Unit-iv unit-iv environmental Hygiene

UNIT-IV

UNIT-IV

Environmental Hygiene

(Credit Hours-3+1)

Air Pollution

Introduction

• Atmosphere:
• Gaseous envelope surrounding a celestial body (earth)
• It consists of a mixture of gases (air): vital for the propagation of life processes
• Atmospheric pollution:

The presence of substances in air in concentrations sufficient to cause harmful effects on the health of animals & man, vegetation & property or to interfere with the enjoyment of life & property

• Pollution: means to make (air) impure or unwholesome

(Presence of dust, smoke, fumes, mist, odour or gases (including oxides of carbon, sulphur & nitrogen) in quantities or of a duration that unreasonably alters the average (acceptable purity) condition of the atmosphere)

Pure and impure air

The composition (%) of fresh (pure) air by volume:

Component	Percent
Nitrogen	20.946
Oxygen	78.084
Argon	0.934
Total	99.964
Neon	0.0018
Helium	0.0005
Krypton and methane	0.0001
Hydrogen and Nitrous oxide	0.00005
Xenon	0.000008
Variable components:
Vapour	0-5
Carbon dioxide	0.01-0.1 (average 0.032)
Ozone	0-0.01
Sulphur dioxide	0-0.0001

The composition:

• The composition:
• Change of season,
• Altitude &
• Solar activity
• Oxygen: highly reactive (oxidation)
• Exerts marked influence on various geochemical cycles
• Most of the atmospheric oxygen: photosynthesis & ultraviolet radioactivity
• Expired air: concentration reduced to 16.4%

concentration of CO2 increased to 4.24%

concentration of other gases: unaltered

Composition of air Cont…

The pollution of outdoor air from: diverse sources

• The pollution of outdoor air from: diverse sources

Cause of pollution is traced to one or more of human activities

Ex.

Combustion of coal & oil: pollution by SO2, CO2 & NO

The treatment of wastes: release ammonia & H2S in the atmosphere

• The nature of pollution in an area will, therefore, be related to the type of activities indulged in by the communities inhabiting the area
• Many natural sources: volcanoes and forest fires

Sources of pollution

Zones:

• Zones:
• Homosphere: chemically uniform up to above 100-120 km the earth
• Heterosphere: above homosphere, structurally uneven
• Altitude increases: change in temperature pattern of atmosphere

On the basis of this change atmosphere has been divided into 4 distinct strata/zones:

• Trophosphere
• Stratosphere
• Mesophere
• Thermosphere

Zones of atmosphere

1. Troposphere:

1. Troposphere:

• Immediately above surface of earth,
• A gradual decline in temperature
• Thickness: 10-20 km
• At 20 km the temperature falls to -56O C (from 150 C)
• The rate of temperature drop: 6.40 C/100 m
• The zone contains: 99% mass of gases found in the atmosphere (nitrogen, oxygen and carbon dioxide)