SAChE Atmospheric Dispersion (ELA967) Module 2 Practice Test

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• Which term in the Gaussian plume equation acts as the source term?
• What is a primary purpose of evaluating boundary conditions during model validation?
• ERPG concentration levels are determined by the chemical released.
• In the Gaussian plume equation, what are sigma_y and sigma_z?
• Why is the roughness length important for dispersion modeling?
• In the Pasquill stability classes, B represents which concept according to the source?
• If emissions or meteorology vary with time, what type of model is required instead of a steady-state model?
• In the Briggs parameterization of passive plume dispersion, the predicted values of sigma_y and sigma_z are independent of atmospheric stability classes.
• Why does receptor elevation matter in concentration predictions?
• What does the equation tplume = E/(pi σy σz u) represent in plume dispersion terms?
• Explain the limitations of Gaussian models for complex terrains.
• How does urban geometry influence plume dispersion compared with open rural terrain?
• In the expression 1/√f = 4 log(3.7 D / e), what does e represent?
• What is a Pasquill-Gifford stability class, and why does it matter for dispersion calculations?
• What is the typical difference between centerline concentration and receptor concentration at off-center positions?
• What is the purpose of receptor-specific concentration predictions?
• Stability class G, when used, describes conditions that are less stable than F.
• What does the effective plume height H represent in Gaussian plume modeling?
• What do Pasquill-Gifford stability classes represent?
• What is the typical use of a ground-level concentration estimate in risk assessment?
• Which statement accurately reflects early atmospheric dispersion model development?
• How does terrain (hills, valleys) affect atmospheric dispersion?
• Why is a ground reflection term important for predicting near-ground concentrations?
• In the Pasquill stability class table, what does the letter B represent?
• How does Buoyancy Flux F relate to plume rise calculations?
• How does an elevated emission height alter receptor concentrations at ground level?
• In the absence of deposition and chemistry, where is the plume concentration typically maximum in the crosswind plane at ground level?
• Explain the physical meaning of the term Q/(2π u σ_y σ_z) in the Gaussian plume equation.
• If predicted concentrations are too low near a building, what would you adjust?
• As downwind distance increases, what happens to sigma_y and sigma_z in the Gaussian plume model?
• Which hazard should be considered when nitrogen is present in COTA?
• Explain why an elevated emission release might cause a different receptor location of maximum concentration than a ground-level release.
• What is the role of ambient temperature profiles in dispersion modeling?
• What is the purpose of using both z-H and z+H terms in the vertical Gaussian distribution?
• In Gaussian plume models, what do sigma_y and sigma_z represent?
• What do sigma_y and sigma_z represent in dispersion modeling?
• Which stability classes are considered unstable in this context?
• Which ERPG level corresponds to irreversible or other serious health effects after a 60-minute exposure?
• What is the purpose of model validation in dispersion modeling?
• How does increasing stack height h affect the effective height H and ground-level impact?
• Which statement best describes the effect of model suitability on dispersion predictions?
• Describe the general outcome of a buoyant plume in calm conditions versus windy conditions for plume rise?
• The predicted values of sigma_y and sigma_z for puff models are sensitive to the specification of atmospheric stability class.
• In a very stable atmosphere, what happens to the time for the plume to reach a given ground height?
• A passive release refers to a release where the COTA cloud moves at the same speed and direction as the ambient wind.
• Why are rural and urban surface roughness important in modeling?
• What data might you compare to field measurements to calibrate a Gaussian plume model?
• How do dispersion coefficients σ_y and σ_z depend on stability and distance?
• In a very stable atmosphere, how does it influence the time for a plume to reach a given ground height?
• Why are two exponential terms present in the centerline concentration expression along the vertical axis?
• What is time-integrated concentration (TIC) and why is it used?
• The Britter-McQuaid plume model allows for wind speeds of zero.
• Which statement best contrasts a Lagrangian puff model with an Eulerian Gaussian model?
• Toxic Warning Levels are expressed in which unit?
• Under what release conditions is a puff model preferred over a plume model?
• How do you determine whether a receptor is within the plume envelope?
• IDLH criteria are based on exposure time of 60 minutes.
• What is the effect of plume rise on ground-level concentrations near the source?
• How do plume rise and effective height influence potential exposure for nearby workers?
• True or False: The concept of stability class is relevant for both sigma_y and sigma_z predictions.
• Which meteorological factors most influence how a plume disperses in the lower atmosphere?
