Definitions

• Albedo

  The reflectivity of a surface. The ratio between the amount of incoming insolation and the amount of energy reflected back into the atmosphere. Light surfaces reflect more than dark surfaces and so have a greater albedo.
• Particulate air pollution

  A form of air pollution caused by the release of particles and noxious gases into the atmosphere. Emissions of particles can occur naturally but are largely caused by the combustion of fossil fuels.
• Photochemical pollution

  A form of air pollution that occurs mainly in cities and can be dangerous to health. Exhaust fumes can become trapped by temperature inversions and, in the presence of sunlight, low-level ozone and other noxious gases form (associated with high pressure weather systems).
• Temperature inversion

  An atmospheric condition in which temperature, unusually, increases with height. As temperature inversions do not allow convection, they trap pollution in the lower layer of the atmosphere.
• Urban heat island

  The zone around and above an urban area, which has higher temperatures than the surrounding rural areas.
• Urban microclimate

  The small-scale variations in temperature, precipitation, humidity, wind speed and evaporation that occur in a particular environment such as an urban area.