AQS Data Collection & Analysis 2 — Questions and Answers
Question 1: What is the primary purpose of a collocated monitor in an air quality monitoring network?
- To sample a different pollutant at the same site
- To assess precision and data quality of the primary monitor (Correct answer)
- To provide backup data when the primary monitor fails
- To measure meteorological conditions alongside pollutants
Correct answer: To assess precision and data quality of the primary monitor
Collocated monitors run simultaneously at the same site to assess measurement precision and overall data quality through comparison of duplicate readings.
Question 2: Which statistical measure is most appropriate for describing the central tendency of a skewed pollutant concentration dataset?
- Arithmetic mean
- Geometric mean (Correct answer)
- Mode
- Range
Correct answer: Geometric mean
The geometric mean is preferred for skewed environmental data because it reduces the influence of extreme high values common in pollutant distributions.
Question 3: In EPA Method 18, what technique is used to measure volatile organic compound concentrations in stationary source emissions?
- Flame ionization detection after gas chromatographic separation (Correct answer)
- UV photometry at 254 nm
- Non-dispersive infrared absorption
- Chemiluminescence with ozone reagent
Correct answer: Flame ionization detection after gas chromatographic separation
EPA Method 18 uses gas chromatography with flame ionization detection (GC/FID) to separate and quantify individual VOC species in stack gas.
Question 4: What does a data capture rate of 75% mean in the context of annual ambient monitoring requirements?
- 75% of measured values must be below the NAAQS
- At least 75% of scheduled valid samples must be collected in a calendar quarter (Correct answer)
- 75% of monitoring hours must have wind speeds above the detection threshold
- The monitor must operate 75% of the time with no maintenance windows
Correct answer: At least 75% of scheduled valid samples must be collected in a calendar quarter
EPA requires a minimum 75% data capture rate, meaning at least 75% of the expected valid measurements must be collected in a given quarter for the data to be considered representative.
Question 5: Which type of filter media is required for EPA Reference Method PM2.5 FRM samplers?
- Quartz fiber filter
- PTFE (Teflon) membrane filter (Correct answer)
- Cellulose acetate filter
- Fiberglass filter with binder
Correct answer: PTFE (Teflon) membrane filter
The EPA FRM for PM2.5 (40 CFR Part 50 Appendix L) specifies PTFE membrane filters because they are chemically inert, hydrophobic, and have very low and stable tare weights.
Question 6: A nephelometer measures which air quality parameter directly?
- Ozone concentration via UV absorption
- Light scattering coefficient of particles (bscat) (Correct answer)
- Nitrogen dioxide via chemiluminescence
- Carbon monoxide via infrared absorption
Correct answer: Light scattering coefficient of particles (bscat)
A nephelometer directly measures the light scattering coefficient (bscat) of suspended particles, which correlates with particulate matter concentration and visibility reduction.
Question 7: When conducting a zero/span check on a continuous ambient air monitor, what does a failing span check most likely indicate?
- The sampling inlet is clogged with debris
- The instrument's sensitivity or calibration has drifted (Correct answer)
- The data logger has a communication fault
- The ambient pollutant concentration is below detection limit
Correct answer: The instrument's sensitivity or calibration has drifted
A failing span check — where the instrument response to a known-concentration gas deviates beyond acceptable limits — indicates that the analyzer's sensitivity or calibration has drifted and requires adjustment.
AQS Data Collection & Analysis 2
What is the primary purpose of a collocated monitor in an air quality monitoring network?