AQS Air Dispersion Modeling 2 â Questions and Answers
Question 1: The Pasquill-Gifford atmospheric stability classes are primarily determined by which two parameters?
- Ambient temperature and relative humidity
- Surface wind speed and solar radiation (or cloudiness at night) (Correct answer)
- Stack exit velocity and exhaust temperature
- Terrain slope and receptor distance
Correct answer: Surface wind speed and solar radiation (or cloudiness at night)
P-G stability classes are determined by surface wind speed combined with incoming solar radiation during daytime, or net cloudiness during nighttime.
Question 2: CALPUFF is most appropriate for which air dispersion modeling scenario?
- Single point source in flat terrain within 5 km of receptors
- Long-range transport (>50 km) or complex meteorological conditions with variable winds (Correct answer)
- Modeling indoor air concentrations from infiltration
- Short-term acute releases lasting less than one hour
Correct answer: Long-range transport (>50 km) or complex meteorological conditions with variable winds
CALPUFF is a non-steady-state Lagrangian puff model designed for long-range transport and conditions where steady-state plume assumptions are invalid due to variable winds.
Question 3: In air dispersion modeling, a 'receptor' is defined as:
- The facility emitting pollutants being modeled
- A location (point or grid node) where predicted ambient concentrations are calculated (Correct answer)
- The meteorological monitoring station providing input data
- The regulatory concentration threshold being compared against
Correct answer: A location (point or grid node) where predicted ambient concentrations are calculated
A receptor is a specified locationâpart of a receptor grid or discrete pointâwhere the model computes predicted ambient pollutant concentrations.
Question 4: Which stack parameter has the greatest influence on buoyancy-induced plume rise in a Gaussian dispersion model?
- Physical stack diameter
- Exit gas temperature relative to ambient air temperature (Correct answer)
- Physical stack height
- Stack exit velocity
Correct answer: Exit gas temperature relative to ambient air temperature
Buoyancy rise is driven primarily by the temperature difference between the hot exhaust gas and cooler ambient air, as this determines the density contrast that provides lift.
Question 5: In AERMOD, which source type is most appropriate for modeling fugitive emissions from a large storage pile or parking lot?
- POINT source
- AREA source (Correct answer)
- LINE source
- VOLUME source
Correct answer: AREA source
Area sources in AERMOD represent diffuse emissions distributed over a surface area, making them appropriate for storage piles, parking lots, and land application sites.
Question 6: In air dispersion meteorology, 'fumigation' refers to which phenomenon?
- Deliberate injection of tracer gases to measure atmospheric dispersion
- Rapid downward mixing of an elevated plume to ground level during morning breakup of a nocturnal temperature inversion (Correct answer)
- Chemical scrubbing of pollutants within the plume by ambient moisture
- Wet deposition of pollutants by rainfall intercepting the plume
Correct answer: Rapid downward mixing of an elevated plume to ground level during morning breakup of a nocturnal temperature inversion
Fumigation occurs when morning solar heating destroys a stable nocturnal inversion, causing convective mixing that rapidly brings elevated plume concentrations down to ground level.
Question 7: The mixing height (mixing layer height) is important in air dispersion modeling because it:
- Determines the minimum required stack height for permit compliance
- Defines the upper boundary of the well-mixed layer, limiting vertical dispersion of pollutants (Correct answer)
- Controls the horizontal wind direction used in plume trajectory calculations
- Sets the receptor grid spacing required for regulatory modeling
Correct answer: Defines the upper boundary of the well-mixed layer, limiting vertical dispersion of pollutants
The mixing height defines the top of the convective boundary layer; pollutants are diluted within this layer and vertical dispersion is constrained below this boundary.
AQS Air Dispersion Modeling 2
The Pasquill-Gifford atmospheric stability classes are primarily determined by which two parameters?