (p ¼ 0.00012), and acetaldehyde (p ¼ 0.018) had ratios significantly o1. In fact, the mobile source compounds had measured garage concentrations 5–10 times higher at the median than the measured 1000
# *
* 100
*
#
#
*
#
#
#
# #
#
10
# #
#
1
0.1
Acetaldehyde (S)
Acetaldehyde (W)
Formaldehyde (W)
d-Limonene (W)
Formaldehyde (S)
a-Pinene (W)
d-Limonene (S)
Styrene (W)
a-Pinene (S)
Styrene (S)
o-Xylene (S)
o-Xylene (W)
m,p-Xylene (S)
m,p-Xylene (W)
Ethylbenzene (W)
Toluene (W)
Ethylbenzene (S)
Toluene (S)
Benzene (S)
Benzene (W)
MTBE (S)
MTBE (W)
1,3-Butadiene (S)
1,3-Butadiene (W)
1,4-DCB (S)
1,4-DCB (W)
Tetrachloroethene (S)
Tetrachloroethene (W)
Trichloroethene (S)
Trichloroethene (W)
Chloroform (S)
Chloroform (W)
Methylene Chloride (S)
0.01 Methylene Chloride (W)
Measured Basement/Measured Indoor Concentrations
1575
Fig. 3. Basement/indoor concentration ratios in summer (S) (n ¼ 19) and winter (W) (n ¼ 31). Indoor indicates occupied area of the home. Note: 5th, 25th, 50th, 75th, and 95th percentiles shown in box plots and log scale. Ratios that are significantly 41 are shown with asterisk (*po0.05). Summer ratios that are significantly greater than winter ratios are shown with a pound sign (#po0.05).
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Measured Hallway/Measured Indoor Concetrations
100
10
*
1
0.1
Acetaldehyde
Formaldehyde
d-Limonene
a-Pinene
Styrene
o-Xylene
m,p-Xylene
Ethylbenzene
Toluene
Benzene
MTBE
1,3-Butadiene
1,4-DCB
Tetrachloroethene
Trichloroethene
Chloroform
Methylene Chloride
0.01
Fig. 4. Hallway/indoor concentration ratios across seasons (n ¼ 10). Indoor indicates occupied area of the home. Note: 5th, 25th, 50th, 75th, and 95th percentiles shown in box plots and log scale. Ratios that are significantly 41 are shown with asterisk (*po0.05).
3.3. Contribution to indoor concentrations
dominant source to the occupied area while in others the outdoor or sources within the occupied area are dominant. Each home-compound combination can be represented by a pie chart, for example, see inset in Fig. 5. To summarize the contributions across residences, therefore, for a given compound, we present the distribution across residences of the percent contribution from sources within the attached garage, basement, and common apartment hallway to the occupied area’s estimated concentrations (Figs. 5–7), with contributions from sources within the occupied area and outdoors presented in the Supplemental material. We note that the distributions will not sum to 100% due to variability across homes.
For each residence, treated independently across seasons, we can determine the percent contribution to the indoor concentration from the outside and each compartment within the home. The contributions from each region are highly variable across participants’ residences. Using toluene as an example, in some residences, the basement is the
3.3.1. Garages At the median, approximately 40% of the indoor concentrations of benzene, toluene, ethylbenzene, and xylenes are attributable to the attached garage. Graham et al. (2004) found that between 10% and 85% of the concentrations measured in the one residence during the study can be attributable to the
to lower airflow rates in the basements and higher airflow rates in the occupied area. The median hallway/indoor concentration ratios were near one for almost all compounds; however, the distribution of ratios spanned at least an order of magnitude. Only 1,3-butadiene (p ¼ 0.0059) had a median ratio significantly 41 while only formaldehyde (p ¼ 0.037) had a median ratio significantly o1. Over 75% of the ratios for 1,4-DCB were above one; however, the median was not statistically different than one (p ¼ 0.11). The lack of statistical significance may be due to the small sample number (n ¼ 10).
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100
Percent Contribution from Garage (%)
outdoor
indoor
80
basement
garage
60
40
20
Acetaldehyde
Formaldehyde
d-Limonene
a-Pinene
Styrene
o-Xylene
m,p-Xylene
Ethylbenzene
Toluene
Benzene
MTBE
1,3-Butadiene
1,4-DCB
Tetrachloroethene
Trichloroethene
Chloroform
Methylene Chloride
0
Fig. 5. Garage contribution to estimated indoor concentration (n ¼ 9) across seasons and garage type. Inset: hypothetical pie graph for one residence showing the contribution of the various areas on indoor concentration. Contribution of the attached garage is solid and represents just one of the data points included in the distributions presented in the box plots. Note: box plots include the median and 5th, 25th, 75th, and 95th percentiles.
