AQS Assessment & Monitoring Methods 2 — Questions and Answers
Question 1: Which EPA-designated method is the federal reference method (FRM) for measuring PM2.5 mass concentration?
- Gravimetric filter-based sampler (40 CFR Part 50 Appendix L) (Correct answer)
- Beta attenuation monitor (BAM)
- Tapered element oscillating microbalance (TEOM)
- Optical particle counter (OPC)
Correct answer: Gravimetric filter-based sampler (40 CFR Part 50 Appendix L)
The EPA's FRM for PM2.5 is the gravimetric filter-based sampler described in 40 CFR Part 50, Appendix L.
Question 2: A continuous emissions monitoring system (CEMS) must complete a relative accuracy test audit (RATA) to demonstrate accuracy. What is the acceptable relative accuracy limit for most gaseous pollutants?
- ±20% of the mean reference value or 10 ppm absolute
- ±10% of the mean reference value or 5 ppm absolute (Correct answer)
- ±5% of the mean reference value or 2 ppm absolute
- ±15% of the mean reference value or 7 ppm absolute
Correct answer: ±10% of the mean reference value or 5 ppm absolute
EPA Performance Specification 2 (PS-2) requires RATA relative accuracy ≤10% of the mean reference value, or ≤5 ppm absolute, whichever is less restrictive.
Question 3: When calculating an ambient air quality monitoring network's representativeness, what does the term 'spatial scale of representativeness' refer to?
- The geographic area over which measured concentrations are similar to the monitor's reading (Correct answer)
- The height at which the monitor inlet is placed above ground
- The distance between two co-located monitors in a QA program
- The radius of the monitoring zone required by state regulation
Correct answer: The geographic area over which measured concentrations are similar to the monitor's reading
Spatial scale of representativeness defines the area around a monitor where measured concentrations adequately characterize ambient air quality.
Question 4: In a source emissions test using Method 5 (EPA) for particulate matter, what is the purpose of the Greenburg-Smith impinger train?
- To remove moisture and capture condensable particulate matter from the sample gas (Correct answer)
- To measure the stack gas velocity using differential pressure
- To provide a known leak-free reference for calibration
- To regulate sample flow rate through the filter
Correct answer: To remove moisture and capture condensable particulate matter from the sample gas
The impinger train in Method 5 collects moisture and condensable PM downstream of the filter, completing the total particulate sample.
Question 5: Which quality assurance indicator measures the closeness of repeated measurements to each other, regardless of their closeness to the true value?
- Bias
- Precision (Correct answer)
- Accuracy
- Completeness
Correct answer: Precision
Precision describes the reproducibility of measurements; it does not indicate whether those measurements are correct (that is accuracy).
Question 6: A monitoring station records SO2 concentrations using a pulsed fluorescence analyzer. Which interference must be corrected for in high-humidity environments?
- Water vapor quenching of fluorescence signal (Correct answer)
- Interference from nitrogen dioxide absorption
- Pressure-induced drift in the reference cell
- Temperature effects on the UV lamp intensity
Correct answer: Water vapor quenching of fluorescence signal
Water vapor quenches the SO2 fluorescence signal in pulsed fluorescence analyzers, requiring humidity correction to avoid negative bias.
Question 7: Under EPA's Quality Assurance Handbook for Air Pollution Measurement Systems, what data completeness rate is required annually for a SLAMS monitoring station to be considered valid?
- 90%
- 75% (Correct answer)
- 85%
- 95%
Correct answer: 75%
EPA requires a minimum 75% data completeness rate annually for SLAMS monitors as defined in 40 CFR Part 58.
AQS Assessment & Monitoring Methods 2
Which EPA-designated method is the federal reference method (FRM) for measuring PM2.5 mass concentration?