7.3

• Urban heat island effect:

  • Urban areas tend to have higher surface and air temperature than surrounding suburban and rural areas due to:
  • Lower albedo: concrete/asphalt absorb more sun's energy than areas with more vegetation
  • Less evapotranspiration: water evaporating from surfaces and transpiration from plants carries heat from surfaces into the atmosphere
  • Cools off rural and suburban areas which have more vegetation
• Thermal inversion:

  • Normally the atmosphere is warmest at the earth's surface, and cool as altitude rises
  • Because warm air rises, air convection carries air pollutants away from earth's surface and distributes them higher into the atmosphere
  • During a thermal inversion, a cooler air mass becomes trapped near earth's surface (inverting normal gradient)
  • Because cool air at the surface is trapped beneath the warmer mass above it, convection doesn't carry pollutants up and away
• Effects of thermal inversion:

  • air pollutants (smog, PM, ozone, SO2, NOx) trapped closer to earth
  • respiratory irritation
  • decreased tourism revenue
  • decreased photosynthesis