Influence of Attached Influence of Attached Garages on Indoor Garages on Indoor

VOC Concentrations in VOC Concentrations in Anchorage HomesAnchorage Homes

Stephen S. Morris, P.E.Stephen S. Morris, P.E.Municipality of AnchorageMunicipality of Anchorage

Department of Health and Human ServicesDepartment of Health and Human Services

AcknowledgementsAcknowledgementsAnne Schlapia, Matt Stichick and Larry Taylor – MOA DHHSAnne Schlapia, Matt Stichick and Larry Taylor – MOA DHHS

John Freeman, Phil Kaluza, Ginny Moore – ABSNJohn Freeman, Phil Kaluza, Ginny Moore – ABSN

Sally Liu, Tim Gould, Dave Hardie and Timothy Ting Sally Liu, Tim Gould, Dave Hardie and Timothy Ting University of WashingtonUniversity of Washington

BackgroundBackground

A previous Anchorage study A previous Anchorage study sparked interest in a further sparked interest in a further

investigation of the influence of investigation of the influence of attached garages on air quality attached garages on air quality

inside Anchorage homes.inside Anchorage homes.

Architectural, Behavioral, and Environmental Factors Associated with

Indoor VOCs in Anchorage Homes (1995)

• Sampled 137 homes for BETX between December Sampled 137 homes for BETX between December 1994 and February 1996 1994 and February 1996

• Summa canisters deployed in living space of homes Summa canisters deployed in living space of homes for 24 hoursfor 24 hours

• Documented architectural, behavioral and Documented architectural, behavioral and environmental characteristics of each home sampledenvironmental characteristics of each home sampled

The most important factor influencing [benzene] and other BTEX compounds

was the presence of an attached garage.

• Cigarette smoking was not an important factor in determining benzene concentration in living space of the home.

• The presence of an attached garage was the single most important variable associated with elevated benzene inside the home.

Comparison of Mean Benzene Concentrations in Single Family Homes 1994-1996 Anchorage Study

18.0

6.8

3.2

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

garagewith parked cars

N = 46

garagew/o parked cars

N = 16

no attached garageN = 14

[ben

zene

] pp

b

Data suggested that Data suggested that attached garages increase attached garages increase

in-home exposure to benzene in-home exposure to benzene five-fold. five-fold.

Incremental increase in lifetime Incremental increase in lifetime exposure cancer risk was exposure cancer risk was

approximately approximately 1 in 6,000.1 in 6,000.

Benzene content (3.9%) and volatility Benzene content (3.9%) and volatility of Alaska gasoline is higher thanof Alaska gasoline is higher than

most of the U.S. most of the U.S.

We wanted to explore the We wanted to explore the mechanisms responsible for elevated mechanisms responsible for elevated

benzene in homes with attached benzene in homes with attached garages.garages.

Study ObjectivesStudy Objectives Measure VOC concentrations in a representative sample Measure VOC concentrations in a representative sample

of 50 Anchorage homes with attached garages to assess of 50 Anchorage homes with attached garages to assess personal exposures.personal exposures.

Measure garage to house air infiltration rates. Measure garage to house air infiltration rates. Determine architectural / mechanical factors affecting the Determine architectural / mechanical factors affecting the amount of air entering house from the garage.amount of air entering house from the garage.

Identify possible strategies for reducing in-home VOC Identify possible strategies for reducing in-home VOC exposures through modification of architectural features, exposures through modification of architectural features, mechanical systems and/or modification of personal mechanical systems and/or modification of personal behaviors. behaviors.

How much garage air infiltrates How much garage air infiltrates into the home and what are the into the home and what are the responsible mechanisms?responsible mechanisms?

How high are benzene and other How high are benzene and other VOCs inside the garage and what VOCs inside the garage and what sources are responsible?sources are responsible?

We narrowed study scope to include non-smoking, detached single family

homes with attached garages only.

• Simplified analysis of air exchange rates.Simplified analysis of air exchange rates.

• Eliminated other possible confounding variables.Eliminated other possible confounding variables.

• Confined sampling to winter season when previous study Confined sampling to winter season when previous study showed VOC concentrations were highest.showed VOC concentrations were highest.

House selectionHouse selection

A representative sample of A representative sample of Anchorage homes was selected for Anchorage homes was selected for

sampling.sampling.

Used Anchorage municipal property tax Used Anchorage municipal property tax database to characterize housing stock by age database to characterize housing stock by age and square footage.and square footage.

Selected proportional number of houses in each Selected proportional number of houses in each sampling bin.sampling bin.

