METEOROLOGICAL FACTORS INFLUENCING AIR POLLUTION

Wind direction and speed: The higher the

wind speed, the more rapidly the pollutants

would be carried away from the source and

concentration of the pollutants will get

decreased.

Atmospheric stability and temperature

inversions: The degree of stability of the

atmosphere depends upon the rate of

change of temperature of the air with

altitude.

a) Lapse Rate: The rate of change of

temperature of air with altitude is

known as “Lapse rate” (Environment

Lapse Rate,ELR). In the lower

atmosphere (known as troposphere) up

to a distance of about 11 km above the

earth’s surface, the temperature

decreases linearly with increases in

altitude. In the upper region of the

atmosphere which is know as

stratosphere which extends from about

11 km to 32 km, constant temperature

prevails.

b) Adiabatic Lapse Rate (ALR): The

internal decrease of temperature with

height which occurs in the rising parcel

of air mass can be theoretically

calculated by assuming the cooling

process to be adiabatic (i.e. occurring

without the addition or loss of heat).

This rate of decrease of temp. with

height is referred to as Adiabatic Lapse

Rate (ALR).

c) Super-Adiabatic Lapse Rate (SALR):

When the prevailing environmental

Lapse Rate (ELR) is greater than the

ALR, the ELR is known as Super -

Adiabatic Lapse Rate.

In such a case, the rising parcel of air

will always remain warmer and lighter

than the surrounding environment and the parcel of air will continue to

accelerate and go up. In such a case, the

atmospheric condition is said to be

‘unstable’ and the dispersion of the

pollutants will be rapid, effective and

less intensity of air pollution.

d) Sub-Adiabatic Lapse Rate: When the

prevailing environmental lapse rate

(ELR) is less than the ALR. then the ELR

is known as sub-adiabatic lapse rate.

In such a case, the rising parcel of air

will be cooling more quickly than its

surroundings and hence it will not be

able to rise up to greater altitudes. Such

an atmospheric condition is said to be

‘stable’ which is however, not favorable

for effective dispersion of the

pollutants. It results in more pollution.

e) Neutral atmosphere: When the

prevailing ELR is equal to the ALR, the

atmospheric condition is said to be

neutral.

f) Negative Lapse Rate: When the temp

of the ambient air increases with

increase in altitude, then the lapse rate

is termed as negative or inverted lapse

rate. The condition under which

negative lapse rate occurs is referred to

as “inversion”. During inversion the

atmosphere is said to be stable. It

results in more pollution

Inversion: It is an atmospheric condition

in which a layer of warm air traps cool air

near the surface of the earth thus

preventing the normal rising of surface.

Therefore pollutants will not disperse in

the air. Inverse is a frequent occurrence in

the winter and autumn seasons. During

inversion the atmosphere is said to be

stable. It results in more pollution.

Precipitation: It cleans the atmosphere.

Rainfall removes the particulate matter

from the atmosphere and also reduces the

concentration of gaseous pollutants which

one soluble in water.

Humidity: It influences the corrosive

action of the air pollutants and also fog

formation.

Plume: It is defined as the path taken by

gaseous effluents emitted continuously

from a specific outlet such as chimney or

stack or vent.