Thomas H. Stock, Maria T. Morandi, Masoud Afshar, Valerie Murray, Silvia Maberti

Investigation of Spatial Variation of Investigation of Spatial Variation of Air Toxics in Three Houston-Area Air Toxics in Three Houston-Area

Neighborhoods Using Passive Neighborhoods Using Passive SamplingSampling

Thomas H. Stock, Maria T. Morandi, Masoud Thomas H. Stock, Maria T. Morandi, Masoud Afshar, Valerie Murray, Silvia MabertiAfshar, Valerie Murray, Silvia Maberti

University of Texas School of Public Health, Houston, TXUniversity of Texas School of Public Health, Houston, TX

Kuenja C. ChungKuenja C. ChungU.S. EPA, Region 6, Dallas, TXU.S. EPA, Region 6, Dallas, TX

Advantages of Passive SamplersAdvantages of Passive Samplersfor Ambient Air Monitoringfor Ambient Air Monitoring

Small, light weight and requires no Small, light weight and requires no powerpower

Easy to handle in the fieldEasy to handle in the field Relatively unobtrusiveRelatively unobtrusive Multiple simultaneous samplesMultiple simultaneous samples Locations not accessible with Locations not accessible with

conventional methodsconventional methods Fewer security concernsFewer security concerns

Field Evaluation Studies of 3M Field Evaluation Studies of 3M OVMOVM

for Ambient Air Monitoringfor Ambient Air Monitoring

Phase 1. Feasibility and determination Phase 1. Feasibility and determination of operational parameters, including of operational parameters, including limited method comparisonlimited method comparison

Phase 2. Year-long comparison of Phase 2. Year-long comparison of central monitoring site vs. nearby central monitoring site vs. nearby centroidcentroid

Phase 3. Intensive spatial variation Phase 3. Intensive spatial variation studystudy

Phase 3 Study DesignPhase 3 Study Design

Simultaneous monitoring in three areas, Simultaneous monitoring in three areas, defined as a 2-mile radius around each defined as a 2-mile radius around each TCEQ monitoring site: Aldine, Clinton Dr. TCEQ monitoring site: Aldine, Clinton Dr. and Deer Park.and Deer Park.

In each area, simultaneous monitoring at In each area, simultaneous monitoring at TCEQ monitoring site, census tract TCEQ monitoring site, census tract centroid, and 10 homes of volunteers.centroid, and 10 homes of volunteers.

72-hour sampling, performed 6 times 72-hour sampling, performed 6 times during May-September.during May-September.

Houston Area Monitoring SitesHouston Area Monitoring Sites

Study AreasStudy Areas

Aldine Monitoring StationAldine Monitoring Station

Clinton Drive Monitoring StationClinton Drive Monitoring Station

Deer Park Monitoring StationDeer Park Monitoring Station

OVM Sample ShelterOVM Sample Shelter

OVM Samples and Field BlankOVM Samples and Field Blank

Target Compounds and 72-hr Target Compounds and 72-hr MDLsMDLs

VOCVOC Lot 1 MDL (ug/m3)Lot 1 MDL (ug/m3) Lot 2 MDL (ug/m3)Lot 2 MDL (ug/m3)

n-Pentanen-Pentane 0.460.46 1.361.36

Methylene chlorideMethylene chloride 0.680.68 0.410.41

MTBEMTBE 0.610.61 0.080.08

n-Hexanen-Hexane 0.340.34 0.340.34

MethylcyclopentaneMethylcyclopentane 0.180.18 0.180.18

Methyl ethyl ketoneMethyl ethyl ketone 9.809.80 6.306.30

ChloroformChloroform 0.070.07 0.070.07

2,3-Dimethylpentane2,3-Dimethylpentane 0.160.16 1.441.44

Carbon tetrachlorideCarbon tetrachloride 0.160.16 0.160.16

BenzeneBenzene 1.241.24 0.480.48

TrichloroethyleneTrichloroethylene 0.150.15 0.150.15

TolueneToluene 1.651.65 2.632.63

TetrachloroethyleneTetrachloroethylene 0.180.18 0.270.27

Ethyl benzeneEthyl benzene 0.260.26 0.260.26

Target Compounds and 72-hr Target Compounds and 72-hr MDLsMDLs

VOCVOC Lot 1 MDL (ug/m3)Lot 1 MDL (ug/m3) Lot 2 MDL (ug/m3)Lot 2 MDL (ug/m3)

