Attached Garages as a Source of Volatile Organic Compounds in New Homes

Transcription

1 Attached Garages as a Source of Volatile Organic Compounds in New Homes Francis J. Offermann 1, Alfred T. Hodgson 2, Peggy L. Jenkins 3, Ryan D. Johnson 3 Thomas J. Phillips 3 and 1 Indoor Environmental Engineering, San Francisco, CA, USA 2 Berkeley Analytical, Richmond, CA, USA 3 California Air Resources Board, Sacramento, CA, USA * Corresponding Offermann@iee-sf.com KEYWORDS Air leakage, benzene, motor vehicle, residence, xylene SUMMARY A majority of new single-family residences in the USA are constructed with attached garages. Many are two story structures with garages situated under living spaces. The air in garages communicates with air in living spaces through passage doorways and unsealed structural gaps and cracks. Consequently, benzene and other air pollutants originating from vehicles parked in garages contaminate indoor air. This study examines home-to-garage leakage areas and coupling and indoor concentrations of garage related VOCs for a sample of 105 new California, USA homes. Homes with garages under living spaces had higher home-to-garage coupling and higher emission rates of benzene and xylenes compared to homes with garages to the side. A sub-study found that the typical impact ratio (i.e., I-O / G-O concentrations) of garage pollutants on indoor air quality was A comparison with previous studies suggests that typical recent construction practices have not substantially reduced garagerelated impacts. 1 INTRODUCTION A majority of single-family homes and a large fraction of multi-family homes in the USA have attached garages. These garages often have high concentrations of volatile organic compounds (VOCs), carbon monoxide and other combustion pollutants that frequently impact indoor air quality (IAQ) in adjoining residences. These pollutants derive from the evaporative and tailpipe emissions of gasoline powered vehicles and equipment stored in garages. The health impacts are significant. Carbon monoxide emissions from idling vehicles in garages lead to fatal and sub-lethal poisoning in the USA every year (CDC, 2011). Benzene exposure from attached garages in three USA cities has been estimated to increase cumulative exposures to ten times higher than those experienced while commuting in a car in heavy traffic and to result in excess cancers of 17 per million persons (Hun et al., 2011). A number of studies have been published on pollutant transport from garages into residences. Studies up through 2001 have been reviewed by Emmerich et al. (2003). Most of the crosssectional studies have included structures of various ages and home/garage configurations. Building code regulations now often include requirements that are intended to mitigate garage impacts on IAQ and/or conserve energy, e.g., gasketing and self-closing mechanisms on home-to-garage doors. Home configuration also is evolving. Due to generally reduced parcel sizes, the majority of new homes in the USA now consist of two stories (NAHB, 2006) frequently with the garage located below living spaces. The analysis reported here is taken

2 from the California New Homes Study (CNHS) conducted in to assess ventilation and IAQ in a sample of new, single-family, California (CA), USA homes (Offermann, 2009). The detailed study data provides an opportunity to investigate home-togarage leakage characteristics and garage pollutant impacts representative of new residential construction. Specifically, our objectives were to: 1) characterize home-to-garage leakage areas, home-to-garage coupling factors, and indoor concentrations of garage related VOCs for this sample of homes; 2) compare leakage and pollutant factors between homes with garages under living areas and homes with garages to the side of living areas; and 3) discern if new construction practices produce lower garage impacts in comparison with previously reported studies. 2 MATERIALS/METHODS In the CNHS, a total of 108 owner-occupied, single family homes, from years old, were recruited in Northern and Southern CA (Offermann, 2009). The concentrations of 22 volatile organic compounds (VOCs) including formaldehyde and acetaldehyde and ambient air contaminants were measured simultaneously indoors and outdoors over a 24-hour period. Indoor measurements were made in the main living/dining/kitchen area. Outdoor measurements were made at one location for pairs of closely located homes. VOCs were collected and analyzed by U.S. EPA Method TO-17. Chemicals of concern (COC) plus some VOCs representative of known indoor sources were selected as targets. VOC sample volumes were ~14 L yielding method detection limits (MDLs) of µg/m 3 for all but one VOC. Sample values were blank corrected using the average of the field blank for each batch of samples or 0.5 x MDLs, as appropriate. In a subset of 24 homes, air samples were simultaneously collected over 24 h with flow controlled, 6-L, evacuated stainless-steel canisters in the garage and adjacent to indoor and outdoor sorbent tube locations (Jenkins et al., 2011). These samples were analyzed for 60 target VOCs by U.S. EPA Method TO-15. The MDLs for the canister analyses were similar to those of the sorbent tube analyses. Garage IAQ impact ratios were calculated from the TO- 15 concentration data as the ratio of indoor-outdoor to garage-outdoor (I-O / G-O) values. The outdoor air exchange rate was simultaneously measured using passive perfluorocarbon tracer (PFT) sources and samplers. The PFT sources (PMCH) were placed at 3-5 locations in each home ~1 week in advance of sampling to allow for their emission rates to equilibrate. A passive PFT sorbent sampler was co-located with the indoor air sampling equipment. The 24- h average outdoor air exchange rate (h -1 ) was calculated following ASTM E741. Building envelope air leakage area was determined by depressurization using a multi-point, blower door test following ASTM E779. The zone pressure diagnostic test of the garage-tohome connection consisted of two home depressurization tests; one with the home door to the garage closed and one with the door open. From these data, the equivalent leakage area Pa, cm 2 ) was calculated between the garage and the home and between the garage and outdoors. We also measured the home-to-garage coupling factor which is the ratio of the garage-to-outdoor differential pressure to the home-to-outdoor differential pressure at -50 Pa. A coupling factor of zero indicates no home-to-garage coupling and a value of 1.0 indicates total coupling. In the CNHS pilot study, the transport of garage air contaminants into the indoor air was measured for three homes by introducing a second PFT (p-pdch) during the 24-hour air contaminant measurement period (Offermann, 2009). Two sources of this PFT were placed at

