Air Pollution: Causes, Types, and Sources

Air pollution is the presence of harmful substances in the atmosphere due to human activities.
These pollutants, in higher concentrations, can cause damage to plant, animal, and human life.
Air pollutants are categorized based on their physical state and origin. The primary types of air
pollutants include particulates, gases, and aerosols.

Types of Air Pollutants

1. Particulates

Particulates refer to both solid and liquid particles suspended in the air. These particles,
depending on their size, can have harmful effects on health and the environment. They include:

 Suspended Particulate Matter (SPM): Solid and liquid particles small enough to
remain airborne and not settle due to gravity.
 Respirable Particulate Matter (RPM) or PM10: Particles smaller than 10 micrometers
(µ), which can penetrate the respiratory tract and enter the lungs. Special attention is
given to RPM because of its potential harm to human health.
 Dust: Formed from the breakdown of larger particles during mechanical operations like
grinding or sawing. Dust particles typically range from 10 to 10,000 µ.
 Smoke: Results from incomplete combustion of organic matter like wood, coal, and
tobacco. Smoke particles are usually between 0.5 to 1 µ in size.
 Fumes: Formed from the condensation of vapors of solid materials during processes like
calcination and distillation. Fume particles range from 0.03 to 0.3 µ.
 Fly Ash: The inorganic residue left after burning coal, fly ash consists of non-
combustible particles contained in combustion gases. Its particle size varies between 1.0
to 1,000 µ.

2. Liquid Particulates

Liquid particulates are fine droplets suspended in the air, often resulting from vapor
condensation or the atomization of liquids.

 Spray: Produced by the atomization of liquids, such as in the use of insecticides. Spray
particles are typically less than 10 µ.
 Mist: Formed from the condensation of vaporized liquids. Mists are generally smaller
than 10 µ. When mist concentration is high enough to obscure visibility, it is called fog.

3. Aerosols

Aerosols are particulates suspended in a gaseous medium. They can be solid or liquid, and they
include dust, smoke, mist, and fog.
4. Gases

Gaseous pollutants are further classified into inorganic and organic gases. Examples include:

 Inorganic Gases: SO2 (Sulfur Dioxide), NOx (Nitrogen Oxides), CO (Carbon

Monoxide), CO2 (Carbon Dioxide), etc.
 Organic Gases: CH4 (Methane), H2S (Hydrogen Sulfide), O3 (Ozone), etc.

Types of Pollutants Based on Origin

1. Primary Pollutants

Primary pollutants are directly emitted into the atmosphere from their source. Examples include:

 SO2: Sulfur Dioxide from burning fossil fuels.

 CO: Carbon Monoxide from combustion engines.
 CO2: Carbon Dioxide from fossil fuel combustion.

2. Secondary Pollutants

Secondary pollutants form as a result of chemical or photochemical reactions in the atmosphere

between primary pollutants. Examples include:

 H2SO4: Sulfuric Acid, formed from SO2.

 O3: Ozone, formed from a reaction between nitrogen oxides and sunlight.
 PAN: Peroxyacetyl Nitrate, a result of photochemical reactions.

Pollutants Based on Nature and Creation

1. Natural Pollution

Natural pollutants are substances that occur in nature. These include:

 Oil and natural gas: Emissions in river waters and natural deposits.
 Mercury and lead: Occurrence in water bodies and soils.
 Sulfur: Emissions from volcanic activity.

2. Man-made Pollution

Man-made pollution refers to pollutants that result from human activities, such as:

 Wastes from factories

  Exhaust from automobiles
 Pesticides from farms
 Smoke from chimneys

3. Biodegradable Pollutants

Biodegradable pollutants are those that can be decomposed naturally. Examples include kitchen
waste, organic matter, and plant material.

4. Non-Biodegradable Pollutants

Non-biodegradable pollutants take longer to break down, or do not degrade at all. These include:

 Aluminum cans
 Mercuric salts
 Plastics
 Long-chain phenolic compounds

Sources of Air Pollution

1. Stationary Combustion Sources

These sources involve the burning of fuels in industries and residential establishments. Common
pollutants from stationary combustion include:

 Carbon Oxides (CO, CO2)

 Sulfur Oxides (SO2, SO3)
 Nitrogen Oxides (NO, NO2)
 Hydrocarbons: Produced naturally from decomposition of organic matter.

2. Mobile Combustion Sources

Mobile sources include vehicles, aircraft, and locomotives. The pollutants emitted by these
sources are:

 Gaseous Pollutants: CO, HC (Hydrocarbons), NO2.

 Particulate Lead: Found in petroleum-based fuels used in automobiles.
 Aerosols: Chemicals released into the atmosphere as vapors or fine mist.

3. Industrial Processing and Other Sources

 Gaseous Pollutants: CO2, SO2, NO2.

 CFM (Chlorofluorocarbons): Used as propellants and refrigerants, contributing to
ozone depletion.
  Particulates: Metal dust, fly ash, cotton dust, radioactive substances, and harmful metals
like As, Be, Cd, Ge.
 Plastic Processing: Burning plastics produces toxic substances like PCBs
(Polychlorinated Biphenyls).

