Atmospheric Stability Questions and Answers

Q: Which magnitude does the urban heat island typically reach?

Urban rural temperature differences of two to five kelvin are typical for a large city on a clear calm night, with extremes above ten kelvin recorded occasionally. The effect is largest at night and smallest by day, since it depends on the release of stored heat and the suppression of radiative cooling rather than on daytime absorption.

Q: Which conditions maximise the urban heat island?

The island arises because the countryside cools strongly while the city does not, and rural cooling requires clear calm conditions, so the difference is greatest then. Wind and cloud suppress the rural cooling and therefore the contrast. Daytime absorption contributes to the heat stored but the effect itself is a nocturnal phenomenon.

Q: Which consequence does the urban boundary layer have for pollution?

The city mixes more effectively than the surrounding countryside at night, which helps, but concentrates emissions into a small area, which more than offsets the advantage. The net result is higher concentrations. Street canyons can also trap pollutants at the very smallest scales despite the enhanced mixing above roof level.

Q: Which structure traps pollutants at street level?

Flow across a street canyon separates at the upwind roof and sets up a recirculating vortex within the canyon, so pollutants emitted at street level accumulate on the leeward side. Concentrations can differ by a factor of several between the two sides of the same street. This is why roadside monitoring station siting requires such care.

Q: Which aspect ratio produces the strongest canyon recirculation?

When the height to width ratio approaches or exceeds one the flow skims over the top and a single stable vortex fills the canyon, which is the skimming flow regime. Wider streets allow the flow to reattach and ventilate better. A canyon aligned with the wind channels the flow along it and ventilates well, which is the opposite of the trapping case.

Q: Which design change improves street level ventilation?

Irregular building heights disrupt the skimming flow and allow air from above to penetrate into the canyon, improving exchange. Uniform tall rows produce the most stable recirculating vortex and the worst trapping. Urban design guidance for air quality now addresses exactly this, alongside the positioning of green space and the alignment of major streets.

Q: Which measurement network monitors urban air quality?

Networks combine roadside sites, which capture the highest exposures, with urban background sites away from immediate sources, which represent the general population exposure. Rural sites provide the regional baseline against which the urban increment is measured. A single station cannot represent a city where concentrations vary by a factor of several between a busy street and a park a hundred metres away, which is precisely why the classified network design was adopted.

Q: Which pollutant shows the steepest gradient away from a road?

Nitrogen dioxide is emitted directly by vehicles and has a short lifetime, so concentrations fall sharply within tens of metres of a busy road. Fine particles have a regional component that dilutes the gradient. Ozone behaves in the opposite sense, being destroyed by fresh nitric oxide emissions and therefore lowest beside the road, which makes that option instructive as well as wrong. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Q: Which reaction destroys ozone near a busy road?

Nitric oxide reacts rapidly with ozone to give nitrogen dioxide and oxygen, so ozone is depleted close to sources of fresh emissions and recovers downwind as the mixture ages. This is why urban ozone is often lower than rural ozone despite the urban precursor emissions. The apparent paradox is resolved by considering the timescale for the photochemistry to produce ozone further downwind. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Q: Which conditions favour a photochemical smog episode?

Photochemical ozone formation requires sunlight, warmth and time, so stagnant sunny anticyclonic conditions in summer produce the classic episodes. Winter inversions trap primary pollutants instead and produce a different kind of episode. Distinguishing the summer photochemical from the winter primary pollution episode is essential for understanding air quality forecasts. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

81.

Which magnitude does the urban heat island typically reach?

A.A few kelvin on clear calm nights
B.About twenty kelvin, which is comparable with the strength of a nocturnal inversion over open countryside
C.Under a tenth of a kelvin
D.About ten kelvin during the daytime, when the absorption of solar radiation by the dark surfaces is greatest

Answer: A

Urban rural temperature differences of two to five kelvin are typical for a large city on a clear calm night, with extremes above ten kelvin recorded occasionally. The effect is largest at night and smallest by day, since it depends on the release of stored heat and the suppression of radiative cooling rather than on daytime absorption.

Discuss in Forum

82.

Which conditions maximise the urban heat island?

A.Strong daytime sunshine, since the effect depends upon the absorption of solar radiation by the dark surfaces
B.Clear skies and light winds
C.Overcast skies with strong winds, which allow the stored heat to be released most rapidly into the air above
D.Heavy rainfall

Answer: B

The island arises because the countryside cools strongly while the city does not, and rural cooling requires clear calm conditions, so the difference is greatest then. Wind and cloud suppress the rural cooling and therefore the contrast. Daytime absorption contributes to the heat stored but the effect itself is a nocturnal phenomenon.

Discuss in Forum

83.

Which consequence does the urban boundary layer have for pollution?

A.No consequence
B.Complete removal of the pollutants, which are dispersed by the enhanced turbulence generated by the buildings
C.Better vertical mixing but higher emission density
D.Worse vertical mixing, since the buildings obstruct the flow and prevent the pollutants from being carried away

Answer: C

The city mixes more effectively than the surrounding countryside at night, which helps, but concentrates emissions into a small area, which more than offsets the advantage. The net result is higher concentrations. Street canyons can also trap pollutants at the very smallest scales despite the enhanced mixing above roof level.

