Objective
• Finish with VOCs
• Prepare for the field measurements on
Friday
VOCs in Buildings
•
•
•
•
Sources
Fate
Effects
Measurement
Volatile Organic Compounds (VOCs)
VOC
• What is a VOC?
–
–
–
–
Organic = C, H
“affinity for gas phase”, “significant” evaporation rate
Tb < 260 oC
Thousands (reduce list to 50 to 100)
• What is TVOC?
Categories
• Odor-causing
• Irritating
• SBS – fatigue, eyes, headaches, upper resp., etc
• Other – skin irritation, asthma, MCS
• Toxic/Hazardous
• Carcinogen
• Teratogen
• Neurotoxin, etc.
• Reactive
• Generally w/ ozone
Representative Examples
•
•
•
•
•
•
•
•
•
•
•
•
Benzene
Toluene
BTEX
Ethylbenzene
Xylenes (all isomers)
Trimethylbenzenes (all isomers)
Dichlorobenzenes (not all isomers created equal)
Tetrachloroethene (PERC)
Chloroform (a THM)
4-Phenylcyclohexene (4-PCH)
Styrene
Terpenes (limonene, pinene, etc.)
Formaldehyde (HCHO) – often not classified as a VOC
Relative Exposure to VOCs
Cin t in Bin
Exposure (I / O) 
C out t out Bout
 Cin  t in  Bin 
 



 C out  t out  Bout 
Exposure (I/O) = 3 x 18 x 0.4 = 22
indoor contribution > 95% (most volatile HAPs, etc.)
Some Important Sources
•
•
•
•
•
•
Building materials and furnishing (wood, adhesives, gyp board)
Flooring materials (carpet, vinyl flooring, wood)
Architectural coatings (paints, varnishes, waxes, etc.)
Consumer products (cleaners, detergents, fresheners, personal, etc.)
Combustion sources (ETS, candles, gas stoves, space heaters)
Electronics (computers, photocopiers, printers, TVs/VCRs)
•
•
•
•
•
Heating of particulate matter
Soil vapor intrusion
Drinking water
Mold (MVOCs)
People
Measurement Issues
Objective(s)
Required detection limits
(Real-time) vs. (collect and analyze)
Non-specific vs. species specific (speciated)
Grab versus integrated
Interferences
Preservation requirements
Quality assurance requirements
EPA/OSHA/NIOSH methods exist?
Cost/Budget
Measurement Method
•
•
•
•
•
•
•
•
•
•
Sample Collection Methods
• Real-time (field) measurement/analysis
– generally = sensor (mostly FID, PID)
– some = separation (w/ GC) + sensor
– Also – colorimetric tubes (general: MDL > 1 ppm)
• Collect for analysis
– whole-volume samplers (canisters, bags)
– concentration samplers (sorbents, SPME)
– either case = preservation and analysis in laboratory
Canisters
• Whole volume
• Grab versus integrated
• EPA Methods TO-14 / 15
• Benefits
• Inert/impermeable
• Experience
• Multiple analyses
1 – 15 L
• Drawbacks
• bulky
• cleaning
• Scratch
• Ozone / Sample stability
http://www.skcinc.com
400 mL
Tedlar Bags
•
•
•
•
•
Whole volume
Tedlar = polyvinylfluoride
Pump to collect (unlike cans)
Issues:
Benefits:
–
–
–
–
inert / impervious (like cans)
repeat samples (like cans)
lighter than cans
lower initial cost than cans
• Drawbacks
–
–
–
–
not as reuseable as cans
tearing
cleaning
stability with some compounds
http://www.essvial.com/products/airsample.html
0.5 – 100 L
Sorbent Sampling
• VOC adsorbs to solid adsorbent
• Passive sampling
– Similar to ozone badge
– Integrated sample over 24 hours, etc.
