44
Quantitative Passive Diffusive Quantitative Passive Diffusive- Adsorptive Sampling Techniques for Adsorptive Sampling Techniques for Vapor Intrusion Assessment Vapor Intrusion Assessment Vapor Intrusion Assessment Vapor Intrusion Assessment ESTCP Project 08 30 ESTCP Project 08-30 T M Al HG lt T G ki S S th th T. McAlary, H. Groenevelt, T. Gorecki, S. Seethapathy, D. Crump, P.Sacco, H. Hayes, M. Tuday, B. Schumacher, J. Nocerino, P. Johnson AWMA Specialty Conference – Vapor Intrusion 2010 September 30, 2010 Chi IL 1 Chicago, IL

Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

  • Upload
    dothuan

  • View
    241

  • Download
    5

Embed Size (px)

Citation preview

Page 1: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive Sampling Techniques for Adsorptive Sampling Techniques for

Vapor Intrusion AssessmentVapor Intrusion AssessmentVapor Intrusion AssessmentVapor Intrusion Assessment

ESTCP Project 08 30ESTCP Project 08-30

T M Al H G lt T G ki S S th thT. McAlary, H. Groenevelt, T. Gorecki, S. Seethapathy, D. Crump, P.Sacco, H. Hayes, M. Tuday, B.

Schumacher, J. Nocerino, P. Johnson

AWMA Specialty Conference – Vapor Intrusion 2010

September 30, 2010Chi IL

11

Chicago, IL

Page 2: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Outline• Challenges with conventional sampling

• Introduction to quantitative passive sampling

• Comparative Studies• Comparative Studies• ESTCP Project 08-30• NAVY SPAWAR Projectj

• Summary of Findings to date

22

Page 3: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Challenges withgConventional Sampling

33

Page 4: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Summa Canister and TO-15

Complex procedure, requires special training ($)

Must be cleaned and certified ($)

Bulky ($) to ship and handleBulky ($) to ship and handle

Maximum ~24 hour samples

Costly: $200 to $300/sample, depending on reporting limit

Not useful for analytes heavier than naphthalene (poor recovery)

4444

Page 5: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

55

Page 6: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Automatic Thermal Desorption Tubes / TO-17

Typically customized for each application –high level of training required

Allows longer than 24-hour samples, but the pump must run reliably throughout the sampling periodsampling period

Capable of a larger list of analytes

Typically <$200/sample, depending on analyte list

Potential for breakthrough and competition in high concentration zones

66

Challenging to get sufficient sample volume in low permeability soils

Page 7: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Introduction to Quantitative QPassive Sampling

77

Page 8: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Quantitative Passive Sampling• Expose a sampler for a known time• Ship to laboratory for analysis of adsorbed mass• Calculate concentration

M C0 = concentration of analyte in air (µg/m3)

tkMC 10 M = mass of analyte collected by the sorbent (pg)

k-1 = uptake rate (mL/min)

• Uptake rate is unique to each sampler/analyte pair

tk t = sampling time (min)

• Uptake rate is unique to each sampler/analyte pair• Usually requires expensive controlled experiments• Some passive samplers don’t control uptake – qualitative!

88

Page 9: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Benefits of Passive Sampling• Simple (minimal training)

L i• Less expensive• Low reporting limits with no premium cost

Ti i ht d t ti• Time-weighted average concentration(up to a week or a month if needed)

S ll t hi di t t d l• Smaller – easy to ship, discrete to deploy• Long history of use in Industrial Hygiene

Oth b fit i t h l• Other benefits unique to each sampler

99

Page 10: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

ESTCP Study TeamOrganization Name RoleGeosyntec Consultants, Inc.Guelph (Canada)

Todd McAlaryHester Groenevelt

Overall project direction &reporting

US EPA Labs, Las Vegas (NV) Brian SchumacherJohn Nocerino (D)

Experimental Design &Statistics

Arizona State University (AZ) Paul Johnson Practicality for Vapor IntrusionSitesSites

University of Waterloo(Canada)

Tadeusz GoreckiSuresh Seethapathy

PDMS Membrane Sampler

Cranfield University (UK) Derrick Crump ATD Passive and Active Samplers

Fondazione Salvatore Maugeri(Italy)

Paolo Sacco Radiello Samplers

Columbia Analytical Services(CA)

