Tag Archives: What are air pollution causes?

Air Pollution Control measures – Top 9 Air pollution control devices

It’s the need of the hour to take measures for air pollution control and prevention since millions of Indians are constantly exposed to polluted air. For instance, they breathe up to 25 micrograms/cubic metre of the lethal, microscopic pollutant PM 2.5 on a 24-hour average. This is well above the World Health Organization’s (WHO) limit of 10 micrograms/cubic metre.

To begin with, let’s first look at the causes of air pollution.

Air Pollution Causes

Industrialisation and urbanisation have technologically upgraded our lives. But, they had some negative byproducts like degradation of the environment, air pollution etc. The air quality index in most of the metropolitan cities is alarmingly high. Let’s have a quick glimpse at some of the major causes of air pollution:

  • Emissions from Industries and Power Plants
  • Construction and Demolition
  • Mining
  • Vehicular Emissions
  • Burning of waste and stubble

If you wish to dig deeper into the causes of air pollution, please check our blog Air Pollution Causes – A Comprehensive Guide

 If we can prevent the release of toxic gases by removing them from the flue gas stream or converting it into harmless compounds, we can control air pollution to a great extent. Similarly, if we can collect the dust and dispose of it properly, we can avoid particulate pollution. 

Also read: Air Pollution Effects and Causes – A complete overview

Air Pollution Control Measures and Devices

Air pollution control equipment refers to devices and facilities used in industries to control and prevent the emission of particulate matter and toxic gases. Fans or blowers direct industrial emissions and pollutants into air pollution control equipment and systems. Subsequently, they eliminate or reduce air pollutants using one or more of the following procedures:

  • Combustion i.e., destroying the pollutant.
  • Conversion i.e., chemical conversion of the pollutant to a less harmful compound.
  • Collection i.e., removal of the pollutant from stack gas before releasing into the atmosphere.

Having understood the basic mechanism of pollution control devices, let’s have a closer look at each of the devices.


  • Scrubbers are the most widely used air pollution control devices in production and manufacturing facilities.
  • They use a physical process called scrubbing to remove particulates and gases from industrial emissions before releasing them into the atmosphere.
  • Scrubbers are of two types: dry scrubbers and wet scrubbers.
Industrial air scrubber- Air pollution control device
Industrial air scrubber- Air pollution control device

Dry Scrubbers

  • Dry scrubbers inject dry, neutralising chemical agents such as sodium bicarbonate into the exhaust stream.
  • Subsequently, the gaseous pollutants undergo a chemical reaction that either neutralises or transforms the pollutants into harmless compounds.
  • When the chemical reaction is finished, the expended agents are collected and removed from the cleansed emission gas by filters within the scrubber chamber.
  • Dry scrubbers are typically used to neutralise acid gas in oil refineries, wastewater treatment plants and metallurgical plants

Wet Scrubbers

  • Also known as wet adsorption scrubbers or wet collectors.
  • Wet scrubbers capture and remove water-soluble gas and particulate emissions from industrial emissions using liquid solutions—typically water.
  • A gas stream is passed through a liquid solution or a liquid solution is injected into a gas stream in the wet scrubbing process.
  • The solution on coming in contact with the gas stream absorbs the pollutant.
  • This process eliminates the pollutants from the gas and clean gas is released into the atmosphere.
  • The types of wet scrubbers include venturi, packed bed and bubbling scrubbers.
  • Flue gas desulphurisation employs wet scrubbing with a slurry of alkaline sorbent, usually limestone or lime.

Air Filters

  • Air filters are air pollution control systems that use a certain type of filtration media such as fabric, sintered metal, ceramic, etc.
  • They capture and remove dry particles and contaminants from air passing through them, such as dust, pollen, microorganisms, chemicals, and so on.
  • These devices remove pollutants from exhaust air and enhance the air quality in residential, commercial, and industrial buildings.
  • There are various types of air filters available for industrial purposes, including HEPA filters, fabric filters, and cartridge dust collectors.

Bag Filters

  • Also known as baghouses or fabric filters.
  • The bag filter uses cylindrical fabric bags to trap and remove dust and other pollutants in the air.
  • Particulates aggregate on the filter’s surface as the polluted air travels through a baghouse.
  • This particle buildup improves the filter’s efficiency by reducing the surface area of openings.
  • This allows even smaller particles to be collected.
  • Fabric filters usually offer collection efficiencies exceeding 99.9%.
  • These filters find wide applications in industrial processes, such as power plants, metal processing centres, and foundries.

