Variables affecting severity of pollution

The meteorological variables which influence severity of a pollution are as follows:

• a)      Wind speed and direction

• b)      Atmosphere diffusion

• c)      Temperature variation with height, includes lapse rate and inversion

• d)     Mean maximum depths

• e)      Precipitation

The non-meteorological variables which influence severity of as pollution are as follows:

a)      Topographical features

b)      Quality and quantity of pollution let us discuss these one by one

Wind speed and direction: Pollution gets dissipitated in the atmosphere by involving both horizontal and vertical movements of the wind. In general, greater the wind velocity, the greater will be the dilution. Turbulence has been a stirring action of wind and, therefore, gets related to the vertical movement of wind moving across the surface of the earth i.e., fluid moving along the surface of the containing structure. Wind speed tends to increase very rapidly with height up to 10 meter. Above, this, it continues to increase in speed with height but at a much lower rate.

Atmospheric diffusion: Atmospheric diffusion means the movement of large parcels of air from one point to another.

Temperature variation: The temperature distribution of the atmosphere has been found to depend upon the rate at which energy being received from the sun and from various transport mechanism i.e., electromagnetic radiation, convection, evaporation, etc. Because of this, the temperature does not remain constant but varies with height, season, time of day, amount of cloud cover and many other variables.

1. Lapse rate: Lapse rate may be defined as equal to the adiabatic lapse rate minus the temperature lapse rate. Temperature lapse rate may be defined as the ratio of the change in temperature to change in height in 100s of meters. The adiabatic lapse rate may be defined as the rate of cooling with lofting of a parcel of air with no heat exchanges. A parcel of dry air expands upon rising. When air expands, it cools at the adiabatic lapse rate if no heat exchange occurs. If the surrounding air becomes cooler, the parcel will continue to rise and therefore, unstable conditions or strong lapse rate exists. A strong lapse rate reveals unstable conditions and therefore, good air mixing.
2. Temperature inversion: temperature inversion may be considered to be a meteorological condition in which air pollutants are not able to rise and get disbursed in the atmosphere and produce high concentration of pollution. A temperature inversion is said to exist when the normal lapse rate in the lower atmosphere gets inverted and the temperature actually increases with height, i.e., Exhaust gases and pollutants which rise only a certain distance under these conditions and persistent inversion that last several days can be dangerous.

Mean maximum depths: The mean maximum depth (MMD) may be defined as the height to which the unstable air mixes. In the absence of radio sound observations, the maximum mixing depth could be estimated as being the height of the loop of the low altitude cloud layer.

Precipitation: Pollutants may get washed out of the air by the natural scrubbing action of rain, snow and all other forms of precipitations when it falls to the ground. Not only can precipitation influence the atmospheric pollution, but the pollution can affect the precipitation.

Topographical features: Topography can very seriously alter local atmospheric conditions. Most important of these have been valleys, shore-lines and hills. Most of the famous air pollution episodes occurred in locations with adverse topographical conditions, valley affects take place due to the channeling of winds. Shore-line winds get created due to the differences in heating rates of the earth and the water under the same amount of the sun shine land absorbs heat faster than water.

Quality and quantity: Quality and quantity of air pollution could be estimated with regard to different sources of pollutions such as transportation, industry, power generation, space heating and refuse burning. Nearly 90 percent by weight of this pollution has been gaseous and 10 percent particular matter. This pollutants from the different physical and chemical composition like inorganic or organic gases and particulates.

The air pollution problems of one city or country may differ greatly from those of another city or country. Meteorology has played a vital role in determining the significant level of air pollution.