Michael TudayKu-Jih Chen

High Conc. Laboratory TestingUltra II™ samplers & canisters(CA) Ku-Jih Chen Ultra II samplers & canisters

Air Toxics Limited (CA) Heidi HayesStephen Disher

Low Conc. Laboratory TestingATD Passive and Active Samplers

International Team incl ding the labs most familiar ith each of the samplers

1010

International Team, including the labs most familiar with each of the samplers

Page 11: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Four Different Passive Samplers

Waterloo Membrane S l TM

Automated Thermal Desorption (ATD) T bSampler TM

(1-D permeation across a

b CS

Tubes

(1-D diffusion through air, thermal desorption)

membrane, CS2extraction or thermal desorption)

Radiello™

SKC Ultra II

(Badge sampler,

(Radial uptake through porous cylinder, thermal desorption or( g p

1-D uptake through porous plate, thermal desorption)

desorption or solvent extraction)

1111

p )

Page 12: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Desorption Methods

Thermal desorptionThermal desorptionThermal desorptionThermal desorption

Solvent

Sorbent

Solvent desorptionSolvent desorption

1212

Thermal desorption

Page 13: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Sorbent Media SelectionSorbent Description Sampling Properties

Anasorb 747 Beaded active carbon

High capacity for VOCs, solvent desorption

Tenax TA Porous polymer Low capacity, medium to high boiling compounds, thermal

60/80 mesh

g pdesorption

Non porous high capacity forCarbopack B

60/80 mesh graphitized

carbon black

Non-porous, high capacity for VOCs, thermal desorption

1313

There are many, many more sorbents available

Page 14: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Laboratory Analyte List

43

Selected to span a range of compounds of interest for vapor intrusion studies

1414

Selected to span a range of compounds of interest for vapor intrusion studiesChlorinated ethenes, ethanes, methanes, and VOCs of differing solubility and sorptive properties

Page 15: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Low Concentration Tests:To Mimic Indoor and Outdoor Air ConditionsTo Mimic Indoor and Outdoor Air Conditions

Concentration : 1, 50 and 100 ppbvTemperature: 22, 25, 28 °CTemperature: 22, 25, 28 CHumidity: 30, 60 and 90% RHFace velocity: 0.01, 0.2 and 0.4 m/sExposure time: 1 4 and 7 days

High Concentration Tests:

Exposure time: 1, 4 and 7 days

High Concentration Tests:To Mimic Soil Gas Conditions

C t ti 1 10 d 100Concentration : 1, 10 and 100 ppmvTemperature: ambientHumidity: 90-100%Face velocity: very low (5x10-5 m/s)

1515

Face velocity: very low (5x10 5 m/s)Exposure time: 30 minutes

Page 16: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Exposure Chamber• Conditioned gas enters at

bottom and flows past lsamplers

• Samplers rotate on a carousel to control facecarousel to control face velocity

• Baffles help to minimize t b lturbulence

• All surfaces passivated to minimize adsorptionminimize adsorption

1616

Page 17: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Exposure Chamber (cont’d)Off th h lf All fOff the shelf glassware, modified by glass blower

All surfaces passivated

glass-blower

Surrounded by tube of circulating fluid and insulated for temperature controlcontrol

1717

Page 18: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

1818

Page 19: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Inter-Laboratory TestingSecondary # of Samplers to

Sampler Type Home Laboratory Laboratories Each Laboratory

W t l M b Ai T i LtdWaterloo Membrane       Sampler University of Waterloo

Air Toxics Ltd2

Airzone One

ATD Tubes with Tenax TA Air Toxics Ltd

Columbia Analytical Services 2ATD Tubes with Tenax TA Air Toxics Ltd Services 2

University of Waterloo

ATD Tubes with b k Air Toxics Ltd

Columbia Analytical Services 2CarboPack B Air Toxics Ltd 2

University of Waterloo

SKC Ultra Columbia Analytical Services

Air Toxics Ltd2Services

Airzone One

Radiello Fondazione Salvatore Maugeri

Columbia Analytical Services 2

Air Toxics Ltd

1919

Air Toxics Ltd

Page 20: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Interlab Test – Youden Plot

(blank contamination)