• True or False: The lowest wind speed that can typically be measured with a modern cup anemometer is 0.5 m/s (1.6 ft/s).
• Dense-gas effects become more significant as wind speeds decrease.
• How does atmospheric stability influence the dispersion parameters σ_y and σ_z in the Gaussian plume model?
• Briggs plume rise is used to estimate which quantity in SAChE calculations?
• Which hazard modeling program is mentioned as capable of accommodating various gas cloud sources?
• How do time-averaged concentrations differ from instantaneous concentrations in dispersion modeling?
• The rate of heat transfer, Q, from a solid surface is expressed as:
• In rural Briggs parameterization, the surface roughness length used for passive plume dispersion corresponds to which landscape type?
• What happens to plume concentration predictions if you mis-specify the roughness length by a factor of 2?
• Describe the reciprocal relationship between sigma_y, sigma_z and distance.
• Which of the following adds confidence to dispersion model results?
• Inversions are accounted for in nearly all basic atmospheric dispersion models.
• What is the effect of receptor height z on ground-level concentration predictions?
• Briggs plume rise estimation is used to estimate which quantity in the plume-height calculation?
• In what scenarios would plume-rise corrections be negligible?
• How can you address the limitations of a Gaussian plume model in a SAChE assessment?
• Theoretical analysis dictates that a dispersing plume that does not change the atmospheric flow field will have a Gaussian spatial distribution in:
• In Gaussian dispersion, which type of receptor typically experiences strong ground reflection effects?
• What is the maximum airborne concentration below which nearly all individuals could be exposed for up to one hour without experiencing irreversible or serious health effects?
• True or False: The predicted sigma values are unaffected by atmospheric stability class.
• The Britter-McQuaid plume model's performance is expected to be less reliable as wind speed approaches zero, such as under light and variable winds.
• When meteorology is unknown, which dispersion assessment approach is recommended?
• What is the difference between ground-level concentration and effective emission height?
• What is the primary goal of specifying the stability class in puff dispersion modeling?
• What role does deposition velocity play in dispersion modeling?
• What is the approximate dry adiabatic lapse rate per 100 meters?
• ERPG concentration levels are determined by the chemical released.
• Sigma_y and sigma_z values characterize the plume's dispersion in which directions?
• Which technique is used to account for ground reflection in Gaussian plume calculations?
• What is the role of deposition processes in dispersion predictions?
• If stability class is mis-specified, predicted sigma values may be:
• The Britter-McQuaid puff model should not be used for a passive release when the most conservative result is desired.
• Which action would improve the accuracy of puff predictions?
• Which term describes the concentration measured along the plume centerline?
• Why is the assumption of steady-state essential in Gaussian plume modeling?
• In case of uncertain stability class, a prudent approach is to:
• Denser-than-air effects are most importantly influenced by which atmospheric parameter?
• What does the term exp(-y^2/(2 σ_y^2)) represent in the Gaussian plume model?
• If a problem involves both mechanical and thermally induced turbulence but cannot be scaled by CFD verification, which model type is suggested?
• What is the significance of the x-distance in Gaussian plume equations?
• How does ground reflection affect the Gaussian plume concentration at ground level?
• What do the dispersion parameters σ_y and σ_z characterize in Gaussian plume modeling?
• The CDC developed IDLH to:
• What are the Briggs plume rise correlations used for?
• Which statement is true about the dispersion coefficients relative to atmospheric stability?
• How do continuous point sources differ from puff releases in atmospheric dispersion?
• How do continuous and instantaneous releases differ in concentration predictions?
• According to Britter and McQuaid, tplume, the average plume correlation time, is approximately:
• What is the significance of the mixing height in dispersion?
• What is a dense gas plume, and how does it differ from a buoyant plume in dispersion behavior?
• Passive dispersion coefficients are typically not provided for distances:
• Which statement best describes the wind speed measurement limit mentioned in the material?
• In a dense gas plume, what is the typical behavior compared to buoyant plumes?
• Which models are typically easily solved on a computer with less user interaction than required for solving partial differential equations?
• Which term describes release scenarios with finite duration?
• Why might a dispersion model overpredict concentrations at a receptor?
• What is the fundamental assumption of the Gaussian plume model regarding pollutant concentration distribution?
• Give an example of a scenario where plume rise would significantly alter predicted concentrations.
• Regarding stability classes, what does the term, "3 D," refer to?
• What is plume rise, and why is it important in dispersion modeling?
