Environmental Engg.

Lesson-29 Types of primary air pollutants and their properties

Primary air pollutants

The atmosphere has hundreds of air pollutants from natural or from anthropogenic sources.  All such pollutants are called as primary pollutants

The important primary pollutants are:

1. Sulphur oxides, specifically sulphur dioxide

2. Carbon monoxide

3. Nitrogen oxides

4. Lead

5. Hydrocarbons

6. Radioactive substances

7. Hydrogen sulphide

Sulphur dioxide

Sulphur dioxide is an irritant gas, and when inhaled, affects our mucous membranes.  It increases the breathing rate and causes oxygen deficits in the body, leading to bronchial spasms.  Patients of asthma are very badly affected by this pollutant.  Sulphur dioxide is also responsible for causing acidity in fogs, smokes and in rains and hence is the major source of corrosion of buildings and metal objects.

Major sources of Sulphur dioxide

• Burning of fuels

• Thermal power plants

• Oil refineries and chemical plants

• Open burning of garbage

Carbon monoxide

Carbon monoxide possesses about 200 times affinity for blood haemoglobin than oxygen.  Eventually, then inhaled, CO replaces O₂ from the haemoglobin and form what is known as carboxy-haemoglobin. This carboxy-haemoglobin is of no use for respiratory purposes, and hence when about half of the haemoglobin of the blood is used up in forming carboxy-haemoglobin, death becomes a certainty.  Persons dying of carbon monoxide inhalations exhibit characteristics bright pink colour of the flesh due to the presence of pink coloured carboxy-haemoglobin in their bloods.

Carbon monoxide also affects the central nervous system, and is even responsible for heart attacks, and high mortality rates.

Carbon monoxide chiefly originates from automobile exhausts, and is caused by incomplete combustion of organic matter.

Oxides of Nitrogen

Nitric oxide and Nitrogen dioxide are found to be injurious to human health.  Nitrogen dioxide is more injurious than nitric oxide.

Eye and nasal irritations are the common problems caused by nitrogen dioxide.  Also respiratory discomfort occurs with brief exposure to NO₂.

Hydrogen sulphide

It is a foul smelling gas with a typical odour of rotten egg.  Exposure to hydrogen sulphide for short periods may lead to loss of smell sense .  This gas may also cause headaches, conjunctivitis, sleepnessness and pain in the eyes.  Its higher concentration may block oxygen transfer and damage the nerve tissues.  However, hydrogen sulphide is generally not found in any trouble some concentrations in our atmosphere mainly because it is not emitted in automobile exhausts.

Lead

Lead is mainly injected into the atmosphere through the exhausts of automobiles, particularly, by automobiles running on petrol.  The concentrations of lead in inhaled air, may cause irritation of mucous membranes of nose, throat and lungs.  Lead poisoning may also cause damage to gastro-intestinal tracts, liver and kidney.  It may also cause abnormalities in preganancy and fertility.  Lead poisoning is also found to be responsible for retarding mental growth in children.

Hydrocarbons

The compounds containing only hydrogen and carbon are hydrocarbons.  Hydrocarbons are chiefly released into the atmosphere by automobile exhausts.  Substances like formaldehyde cause irritation of eyes, skins and lungs and hence may be quite injurious to health

Radioactive isotopes

The radioactive isotopes viz., Strontium-90, Cesium-137 and Iodine-131 have been the main products of atomic explosives and accidental discharges from atomic and nuclear reactors; although, however, other isotopes may also be present.  The serious health hazards caused by such radioactive emissions are anemia, cancers, shortening of life spans and above all the genetic effects, like sterility, embroyo defects, congenital malformations, etc.  Radioactivity is notorious for its delayed and long term evil effects on human health.