DISCUSS ABOUT SOME AIR POLLUTANTS.

Air pollutants are classified in two aspects.
1. Primary air pollutants
2. Secondary air pollutants
Primary pollutants are substances directly emitted from a process, such as ash from a volcanic eruption, the carbon monoxide gas from a motor vehicle exhaust and sulphur dioxide released from factories.

Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact. An important example of a secondary pollutant is ground level ozone — one of the many secondary pollutants that make up photochemical smog. The details of each pollutants are discuss below.

1. CO [Carbon monoxide] :

• Carbon monoxide is produced by the incomplete combustion of carbon-containing fuels, such as gas (domestic or bottled), coal, oil and wood. In short, it forms when there is not enough oxygen to produce carbon dioxide. Vehicular exhaust is a major source of carbon monoxide.
• Carbon monoxide is a deadly poisonous gas in high concentration.If its value reaches above the permissible value than it will be very harmful for human health.
• Carbon monoxide is colorless, odorless, and tasteless, but highly toxic. 
• The chief sources of this gas are combustion of automobiles, furnaces, domestic fires, forest fire, coal in factories, houses and power plants etc.

• Effects of carbon monoxide on human being.

1. Carbon monoxide reduces the oxygen carrying capacity of hemoglobin of human blood cells.
2. Its presence in air even small amount may cause headache, breathing trouble and vomiting tendency.
3. It can also occur food poising in human being.
4. Exposures to carbon monoxide may cause significant damage to the heart and central nervous system.

Main sources of carbon monoxide (CO) :

1. Automobiles                         CO emission

 (i)   Transportation                          64%

 (ii)  Motor vehicles                          59.5%

 (iii)  Air crafts                                   2.5%

 (iv) Rail roads                                  1.0%

2. Industrial process

Iron steel, paper and 

petroleum industries                         9.6%

3. Other sources

 (i)  Forest fires                                  6.9%

 (ii) Agriculture burning                      8.3%

2. HC [Hydro carbon] :

• Hydro carbon present in the air is primary air pollutant. Unburnt or partially burnt gasoline or petroleum are the main source of hydrocarbons. Decomposed organic waste and garbage also produce hydrocarbons. It is methane, ethane and propane.

Effects of hydrocarbon (HC) on plants and man.

1. Damage to bological system
2. Cause leaf damage to sensitive plants.
3. HC has several effects on human lungs.
4. It causes irritation to eyes, nose and throat.

3. Sulphur dioxide (SO2)

• SO2 is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulphur compounds, their combustion generates sulphur dioxide. Further oxidation of SO2, usually in the presence of a catalyst such as NO2, forms H2SO4, and thus acid rain. This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
• The chief source of SO2 emission are given below:

1. Burning of fossil fuels

2. Automobiles

3. Chemical industries

4. Oil and petroleum refineries

5. Forest fire

6. Volcanic eruption

• Effects of SO2 on man and plants

1. The plant leaf is changed to yellowish color.
2. It damages biochemical of plants.
3. Oxides of sulphur when absorbed by rain water forms sulphuric acid (H2SO4) which is harmful for environment.
4. SO2 reaching to the lungs cause respiratory problems.
5. Inhaling of his odour gas cause headache and irritation to eyes.
6. It increases the rate of corrosion of iron, steel, aluminum etc.

4. Nitrogen oxide (NOx)

• There are several oxides of nitrogen present in atmosphere. They are primary air pollutant. These are nitrous oxide, nitric oxide, nitrogen dioxide, dinitrogen trioxide, dinitrogen tetroxide, dinitrogen pentoxide and nitrogen trioxides. In which, NO and NO2 are the most important primary air pollutants.
• Combustion of fossil fuels, i.e coal and petroleum produce about 90% of oxides of nitrogen which emits in atmosphere.
• Denitrification process by bacterial activity also emits small amount of NO and NO2 in atmosphere. In which 95% of NO and 5% of NO2.
• Contribution of NO in the formation of photochemical smog is important. NO plays an important role in the formation of several photochemical pollutants such as PAN (Peroxyl acteyl nitrate) and O3 ozone.

• Source of NO and NO2 :

1. Combustion of fossil fuels.
2. Automobile exhausts
3. Forest fires 
4. Electric generation plants 
5. Smelting plants 
6. Industrial boilers 
7. Petroleum refineries

• Effects of NO and NO2 :

1. Erosion of metal surface.
2. Reduction in visibility.
3. Irritation in eyes, nose and throat.
4. Adversely affect kidney, heart and liver at high concentration.
5. Inhibition of growth of plants.

5. Particulate matters (PM) :

• Particulate matters are the third largest category of air pollutants. They are small pieces of solid materials which include fine liquid droplets. They diffuse into the atmosphere and called aerosols. In short, aerosols are mixture of particles and gas together.
• Sources of particulate matter can be manmade or natural. Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes also generate significant amounts of aerosols.
• Particulate matters are quickly recognized because they are easily detected by the human eyes. For example heavy black smoke can be seen with naked eyes, whereas carbon monoxide and sulphur dioxide goes unnoticed because the emission of these gases are colorless.
• There are different types of particulate matters are present in an atmosphere. They are collectively known as Suspended particulate matters (SPM). Among them, the particulate matters which are respirable particulate matter (RPM) and remaining part is known as Residual dust (RD).
• Effects of particulates :

1. PM are responsible for different ENT disease and serious damage to lungs.
2. Different  metallic particles like cadmium, lead, cobalt etc and their compounds cause various pulmonary and cardiac disease.
3. Main particulate matters being washed by rain and fall on soil and affect the soil fertility.
4. These particulate matters may reduces the photosynthesis of plants.
5. Respiratory system can be damaged directly by particulate matter that enter the blood system through lungs.

5. Volatile organic compounds:

• VOCs are an important outdoor air pollutant. In this field they are often divided into the separate categories of methane (CH4) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming.
• Other hydrocarbon VOCs are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in the atmosphere, although the effect varies depending on local air quality. Within the NMVOCs, the aromatic compounds benzene, toluene and xylene are suspected carcinogens and may lead to leukaemia through prolonged exposure. 1-3 butadiene is another dangerous compound which is often associated with industrial uses.