Air pollutants and sources of air pollutants

Question: Define pollutants. Describe various pollutants that cause pollution.

Answer.

Pollutant

Any substance that is present in air, water or soil and has an adverse effect on some other part of environment is called pollutants.

Pollutants have harmful effect on both health and quality of health of human being. Some of important air pollutants are given as follows.

i. Sulphur oxides (SOx)

ii. Carbon monoxides

iii. Nitrogen oxides (NOx)

iv. Methane

v. Chlorofluorocarbons (CFCs)

vi. Lead compounds

vii. Ozone

Sulphur oxides (SOx)

Sulphur oxides are produced when fossil fuels such as coal and petroleum are burnt.

Sulphur dioxide (SO₂)

Sulphur dioxide (SO₂) easily reaches the lung and disturb respiratory system.

Patients with asthma are at high risk in presence of SO₂.

It reduces lung function, increases the respiratory disease and causes irritation of eyes, nose and throat.

Sulphur trioxide (SO₃)

Sulphur trioxide is produced in air from reaction of SO2 and O2.

SO3 combines with rain water and causes acidic rain.

ii. Carbon oxides (COx)

Carbon oxides are produced when a piece of wood is burnt.

Carbon monoxide

Carbon monoxide is formed under limited supply of oxygen.

It is a poisonous’ gas.

It can cause headache and dizziness.

It can lead to death, when inhaled for long time.

Carbon dioxide

Carbon dioxide is formed under excess supply of oxygen.

Carbon dioxide is not considered as air pollutants. It is used in photosynthesis.

However, it causes global warming.

Nitrogen oxides (NOx).

Nitric oxide and nitrogen dioxide are collectively called nitrogen oxides. Nitrogen oxides are produced from reaction of nitrogen with oxygen during burning of fuels.

Nitric Oxide Nitric oxide is a colorless, odorless gas.

It has higher density than air and sparingly soluble in water.

It can damage lungs and causes headache and cough.

Nitrogen dioxide Nitric oxide is a radish brown gas. It has pungent smell.

It is heavier than air and readily soluble in water.

It affects lung function and increases respiratory symptoms such as bronchitis and cough.

Methane (CH4)

Methane is produced from decay of dead plants in the absence of air.

It arises in air usually from marshes, swaps and rice-paddy fields.

Methane reacts with other compounds in the presence of sunlight and forms toxic compounds.

It also absorbs heat and causes global warming.

Chlorofluorocarbons (CFCs)

Chlorofluorocarbons are compounds containing chlorine, fluorine and carbons.

CFCs are usually released from refrigerators air conditioner and aerosol sprays.

CFCs destroy the ozone layer in stratosphere that blocks ultraviolet radiations.

CFCs can cause skin allergy and affect liver, kidney and nervous system.

Lead Compounds 7

Lead particles are naturally toxic and directly come from combustion of leaded fuels in vehicles and industries.

Lead can also come from lead based paints.

Lead particles attack the brain and central nervous system and causes coma especially in children.

Lead compounds also causes mental retardation.

Ozone (O3)

Ozone is a triatomic oxygen molecule. Although, it is good in stratosphere as it absorbs UV radiations in stratosphere, but it is bad at ground level as it causes various problems for all people suffering from lung diseases such asthma. It also causes irritation in eyes.

Sources of Air pollutants

Air containing harmful substances is called polluted air.

Air pollution arises both from natural sources and human activities.

Natural sources Some of the natural sources of air pollution are:

• Forest fires

• Volcano

• Dust particles

• Living things

• Electrical discharge

Forest fires produce carbon monoxide, carbon dioxide and heat.

Volcano produces poisonous gases such as carbon dioxide, sulphur dioxide, carbon monoxide and hydrochloric acid.

Livestock (i.e. cows) Insects (i.e. termites) also produced large quantity of methane, ammonia and carbon dioxide.

Electrical discharge during thunderstorm produces large quantity of nitrogen oxides.

Human activities

Human activities based sources of air pollution include:

• Motor vehicles

• Power generation plants

• Waste incineration

• Household source

• Ozone

Most of air pollution (≈ 50 %) arises from combustion of fossil fuels from cars and heavy duty motor vehicles.

Power generation plants burn coal and oil and release poisonous gases.

Incineration of both agricultural and human waste release carbon monoxides, nitrogen oxides and sulphur oxides.

Household source such refrigerators, air conditioner and aerosol sprays use chlorofluorocarbons as refrigerants, air conditioning units and propellants, respectively. CFCs are not environmental friendly and continuously release into air during use of these appliances.

Ozone is produced when electrical current is passed through oxygen usually in photocopy machine television, microwave oven and other electrical equipment.

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