Air Pollution

Air Pollution

Definition :

• Air pollution is defined as the undesirable contamination of gas. smoke, dust, fume, mist, odour or chemical particulates in the atmosphere which are injurious to human beings, plants and animals.

Causes of air pollution

1. Industrialization        

2. Urbanization

3. Vehicles emission     

4. Deforestation  

5. Population

 

1. Classification of Air Pollutants

• Air pollutants can be broadly classified into two types -

1. Primary pollutants

2. Secondary pollutants

1. Primary pollutants

i) Pollutants that are emitted directly from either natural events or from human activities are called primary pollutants.

ii) The natural events are dust storms, volcano etc and human activities can be. emission from vehicles, industrial wastes.

iii) About 90 % of global air pollution is constituted by five primary pollutants.

Examples

i) Carbon oxides (CO and CO₂)

ii) Nitrogen oxides

iii) Sulphur oxides

iv) Hydrocarbons

v) Particulate matter.

2. Secondary pollutants

• Primary pollutants when reacting with each other or from basic components of air  forms a new pollutant called secondary pollutant.

Examples : Sulphuric acid, nitric acid, carbonic acid. etc.

 

2. Difference between Primary and Secondary Air Pollutants

 

3. Common Air Pollutants

1. Carbon monoxide (CO)

• Carbon monoxide (CO) is a colourless odourless, flammable gas, which is a product of incomplete combustion. If carbon were completely oxidized during burning, complete combustion to carbon dioxide would occur and carbon monoxide would not be a problem.

• It is important not to confuse carbon monoxide with carbon dioxide. Carbon monoxide (CO) is an incomplete combustion product and can be toxic even at low concentrations, whereas carbon dioxide (CO2) is a complete oxidation product.

Sources of carbon monoxide

• Carbon monoxide is formed whenever a carbon containing material is burned.

• For example : Automobile exhausts, cigarettes etc. In addition to motor vehicles, sources of carbon monoxide include burning coal, natural gas or biomass.

• Biomass combustion can be a significant source of exposure in rural areas or in underdeveloped countries where it is burned for cooking, heating and even light.

• Atmospheric oxidation of methane gas and other hydrocarbons also produces carbon monoxide.

Effects of carbon monoxide

1. Health effects

• Many thousands suffer from carbon monoxide-related illness, which include headaches, dizziness and drowsiness. Reports shows that about 11 % heart failure caused by excess carbon monoxide.

• Carbon monoxide also has other adverse effects in the body. For example, it interferes with the oxygen-carrying proteins in muscles.

• If the victim continues to receive a high dosage of CO, then permanent brain damage and even death will result. Initial symptoms include dizziness, headache, nausea and faintness.

2. Environmental effects

• It increases globe temperature.

Measures to reduce carbon monoxide

• About half of the motor vehicle carbon monoxide emissions in this country are produced by only 10 % of the vehicles. Efforts are being made to find and remove these vehicles from the road.

• Car and truck owners need to maintain their vehicles so that they operate as cleanly as they were designed to operate.

• Other measures to control carbon monoxide emissions include facilities that bum fossil fuels or wood to maintain high burning efficiencies and prohibiting open burning of trash and garbage.

2. Sulphur dioxide (SO₂)

• Sulphur dioxide (SO₂) is a colourless gas with a sharp odour that accounts for about 18 % of all air pollution.

Sources of sulphur dioxide

1. Chemical industries

2. Metal smeltings

3. Pulp and paper mills

4. Oil refineries.

Effects of sulphur dioxide

i) Health effect

• Sulphur dioxide reacts with moisture in eyes, lungs and mucous membranes to form strong irritating acid. It can trigger allergic reaction and asthama.

ii) Environmental effect

• Reduced visibility; acid deposition of H₂SO₄ can damage trees, soils and aquatic life.

• The stratospheric ozone depletion, where by sulphate particles in the stratosphere provide surfaces on which ozone-destroying reactions occur. A third major effect is the antiwarming influence they exert in global climate change.

3. Nitrogen dioxide (NO₂)

• Nitrogen dioxide is a reddish brown irritating gas. They account for about 6 % of pollution.

Sources of nitrogen dioxide

1. Motor vehicle exhausts

2. Gasoline

3. Volcanoes

4. Lightning

Effects of nitrogen dioxide

i) Direct, exposure of NO₂ irritates eyes and causes infection, asthma.

ii) Poisonous to plant life. HNO₃ can canoed metals and eat away stones.

