Dosimeters Flashcards
What dosimeters are sensitive to volatile organic acids?
- Lead coupons
- Lead coated piezoelectric quartz (PQC) crystals
- Glass dosimeters
What are lead coupons for?
Monitoring corrosive quality from acidic environments caused by emission of volatile organic acids (Oddy test)
What are glass dosimeters used for?
To evaluate levels of corrosivity of environments
What dosimeters are sensitive to inorganic pollutant gases?
- EWO developed, used by Norwegian Institute for Air Quality NILU
- Resin mastic coated PQC crystals
- Elastomer dosimeter for ozone
What is lead coating applied to and how?
To Quartz Crystal Microbalance (QCM) by thermal evaporation under vacuum, As the lead is deposited the crystal becomes heavier (mass gain) and its frequency of oscillation changes.
- Measurement of frequency made at selected periods or continuously.
How are lead coated PQC
crystals prepared?
- Coating deposited by thermal evaporation
- Change (%) in coated crystals monitored
- Rapid oxidation of lead surface followed by passivation as oxide layer forms
- Typical change 6-10%
What is NOAEL?
A No Observed Adverse Effect Level: the highest level of pollutant that does not produce an observable adverse effect on a specific chemical or physical property of a material in an experiment.
How is the NOAEL determined?
- Expose material to different concentrations of pollutants
- The level just below concentration where there an adverse effect is observed
What is LOAED?
The Lowest Observed Adverse Effect Dose:
1. used to quantify the exposure-effect relationship
2. The cumulative dose (LOAED x time) at which the first signs of adverse effects are observed
3. Used only if NOAEL cannot be determined with confidence
When is NOAEL at risk. and when is it not?
- At risk: in an enclosure with acid-emissive products
- Not: in an open room where levels of acetic acid are below NOAEL lead
What are Lead-based dosimeters sensitive to?
- Volatile Organic Acids
- RH
- T
What are EWO-G dosimeters sensitive to/
- RH + T
- Light/UV
- Inorganic pollutants (SO2, NOx, O3)
What is the dosimeter instrumentation?
1 A glass substrate coated with organic polymer
2 The film applied by spin coating, giving uniform film thickness
What is the measuring procedure of a dosimeter?
- Dosimeter analyzed (initial abs. measurement)
- Exposed for 3 months
- Analyzed again (2nd)
- Response is change in absorption at 340 nm
- Result: EWO-response level
How does the dosimeter operate?
- Polymer film reacts with air pollutants
- Becomes less transparent
- Dose quantified as change in UV absorption (340 nm) using photo spectrometer
How do you calculate the concentration of a pollutant in the air of a room?
From the mass balance equation, take into account amount of contaminant in the air entering and leaving the room, and any reduction due to deposition on internal surface of room (I/O).
What is an assumption made when calculating the concentration of a pollutant?
Once pollutant gas adsorbed by surface, does not desorb at a later stage.
What is a resin mastic? And to what is it sensitive to?
A triterpenoid resin, very sensitive to light and oxidizing agents (NO2)
What are properties of Ozone O3?
- Mainly outdoor sources
- Photochemical reactions between Nitrogen Oxides and VOC in sunlight
- Outdoor level: 20 -60 ppb (150 ppb)
- Highest levels during summer
- Indoor levels: 5 - 80% of outdoors
- Low levels indoors when low aer, or filtered ventilation
What are the properties of rubber bands as dosimeter material?
- Stretched to double length
- Exposed for 3-6 months
- Surface examined by light microscopy
Why is Ozone considered a strong oxidant?
- Attacks rubber by breakage of molecular bonds causing surface cracks
- Also attacks other types of materials (colorants)
What are properties of ATR-FTIR on dosimeters?
- Used for low exposures
- Difficult to use when surface cracked
- Formation of carbonyl bonds can be detected by surface spectroscopy
- Rubber bands (have talc) disturb latex spectra, thus pure latex sheets used
How does ATR/FTIR operate?
- Sample brought to close contact with surface of prism
- Prism made of crystal with high RI:
a) KRS-5 Thallium Bromo-Iodide, n=2.4
b) Zinc Selenide ZnSe (n=2.4)
c) Germainum Ge (n=4.0)
What are the changes in rubber dosimeters on exposure to Ozone?
- Carbonyl peaks broaden 1720 - 1716 cm-1
- Increase in dose received (ppb)
What are ATR/FTIR working principles?
- Used for low ozone exposure
- Better latex quality must be used instead of rubber bands