Pre 1960 1960-1969 1970-1979 1980-1989 1990-2003 Grand Total

Less Than 1,200 SF 1.71% 1.52% 1.61% 1.99% 0.30% 7.13%1200-1799 SF 1.28% 2.70% 6.60% 9.62% 6.81% 27.02%

1,800-2,499 SF 1.06% 4.98% 15.55% 10.00% 12.27% 43.86%2,500-4,999 SF 0.73% 2.06% 6.07% 5.67% 6.51% 21.03%

5,000 & Greater SF 0.02% 0.04% 0.19% 0.27% 0.43% 0.96%

Grand Total 4.80% 11.30% 30.02% 27.56% 26.32% 100.00%

Pre 1960 1960-1969 1970-1979 1980-1989 1990-2003 Grand Total

Less Than 1,200 SF 1 1 1 1 0 41200-1799 SF 1 1 3 5 3 14

1,800-2,499 SF 1 2 8 5 6 222,500-4,999 SF 0 1 3 3 3 11

5,000 & Greater SF 0 0 0 0 0 0Grand Total 2 6 15 14 13 50

Age and size distribution of detached single family homes with attached garages in Anchorage.

Resultant sampling profile (50 home target)

Tracer gases were used to Tracer gases were used to estimate air exchange rates estimate air exchange rates between garage and house.between garage and house.

A PMCH tracer gas source emitter was deployed in each house and a PDCH source in each garage. The emission rate of each source was known.

PMCH

PDCHhouse

garage

Capillary absorption tubes (CATs) were deployed in the house and garage to measure concentrations of PMCH and PDCH over a 24-hour period.

PMCH

PDCHCAT C

AT

Mass balance approach was used to compute air exchange

rates between garage and house, house and outside, and

garage and outside.

Four simultaneous equations were developed to estimate 4 unknown flows from measured [PMCH] and [PDCH] and the known emission rates of the two tracer gases.

QGA

QGL

QLG

QLA

PMCH

PDCH

Simultaneous equations could be solved and flow rates Simultaneous equations could be solved and flow rates QQGLGL, Q, QGAGA, Q, QLGLG, and Q, and QLALA could be computed for each house. could be computed for each house.

The proportion of air in the house coming from The proportion of air in the house coming from the garage could be easily derived.the garage could be easily derived.

Proportion of house air coming from garage =

QGL/(QGL + QAL)

PMCH

PDCH

QAL

QGL

VOC sampling methodologyVOC sampling methodology

ATD tubes were ATD tubes were used to collect VOC used to collect VOC samples in the samples in the house and garage.house and garage.

Samplers were Samplers were deployed in active deployed in active living space in living space in home, typically in home, typically in living room.living room.

Ambient CO measurements were used to estimate outdoor concentrations of BTEX and butadiene.

Relationship Between Outdoor [CO] and [benzene]

y = 1.7858x + 1.6288

R2 = 0.5882

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Outdoor [CO] ppm

Ou

tdo

or

[be

nze

ne

] p

pb

VOC resultsVOC results

Summary of In-house VOC ConcentrationsSummary of In-house VOC Concentrations

N mean median max

1,3-butadiene 46 0.73 0.44 6.26

benzene 45 7.60 5.16 35.49

carbon tetrachloride 46 0.08 0.09 0.13

chlorobenzene 46 0.14 0.09 0.62

ethylbenzene 46 2.51 1.65 9.34

methylene chloride 46 2.79 0.35 73.16

napthalene 46 0.14 0.08 1.20

o-xylene 46 2.98 2.15 11.21

toluene 46 18.89 12.91 81.73

trichloroethene 44 0.03 0.02 0.49

m,p-xylene 46 6.92 5.19 33.78

Distribution of Benzene Concentrations Inside Homes with Attached Garages

22

12

6

21

0

2

0

5

10

15

20

25

0 to 5 ppb

5 to 10 ppb

10 to 15 ppb

15 to 20 ppb

20 to 25 ppb

25 to 30 ppb

>30 ppb

Nu

mb

er o

f H

om

es

For benzene and other BTEX compounds, mean For benzene and other BTEX compounds, mean concentrations in the house were approximately concentrations in the house were approximately

5 times higher than outside.5 times higher than outside.

Garage concentrations were 10 to 15 times Garage concentrations were 10 to 15 times higher than outside.higher than outside.

Mean Benzene

7.60

26.08

1.66

0.00

5.00

10.00

15.00

20.00

25.00

30.00

House Garage Outdoor

ppb

Toluene

18.89

61.35

5.42

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

House Garage Outdoor

o-Xylene

2.98

8.50

0.72

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

House Garage Outdoor

Ethylbenzene

2.51

6.51

0.46

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

House Garage Outdoor

m,p- Xylene

6.92

21.82

1.44

0.00

5.00

10.00

15.00

20.00

25.00

House Garage Outdoor

Data Analysis and Data Analysis and DiscussionDiscussion

Garage to house infiltration rates varied Garage to house infiltration rates varied considerably among homes sampled.considerably among homes sampled.

