Monday, March 13, 2017

Meteorology of air pollutants

Meteorology is the interdisciplinary scientific study of the atmosphere. Meteorological phenomena are weather events that are observed and they can be explained by the science of meteorology. These events are described and measured using variables of Earth's atmosphere such as temperature, air pressure, water vapour and bulk flow. These variables, their interaction and variability over time and space is used to describe and predict weather on a local, regional or global level.
  • Atmospheric processes such as movement of air and exchange of heat (convection and radiation) dictate the fate of pollutants as they go through the stages of transport, dispersion, transformation and removal.
  • Air pollution meteorology is the study of how these atmospheric processes  affect the fate of air pollutants.
  • Knowledge of air pollution meteorology helps to manage and control the release of pollutants in the atmosphere
  • Knowledge of air pollution meteorology is essential to understand the fate and transport of air pollutants
  • Air pollution problems involve three parts:
    • The pollutant source
    • The dispersion of pollutant and
    • The recepient
  • Transport of the pollutant is determined by the meteorological conditions
  • Air pressure difference causes movement of air
  • Air moving parallel to the ground is called wind whereas air moving up or down is called a current
  • Calm conditions, emissions from low elevations, temperature inversion, high buildings and narrow streets prevent air circulation and concentrate air pollutant into specific regions.
  • Turbulent atmospheric conditions, areas with thick vegetation, emission at elevated positions using smoke stacks and rain lower air pollution by creating conditions that encourage circulation and eventually remove pollutants from the atmosphere.
  • As air rises, it encounters lower pressure. However, the air parcel that rises has higher pressure than surrounding molecules. This means that more force is exerted by the inside the parcel than the particles outside. Hence the parcel expands. For the parcel to expand the particles inside the parcel must use some internal energy to do this work.
  • Since the internal energy decreases, temperature decreases (temperature is a function of internal energy).
  • Hence, the rising parcel expands and cools. This is called adiabatic cooling

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