Unit-iv unit-iv environmental Hygiene

Zones of atmosphere cont….
2. Stratosphere:

• Height from the earth: 40-50 km
• Thin layer above troposphere
• Uniform temperature
• The zone comprises of ozone layer
• Protects the earth against the ill-effects of UV irradiation
• Ozone shield increases the temperature from -560 C to -20 C at 50 km height

3. Mesophere:

• Height from the earth: 70-80 km
• Marked reduction in the temperature
• At an altitude of 70 km,
• the temperature falls to -92oC (from -20C)

4. Thermosphere:

• Height from the earth: above 80 km
• Temperature: very high (upto 12000 C)
• Thickness of the zone is 500 km
• It contains O2, nascent oxygen & nitrogen oxide.

The atmospheric pollution is influenced: meteorological conditions present in an area

• The atmospheric pollution is influenced: meteorological conditions present in an area
• Meteorological factors influences: magnitude of vertical & horizontal transfer of air pollution

Major parameters are:

Temperature:

• Direct bearing on the movement of air pollutants
• Influences the diffusion of pollutants

Wind:

• The direction & speed of wind is an important determinant in the movement of air pollutants

Humidity

• Influences the precipitation of pollutants on earth
• Many toxic pollutants combine with water vapor precipitate to the surface of earth

Atmospheric pressure

• Influenced the movement of pollutants in an area
• Important consideration for many pollutional parameter

Influence of metrological conditions

1. Meuse Valley (Belgium), December, 1930

1. Meuse Valley (Belgium), December, 1930

• The area was covered by a blanket of thick fog for about 5 days
• More than 60 persons died as a result of toxicity due to oxides of sulphur (and metals) & soot
• A large section of the population became ill

Air pollution: a historical perspective