AQS Monitoring Tools 3 — Questions and Answers
Question 1: UV fluorescence technology is the Federal Reference Method (FRM) measurement principle used for which criteria pollutant?
- Sulfur dioxide (SO2) (Correct answer)
- Nitrogen dioxide (NO2)
- Carbon monoxide (CO)
- Ozone (O3)
Correct answer: Sulfur dioxide (SO2)
UV fluorescence analyzers (EPA FRM Method No. RFSA-1293-099) excite SO2 molecules with UV light and detect the resulting fluorescent emission to quantify SO2 concentration.
Question 2: Which measurement principle is used in the EPA-designated FRM analyzer for ambient nitrogen dioxide (NO2)?
- Chemiluminescence with photolytic conversion (Correct answer)
- Non-dispersive infrared absorption
- UV fluorescence spectroscopy
- Beta attenuation
Correct answer: Chemiluminescence with photolytic conversion
The EPA FRM for NO2 uses a photolytic converter to convert NO2 to NO, then measures via chemiluminescence reaction between NO and ozone.
Question 3: Non-dispersive infrared (NDIR) absorption analyzers are most commonly used in ambient air monitoring to measure which gas?
- Carbon monoxide (CO) (Correct answer)
- Sulfur dioxide (SO2)
- Ozone (O3)
- Hydrogen sulfide (H2S)
Correct answer: Carbon monoxide (CO)
NDIR analyzers exploit CO's strong absorption band at ~4.7 µm infrared wavelength, making it the FRM-class technology for ambient CO measurement.
Question 4: A Beta Attenuation Monitor (BAM) measures PM2.5 mass concentration by which physical principle?
- Attenuation of beta radiation (electrons) passing through particles collected on a filter tape (Correct answer)
- Oscillation frequency change of a vibrating element as particles deposit on it
- Optical scattering intensity of a laser beam passing through sampled air
- Fluorescence emission of particles excited by UV radiation
Correct answer: Attenuation of beta radiation (electrons) passing through particles collected on a filter tape
A BAM collects particles on a moving filter tape and measures the attenuation of beta rays emitted by a C-14 source; greater attenuation corresponds to higher PM mass.
Question 5: The Tapered Element Oscillating Microbalance (TEOM) measures particulate matter mass using which principle?
- The resonant frequency of a vibrating tapered tube changes as PM deposits on the filter at its tip (Correct answer)
- The differential pressure across a filter increases as PM accumulates
- The attenuation of a laser beam is proportional to PM concentration
- The fluorescence intensity of collected particles indicates their mass
Correct answer: The resonant frequency of a vibrating tapered tube changes as PM deposits on the filter at its tip
The TEOM measures the shift in oscillation frequency of a tapered hollow tube; as PM accumulates on the filter at the tube tip, the added mass reduces the resonant frequency.
Question 6: UV photometric ozone analyzers operate at approximately which ultraviolet absorption wavelength?
- 254 nm (Correct answer)
- 320 nm
- 193 nm
- 185 nm
Correct answer: 254 nm
O3 has a strong Hartley band absorption peak near 254 nm; UV photometric analyzers use a mercury lamp at this wavelength to quantify ozone concentration by Beer-Lambert law.
Question 7: In a chemiluminescence NOx analyzer, what reagent gas is used to react with nitric oxide (NO) to produce the light signal?
- Ozone (O3) (Correct answer)
- Hydrogen (H2)
- Ammonia (NH3)
- Chlorine (Cl2)
Correct answer: Ozone (O3)
Chemiluminescence NOx analyzers react NO with ozone to form excited NO2*, which emits light upon returning to ground state; photon count is proportional to NO concentration.
AQS Monitoring Tools 3
UV fluorescence technology is the Federal Reference Method (FRM) measurement principle used for which criteria pollutant?