3 a central location in the garage. Their emission rates were temperature corrected by calculation. The percent of garage air contaminant emissions entering the home was determined from the ratio of the calculated emission rate of the garage PFT entering the home to the calculated emission rate of the garage PFT. The emission rate of the garage PFT entering the home was determined as the product of the concentration of this PFT in the home and the outdoor airflow rate entering the home, i.e., the product of the outdoor air exchange rate from the first PFT measurements and the indoor air volume of the home. The measured parameters were not normally distributed as determined by a Shapiro-Wilk test. A nonparametric Mann-Whitney rank sum (U) test was used to assess the differences between median values for the garage under living vs. the garage to the side comparisons. 3 RESULTS Characteristics and field measured parameters for study of 105 new homes For this analysis, three homes were excluded because they lacked a garage (1 home) or had incomplete measurements. For homes tested more than once, only the results of the first test were considered. The 105 homes had from two to four bedrooms (median = 4) with floor areas ranging from 119 to 470 m 2 (median = 250 m 2 ). Sixty-nine homes (66%) were twostory construction. All had attached garages. In 63 homes (60%, all two story), the garages were situated below a living space (Garage Under). In the others, the garages were located on the side (Garage Side). The occupant surveys indicated that 90+% of the garages were used regularly for vehicle parking. Field observations confirmed that all garage/home passageways were gasketed and had automatic door closers as required by the CA building code. Distributions of the home outdoor air exchange rates, equivalent leakage areas (EqLAs, cm 2 ) between living spaces and garages, and garage-to-home coupling factors are presented in Table 1. The median air change rate was 0.26 h -1. High rates measured in a few homes were associated with open windows and doors. Table 1. Distributions of outdoor air exchange rates; home-to-garage leakage areas and coupling factors; and indoor minus outdoor (I-O) concentrations of benzene, toluene and xylenes for 105 new homes Parameter Units 10% 25% 50% 75% 90% Max Air exchange rate 1/h Leakage area* cm Coupling factor* Benzene, I-O µg/m 3 <0.17 < Toluene, I-O µg/m Xylenes, I-O µg/m 3 < *No. observations: leakage area, n=101; coupling factor, n=91, all others, n=105 Of the 60 compound TO-15 target list, just 39 VOCs were above their MDL in the garage samples. The 10 most abundant compounds with median garage concentrations exceeding 10 µg/m 3 were; ethanol (300 µg/m 3 ), toluene (68 µg/m 3 ), xylenes (55 µg/m 3 ), acetone (50 µg/m 3 ), 2-propanol (21 µg/m 3 ), benzene (13 µg/m 3 ), hexane (12 µg/m 3 ), ethylbenzene (11 µg/m 3 ), 2-butanone (11 µg/m 3 ), and 1,2,4-trimethylbenzene (11 µg/m 3 ). The hazard quotient as calculated from the ratio of the median garage concentrations and their health exposure guidelines (i.e., the OEHHA CRELs or if not available then 1% of the Cal/OSHA PELs) only exceeded 0.01 for three compounds; benzene, toluene, and xylenes (BTX). As a result, the analyses in this paper are focused upon BTX.

