Urban environmental and social stresses practice questions.

Night-time temperatures in a city centre are consistently several degrees higher than in surrounding countryside. Which combination of causes is mainly responsible?

• Heat stored by dense construction materials plus waste heat and reduced evaporation
• Higher solar input over the city than over the countryside
• Stronger winds in the centre transporting warm air from the suburbs
• Greater vegetation cover in the centre releasing stored heat at night

Answer: Heat stored by dense construction materials plus waste heat and reduced evaporation

Concrete, brick and asphalt absorb heat during the day and release it slowly at night, buildings trap outgoing radiation in street canyons, vehicles and air conditioning add waste heat, and the lack of vegetation and open water removes the evaporative cooling that operates in rural areas. Solar input is no greater over the city, and urban haze can even reduce it slightly.

A city in a basin experiences its worst air quality on cold, still winter mornings. Which mechanism explains the timing?

• A temperature inversion traps pollutants beneath a layer of warmer air
• Emissions of pollutants are highest on cold mornings and nil at other times
• Photochemical reactions are fastest at low temperatures and low light
• Cold air holds more moisture, which increases particulate formation

Answer: A temperature inversion traps pollutants beneath a layer of warmer air

Normally air cools with height and pollutants disperse upwards; under an inversion the surface layer is colder than the air above, so vertical mixing stops and emissions accumulate. Topography that shelters the city from wind makes the effect worse, which is why basin cities suffer most.

Two districts of one city have life expectancies differing by nearly ten years. Which explanation is most consistent with the evidence on urban health inequality?

• Differences in income, housing, air quality and access to services compound
• Genetic differences between the populations of the two districts
• One district has a hospital and the other does not, which explains it entirely
• The difference is a statistical artefact with no real basis

Answer: Differences in income, housing, air quality and access to services compound

Health follows the accumulation of advantage and disadvantage across housing quality, income security, exposure to pollution and traffic, food environment and access to care. Single-cause explanations fail because the factors correlate spatially and reinforce each other.

After heavy rain, an old industrial city discharges a mixture of storm water and untreated sewage straight into its river. Which feature of the drainage system explains this?

• Foul sewage and storm water share one pipe network that overflows when full
• Storm water runs in separate pipes that bypass the treatment works entirely
• The treatment works releases its cleaned effluent more quickly during storms
• Detention basins hold storm water back until the river level has fallen

Answer: Foul sewage and storm water share one pipe network that overflows when full

In a combined system the treatment works is sized for dry-weather flow, so rain quickly exceeds its capacity and the relief outfalls spill the diluted mixture into the river. Separate storm drains carry rainwater only, and detention basins reduce the peak rather than causing the spill.

One city reports mean annual PM2.5 from a monitor at the kerb of a main road; another reports it from a monitor in a park 300 m from any road. A student concludes that the first city's air is dirtier. Why is that conclusion unsafe?

• PM2.5 can only be compared between cities in the same climate zone
• The two monitors are of different site types, so the readings are not comparable
• Annual means are unreliable unless collected over at least ten years
• A park monitor always records higher particle levels because of pollen

Answer: The two monitors are of different site types, so the readings are not comparable

Concentrations from traffic fall steeply within tens of metres of the kerb, so a roadside and a background site measure different things in the same city; comparisons require sites of the same class, which is why monitoring networks classify each station.

Around London, planning policy has since the 1950s protected a ring of largely open land in which new building is tightly restricted; this ring is known as the ___ (two words).

Answer: green belt

Its stated purpose is to check the outward sprawl of the built-up area, not to guarantee public access or high ecological quality. A frequent consequence is that development leapfrogs the ring into commuter towns beyond it, lengthening journeys.