Objective Finish with VOCs Prepare for the field measurements on Friday.

Objective

• Finish with VOCs

• Prepare for the field measurements on Friday

VOCs in Buildings

• Sources

• Fate

• Effects

• Measurement

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?

Volatile Organic Compounds (VOCs)

• 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

Categories

• Benzene• Toluene• 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

BTEX

Representative Examples

out

in

out

in

out

in

outoutout

ininin

B

B

t

t

C

C

BtC

BtC)O/I(Exposure

Exposure (I/O) = 3 x 18 x 0.4 = 22

indoor contribution > 95% (most volatile HAPs, etc.)

Relative Exposure to VOCs

• 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

Some Important Sources

• 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 IssuesM

easurement M

ethod

• 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

Sample Collection Methods

Canisters

http://www.skcinc.com

• Whole volume• Grab versus integrated• EPA Methods TO-14 / 15• Benefits

• Inert/impermeable• Experience• Multiple analyses

• Drawbacks• bulky• cleaning• Scratch• Ozone / Sample stability

400 mL

1 – 15 L

• 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

Tedlar Bags

http://www.essvial.com/products/airsample.html

0.5 – 100 L

• VOC adsorbs to solid adsorbent• Passive sampling

– Similar to ozone badge– Integrated sample over 24 hours, etc.– Indoor, personal, outdoor

• Active Sampling– Pump through packed tube– Collect mass over known volume– C = m/V– Short-term vs. integrated– More control, but more difficult

Sorbent Sampling

http://www.sisweb.com/index/referenc/resin10.htm

http://www.aerotechpk.com/

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

• Type of injection?

• Need to cryofocus?

• Type of column?

• Type of detector?

– If MS, model of detection

• Temperature programs

• Instrument calibration / response

GC Issues

Detectors

• Flame ionization detector (FID)

• Photoionization detector (PID)

• Electron capture detector (ECD)

• Mass spectrometer (MS)

• These are primary detectors for VOCs in indoor air

• Specific uses vary considerably

Non-specific or speciated (w/ GC)

w/ speciated (w/ GC)

• 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

Flame Ionization Detectors (FID)

www.chem.agilent.com

• UV light ionizes VOCs --- R + hv R+ + e-

• Collected 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

Photoionization Detectors (PID)

http://www.chemistry.adelaide.edu.au/external/soc-rel/content/pid.htm

• 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– O2 contamination issues– Response strong function of T, P, flowrate

Electron Capture Detectors (ECD)

http://www.chemistry.adelaide.edu.au/external/soc-rel/content/ecd.htm

• 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

Mass Spectrometer (MS)

• Electron source• Four rods (electromagnets)

– Applied Voltage– DC/AC components– Voltages = fn(time)– Affects trajectory– Selective M/Z to detector

Quadrupole MS

http://www.chemistry.adelaide.edu.au/external/soc-rel/content/quadrupo.htm

Total Ion Chromatogram (TIC)

limonene

linalool

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 • ….