Environment and pollution - class-IX

Wars among nations and industrialization release lots of harmful gases into the air which cause air pollution. Growth of algae in water causes the dissolved oxygen levels in water to deplete, resulting in death of aquatic animals due to water pollution. Afforestation does not cause pollution directly.

Environmental pollution is defined as the undesirable change in physical, chemical and biological characteristics of our air, land and water. As a result of over-population, rapid industrializations, and other human activities like agriculture and deforestation etc., the earth became loaded with diverse pollutants that were released as by-products. 

The air in the area near Taj Mahal contains serious levels of sulphur and nitrogen oxides. This is due to the large number of industries set up nearby and pollution of Yamuna River. As per metrological studies the wind direction is usually move in the direction where Taj is situated. All these led to acid rain. Acid rain reacted with the marble (calcium carbonate) of Taj Mahal and this causing damage to heritage structure.

Deforestation means cutting of trees. It is a major cause which leads to the change in soil properties. The nutrients are not replenished in the soil and the roots cannot hold the fertile soil in a place, leading to erosion. 

The increase in temperature on the earth (due to deforestation - cutting down of trees) disturbs the water cycle and reduces rainfall. The situation may lead to droughts (high scarcity of water).

The details of polar ozone hole formation differ from that of mid-latitude thinning but the most important process in both is catalytic destruction of ozone is by atomic halogens. 

The main source of these halogen atoms in the stratosphere is photo dissociation of man-made halocarbon refrigerants, solvents, propellants, and foam-blowing agents (chlorofluorocarbon (CFCs), HCFCs, freons, halons). These compounds are transported into the stratosphere by winds after being emitted at the surface.

So, $C{ H } _{ 4 }$ does not contain a halogen therefore it is not responsible for the depletion of ozone layer.

Primary Pollutants are the ones which are injected into the atmosphere directly.  Examples include:

1. Carbon monoxide (CO)
2. Oxides of nitrogen ($N{ O } _{ x },NO$ )
3. Sulfur oxides ($S{ O } _{ x }$)
4. Volatile organic compounds (VOCs)
5. Particulate matter (dust, ash, salt particles)

PM stands for particulate matter (also called particle pollution) the term for a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, fumes, soot, smoke, mist or fly ash are large or dark enough to be seen with the naked eye.

Causes of Air pollution:
1. Burning of Fossil Fuels:
Sulfur dioxide emitted from the combustion of fossil fuels like coal, petroleum and other factory combustibles is one the major cause of air pollution. Carbon Monooxide caused by improper or incomplete combustion and generally emitted from vehicles is another major pollutant along with Nitrogen Oxides, that is produced from both natural and man made processes.
2. Agricultural activities: Ammonia is a very common by product from agriculture related activities and is one of the most hazardous gases in the atmosphere. Use of insecticides, pesticides and fertilizers in agricultural activities has grown quite a lot. They emit harmful chemicals into the air and can also cause water pollution.
3. Exhaust from factories and industries: Manufacturing industries release large amount of carbon monoxide, hydrocarbons, organic compounds, and chemicals into the air thereby depleting the quality of air. Manufacturing industries can be found at every corner of the earth and there is no area that has not been affected by it. Petroleum refineries also release hydrocarbons and various other chemicals that pollute the air and also cause land pollution.
4. Mining operations: Mining is a process wherein minerals below the earth are extracted using large equipments. During the process dust and chemicals are released in the air causing massive air pollution.
5. Indoor air pollution: Household cleaning products, painting supplies emit toxic chemicals in the air and cause air pollution.

The medium which is effected by pollutants is called as receptor.
Hence option A is correct.

Forest fires are one of the main natural sources of pollution. The forests catch fire due to high temperature in summers

Pollutants can be classified as solid, gaseous or liquid pollutants. Also, it can be classified as physical, chemical and biological. They can be further classified as degradable and non-degradable. $NO _2$, $SO _2$  and CO are gases which if present in great quantity in the atmosphere can cause pollution.

Sewage is a biodegradable pollutant which can be degraded. DDT is a type of non biodegradable pollutant. $ S0 _2 $ is a primary pollutant, affecting the environment. PAN is considered as a secondary pollutants among all the pollutants. 

The concentration of pollutants like lead is 50 ppb. So the water gets contaminated with lead. The concentration of sulphate is 500 ppm. The concentration of nitrate is 50 ppm. Concentration of fluoride is 10 ppm.