n-Nonanen-Nonane 0.170.17 0.170.17

m/p-Xylenem/p-Xylene 0.370.37 0.550.55

o-Xyleneo-Xylene 0.200.20 0.200.20

StyreneStyrene 0.400.40 0.130.13

αα-Pinene-Pinene 0.200.20 0.610.61

n-Decanen-Decane 0.670.67 0.380.38

1,3,5-1,3,5-TrimethylbenzeneTrimethylbenzene

0.090.09 0.090.09

1-ethyl-2-methyl 1-ethyl-2-methyl benzenebenzene

0.090.09 0.190.19

ββ-Pinene-Pinene 0.200.20 0.200.20

1,2,4-1,2,4-TrimethylbenzeneTrimethylbenzene

0.190.19 0.190.19

d-Limonened-Limonene 0.640.64 1.061.06

1,2,3-1,2,3-TrimethylbenzeneTrimethylbenzene

0.100.10 0.190.19

p-Dichlorobenzenep-Dichlorobenzene 3.773.77 0.890.89

NaphthaleneNaphthalene 0.180.18 0.180.18

Results of Phase 3 SamplingResults of Phase 3 Sampling

In both the Aldine and Clinton study areas, In both the Aldine and Clinton study areas, concentrations of many VOCs outside concentrations of many VOCs outside some homes frequently exceeded some homes frequently exceeded measurements at the central site.measurements at the central site.

In the Deer Park area, house In the Deer Park area, house measurements were in closer agreement measurements were in closer agreement with the central site measurements.with the central site measurements.

Concentrations measured at Aldine House Concentrations measured at Aldine House 7 (A7) had the highest median values for 7 (A7) had the highest median values for 20 compounds in the Aldine area.20 compounds in the Aldine area.

Concentrations measured at Clinton House Concentrations measured at Clinton House 10 (C10) had the highest median values 10 (C10) had the highest median values for 11 compounds in the Clinton area.for 11 compounds in the Clinton area.

Supplementary SamplingSupplementary Sampling

In order to differentiate between very In order to differentiate between very localized sources of VOCs outside localized sources of VOCs outside homes and more area-wide sources, 5 homes and more area-wide sources, 5 OVMs were placed in different positions OVMs were placed in different positions around each of two homes with around each of two homes with elevated concentrations (House A7 and elevated concentrations (House A7 and C10).C10).

72-hour sampling performed twice 72-hour sampling performed twice during February-April.during February-April.

Results of Supplementary Results of Supplementary SamplingSampling

Samples from House A7 showed elevated Samples from House A7 showed elevated levels of many compounds at only one levels of many compounds at only one position, that employed previously for the 6 position, that employed previously for the 6 warm weather samplings.warm weather samplings.

Interviews indicated that this position (above Interviews indicated that this position (above the garage door) was influenced by nearby the garage door) was influenced by nearby resident activities (servicing/refueling of resident activities (servicing/refueling of tree-cutting equipment, frequent idling and tree-cutting equipment, frequent idling and washing/waxing of vehicles in driveway).washing/waxing of vehicles in driveway).

Samples from House C10 were uniformly Samples from House C10 were uniformly elevated, indicating the influence of more elevated, indicating the influence of more remote source(s) affecting a wider area, but remote source(s) affecting a wider area, but not characterized by the central site not characterized by the central site measurements.measurements.

ConclusionsConclusions

Passive sampling is a useful technique for Passive sampling is a useful technique for evaluating spatial heterogeneity of ambient air evaluating spatial heterogeneity of ambient air concentrations of VOCs.concentrations of VOCs.

Concentrations of many VOCs in two Houston Concentrations of many VOCs in two Houston areas are frequently underestimated by areas are frequently underestimated by measurements at central monitoring sites.measurements at central monitoring sites.

Elevated levels of compounds appear to be Elevated levels of compounds appear to be persistent, i.e., similar results were observed persistent, i.e., similar results were observed during warm and cooler weather sampling.during warm and cooler weather sampling.

Spatial mapping of concentrations around homes Spatial mapping of concentrations around homes can be used successfully to differentiate between can be used successfully to differentiate between observed elevated concentrations caused by observed elevated concentrations caused by specific localized resident activities (House A7) specific localized resident activities (House A7) and those due to more remote sources affecting a and those due to more remote sources affecting a larger area (House C10).larger area (House C10).