Effects of Air Pollution

• Effect of Particulates

The black smoke released into the air by a diesel truck is often the most obvious form of pollution that we routinely encounter. This smoke is composed of particulate matter. Particulate matter are the tiny solid or liquid particles suspended in air which are usually individually invisible to the naked eye. Collectively, however, small particles often form a haze that restricts visibility. Particulates in the atmosphere may be viable or non-viable. Viable particulates are the minute living organisms that are dispersed in atmosphere like fungi, bacteria and algae. Non-viable particulates are formed  either by the breakdown of large materials or by the condensation of minute particles and droplets. There are four types of non-viable particulates in the atmosphere : mist, smoke, fumes and dust.

(a) Mist: It is produced by particles of spray liquids and the condensation of vapours in air. Examples are portions of herbicides and insecticides that miss their targets and travel through the air to form mist

(b) Smoke: It denotes very small soot particles produced by burning and combustion of organic matter. Oil smoke. tobacco smoke and carbon smoke are typical examples of this.

(c) Fumes: These are condensed vapours. Example,fumes of metals

(d) Dust: It consists of the particles produced during crushing, grinding and attribution of solid materials. For example, ground limestone, sand tailing etc.

The effect of particulate particles largely depends on the particle size. Whereas the particles of size greater than 5 microns are likely to lodge in the nasal passage, the smaller ones are more likely to penetrate into the lings-the rate of penetration being inversely proportional to the size of particles. A number of these fine particulates are carcinogens. Inhalation of small particles irritates the lungs and exposure to such particles for long periods of time causes “scarring” of “fibrosis” of the lung lining. This type of disease is well known in industrial setting and is termed as Pneumoconiosis.

• Smog

Smog which describes “smoke-fog” like condition, is the best-known example for air pollution that occurs in many cities throughout the world.word smog is derived from smoke and fog. This is the most common example of air pollution that occurs in many cities throughout the world. There are two types of smog

1. Classical Smog:  Classical smog occurs in cool humid climate. It is a mixture of smoke, fog and sulphur dioxide. Chemically it is a reducing mixture and so it is also called as reducing smog.

2. Photochemical Smog:  Smog occurs in warm, dry and sunny climate. The main components of the photochemical smog result from the action of sunlight on unsaturated hydrocarbons and nitrogen oxides produced by automobiles and factories. Photochemical smog has high concentration of oxidising agents and is, therefore, called as oxidising smog

• Formation of Photochemical Smog

?The chemistry of formation of photochemical smog centers around nitric oxide (NO). At high temperatures, in the petrol and diesel engines of car and trucks, N₂ and O₂ .react to form  a small quantity of NO, which is emitted into air with the exhaust gases. This NO oxidises in air to NO₂, which in turn absorbs energy from sunlight and breaks up into nitric oxide and free oxygen atom. 

NO₂ (g) +hv → NO(g) + O(g)

Oxygen atom are very reactive and can combine with O₂ to  form ozone.

O (g) +O_²(g) → O₃(g)

Ozone thus formed oxidize  NO(g) to NO₂(g). Both NO & O3 are strong oxidizing agents and react with unburnt hydrocarbons in the polluted air to produce chemicals such as formaldehyde, acrolein and peroxyacetyl nitrate (PAN). PAN cause eyes to water and burn and is harmful to respiratory system.

Effects of photochemical smog: 

Photochemical smog contains ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate (PAN). Photochemical smog causes serious health problems.

• Ozone and PAN act as powerful eye irritants.
• Ozone and nitric oxide irritate the nose and throat and their high concentration causes headache, chest pain, dryness of the throat, cough and difficulty in breathing.
• Photochemical smog leads to cracking of rubber and extensive damage to plant life.
• It also causes corrosion of metals, stones, building materials, rubber and painted surfaces.

Control of Photochemical Smog

Installation of efficient catalytic converters  in the automobiles is the most significant way for reducing smog formation as it prevents the release of nitrogen oxides and hydrocarbons to the atmosphere. Photochemical can also be suppressed by certain compounds, which act as free radical trap. Certain plants e.g., Pinus, Juniparus, Quercus, Pyrus and Vitis can metabolise nitrogen oxide and therefore, their plantation could help in this matter.

• Acid Rain

Normally rain water has a pH of 5.6 due to the presence of H⁺  ions formed by the reaction of rain water with carbon. The rain containing H₂SO₄ and HNO₃ which are formed from the oxide of S and N₂ present in air is called acid rain. pH of acid rain is 4-5.

Formation of Acid Rain

The oxides of nitrogen undergo oxidation reaction and reaction with water vapours present in atmosphere from HNO₃.

NO₂+O₃ + hv → NO₃ +O₂

NO₂+NO₃+hv → N₂O₅

 N₂O₅ + H₂O + hv → 2HNO₃

This HNO₃ comes down with the rain.

Also, 

2SO₂ + O₂ → 2SO₃

This SO₃ reacts with water vapours and form H₂SO₄ which also comes down with the rain.

• Effects of Acid Rain

?1. It damage buildings and statues which contain marble, lime stone, mortar etc.

CaCO₃ + H₂SO₄ → CaSO₄ + H₂O +CO₂
White                           Yellow

2.  It damage irons and steel structure.

3. It corrodes water pipes. As a result, water gets contaminated with heavy metals.

4. It increases the acidity of lakes and rivers which is harmful for fishes.

5. It increases the acidity of soil which damage trees, plants and crops.

• Green House Effect and Global Warming?

The green house gases (CO₂, CH₄, O₃, CFC’S ) in the atmosphere form a thick cover around the earth. About 75% of the solar energy reaching the earth is absorbed by the earth surface. The IR radiations coming from sun are not absorbed by atmospheric gases but Earth absorbs these IR radiations of short wavelength. As a result of this the temperature of earth stands rising. Eventually, earth starts emitting infrared radiations of longer wavelengths. The partially radiated infrared radiations from the earth are absorbed by the greenhouse gases.  This results in excessive heating of Earth’s atmosphere. Thus the greenhouse gases add to the heating of atmosphere. This causes global warming. The atmosphere traps the sun’s heat near earth’s surface and keeps it warm. The reemission of the earth’s energy absorbed by CO₂ and other greenhouse gases present near the earth’s surface and its radiation back to the earth is called green house effect.

Advantages of green house effect : 

1. It is necessary for evaporation of water, formation of clouds, rainfall etc.

2. The warm atmosphere helps in rapid growth of plants, trees etc.

Harmful effects of green house effect :

1. High temperature of atmosphere may melt polar ice caps which are likely to raise the level of sea thereby sinking most of the coastal areas and causing large scale destruction.

2. The high temperature may reduce crop product.

3. The high temperature will reduce work efficiency of human being.

4. Tropical rains and hurricane will become more frequent and also  stronger causing more devastation.

5. The change in ocean temperature will adversely affect the warm life.
    

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