2020

Most results show good agreement between labsMEK was problematic

Page 21: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

ANOVA TestingSet the five factors at their midpoints, and run test multiple times

to determine variance from experimental procedures

Factor Units Center Value

Concentration ppb 50

Temperature °C 20Temperature C 20

Gas Flow Velocity m/s 0.2

Sampling Duration days 4

Relative Humidity % 60

2121

e at ve u d ty % 60

Page 22: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Fractional Factorial TestingA series of experiments strategically changing the 5 key factors

Concentration

Temperature

Face Velocity

Sample Time

HumidityHumidity

2222

Page 23: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Chamber Test Results to DateChamber Test Results to Date

2323

Page 24: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Chamber Test Results to DateChamber Test Results to Date

(l bi )(low bias)

2424

Page 25: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Chamber Test Results to DateChamber Test Results to Date

(blank)(blank)

(1-day)

(Calculated Uptake Rate)

2525

Page 26: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Chamber Test Results to DateChamber Test Results to Date

(high bias)

?

?

2626

Page 27: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Chamber Test Results to DateChamber Test Results to Date

2727

Page 28: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Field Testing (SPAWAR/NESDI)Comparative sampling of indoor air, outdoor air, and soil vapor

Indoor Air:

ATD Tubes3M OVM 3500RadielloSKC Ult IISKC Ultra IIWaterloo Membrane

VersusVersus

6-day Summas

With

3 Replicates

2828

Acknowledgements to Ignacio Rivera and Bart Chadwick of SPAWAR for Support

p

Page 29: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Indoor Air (3 Locations in Triplicate)Indoor Air (3 Locations in Triplicate)Indoor Air AverageTrichloroethene

8

10Indoor Air - AverageTrichloroethene

SummaWMS3M OVM

(Anasorb 747)(Activated carbon wafer)

6

8

m3)

ATDRadielloSKC Ultra

Each bar is an average of the three

(Chromosorb 106)(Activated charcoal)

(Chromosorb 106)

4

atio

n (µ

g/m Each bar is an average of the three

samples collected at that location

2

Con

cent

ra

0

IA-1 IA-2 IA-3 Average

C

Sample Location

2929

The low bias for SKC is believed to be due to sorbent selection (Chromosorb 106 worked well for ATD, but SKC has 20X higher uptake rate)TCE was the dominant compound

Page 30: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

SubSub--Slab SamplingSlab SamplingTwo types:

1) Fully passive (drop and cork for 24 hours)

2) Semi-passive(drop and purge

ith PID f 10with PID for 10 minutes)

3030

Page 31: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

SPAWAR Subslab DataSPAWAR Subslab DataFully passive samples (left)

Fully Passive With Purging

showed “Starvation Effect” in proportion to

t k tuptake rate

Much less “starvation” when PID used to purgePID used to purge gas from hole during 10 min sampling interval

3131

p g

Page 32: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Starvation Factor vs Uptake RateStarvation Factor vs Uptake Rate1000.0

WMS cis-1,2-DichloroetheneWMS Trichloroethene

Starvation Factor = Summa conc’nPassive conc’n

100.0

TrichloroetheneSKC cis-1,2-DichloroetheneSKC Trichloroethene

on F

acto

r

Radiello TrichloroetheneATD cis-1,2-

10.0

Star

vatio

ATD cis 1,2DichloroetheneATD Trichloroethene

3M OVM i 1 2

1.00.01 0.1 1 10 100

Uptake Rate (ml/min)3M OVM cis-1,2-Dichloroethene3M OVM Trichloroethene

3232

Consider a custom “low-uptake” sampler

Page 33: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Modified Uptake RatesModified Uptake Rates

WMS Sampler

ATD Tube & Pinhole Cap

SKC Ultra II and 12-hole Cap

Reduce the uptake rate by reducing the area

3333WMS Pinhole Sampler

p y gLower uptake = less starvation

Page 34: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Passive Soil Gas Passive Soil Gas –– Utah HouseUtah House

3434

Page 35: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

6 Passive Samplers6 Passive Samplers(Tenax) (Carbopack) (Cap)

Uptake rates: 0.01 to 75 mL/min

Void space was larger than SPAWAR sub-slab sampling

3535

Page 36: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

6 Passive Probes + 1 Conventional6 Passive Probes + 1 Conventional

Modified Latin Square TestAdded one Duplicate

3636

Added one DuplicateTested 1 to 12 day exposuresDrop the sampler/Purge 3 PV

Page 37: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Active Sampler DataActive Sampler Data120