4. Lead (Pb)

• Lead a highly useful metal has been mined for thousands of years. And it has been known for thousands of years that lead is toxic to the nervous system. The level of lead in modem human skeletons and teeth is at least a hundred-fold greater than the level found in pre-industrial age skeletons.

Source of Lead

• The combustion of alkyl lead additives in motor fuels accounts for the major part of all lead emissions into the atmosphere. An estimated 80-90 percent of lead in ambient air derives from the combustion of leaded petrol.

. • Paint and storage batteries.

Effects of Lead

• Mental retardation, digestion problems, cancer.

• Harmful to wild life.

5. Particulate Matter

• Suspended particulate matter is defined as single particle or aggregates of particles with diameters greater than 2 × 10^-10 m.

• Some particulate matter is natural i.e. rain. snow. fog. hail and mist, while others are often the result of human processes, e.g. smoke, soot and fumes.

• Some natural particulates are affected by human actions such as fog and wind-blown soils.

• Smoke and soot are the products of incomplete combustions of coal, petrol and diesel fuels in furnaces, domestic heating systems and vehicle engines.

Effects of SPM

• Aerosols are mixtures of minute solid or liquid particles suspended in air that form a haze or spoil visibility.

• The main problem to humans caused by atmospheric particulate matter is how far it is able to penetrate the respiratory system.

• Particles in the size range 30 × 10^-6 to 100 × 10^-6 m lodge in the nasal cavity, larynre and trachea. Some examples of particles of this size are pollen, fungal spores, cement dust and coal dust.

• Particles less than 15 × 10^-6 m find their way into the bronchus and bronchioles e.g. tobacco, smoke and fumes.

• Particles of 4 × 10^-6 m and less can enter the alveoli where gaseous exchange take place between tile bloodstream and air e.g. asbestos dust, glass fibre and viruses.

Sources of Suspended Particulate Matter (SPM)

• Particulate matter comes from two major sources. First, those emissions that come directly from sources such as coal combustion, wind-blown dust and quarrying. These are called primary particulates.

• Other particulates can be formed from chemical reactions between pollutant gases such as sulphur dioxide, the oxides of nitrogen and ammonia such reactions lead to the formation of solid sulphate and nitrates.

• Organic aerosols may also be formed by the oxidation of volatile organic compounds. These particulates are termed as secondary particulates.

Reducing Particulate Emissions

• Emissions of particles smaller than 10 pm in diameter (PM₁₀) are controlled to meet an 3 EPA standard of 150 micrograms per cubic meter (µg/m³ ) of air.

• Although many cities barely meet this standard - studies have shown Associations between very fine particulates and increased respiratory problems and premature death rates at lex els only one-third of the standard. In the near future, particulates of diameters 2.5 pm and less may be regulated.

6. Dioxins

• Dioxins are a class of chemical contaminants that are formed during combustion process such as waste in cineration. forest fires and paper pulp bleaching. 

Air Pollutants, Major Source and their Human Health Effect

 

4. Photochemical Smog

• Smog is a type of air pollution. The photochemical smog is a chemical reaction of sunlight, nitrogen oxides and volatile organic compounds in atmosphere which leaves airborne particles and ground-level ozone.

• The noxious mixture of air pollutants are highly reactive and oxidizing.

• Photochemical smog is considered to be a problem of modern industrialization.

 

5. Control Measures for Air Pollution

• For controlling air pollution in long term, control of contaminants at their source is more desirable and effective method.

1. Source control

i) By using unleaded petrol only

ii) Use of petroleum products having low sulphur

iii) Use of public transport system rather than private vehicle

iv) Plantation of trees helps to remove particulate and carbon monoxide also they absorb noise.

v) Industries and waste disposal should be outside of city and preferably downwind of city.

vi) Use catalytic converters to help control the emissions of carbon monoxide and hydrocarbons.

2. Control measures in industries

i) Emission rate should be restricted to permissible levels.

ii) Incorporating air pollution control equipment in design of plant layout must be made mandatory.

iii) Continuous monitoring of emission to check pollution.

Equipments used to control air pollution

i) Ensuring sufficient supply of oxygen to combustion chamber to complete the combustion

ii) Use of mechanical devices such as :

- Scrubbers

- Cyclones

- Bag houses

- Electrostatic precipitators 

• In manufacturing process, electrical power and industrial plants above devices are used for removing particulates from exhaust gases.

• All these methods retain hazardous materials of the exhaust which can be disposed of safely.

• The set scrubber can be used to remove sulphur dioxide emissions.

Review Questions

1. Define air pollution. What are the sources of air pollution ?

2. What are the global impacts of air pollution ?