Environmental Pollution

Environmental Pollution

Environmental pollution is an undesirable change in physical, chemical or biological characteristics of our surroundings (air, water or land). It can affect human, animal and plant life as well as materials. Pollution may be natural or man-made. It can be classified according to the components of the environment being damaged. These are:-

(i)Air Pollution

(ii)Water Pollution

(iii) Soil (land) Pollution

Pollutant

When the concentration of a substance already present in nature or of a new substance increases to undesirable proportions causing danger to human beings, other animals or vegetation and other materials, the substance is treated as a pollutant. The pollutants spoil the environment and are harmful to living organisms and other materials. The common pollutants are :

(i)Gases like carbon monoxide, sulphur dioxide, oxides of nitrogen, etc.

(ii)Compounds of metals like lead, mercury, zinc, cadmium, arsenic, etc

(iii) Pollen grains, dust.

(iv)  Pesticides and detergents

(v) Sewage and

(Vi)  Radioactive substances.

Threshold Limit Value (TLV)

This indicates the permissible limit of a pollutant toxic in atmosphere to which a healthy worker is exposed during 8 hours a day or 40 hours a week for life time without any adverse effects. For example, TLV of CO is 50 ppm and that of CO2 is 5000 ppm. But TLV for a poisonous gas phosgene is only 0.1 ppm.

Atmosphere

The gaseous envelope surrounding the earth is known as atmosphere. The two major components of dry and clean air in the atmosphere (by volume) are nitrogen (78.09%) and oxygen (20.95%). Argon (0.934%) and carbon dioxide (0.034%) are the minor components of the atmosphere. Air can hold water vapour from 0.1 to 5% by volume and also contains traces of elements such as noble gases (neon, helium, krypton, xenon), hydrogen, methane, Sulphur dioxide, ammonia, ozone etc. The atmosphere surrounding us may be divided into four regions :

(i)Troposphere (8 to 12 km above earth’s surface)

(ii) Stratosphere (11 to 50 km above earth’s surface)

(iii) Mesosphere (50 to 90 km above earth’s surface)

(iv) Thermosphere (90 to 500 km above earth’s surface)

About 80% of the total mass of air and almost all of the water vapours of the atmosphere is found in the inner layer known as troposphere.

The chemical and photochemical reactions play a significant role in governing the chemical species present in the atmosphere.

Air Pollutants

 There are two types of air pollutants:-

1.Primary air pollutants

2. Secondary air pollutants

1. Primary air pollutants :- A primary air pollutant is a harmful chemical substance that directly enters the air as a result of natural events or human activities. For example,

(i)Carbon oxides (CO and CO2)

(ii) Nitrogen oxides (NO)

 (iii) Sulphur oxides 

(iv) Hydrocarbons

(v) Suspended Particulate matter.

2. Secondary air pollutants:- A secondary air pollutant is a harmful chemical that forms in the air due to a chemical reaction between two or more air components or a primary pollutant and one or more air components. For example, Sulphur dioxide is a primary pollutant in air. It reacts with oxygen gas in the atmosphere to form the secondary pollutant sulphur trioxide (So3). Even the sulphur trioxide formed may react with the water vapour in air to form sulphuric acid.

Sulphuric acid is, therefore, also a secondary pollutant.

The common secondary pollutants are :
nitrate and sulphate salts, etc.

Usually Co2 is not considered as pollutants.

Other air pollutants are metals like Be, Ba, Cd, Fe, Mn, Pb, Hg, Ni, Zn (from mining and metallurgy), non-metals such as As, P, Se (from combustion of industrial fuels, fertilizers), radioactive substances (from nuclear power plants).

Tropospheric Pollution

The tropospheric pollution occurs because of the presence of undesirable solid or gaseoud particles in the air. The pollutants may be brodly classified into two major types :

1. Gaseous air pollutants:- these include oxides of Sulphur, nitrogen and carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidants.

2. Particulate pollutants:- These are dust, dumes, mist, spray, smoke etc.

Particulates in Air Pollution

1. Particulates :- The small sized solid particles and liquid droplets which range in size from  are collectively called as Particulates. These particles are usually individually not visible to the naked eye. However, small particles often collectively form a haze that restricts the visibility. The common particulates are smoke, mists, fumes, dust etc.

The particulates in the atmosphere may be viable or non-viable. The viable particulates are the small living organisms which are dispersed in the atmosphere. These include bacteria, moulds, fungi, algae, etc. Some of these viable particulates cause allergic reactions on human beings. Fungi can also cause plant diseases.

Non-Viable particulates are formed either by the breakdown of large materials or by the condensation of minute particles and droplets.

The effect of particulates pollutants depend upon the size of the particles. The coarser particles of size more than 5 microns are likely to lodge in the nasal passages whereas the smaller ones are more likely to penetrate into the lungs. The rate of penetration is inversely proportional to the size of the particles. Some of these particles are carcinogens. Continuous inhaling of these small particles for long periods of time irritates the lungs and causes scarring or fibrosis of the lung lining. This type of disease is very common in industrial settings and is known as ‘pneumoconiosis’.