4 The correlations of co-located indoor measurements of BTX by Methods TO-17 (sorbent tube sampling) and TO-15 (canister sampling) had correlation coefficients >0.93. On average, the TO-15 concentrations were typically 15% higher than TO-17 values for benzene and xylenes and 2% lower for toluene. For the co-located outdoor air samples, correlation coefficients were <0.3 with TO-15 concentrations exceeding TO-17 values by as much as a factor of two. Also, since this paper focuses on garages as an indoor source of air pollutants, the concentration distributions of BTX are shown as indoor minus outdoor (I-O) values (Table 1). Median outdoor concentrations by TO-17 were: benzene <0.3 µg/m 3 (max 2 µg/m 3 ), toluene 1.2 µg/m 3 (max 6 µg/m 3 ), and xylenes 1.2 µg/m 3 (max 4 µg/m 3 ). The percentage of the garage air contaminant emissions entering the three CNHS pilot homes as determined from the PFT sources installed in the garage, were 2.6% (Home P1), 10.1% (Home P2) and 9.8% (Home P3). The corresponding home-to-garage coupling factors were 0.010, and < These coupling factors compare to the median of observed in the full study. The lower percentage of garage emissions entering home P1 may be attributed to this home having just one garage wall adjacent to the home, whereas home P2 had one and one-half walls and home P3 had two walls and the garage ceiling adjacent to the home. Impact of garage location on home/garage parameters and indoor BTX emission rates We looked for associations between garage location (Garage Under vs. Garage Side) and home-to-garage EqLAs and coupling factors (Table 2). While there was a trend of higher EqLAs for Garage Under homes, the median values were not significantly different at a 5% probability of no difference (P = 0.059). However, the median coupling factor for Garage Under homes was significantly higher (P < 0.001). We also looked for associations between garage location and I-O BTX concentrations and BTX emission rates. An emission rate (mg/h) was calculated as the product of the I-O concentration (mg/m 3 ) and the home outdoor air flow rate (m 3 /h) from the PFT measurement and home volume. There was no apparent association with concentrations. But, Garage Under homes had significantly higher (P <0.05) median emission rates of benzene and xylenes. The lack of an association for toluene emissions is indicative of other indoor toluene sources. Table 2. Comparisons of home-to-garage leakage areas and coupling factors and emission rates of benzene, toluene and xylenes between new homes with attached garages under and to the side of living spaces Parameter Units Garage n 25% 50% 75% P* Leakage area cm 2 Under Side Coupling factor -- Under Side <0.001 Benzene ER mg/h Under Side Toluene ER mg/h Under Side Xylenes ER mg/h Under Side *Probability of no significant difference between medians by Mann-Whitney rank sum test