attached garage. In a recent study by Batterman et al. (2007) approximately 50–60% of the indoor BTEX concentrations were attributable to the garage, which substantiates our findings. The impact of other similarly measured compounds on the indoor concentrations is not remarkable. Due to the small sample size, the contribution box plot for the attached garages contains both the sub-terranean (sub) and lateral garages; however, in general, the lateral garages had a larger median percent contribution than the sub-garages. All of the sub-garages in this analysis were connected to the basement of the residence and so the contributions reflect the transport through an intermediate zone, through which it was assumed that all air traveled from the garage to the occupied area. We should note, however, that the airflow rate between the sub-garage and the basement was higher than the airflow rate between the lateral garage and the occupied area and the lower percent contributions are a result of the transport through the inter-
mediate zone (i.e., the basement). The results of this study highlight a potentially important issue in home design; establishing living areas in zones immediately adjacent to the sub-garages can result in higher exposures. 3.3.2. Basements The median percent contributions from the basement range from effectively 0% for 1,3-butadiene to 22% for m,p-xylene, although significant variability exists in contribution estimates for most compounds. While we saw higher concentration ratios in summer than winter, this effect was not consistently seen in the source contributions because, in part, the airflow rates were shown to be lower in the summer than in the winter in a previous paper (Dodson et al., 2007). As a result, the contribution from the basement of 1,4-DCB (p ¼ 0.0016) and acetaldehyde (p ¼ 0.013) is significantly less in the summer season. In general, 1,3-butadiene, tetrachloroethene, styrene, o-xylene, a-pinene, and
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Percent Contribution from Basement (%)
100
80
60
40
20
Acetaldehyde
Formaldehyde
d-Limonene
a-Pinene
Styrene
o-Xylene
m,p-Xylene
Ethylbenzene
Toluene
Benzene
MTBE
1,3-Butadiene
1,4-DCB
Tetrachloroethene
Trichloroethene
Chloroform
Methylene Chloride
0
Fig. 6. Basement contribution to estimated indoor concentration (n ¼ 42) across seasons. Note: box plots include the median and 5th, 25th, 75th, and 95th percentiles.
d-limonene contributed to occupied area concentrations to a slightly greater extent in the summer than in the winter season. All other compounds had higher contributions, on a mass basis, in the winter. 3.3.3. Hallways The median percent contribution from the hallway ranges from o1% for tetrachloroethylene to 18% for 1,4-DCB. As an example, very few participants reported using products containing 1,4-DCB, indicating the potential impact of other units on hallway concentrations and ultimately exposures within individual units. 3.4. Potential limitations Potential limitations to this work include elevated LODs for some compounds and uncertainty in the air exchange, measured chemical concentrations, and estimated concentration contributions. A standard approach of using one-half the detection limit for undetected compounds was used; however, we
note that the results for methylene chloride, the outdoor and garage results for 1,4-DCB, 1,3butadiene, outdoor results for styrene, and the hallway and outdoor results for benzene should be interpreted with caution given the small fraction of samples above the LOD. There are uncertainties in the airflow estimates as a result of the mass-balance model assumptions; however, the range of uncertainty is less than the range of variability, as discussed in a previous paper (see Dodson et al., 2007). Uncertainties related to measurement error (i.e., precision) and its impact on the chemical concentrations, since they are non-differential, will only bias the results towards a null finding due to increased variability. Another potential limitation is that we were unable to account specifically for any soil vapor intrusion contribution into the basement and thereby into the home. We believe the influence of soil vapor as a source of VOCs to the basement to be small, if not negligible, as none of our homes were reported to be above or in close proximity to
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Percent Contribution from Hallway (%)
100
80
60
40
20
Acetaldehyde
Formaldehyde
d-Limonene
a-Pinene
Styrene
o-Xylene
m,p-Xylene
Ethylbenzene
Toluene
Benzene
MTBE
1,3-Butadiene
1,4-DCB
Tetrachloroethene
Trichloroethene
Chloroform
Methylene Chloride
0
Fig. 7. Hallway contribution to estimated indoor concentration (n ¼ 9) across seasons. Note: box plots include the median and 5th, 25th, 75th, and 95th percentiles.
a major contaminated groundwater plume (Hers et al., 2001). 3.5. Conclusions This work adds substantially to the literature on the impact of attached garages, basements, and common apartment hallways on occupied area concentrations. Residences with attached garage, basements, or common apartment hallways areas are associated with different residence types; however, it is apparent that occupied areas may be affected by sources within associated areas. While the outdoor air and sources in the occupied area generally make up the majority of the observed concentration in the occupied area, mass flows from other regions do represent a potentially substantial contribution in some of the homes studied. Understanding the potential impact of attached garages, basements, and common apartment hallways on exposures experienced within the home is important for both future modeling efforts characterizing the
impact of indoor residential exposures on personal concentrations as well as exposure reduction. These results suggest that proper storage of products containing solvents within basements or attached garages as well as increased ventilation within these areas is important to mitigate exposures within the home. It also verifies our hypothesis that activities within an apartment building but outside of the individual units may impact the residents within the individual units. Acknowledgments This work is funded by a grant from the American Chemistry Council. Laboratory analyses were partially funded by the Harvard NIEHS Center for Environmental Health (Grant no. P30ES00002). We would like to thank the study participants for letting us study their residences. We would also like to acknowledge the field staff (J. Allen, S. Sax, M. Loh, M. Anand, M. Anand, K. Kopko, T. Goldberg, and M. Penterson),
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sampler design engineer (M. Davey), the laboratory staff (B. LaBrecque, S. Forsberg, and R. Weker), database manager (S. Melly), and QA/QC supervisor (J. Vallarino) for their help with this study. Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at doi:10.1016/ j.atmosenv.2007.10.088.
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