• Which term in the Gaussian plume equation reflects the ground-level boundary condition?
• Under stable atmospheric conditions, how does dispersion near the ground typically change?
• If sigma_y increases, what happens to the peak concentration along the plume centerline at a fixed downwind distance?
• How would a significant nearby obstruction influence dispersion calculations?
• Negative buoyancy of an airborne COTA can exist when:
• What is a receptor pool, and how does it relate to dispersion modeling?
• What is the physical meaning of σ_y and σ_z growth with distance?
• Which modeling approach is described as easier to solve with less user interaction than PDE-based methods?
• What is the significance of solar heating on daytime atmospheric stability?
• In the hazard time scale discussion, the correction factor is triggered when th is less than t_plume. Which relation represents this condition?
• How would you identify the potential for downwind hazard zones using dispersion concepts?
• The Pasquill-Gifford model and the Britter-McQuaid model are examples of:
• Why are ground-level downward-facing boundary conditions incorporated using a mirror image term in plume models?
• If the total airborne mass is doubled, the concentration at a fixed downwind distance is:
• The stability class influences sigma_y and sigma_z because it defines:
• Why is model input data quality critical in dispersion modeling?
• In the presented material, which factor is identified as the primary influence on denser-than-air effects?
• What is the typical ground-level concentration expression for y=0 and z=0?
• Which statement about the Gaussian plume centerline on the downwind axis is true?
• What is mixing height in dispersion modeling and its effect on dispersion?
• What is the significance of the reflection boundary at z=0 in Gaussian models?
• How are stability classes typically categorized for daytime and nighttime conditions?
• What is the role of receptor height in Gaussian plume predictions?
• The stability class is a representation of atmospheric turbulence affecting dispersion.
• Why is it necessary to consider both buoyancy and momentum in Δh?
• ERPG-2 is defined as the maximum airborne concentration below which nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms.
• Which program is associated with rapid hazard assessment and can model both plume and puff scenarios?
• How can atmospheric stability influence downwind maximum concentration?
• If heat transfer is dominated by forced convection, increasing the fluid velocity will cause the heat transfer coefficient to:
• In the Gaussian plume model, what do h and Δh represent in H = h + Δh?
• The dry adiabatic lapse rate is approximately how many degrees Celsius per 100 meters?
• What are common source terms used in SAChE practice tests?
• In Gaussian plume notation, what does x represent?
• Positive buoyancy of an airborne COTA exists when the ambient air density is ____ the density of the airborne COTA.
• The Pasquill-Gifford puff model predicts that doubling the total airborne mass doubles the COTA concentration at a fixed downwind distance.
• What do σ_y and σ_z represent in plume modeling?
• Denser-than-air COTAs can fail to travel in the wind direction.
• Which type of models require a significant investment when simulating a release scenario with detailed piping and equipment geometry?
• Which of the following is not included in the Britter-McQuaid correlations?
• Which parameter in puff models is adjusted by selecting a stability class?
• What is the overarching concept that links Q, u, σ_y, σ_z, H, and receptor height in predicting concentrations?
• The ALOHA hazard modeling program can model which release scenarios?
• Increasing atmospheric instability generally leads to:
• Which conditions most directly affect the mixing height?
• What is the primary goal of Gaussian dispersion calculations in SAChE Module 2?
• Denser-than-air COTAs can significantly change the downward distance to a fixed concentration level compared with a passive atmospheric model.
• When heat is transferred by forced convection, the heat transfer coefficients _____.
• What is a typical scenario when a Gaussian puff model is preferred due to changing wind conditions?
• A robust approach to model uncertainty due to stability class is to:
• For atmospheric dispersion models, the minimum relevant time scale th for flammability hazards is approximately how long?
• How does a puff release evolve compared to a continuous point source?
• In SAChE, why might you apply a conservative assumption in Gaussian plume modeling?
• Which of the following are typical inputs to run a Gaussian plume calculation?
• For atmospheric dispersion modeling of flammable hazards, the pseudo-component properties should represent depressurized properties of the airborne COTA.
• How do wind speed and atmospheric stability influence plume residence time near a receptor?
• Which statement best describes the approach of similarity models in plume dispersion?
• Under which condition is downwash most likely to increase ground-level concentrations near a tall obstacle?
• What is the primary objective of atmospheric dispersion modeling?
• What is the main limitation of Gaussian plume modeling on complex terrain?
• How does increasing source height relative to building height influence downwash probability?