– Indoor, personal, outdoor
http://www.aerotechpk.com/
• Active Sampling
–
–
–
–
–
Pump through packed tube
Collect mass over known volume
C = m/V
Short-term vs. integrated
More control, but more difficult
http://www.sisweb.com/index/referenc/resin10.htm
Sorbent Tubes
• EPA Method
•Various sorbents can be used
•Note VOC types/ranges
• Some issues
• Method detection limit, precision, accuracy
•Sample preservation
• Breakthrough volume
•Artifact formation (especially via ozone)
• Sorbent pre-conditioning / breakdown over time
• Use of multi-sorbent beds
• Focus on Tenax-TA
Tenax-TA
• 2,6-diphenylene oxide polymer resin (porous)
• Specific area = 35 m2/g
• Pore size = 200 nm (average)
• Density = 0.25 g/cm3
• Various mesh sizes (e.g., 60/80)
• Low affinity for water (good for high RH)
• Non-polar VOCs (Tb > 100 oC); polar (Tb > 150 oC)
•Artifacts w/ O3: benzaldehyde, phenol, acetophenone
Gas Chromatography (GC)
• Goal = separate compounds
• Use capillary column
• Properties of column
• Properties of chemical
• Thermal program of GC oven
• Temporal passage to a detector
• analyze “peaks”
• analyze molecular fragments (MS)
Gas Chromatography (GC)
http://www.chromatography-online.org/GC/Modern-GC/rs2.html
Figure 5: Chromatogram of Tenax-sampling in a show case (sample
volume 1l) - iaq.dk/iap/iaq2003/posters/hahn5.gif
Blue slides = www.sisweb.com/art/referenc/aap54
GC Issues
• Type of injection?
• Need to cryofocus?
• Type of column?
• Type of detector?
– If MS, model of detection
• Temperature programs
• Instrument calibration / response
Detectors
• Flame ionization detector (FID)
• Photoionization detector (PID)
Non-specific or
speciated (w/ GC)
• Electron capture detector (ECD)
• Mass spectrometer (MS)
w/ speciated (w/ GC)
• These are primary detectors for VOCs in indoor air
• Specific uses vary considerably
Flame Ionization Detectors (FID)
•
•
•
•
•
Relatively simple system 
Ions formed – migrate to plate
Generate current
Detection – typical to pg/s
Benefits
– Rugged, low cost, workhorse
– Linear response over wide range
– Insensitive to H2O, CO2, SO2, CO, NOx ..
• Drawbacks
– No identification
– Lower response if not simple HC
– Destructive
www.chem.agilent.com
Photoionization Detectors (PID)
•
•
•
•
UV light ionizes VOCs --- R + hv  R+ + eCollected by electrodes = current
VOCs with different ionization potentials
Benefits
– Simple to use
– Sample non-destructive (relatively)
• Drawbacks
–
–
–
–
No identification
Highly variable responses
Not all VOCs detected
Lamp burnout / contamination
http://www.chemistry.adelaide.edu.au/external/soc-rel/content/pid.htm
Electron Capture Detectors (ECD)
• Low energy Beta emitter = 63Ni
• e- attracted to positively charged electrode (anode)
• Molecules in sample absorb e- and reduce current
– effective: halogens, nitrogen-containing
• Benefits
– 10-1,000 x more sensitive than FID
– femtogram/s ----- ppt levels
• Drawbacks
–
–
–
–
More limited linear range than FID
Radiological safety requirements
http://www.chemistry.adelaide.edu.au/exte
O2 contamination issues
rnal/soc-rel/content/ecd.htm
Response strong function of T, P, flowrate
Mass Spectrometer (MS)
• Bombard molecules w/ intense electron source
• Generate positive ion fragments
• Use fragment fingerprint to identify molecule
• Quantify amount of fragments to determine mass
• Most common MS = quadrupole
Quadrupole MS
• Electron source
• Four rods (electromagnets)
–
–
–
–
–
Applied Voltage
DC/AC components
Voltages = fn(time)
Affects trajectory
Selective M/Z to detector
http://www.chemistry.adelaide.edu.au/exter
nal/soc-rel/content/quadrupo.htm
Total Ion Chromatogram (TIC)
linalool
limonene
Mondello et al., J. of Chromatography A, 1067: 235-243 (2005)
Summary
• VOCs important in indoor environments
• Many types of VOCs
– Different properties
– Different effects
– Different sample collection and analysis protocols
• Sampling and analysis protocols NOT TRIVIAL
– Many types of collection methods
– Many types of analysis methods / including detectors
– A lot of issues involved w/ sample/analysis decisions
– A lot can go wrong (difficult business)
– Cumbersome and costly -------- but really important
Field trip
• Friday afternoon
– 10800 Pecan Park Boulevard Suite 210. Austin, TX 78750
• Measurement of
– Primarily IAQ parameters
• ……
• Prepare on Thursday
– Distribute duties
• Equipment assembly
• Packing and check out
• ….