What is Pollution?

The excess accumulation of pollutants or undesirable alterations in the environment and its resources such as air, water, and land can be referred to as pollution. Pollution affects the components of the environment. Pollution is considered a global issue as it is showing harmful effects worldwide. Metropolitan cities are more impacted by pollution than countryside or villages.

What are the different types of pollution?

Pollution is classified into different types based on the affected part of the environment. These are air, water, sound, and soil pollution. Radioactive and thermal pollution are the rarest types of pollution, but these pollutions show deadlier effects than those mentioned before. All kinds of pollution are mainly caused due to the constant overuse of resources. 

Air pollution

The properties of the air change by the contamination of undesirable substances and adversely affect all living creatures; such a condition is called air pollution. This pollution changes the physical, chemical, and biological compositions of the air. Approximately seven million deaths occur due to air pollution. The natural environment is damaged due to poor air quality. Various regulations have been implemented nationally and internationally to avoid the impact of air pollution. 

Air pollutants

The pollutants that cause air pollution and degrade air quality can be distinguished into two types based on their origin. They are as follows:

• Natural: These types of pollutants occur as a byproduct of natural processes. Such pollutants include dust, pollen grains, forest fire debris, and ash produced from volcanoes. 
• Anthropogenic (human-made): These types of pollutants originate from human activities. Examples of such pollutants include the emission from automobiles, industries, and power plants.

List and nature of air pollutants

Air quality is considered good when it ranges between 0–50. The rise in the air quality index to more than 100 indicates degradation in air quality and signifies increased pollutants in the air. The air consists of various pollutants. Pollutants cause asthma and different lung disorders in humans. The different types of pollutants are listed below.

Primary air pollutants

• Particulate matter: The substances, either in solid or liquid states, that remain suspended in air are particulate matter. These tiny substances can alter the physical and chemical properties of air. Examples of particulate matter are dust, smoke, pollens, and soot. 
• Carbon monoxide (CO): Carbon monoxide is formed when incomplete combustion occurs in fossil fuel. It is poisonous and emitted by automobiles and industries. 
• Sulfur dioxide (SO₂): Sulfur dioxide is produced by oil refineries and ore smelters. The accumulation of these gases in the atmosphere causes acid rain and various respiratory disorders in organisms. 
• Nitrogen oxide (NO and NO₂): When the combustion of fossil fuels occurs at a high temperature, it releases nitrogen oxide. It also causes acid rain and is harmful to the development of the plant. In humans, it contributes to skin disorders and chronic heart and lung diseases.

Secondary air pollutants

Smog formation occurs when ozone and peroxyacetyl nitrate (PAN) combine in the presence of UV rays. The brown air and grey air in metropolitan cities are the result of photochemical smog. The photochemical smog is formed by the combination of primary and secondary pollutants. The secondary air pollutants that form photochemical smog are as follows:

• Phenol: Phenol originates in the air when primary pollutants go through photochemical reactions. It causes kidney damage and dysfunction of the spleen and lungs. 
• Aldehyde: It forms when incomplete combustion occurs in fossil fuels and biomass. These secondary pollutants can irritate the digestive and respiratory tract. 
• PAN: It is produced from the power plants and causes damage to the chloroplast, and reduces the photosynthetic efficiency in plants. It is also responsible for irritation of the eyes in humans. 
• HNO₃: Nitric acid is formed from the oxidation of the primary pollutant that is nitric oxide. It causes acid rain. 
• H₂SO₄: The combination of sulfur dioxide and water vapor in the atmosphere results in sulfuric acid. It affects the environment in the form of acid rain.

