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58 Cards in this Set
- Front
- Back
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Define: Microclimate |
small scale climate that differs from surrounding climate
i.e. coastal area |
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Define: Urban heat island |
warm spot in the 'sea' of surrounding cooler rural air |
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How do buildings have an influence on urban micro climates? |
-retain/conduct heat easier than natural surfaces -non-reflective surfaces -absorb heat in day released slowly at night -anthroprogenic heat |
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How do windows have an influence on urban micro climates? |
-high albedo -reflect heat downwards -heat slowly released at night
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How does air pollution have an influence on urban micro climates? |
-industry/vehicles increase cloud cover -pollution dome allows short wave radiation absorbs outgoing radiation & reflects it back to surface -pollution dome insulates heat |
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Why are wind speeds lower in urban areas? |
buildings are wind breakers
wind is channelled through buildings |
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What factors help enhance the urban heat island effect? |
-pollution -anthroprogenic heat -densely constructed = insulates heat
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Under what conditions is the urban heat island effect greatest? |
-calm -high pressure conditions |
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Why do night time temperatures remain high? |
-buildings, sidewalks, parking lots block heat from ground from rising -heat is trapped on lower levels -heat absorbed by dark surfaces during the say is reemitted at night |
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Is the difference between rural and urban areas greatest in the summer or winter and why? |
winter has the greatest difference
due to anthroprogenic heat in urban areas
rural areas have little heating |
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Where is fog most prominent in cold season, rural or urban areas? |
rural areas
more surface moisture
more rain |
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Precipitation is higher over urban areas. Why? |
higher temperatures
air rises
area of low pressure |
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Why is there thicker cloud cover in urban areas? |
convection currents above urban areas
water vapour from industry
pollutants are cloud forming nuclei in air |
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Precipitation is... greater annually in urban areas than rural areas |
5-15% |
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What is fog? |
cloud that touches the ground |
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How and when does fog form? |
water vapour condenses
occurs in humid conditions - need lots of water vapour in the air
needs dust/air pollution to form |
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When does Radiation fog form? |
clear, calm nights winter |
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How does Radiation fog form? |
cold air sinks in anticyclonic conditions
as it sinks it warms
warm air meets cold air at ground level
warm air condenses on cold air = fog |
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When does Advection fog form? |
over sea in summer
common at coasts |
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How does Advection fog form? |
warm air mass moves horizontally across a cooler air or surface
air cooled to dew point creates condensation
fog moves inland and is warmed = evaporation |
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How does fog form in urban areas? |
particles from industrialisation etc act as condensation nucli
this encourages fog to form at night |
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When is it most likely for fog to form in urban areas? |
under high pressure conditions
winds too weak to blow fog away
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What is the difference between fog in urban areas in comparison to rural areas? |
it is thicker
persists longer |
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There is a greater incidence of hailstorms in urban areas. Why? |
strong heating in summer
cumulonimbus clouds height of tropopause
thunderstorms develop in humid air
strong convectional uplift making air unstable |
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When are thunderstorms most likely to occur in urban areas? |
late afternoon
summer months |
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What are the primary pollutants produced by human activity? |
sulphur dioxide nitrogen oxides carbon monoxide photochemical oxidants |
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What does sulphur dioxide produce? |
acid rain haze respiratory problems |
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What do nitrogen oxides produce? |
acid rain respiratory problems |
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What does carbon monoxide produce and what is it? |
incomplete combustion of fuel i.e. wood
heart problems |
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What do photochemical oxidants produce and what are they associated with? |
headaches
eye irritation
smog and increasing cloud cover |
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What is particulate matter? |
smoke and dust from vehicles and power stations |
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Why is the air poorer quality in urban areas than the country side? |
burning fossil fuels; vehicular and industrial
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What is Smog? |
mix of smoke, sulphur dioxdide from coal burning and fog |
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Define: temperature inversion |
reversal of normal decrease in temperature with altitude
instead increase of temperature with altitude |
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How is smog trapped? |
warm air sinking traps fog at ground level |
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How is a temperature inversion created? |
warm air stays by ground
doesnt rise |
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How is smog formed? |
sinking warm air condenses on cold air at ground level
mixes with pollutants
forms smog |
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What can contribute to the formation of smog in urban areas? |
heavy traffic high temperatures anticyclonic conditions high pressure temperature inversion calm winds |
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What is photochemical smog? |
a chemical reaction of sun on
nitrous oxides
hydrocarbons from vehicle exhausts |
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When was the Great smog in London? |
1952 |
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What three factors enhanced it? |
industrial revolution 1700s
factories - gases & particles in atmosphere catalyst for fog
low lying - hard to disperse |
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Under what conditions did it form? |
-v.cold with snow = burning coal in homes for warmth -anticyclone over region -winds were light, clear sky = radiation fog -ground was cool, warm air condensed |
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How many people died in the smog? |
4000 |
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What was a health problem posed by the smog? |
breathing problems |
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What zones were created in response and when? |
smoke free zones 1956 |
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What were UK councils required to do in the future to prevent an event like this occurring again? |
-monitor air pollution levels -air quality management areas where levels will exceed |
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What has has UK CBD's & cities put in place to reduce congestion in city centres? |
park and ride
i.e. Oxford |
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How does the UK control vehicle numbers? |
congestion charge = pay to enter city centre |
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What regular system has Mexico city put in place? |
driving restrictions ban all vehicles from driving 1 day a week |
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Why is wind slower in urban areas than rural areas? |
frictional drag between buildings
surface area is uneven |
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How can tall buildings affect wind? |
tunnel winds
canyon effect
wind speeds higher |
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How is wind displaced around a building? |
upwards
around
downwards in lee of structure |
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Outline the concept of Eddying: |
-wind hits/gets stuck between buildings
-forced to move in a circular motion
-responsible for bringing smoke/pollutants to ground level
-increased fog risk |
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Outline the Venturi effect: |
-winds channeled between buildings
-all wind energy squeezed into a smaller space
-gusts of stronger winds |
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How can we plan the urban environment to be more sustainable in relation to:
Wind |
spacing between buildings/in buildings
will reduce eddying
reduce occurrence of smog
reduce health problems |
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How can we plan the urban environment to be more sustainable in relation to: Smog |
clean air act
pedestrianisation
catalytic converters
park and ride
congestion charging |
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How can we plan the urban environment to be more sustainable in relation to: Precipitation |
relocation of heavy industry
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How can we plan the urban environment to be more sustainable in relation to: Temperature |
increase the amount of glass in buildings to reflect heat |
