Urban Climate Flashcards
What is an albedo ?
The reflectivity of a surface - light surfaces reflect more than dark surfaces and so have a greater albedo.
What is particulate air pollution ?
Form of air pollution caused by the release of particles and noxious gases into the atmosphere normally through combustion of fossil fuels.
What is photochemical pollution ?
Form of air pollution that occurs mainly in cities and is where exhaust fumes become trapped by temperature inversions, and in the presence of sunlight, low-level ozone and other noxious gases form.
What is a temperature inversion ?
An atmospheric condition in which temperature unusually increases with height causing to trap pollution in the lower layer of the atmosphere.
What is the urban canopy ?
Layer of air closest to the surface extending upwards to the mean building height.
What are 3 reasons why cities are warmer than rural areas ?
Building materials have a much lower albedo so absorb heat in day and slowly release at night, Vehicles and industries increase cloud cover and creates a ‘pollution dome’ which allows in short-wave radiation but absorbs a large amount of outgoing radiation, Urban areas designed to shed water quickly so no time for cooling by evaporation.
What are strategies to managing the Urban Heat Island effect ?
Surfaces built with high albedo, Green roads, Green roofs, Urban greening, Cool cars
Why can precipitation be higher in urban areas than rural areas ?
Higher urban temperatures encourage development of lower pressure systems, UHI generates convection as ground surfaces are heated - rapid evapotranspiration takes place and can result in cumulus cloud and convectional weather patterns, City pollution can increase cloud formation as pollutants acts as a water attracting nuclei and assist raindrop formation.
What happened with fog in the industrial times ?
Occurence of fog went up along with industrialisation and these fog particles acted as condensation nuclei so encouraged fog formation at night usually under high pressure weather conditions.
What did the UK Clean Air Act in 1950s result in ?
Dramatic reduction in smoke production and particulate emissions and a decrease in the number of foggy days
How do Urban Areas Influence Thunderstorm Development ?
Warmer temperatures due to the UHI will enhance upwards movement of air (convection), More pollution will make greater cloud formation and potentially thunderstorms, Presence of tall buildings can enhance the formation of thunderstorms.
What is urban canyoning ?
Wind redirected down long, straight canyon like streets where there is less friction.
What is the venturi effect ?
Phenomenon in which wind velocities increase when air flows through an increasingly narrow gap.
What are some effects of wind in urban areas ?
Convectional processes can draw in localised winds from surrounding areas, High rise building can enhance urban canyoning, The closer buildings are together it creates a ‘dead-air’ zone which is where pollution and litter can build up.