140

TCE in Summa and Hapsite GC/MSPSG-1PSG-2PSG-3PSG-4PSG-5

60

80

100

trat

ion

(ppb

v)

PSG-6Summa - PSG-1Summa - PSG-2Summa - PSG-3Summa - PSG-4Summa - PSG-5

20

40

60

Con

cent Summa - PSG-6

Linear (PSG-1)Linear (PSG-2)Linear (PSG-3)Linear (PSG-4)Linear (PSG-5)

007/16/10 07/21/10 07/26/10 07/31/10 08/05/10 08/10/10 08/15/10 08/20/10 08/25/10 08/30/10 09/04/10 09/09/10

Sampling Date

( )Linear (PSG-6)

160 1,1-DCE in Summa and Hapsite GC/MSPSG-1PSG-2PSG-3PSG 4

100

120

140

on (p

pbv)

PSG-4PSG-5PSG-6Summa - PSG-1Summa - PSG-2Summa - PSG-3

40

60

80

Con

cent

ratio Summa - PSG-4

Summa - PSG-5Summa - PSG-6Linear (PSG-1)Linear (PSG-2)Linear (PSG-3)

3737

0

20

07/16/10 07/21/10 07/26/10 07/31/10 08/05/10 08/10/10 08/15/10 08/20/10 08/25/10 08/30/10 09/04/10 09/09/10

Sampling Date

( )Linear (PSG-4)Linear (PSG-5)Linear (PSG-6)

Page 38: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Fully Passive Fully Passive –– Deep 2Deep 2--inch Probesinch Probes

C/Co = Passive data divided by Mean of all Hapsite data

3838

All but about 3 of these measurements are within a half order of magnitudeLonger samples with weaker sorbent show losses (Tenax)

Page 39: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Fully Passive Fully Passive –– Deep 2Deep 2--inch Probesinch Probes

Longer samples show losses with both Carbopack and Tenax for ATD Tubes

3939

Consistent with theory for incomplete retention (11DCE is 3X less sorptive than TCE)

Page 40: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Starvation Factor Versus Uptake RateStarvation Factor Versus Uptake Rate1000

100

1000

Losses from Tenax

10

or (C

o/C

)

1

vatio

n Fa

cto

0.1

Star

v

0.010.01 0.1 1 10 100 1000

4040

Uptake Rate (mL/min)

After removing artifacts of weak sorbent, trend is encouraging

Page 41: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

FlowFlow--Through CellsThrough Cells

Why worry about starvation at all?J st p rge soil gas past the sampler at a modest rate

4141

Just purge soil gas past the sampler at a modest rateComparable to groundwater “Low Flow Sampling Protocol”

Page 42: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

FlowFlow--Through Cell ResultsThrough Cell Results

4242

Flow-through cell neutralizes the starvation effectVariability about 1 order of magnitude, but so did Summa cans

Page 43: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Interim Conclusions Encouraging results to dateEncouraging results to date

No samplers eliminatedNo samplers eliminated Challenges with highly sorptive or highly soluble compoundsChallenges with highly sorptive or highly soluble compounds Challenges with very high humidity or long exposures for Challenges with very high humidity or long exposures for

some sampler/sorbent combinationssome sampler/sorbent combinationssome sampler/sorbent combinationssome sampler/sorbent combinations Much better understanding of how to avoid starvation for soil Much better understanding of how to avoid starvation for soil

gas sampling gas sampling –– quantitative results are likely feasiblequantitative results are likely feasibleg p gg p g q yq y Modifications can overcome some of the limitationsModifications can overcome some of the limitations

Custom sorbents and uptake rates Custom sorbents and uptake rates Based on theory & dataBased on theory & data

This is roughly the “halfThis is roughly the “half--way” point way” point –– stay tuned!stay tuned!

4343

Page 44: Quantitative Passive DiffusiveQuantitative Passive ...events.awma.org/education/Presentations/Session 7/McAlary AWMA... · Quantitative Passive DiffusiveQuantitative Passive Diffusive--Adsorptive

Questions/Comments?Questions/Comments?Questions/Comments?Questions/Comments?

[email protected]