Discuss in Forum

84.

Which structure traps pollutants at street level?

A.The urban heat island, which draws air inward from the surrounding countryside and concentrates the pollutants
B.A subsidence inversion
C.The roughness sublayer, within which the flow is strongly disturbed by the individual roughness elements present
D.A recirculating vortex within a street canyon

Answer: D

Flow across a street canyon separates at the upwind roof and sets up a recirculating vortex within the canyon, so pollutants emitted at street level accumulate on the leeward side. Concentrations can differ by a factor of several between the two sides of the same street. This is why roadside monitoring station siting requires such care.

Discuss in Forum

85.

Which aspect ratio produces the strongest canyon recirculation?

A.A building height comparable with or greater than the street width
B.A very wide street with low buildings, which allows the flow to reattach to the ground between the two rows
C.A street of any width
D.A canyon whose axis lies parallel to the prevailing wind rather than across it at right angles to the flow

Answer: A

When the height to width ratio approaches or exceeds one the flow skims over the top and a single stable vortex fills the canyon, which is the skimming flow regime. Wider streets allow the flow to reattach and ventilate better. A canyon aligned with the wind channels the flow along it and ventilates well, which is the opposite of the trapping case.

Discuss in Forum

86.

Which design change improves street level ventilation?

A.Enclosing the street entirely so that the emissions may be extracted through a mechanical ventilation system
B.Varying building heights along the street
C.Uniform tall buildings on both sides, which channel the flow smoothly along the street and remove the pollutants
D.Narrower streets

Answer: B

Irregular building heights disrupt the skimming flow and allow air from above to penetrate into the canyon, improving exchange. Uniform tall rows produce the most stable recirculating vortex and the worst trapping. Urban design guidance for air quality now addresses exactly this, alongside the positioning of green space and the alignment of major streets.

Discuss in Forum

87.

Which measurement network monitors urban air quality?

A.Satellite observations alone
B.Mobile laboratories operated only during episodes when the concentrations are expected to exceed the limits
C.Fixed monitoring stations at roadside and background sites
D.A single station at the city centre, which is taken as representative of the conditions across the whole area

Answer: C

Networks combine roadside sites, which capture the highest exposures, with urban background sites away from immediate sources, which represent the general population exposure. Rural sites provide the regional baseline against which the urban increment is measured. A single station cannot represent a city where concentrations vary by a factor of several between a busy street and a park a hundred metres away, which is precisely why the classified network design was adopted.

Discuss in Forum

88.

Which pollutant shows the steepest gradient away from a road?

A.Ozone, whose concentration is greatest immediately beside the road where the emissions are most concentrated
B.Sulphur dioxide
C.Fine particulate matter, whose long atmospheric lifetime makes its concentration uniform across a whole region
D.Nitrogen dioxide

Answer: D

Nitrogen dioxide is emitted directly by vehicles and has a short lifetime, so concentrations fall sharply within tens of metres of a busy road. Fine particles have a regional component that dilutes the gradient. Ozone behaves in the opposite sense, being destroyed by fresh nitric oxide emissions and therefore lowest beside the road, which makes that option instructive as well as wrong. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Discuss in Forum

89.

Which reaction destroys ozone near a busy road?

A.Titration by freshly emitted nitric oxide
B.Photolysis by sunlight, which is most intense at street level where the surfaces reflect the radiation upward
C.Deposition to surfaces
D.Reaction with water vapour, whose concentration is enhanced by the exhaust emissions from the passing vehicles

Answer: A

Nitric oxide reacts rapidly with ozone to give nitrogen dioxide and oxygen, so ozone is depleted close to sources of fresh emissions and recovers downwind as the mixture ages. This is why urban ozone is often lower than rural ozone despite the urban precursor emissions. The apparent paradox is resolved by considering the timescale for the photochemistry to produce ozone further downwind. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Discuss in Forum

90.

Which conditions favour a photochemical smog episode?

A.Cold clear winter weather, in which the strong surface inversion traps the emissions in a very shallow layer
B.Sunny weather with light winds and high emissions
C.Overcast conditions with strong winds, which mix the precursors thoroughly through the whole boundary layer
D.Heavy rainfall

Answer: B

Photochemical ozone formation requires sunlight, warmth and time, so stagnant sunny anticyclonic conditions in summer produce the classic episodes. Winter inversions trap primary pollutants instead and produce a different kind of episode. Distinguishing the summer photochemical from the winter primary pollution episode is essential for understanding air quality forecasts. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Discuss in Forum

Loading…

Topics

Other Subjects

Tags: Atmospheric Stability Questions and Answers || Atmospheric Stability MCQ Questions and Answers || Atmospheric Stability GK Questions and Answers || Atmospheric Stability GK MCQ Questions || Atmospheric Stability Multiple Choice Questions and Answers || Atmospheric Stability GK || GK on Atmospheric Stability || Atmospheric Thermodynamics Questions and Answers || Atmospheric Thermodynamics MCQ Questions and Answers || Atmospheric Thermodynamics GK Questions and Answers || GK on Atmospheric Thermodynamics

Atmospheric Stability Questions and Answers

Topics

Other Subjects

About Us

Stay informed about all important Dates & Notifications