Homes with forced air furnaces in the Homes with forced air furnaces in the garage had higher infiltration rates than garage had higher infiltration rates than

homes with other heating configurations.homes with other heating configurations.

Comparison of Median Infiltration RatesProportion of House Air Originating from Garage

36.7%

17.0%18.4%

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

Forced AirFurnace

in GarageN = 15

Forced AirFurnacein House

N = 5

HydronicN=11

Although the [CO] in many garages was Although the [CO] in many garages was high immediately after vehicle start-ups, high immediately after vehicle start-ups,

exhaust emissions do not appear to be the exhaust emissions do not appear to be the primary source of VOCs in the garage.primary source of VOCs in the garage.

House 30

0

10

20

30

40

50

11 12 13 14 15 16 17 18 19 20 21 22 23 0 1 2 3 4 5 6 7 8 9

Hour of Day

[CO

]pp

m

House

Garage

Outside

CO vs benzene in garage

R2 = 0.2729

0

20

40

60

80

100

120

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

CO (ppm)

be

nze

ne

(p

pb

)

There was a stronger relationship There was a stronger relationship between CO and butadiene between CO and butadiene

concentrations.concentrations.

CO vs butadiene in garage

R2 = 0.4111

0

1

2

3

4

5

6

7

8

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

CO (ppm)

bu

tad

ien

e (

pp

b)

The data do not show a significant The data do not show a significant association between the benzene level in association between the benzene level in the garage and:the garage and:

The number of vehicles parked in The number of vehicles parked in the garage;the garage;

The age of the vehicles in the The age of the vehicles in the garage; orgarage; or

The number of trips originating from The number of trips originating from the garage.the garage.

Evaporative emissions may be a Evaporative emissions may be a more important source than more important source than

exhaust emissions.exhaust emissions.

Comparison of Benzene Concentration in the Garage

32.3

7.6

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

Garage Usedfor Gasoline

Equipment StorageN = 23

Garage Not Usedfor Gasoline

Equipment StorageN = 8

med

ian

[b

enze

ne]

p

pb

Having an elevated level of Having an elevated level of benzene in the garage was a good benzene in the garage was a good

indicator that benzene levels in indicator that benzene levels in the house would also be high.the house would also be high.

Garage Benzene vs. House Benzene

y = 0.2789x + 0.4748

R2 = 0.7291

0

5

10

15

20

25

30

35

40

0 20 40 60 80 100 120

measured benzene in garage

me

as

ure

d b

en

zen

e i

n h

ou

se

(p

pb

)

The benzene concentration in the house could The benzene concentration in the house could be precisely predicted from the garage be precisely predicted from the garage

concentration if the air exchange rate between concentration if the air exchange rate between the garage and house was known.the garage and house was known.

[benzeneL] =

[benzeneA] x QAL/(QGL + QAL) + [benzeneG] x QGL/(QAL + QGL)

PMCH

PDCH

QAL

QGL

[benzeneA]

[benzeneG]

[benzeneL]

?

Computed vs. Measured House Benzene

y = 0.9224x + 0.6102R2 = 0.9563

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40

measured benzene in house

co

mp

ute

d b

en

zen

e i

n h

ou

se

(p

pb

)

27% of air from garage

73% of air from outside

[benzene] = 1.4 ppb

[benzene] = 29.8 ppb

Outside air

garage[benzene] = 8.8 ppb

house

The “average” Anchorage house….

- benzene concentration is 6 times higher than outside

- 27% of air in the house comes from garage

- over 90% of benzene in house comes from the garage

BTEX concentrations dropped considerably between BTEX concentrations dropped considerably between 1994-96 study and 2003-2004 study1994-96 study and 2003-2004 study

Comparison of In-home BTEX Concentrations1994-94 study vs. 2003-2004 study

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

Benzene Toluene Ethylbenzene m,p-Xylene o-Xylene

pp

b

1994-96 Study 2003-2004 Study

Phase 2 – Evaluation of Phase 2 – Evaluation of Mitigation StrategiesMitigation Strategies

Candidate StrategiesCandidate Strategies

Remove gasoline-fueled equipment from Remove gasoline-fueled equipment from garage.garage.

Modify forced air systems placed in Modify forced air systems placed in garages to reduce air infiltrationgarages to reduce air infiltration

Ventilate garage to reduce VOC Ventilate garage to reduce VOC concentrationsconcentrations

Lower benzene content in gasolineLower benzene content in gasoline