4. Agricultural and Biological Sources

 Pollen and Microbes: Cause allergies and respiratory diseases.

 Tobacco Smoke: Contains harmful hydrocarbons.

5. Secondary Air Pollutants

Secondary pollutants form from primary pollutants through photochemical reactions. Examples
include:

 Photochemical Smog
 Acid Rain: Formed when sulfur dioxide reacts with water vapor to form sulfuric acid,
which can lead to environmental damage.

Effects of Air Pollution

Global Effects of Air Pollution:

1. Acid Rain: Acid rain occurs when atmospheric gases such as carbon dioxide (CO2),
nitrogen oxides (NOx), and sulfur dioxide (SO2) react with water vapor to form acids
like sulfuric acid (H2SO4), nitric acid (HNO3), and carbonic acid (H2CO3). These acids
can harm aquatic life, building materials, and soil. Acid rain lowers the pH of soil, which
affects plant nutrients and increases the concentration of toxic elements like cadmium and
zinc. It also hampers the biodegradation process in water bodies by lowering the pH.

In the case of the Taj Mahal, acid rain caused by emissions from the Mathura refinery
and other industrial sources has led to yellowing of the marble structure. To control acid
rain, it is essential to reduce emissions of sulfur dioxide and nitrogen oxides by using
cleaner technologies, such as desulfurization and fuel gas treatment processes.

2. Greenhouse Effect: The greenhouse effect is caused by gases like CO2, methane, and
CFCs that trap heat within the Earth’s atmosphere. These gases allow some radiation to
reach Earth but prevent heat from escaping back into space. Human activities such as
deforestation and the combustion of fossil fuels release significant amounts of CO2,
contributing to global warming. This leads to rising global temperatures, melting of ice
caps, and a rise in sea levels. A 1°C rise in temperature could significantly affect
agricultural productivity, especially in regions near the equator. The greenhouse effect is
linked to increased cloud formation and rainfall, which may aid reforestation efforts but
can also contribute to more extreme weather events.
 3. Ozone Depletion: The ozone layer in the stratosphere is crucial for protecting life on
Earth from harmful ultraviolet (UV) radiation. Chlorofluorocarbons (CFCs) and other
chemicals release chlorine, which breaks down ozone molecules, leading to the thinning
of the ozone layer. This depletion increases UV radiation, which can cause skin cancer,
damage plants, and reduce photosynthetic rates. The ban on CFCs has helped reduce
ozone depletion, but further measures are needed to protect the ozone layer.

4. Photochemical Smog: Photochemical smog occurs when pollutants like nitrogen dioxide
(NO2) interact with sunlight, forming secondary pollutants such as ozone and organic
peroxides. This is more common on sunny days with low winds and temperature
inversions. Smog leads to poor visibility, eye irritation, and damage to plants. In addition
to NO2, hydrocarbons and other organic compounds contribute to the formation of smog.
Sulfur dioxide (SO2) also plays a role in smog formation and can lead to acid rain and
corrosion of materials.

5. Inversion and Trapping: Under normal conditions, air temperature decreases as altitude
increases. However, during an inversion, a layer of cold air is trapped beneath warmer
air, preventing the vertical mixing of air. This leads to the accumulation of pollutants near
the surface, creating hazardous conditions with poor visibility and higher pollutant
concentrations. This is especially dangerous when pollutants, like smoke or industrial
emissions, are trapped in the inversion layer, leading to health problems and
environmental damage.

Effects on Human Health:

1. Respiratory Diseases: Air pollution causes various respiratory issues, including asthma,
bronchitis, emphysema, and lung cancer. These diseases occur when inhaled pollutants
damage the lungs and airways, reducing oxygen flow and causing breathing difficulties.

2. Toxic Effects: Fly ash, metal dust, and particulate matter can cause headaches, dizziness,
insomnia, anemia, and other health problems. Chronic exposure to air pollutants can also
lead to miscarriage in pregnant women.
 3. Sulfur Dioxide (SO2): SO2 is a major air pollutant that can cause irritation to the eyes,
throat, and respiratory system. Long-term exposure can lead to severe lung and heart
problems.

4. Carbon Monoxide (CO) and Nitrogen Oxides (NOx): These gases reduce the oxygen-
carrying capacity of blood by binding to hemoglobin, leading to reduced oxygen levels in
tissues and organs. Chronic exposure can result in cardiovascular and neurological
damage.

5. Lead (Pb): Lead, primarily from automobile exhaust, accumulates in the human body
and causes a range of health problems, including developmental delays, reduced IQ, and
anemia. It also affects the blood-forming and respiratory systems.

6. Impact on Plants and Agriculture: Air pollutants like SO2 and particulate matter can
damage plants by affecting photosynthesis and causing chlorosis (yellowing of leaves).
This can result in reduced crop yields and adversely affect food production.

Overall, air pollution poses significant environmental and health risks. Efforts to reduce
emissions from industrial, agricultural, and transportation sources are critical to mitigating these
adverse effects and protecting both human health and the environment.