Effects of Air pollution

Organisms face various problems when they are exposed to air pollution. It affects all living organisms, including their habitat. The effects are as follows:

• Respiratory infections and cardiovascular diseases: As air quality decreases, the heart attack rate in humans increases. It also leads to asthma, bronchitis, allergies, sinus, stroke, and lung cancer inhaling contaminated air. 
• Acid rain: The production of sulfur dioxide and nitrogen oxide causes acid rain, which inhibits the growth of plants, damages buildings, and causes skin disorders in humans. It also increases the acid level of water resources.
• Ozone depletion: The pollutants such as chlorofluorocarbons and halogens cause depletion of the ozone layer. The ozone depletion increases the penetration of UV rays. These radiations are harmful to organisms.
• Effects on wildlife: Animals are also facing the same health-related problems just like humans. Congenital disabilities, extinction of species, and mutation in genes are the results of poor air quality.
• Global climate change: The emission of greenhouse gases such as carbon dioxide, methane, and nitrogen oxide from the industries lead to the greenhouse effect. This condition traps the sunlight and increases the temperature of the Earth. This situation gives rise to natural calamities.

Control measures for Air pollution

Air pollution can be controlled by selecting a suitable fuel that has less sulfur. The industries should modify their emissions by using filtration techniques. The vehicles should have efficient engines to reduce unburnt hydrocarbons. The lead-free petrol causes less toxic contamination. Switching fossil fuels to solar energy, wind power, and electrical energy will reduce toxic gases in the environment. More use of renewable energy decreases the pollutants in the atmosphere.

Some technical procedures to reduce pollutants in the air are listed below:

• Arresters: The pollutants such as particulate matter can be set apart from the contaminated air by arresters.
• Scrubbers: It is used to separate gaseous pollutants from the air. These scrubbers expose the gaseous substances to liquid. It helps in absorbing the harmful pollutants in the emitted air.
• Cyclone and trajectory separator: This technique is used to filter the dust particles from the emission. This separation is done using centrifugal force. 
• Filters: Filters conduct the regulation of fine pollutants. HEPA (high-efficiency particulate air) filtrate and cartridge filters are examples of filters that purify the emission of industries. 
• Electrostatic precipitator (EPS): This technique removes the dust, soot, and ash from the industrial emission. Static electricity operates this filter. 

• Absorption and adsorption: Gaseous pollutants are removed through absorption using absorbent material. Adsorption separates toxic materials using a large solid surface, which cannot be separated by absorption. 

Common Mistakes

Students might get confused between primary and secondary air pollutants. Both of these are Students might get confused between primary and secondary air pollutants. Both of these are anthropogenic pollutants that alter the air quality. Primary air pollutants convert into secondary air pollutants due to the chemical reactions between them in the atmosphere. Primary pollutants are directly emitted from the industries. Environmental temperature and UV rays play a significant role in converting primary pollutants into secondary pollutants. 

Context and Applications

• Bachelors of Science in Biology 
• Bachelors of Science in Environmental Science
• Bachelors of Science in Chemistry
• Masters of Science in Chemistry
• Masters of Science in Environmental Science 
• Environmental Engineering  

Related Concepts

• Water Pollution
• Soil Pollution
• Sound Pollution
• Greenhouse Effect and Global Warming

Practice Problems 

Q1: An example of a secondary pollutant is __________.

(a) carbon monoxide

(b) carbon dioxide

(c) aldehyde

(d) dust

Correct option: (c)

Q2: One of the most common side effects of air pollution is __________.

(a) fungal infection

(b) asthma

(c) acidity

(d) diabetes

Correct option: (b)

Q3: Which one of the following does NOT cause acid rain?

(a) Sulfur dioxide

(b) Nitric acid

(c) Nitrogen oxide

(d) Peroxide

Correct option: (d)

Q4: The air quality mainly decreases due to the _________________.

(a) deposition of air pollutants

(b) utilization of wind power

(c) utilization of solar energy

(d) afforestation

Correct option: (a)

Q5: The major gas involved in ozone depletion is _____________.

(a) copper dioxide

(b) ammonium nitrate

(c) chlorine

(d) chlorofluorocarbon

Correct option: (d)