5 Garage BTX concentrations and their impact on indoor concentrations Three homes with incomplete data were excluded from the garage sub study. Garage minus outdoor (G-O) BTX concentrations (range and median) for the 21 homes were: benzene µg/m 3 (median = 12.4 µg/m 3 ); toluene µg/m 3 (median = 66 µg/m 3 ); and xylenes µg/m 3 (median = 53 µg/m 3 ). The median G-O BTX concentrations were from times higher than their respective median I-O concentrations for the full study (Table 1). Garage impact ratios (I-O / G-O) were calculated for benzene and xylenes (Table 3) to show the impact of garages on the indoor concentrations of these compounds. Toluene was omitted due to the apparent presence of other sources. The median impact ratios were: benzene and xylenes At the 90 th percentile, the impact ratio was for both compounds. The median EqLA and the median coupling factor were significantly higher for the Garage Under vs. the Garage Side homes in this subset of homes (Mann-Whitney rank sum test, P <0.05, comparison not shown). However, there were no significant differences with garage location for the benzene and xylenes garage impact ratios. Table 3. Impact ratios of garage concentrations of benzene and xylenes on their respective indoor concentrations for 21 new homes with simultaneous garage and indoor measurements Parameter 10% 25% 50% 75% 90% Benzene Xylenes Impact ratios calculated as I-O / G-O. 4 DISCUSSION Comparison of BTX concentrations with exposure guidelines We compared the I-O BTX concentrations for the full study to Chronic Reference Exposure Levels (CRELs) for non-carcinogenic health effects (OEHHA, 2008). These guidelines are: benzene 60 µg/m 3, toluene 300 µg/m 3, and xylenes 700 µg/m 3. The median I-O concentrations are <1 2% of the CRELs and the 90 th percentile values are 3 13% of the CRELs. The median G-O concentrations are 8 22% of the guidance values, and the maximum G-O concentrations approach or exceed guidance. Even though the impact ratio of the garage in a typical home is less than 0.10 (Table 3), the garage can significantly increase an occupant s inhaled dose of BTX. Following the Batterman et al. ( 2007) Table 7 example and adding the median outdoor concentration to the I-O and G-O concentrations, the inhaled dose of benzene associated with the garage (0.9 h exposure) somewhat exceeds the indoor dose (13.5 h exposure); the garage doses of toluene and xylenes are below but within a factor of two of their indoor doses. Cancer risk also was considered. In the larger study, 63% of the homes exceeded the CA Proposition 65 No Significant Risk Level for benzene of 0.65 µg/ m 3 (13 µg/20 m 3 /day) (Offermann, 2009). Comparison with previous garage studies Graham et al. (2004) measured home-to-garage leakage areas (EqLAs) for a sample of 25 Canadian homes ranging up to ~40 years old and with various home/garage configurations. The average EqLA was 124 cm 2. Sheltair (2004) made additional measurements in Canadian homes and combined these with the 25 Graham et al. homes. The average EqLA for these 42 homes was 107 cm 2. These average home-to-garage leakage areas compare to the median of 112 cm 2 observed in this study of new homes. Batterman et al. (2007) calculated garage/indoor (G/I) concentration ratios using average values for a sample of 15, new to 70- year old, homes in Michigan, USA. When converted to impact ratios used in this paper (i.e., I/G), the values are benzene and xylenes Based on these literature reports, the

6 new CA homes have about the same EqLAs and home-to-garage leakage rates and impact factors as sets of older North American homes. 5 CONCLUSIONS In this study, the typical impact of garages on indoor concentrations of benzene and xylenes was 5 8%. Although precise comparisons are not possible, it appears that the impact of a typical attached garage on indoor exposures to BTX for this sample of new CA homes is similar to central values reported for samples of multi-age homes in North America. This indicates there has been little progress on isolating garages from living spaces. We established that homes with garages under living spaces typically have higher garage-tohome coupling factors than homes with garages to the side. There were no discernable concentration differences; however, the emission rates of benzene and xylenes, the best VOC indicators of a gasoline source, were higher in homes with garages under living spaces. Efforts should be made to develop and validate construction practices that minimize the garage-to-home leakage areas, particularly for two-story homes with garages situated under spaces. ACKNOWLEGEMENT Financial support for the field study was provided by the California Energy Commission, Contact , and the California Air Resources Board (CARB), Contract REFERNCES Batterman, S, Jia, C. and Hatzivasilis, G Migration of volatile organic compounds from attached garages to residences: A major exposure source, Environ. Res. 104, Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Report 60(30), Emmerich, S.J, Gorgain, J.E, Howard-Reed, C Air and pollutant transport from attached garages to residential living spaces Literature review and field tests, Intl. J. Ventilation 2(3), Graham, L.A, Noseworthy, L, Fugler, D, et al Contribution of vehicle emissions from an attached garage to residential indoor air pollution level, JAWMA 54(5), Hun, D.E, Corsi, R.L, Morandi, M.T. and Siegel J.A Automobile proximity and indoor residential concentrations of BTEX and MBTE, Building Environ. 46, Jenkins, P.L, Johnson, R.D, Phillips, T.J. and Offermann, F.J Chemical Concentrations in New California Homes and Garages. In: Proceedings Indoor Air 2012, Austin TX, USA. National Association of Home Builders (NAHB) Housing facts, figures and trends. Report NAHB Public Affairs and NAHB Economics. 18 pages. Offermann, F.J Ventilation and Indoor Air Quality in New Homes. California Air Resources Board and California Energy Commission, PIER Energy-Related Environmental Research Program. Collaborative Report CEC , OEHHA Acute, 8-hour and Chronic Reference Exposure Levels (chrels). California Office of Environmental Health Hazard Assessment. Sheltair Garage performance testing. Final Report, Canada Mortgage and Housing Corporation, 40 pages. Disclaimer: The opinions expressed in this paper are those of the authors and not necessarily those of CARB.