Introduction
The term environment refers to the natural elements that make up the Earth and surround living organisms, enabling life. The study of the environment and its proper conservation, has gained enormous importance in last three decades. The term environmental pollution has become one of the most important issues of global concern.
Environmental Pollution
The substances/species produced either by a natural source or by human activity, which cause an adverse effect on the environment on being in excess of a desirable limit, are termed as pollutants. Some common examples of pollutants are carbon monoxide, sulphur dioxide, oxides of nitrogen, pollens, dust particles, etc.
Air Pollution
Humans can only live about five minutes without air. Dry air is generally a homogeneous mixture (solution) of nitrogen gas (78%), oxygen gas (21%), and traces of other gases. Some of the other gases are waste products of human activities and are known as air pollutants.
Atmospheric Pollutants
Many of the air pollutants are naturally present in the atmosphere in low concentration. They become pollutants when their concentration is relatively high. For example, SO2 is considered as pollutant when its concentration in the atmosphere exceeds the normal limit of 2 x 10-4 ppm. Similarly, CO acts as pollutant when its concentration exceeds the normal limit of 1 x 10-1 ppm.
Hydrocarbons
These are compounds containing carbon and hydrogen only. The hydrocarbons involved in air pollution are gases (or those that are volatile) under ordinary conditions. The important sources of hydrocarbons in the natural environment are bacterial decomposition of organic matter, forest fires and vegetation. Incomplete combustion of gasoline fuelled vehicles and industrial emissions account for 1/6 th of all hydrocarbons in atmosphere.
Particulates
Particulate refers to 'finely divided solid or liquid particles suspended in air'. The size of particulates varies from about 0.0002 to about 500 (1 = 10-4 cm). In the polluted air, the number of particulate particles is as high as 1011 per m3. In urban areas the mass level of particulates varies from 60 g to 2 x 103 g per cubic meter.
Smog
Smog is mixture of smoke and fog containing particulates. Two types of smog exist, classical or original smog and the more recent photochemical smog.
Ozone Layer
As mentioned before, the natural ozone layer of the atmosphere is very significant because it protect us from harmful effects of infrared/U.V. radiations of the sun. The atmosphere consists of different layers namely troposphere, stratosphere, mesosphere and thermosphere. The role of the ozone layer is better understood after understanding the role and temperature variation of the above layers.
Acid Rain
Normally while rain travels through the air, it dissolves floating chemicals and washes down particles that are suspended in air. At the start of its journey raindrops are neutral (pH = 7). In clean air, rain picks up materials that occur naturally such as dust, pollen, some CO2 and other chemicals produced by lightening or volcanic activities. These substances make rain slightly acidic (pH = 6), which is not dangerous. However, when rain falls through polluted air, it comes across chemicals such as gaseous oxides of sulphur (SOx), oxides of nitrogen (NOx), mists of acids such as hydrochloric and phosphoric acid, released from automobile exhausts industrial plants, electric power plants etc.
Greenhouse Effect
The Greenhouse effect is the rise in temperature that the Earth experiences because certain gases in the atmosphere (referred to as greenhouse gases), trap energy from the Sun. Without these gases heat would escape back into space and living on Earth would be inhospitable with average temperature being about 60 F lower. Because of the way they warm our world these gases are referred to as green house gases.
Control of Air Pollution
Air pollution can be controlled either at source or at the dispersal stage of various pollutants. Although, the problem of controlling air pollution at source is not easy, it can be reduced to some extent by taking steps such as:
- Use of modern techniques for efficient reduction of emissions and effluents.
- Use of appropriate raw materials,
Water Pollution
Water constitutes nearly three-fourths of the Earth's surface and it composes a large proportion of all living plant and animal matter. Approximately 70% of human body is water. Man drinks about 2 liters of water daily and it is required in abundance for domestic use, agricultural activities and industries. The part of Earth that comprises of water is called hydrosphere. All kinds of sources of water including oceans, rivers, lakes, glaciers, polar ice caps and groundwater makes it. About 97% of Earth's water is contained in oceans and is unfit for human consumption due to high salt content. Only 2.5% of the worlds total supply of water constitutes fresh water, which also includes inaccessible polar ice caps and mountain glaciers.
Water Pollution (Continued)
Inorganic Chemicals and Metals
Industrial and municipal waste waters and mine run offs cause various metals and metallic compounds to be released into water. These pollutants also enter the water bodies as acid rain and their sulphate and nitrate ions make water acidic. Most inorganic compounds are toxic, particularly, those of heavy metals such as mercury, chromium, lead, silver, cadmium etc., which come from paint and plastic production, metal and metal plating units etc. These substances get attached to the tissues of aquatic organisms, produce physiological poisoning and are therefore, capable of killing living organisms in water bodies.
Soil Pollution
Soil is the thin layer of organic and inorganic materials that covers the Earth's rocky surface. The organic portion, which is derived from the decayed remains of plants and animals, is concentrated in the dark uppermost topsoil. The inorganic portion made up of rock fragments, was formed over thousands of years by physical and chemical weathering of bedrock. Productive soils are necessary for agriculture to supply the world with sufficient food.
Green Chemistry
Simply stated, Green chemistry is the use of chemistry for preventing environment pollution in order to protect human health. It may give the impression that it is branch of chemistry involving plants, which is not true.
