Meteorological Parameters That Effects The Air Pollution

Meteorological parameters that affect the air pollution

The important meteorological parameters that affect or influence the air pollution are described as follows;

1: The Wind

The direction and the speed of surface wind govern in the drift and diffusion of the air pollutants discharge near the ground level. The higher the wind speed at or near the point of the discharge of the pollution, more is the pollutants are rapidly carried away from the source. Then, the pollutants so dispersed will not exist at the same point or concentration but will rapidly be diluted with the greater volume of air.

2: Atmospheric stability and the temperature

During the temperature inversion, the atmosphere is stable and very little turbulence or mixing takes place. The accumulation of the smoke and other contaminants prevents the sun rays to warm the ground and the adjacent air. Fog is commonly associated with the inversion because the temperature of the air at ground level falls below the dew point of the water vapor in the air.

3: Mixing height

Mixing height can be defined as the height above the earth surface to which related pollutants will extend through the action of the atmospheric turbulence. Mixing ratio is usually related to the wind direction, wind speed, and the wind turbulence.

4: Rainfall

Rainfall exerts the decreasing action on the pollutant discharge into the atmosphere. It accelerates the deposition of the particulate matter on the ground and hence its removal from the atmosphere and goes to the ground. It also helps to remove the concentration of the gases pollutants which are stable in the water.

5: Humidity

The moisture content of the atmosphere influences the corrosive action of the air pollutant and indicates the potentiality for the formation of the fog in relation to the degree of the air pollution.

6: Solar radiation

Depending on the location solar radiation can have an effect on the type and the rate of the chemical reaction in the atmosphere.

Turbulence

Surface wind usually undergoes rapid and irregular fluctuation in both of the speed and the direction which indicates that the air flows have random motion with many eddies occurring near the earth surface are known as turbulence. So, turbulence is an irregular motion of air over short distances in the atmosphere. Turbulent flow has the many eddies occurring in the region near the earth surface. The degree of turbulence has found to depend on a number of factors such as roughness of the surface, the environmental lapse rate and the speed of the winds. Mainly there are two types of the turbulence. They are:

1: Thermal turbulence and

2: Mechanical turbulence

1: Thermal turbulence

When the temperature near the earth surface rises due to the solar radiation, the ELR increase eventually airs become unstable and convection current develop in the atmosphere which results from turbulence structure of wind known as the thermal turbulence.

In convective clouds especially thunderstorm, latent heat is released at cloud height and this energy sets updraft and downdrafts representing large eddy type motion. These, in turn, give rise to the numerous smaller turbulence of various sizes.

2: Mechanical turbulence

Turbulence occurs near the earth surface when the fast moving air passes over the rough surface. Because of the friction, small eddies develop and move upward and downward within the horizontally moving air. Such turbulence is known as the mechanical turbulence and is widespread due to the roughness of the earth surface. This turbulence easily develops when wind speed is high and ELR is great.

Mechanical turbulence tends to lower over the open sea or smooth ground and light wind or calm condition as well as stable atmosphere.

Diffusion

The pollution discharge from the region moves long distance towards receptors does not remain a cylinder tube of the same diameter of the plume. It will be mixed by the turbulence into the surrounding air without any true straight line and tends to make the concentration of plume as it arrives at the receptor less than its concentration that release from the stack. This process is called as diffusion.

There are two kinds of diffusion they are

1: Lateral diffusion:

In the atmosphere, the horizontal transportation by the eddies of heat, water vapor and the momentum from one region to another is known as the lateral diffusion. Lateral diffusion has been shown to have a coefficient value of 1000 times greater than that of the vertical diffusion.

2: Vertical diffusion

The vertical process is the process that involved in the formation and the modification of the air masses. The difference in temperature between diffusion is rarely formed in the atmosphere.

Meteorological principle responsible for the transportation and diffusion of pollutants

Meteorological principle is responsible for the diffusion as well as for the transportation of the pollutants:

Air quality at a given site varies tremendously from day to day even through emission may remain relatively constant. The determining factor has to do with the weather, how strong are the winds, in what direction are their bowings, what is the temperature profile, how much sunlight is available and how long has it been since the strong winds or the precipitation were able to clear the air. Thus, the transport and the diffusion of the air pollutant depends upon the dynamics of the atmosphere. Stable air discourages the dispersion and the diffusion of the pollutants stability of the atmosphere in the large amount determined by the rate of change of air temperature with altitude. Rapid vertical mixing takes place when the air is unstable that encourage the pollution dispersal.

The wind plays the major role in the transportation and diffusion of the pollutants. The gaseous waste or the smoke is taken away or diluted by the wind. The stronger the wind, greater will be the dilution of pollutant. Similarly, during the thermal inversion atmosphere is stable so the pollutant dispersion is minimum. Transportation and the diffusion of the pollutants can be shown by using the plume model.

Thermal wind baroclinicity

When the surface is heated, the air around the surface is also heated then the hot air which has less density rises upward and the cold air lowers down. In the baroclinic zone in the northern hemisphere, the constant density surfaces represented by the isotherms are not parallel to the constant pressure surface or isobars i.e temperature differs along the isobaric surfaces. This condition of an atmosphere which leads to the cause an increase in both the pressure gradient from the cold towards warm air and the resulting wind speed as altitude increases where rising air is replaced by a converging flow cyclonic vorticity develops in response to the earth rotation and a cyclonic storm may form.

References:

.S.C., Santee. Environmental Science. India, New Center: New Center Book Agency (P) Ltd, 2004.

Lal, D.S. Climatology, Sharda Pustak Bhawan, Allahabad.(2010)