• In dispersion modeling, what is meant by upwind vs downwind?
• Which factor directly influences atmospheric stability and vertical mixing, affecting dispersion predictions?
• In the Gaussian plume ground boundary term, what does H represent?
• Which expression represents the maximum ensemble average concentration for a continuous passive plume from a point source at a given downwind distance?
• Under which scenario might a dispersion model underpredict receptor concentrations?
• In Gaussian plume modeling, what is the plume centerline?
• Differentiate between dry deposition and wet deposition.
• In dispersion modeling, which data issue most directly undermines risk assessments?
• In the atmosphere, if the mean wind direction is constant, the wind direction must be zero.
• How do stability and wind speed interact to determine downwind concentration?
• If Q doubles while wind speed and dispersion characteristics remain unchanged, what happens to predicted concentrations?
• The Briggs parameterization implies that the predicted sigma values are dependent on stability classes.
• The Pasquill-Gifford model is used for which type of atmospheric scenarios?
• What is meant by a 'reduction in dispersion' in stable conditions?
• How does the Gaussian model treat ground-level receptors compared with elevated receptors?
• The ALOHA hazard modeling program can accommodate which hazardous gas cloud sources?
• Passive models were the first atmospheric dispersion models developed and were based on visual observations of what?
• If the ground reflection term is omitted, what is the likely effect on predicted near-ground concentrations?
• As the time required for mixing to the hazard concentration decreases, the hazard of a COTA cloud:
• Which variables in the Gaussian plume equation are functions of distance and atmospheric stability and not directly controlled by emission rate?
• What is one reason to use a plume-downdwash model in urban exposure assessments?
• What is the impact of wind shear on plume dispersion?
• The parameters σ_y and σ_z describe which aspect of the plume as it travels from the source?
• In plume models with long averaging times, a correction factor is needed when the hazard time scale th is less than t_plume. Which relation best represents this condition?
• How would you handle an instantaneous release with unknown meteorology in a dispersion assessment?
• Negative buoyancy in a COTA cloud can exist even if the cloud is not strictly denser than air.
• In the expression 1/√f = 4 log(3.7 D / e), the parameter e is defined as surface roughness.
• Which expression represents the centerline concentration along the downwind axis at height z?
• Which type of models are generally considered incapable of simultaneously scaling mechanical turbulence and thermally induced turbulence, presenting verification challenges when both are important?
• What are common validation checks you should perform when applying SAChE Module 2 dispersion models?
• If model predictions suggest ground-level concentrations are higher than expected on a flat terrain with steady wind, which input is most likely mis-specified?
• Which aspect of Gaussian plume model can be validated using field measurements?
• Which inputs are essential for obtaining accurate dispersion model results?
• Which factor influences the accuracy of dispersion predictions in practice?
• For atmospheric dispersion modeling of flammable hazards, all pseudo-component properties should represent
• How does the Gaussian plume model handle multiple receptors along the downwind line?
• Denser-than-air effects are most important under which conditions?
• How might you account for radiation sources or chemical reactions in dispersion modeling?
• In Gaussian plume modeling, what does the term exp(-(z - H)^2/(2 σ_z^2)) represent?
• How do stability class values numerically affect σy and σz?
• When would you consider using a Lagrangian puff model rather than an Eulerian Gaussian model?
• The exponent term exp(-(z - H)^2/(2 σ_z^2)) represents what aspect of the plume distribution?
• Which stability class corresponds to very stable conditions?
• Which hazard should be considered for nitrogen when it is a component of COTA?
• What term refers to the time period during which the contaminant becomes airborne?
• One purpose of IDLH criteria is to ensure workers can escape from a contaminated environment if respiratory protection fails.
• In the Gaussian plume model, how does increasing wind speed affect ground-level concentration for a fixed emission rate?
• How does increasing wind speed affect ground-level concentration for fixed Q and dispersion parameters?
• When would you choose a Gaussian puff model over a Gaussian plume model?
• True or False: Basic dispersion models include the ability to model the thermodynamic effect of mixing air with a suspended aerosol.
• Doubling wind speed in the Pasquill-Gifford puff model will reduce downwind concentration by exactly a factor of 2 only if what condition remains unchanged?
• In dispersion modeling, sigma_y and sigma_z describe the plume's:
• In Briggs' rural parameterization for passive plume dispersion, the surface roughness is approximately:
• What is dry deposition, and how does it influence downwind concentrations?