Periodic cleaning is crucial due to continuous dust accumulation and the associated pressure differential. Baghouses use a variety of methods to remove the accumulation from the filter bags, including:

  • Shaking the filter bags.
  • Increasing the air pressure on the bag such that the bag collapses or deforms and dislodges the accumulated dust. 

Particulates fall from the filter cloth to the bottom of the baghouse enclosure into a collection hopper for processing and disposal.

Bag Filter
Bag Filter

HEPA Filters

  • Also known as high-efficiency particulate air filters.
  • These filters use fibreglass filter mats to physically remove airborne particulates like pollen, smoke, dust, and bio-contaminants from the workspace.
  • Fibres in fibreglass filter mats typically range in size from 0.5 to 2 metres.
  • According to the US Department of Energy (DOE), a filtering system maintaining a 99.97% efficiency for collecting particulates more than or equal to 0.3 m in diameter can be designated as a HEPA filter.
  • Widely used in pharmaceuticals, computer and electronics manufacturing, aerospace applications and nuclear power plants.
HEPA Air filters
HEPA Air filters

Cyclones – Air pollution control measures

  • Cyclones, also known as cyclone dust collectors, are air pollution control equipment that collects and remove particulates using centrifugal force.
  • When gas streams enter a cyclone, they spiral around the cylindrical chamber.
  • The centrifugal force experienced by the spinning gas stream is considerably higher than gravity.
  • Hence the centrifugal force throws the larger particles against the chamber wall, slowing their inertia and forcing them to fall into the collection hopper below.
  • The treated gas streams proceed upward and out of the cyclone.

The separation factor of a cyclone is defined as the ratio of centrifugal force to gravitational force. The higher the separation factor, the better is the cyclone performance. 

Electrostatic Precipitators

  • Electrostatic precipitators (ESPs), like air filters and cyclones, collect and remove particulate matter, such as dust, from industrial emissions and exhaust.
  • ESPs establish a large static electrical potential difference between charging electrodes and collecting plates, using transformers.
  • At very high DC voltages of the order of 50 kV a corona discharge adjacent to the negative electrode.
  • This creates an electric field between the positively charged collecting surface and the emitter.
  • Consequently, the electric field ionises the dust particles as the particle-laden gas flows upwards.
  • The electrostatic force directs ionised particles towards the grounded plates.
  • Particulate Matter deposit is periodically removed from the collecting plates and dumped in a collection hopper below.
  • Wet ESPs uses water to rinse off the dust particles.
  • ESPs’ efficiency reaches 99% since they have several collection plates.
  • The Deutsch equation gives the collection efficiency of an ESP.
Electrostatic Precipitator (ESP)
Electrostatic Precipitator (ESP)

Mist Collectors

  • Also known as mist or moisture eliminator filters.
  • These air pollution control devices remove moisture and vapour from gas streams, such as smoke, oil, mist, etc.
  • Fine mesh-like filters separate liquid droplets from gas and collect them in a separate chamber.
  • Finds wide applications in food and chemical processing, desalination plants, paper and pulp mills etc.
  • For submicron liquid particles, mist collectors have exceptional filtering efficiencies, with some collectors offering 99.9% efficiency for particles 0.3 μm in diameter.

Shall we wrap up?

Conclusion – Air pollution control Measures

In this blog, we saw some air pollution control measures and For the effective control of air pollution, the National Green Tribunal and the pollution control boards should strictly monitor and ensure the usage of these devices in the industries. We are still in need of green technologies like solar cells for power generation instead of coal-fired power stations, clean coal technologies, electric vehicles etc. Together, it is possible to reduce and control air pollution for a green future.

What are air pollutants? | Types,sources and effects of air pollution

Most of the times you can’t see it or smell it, but air pollutants kill. As the level of air pollutants in our atmosphere are rising at an alarming rate we must be aware of them. In the previous blogs, we had described the causes and effects of air pollution. Today let’s dive deep into various air pollutants.

Let’s get started.

What are Air Pollutants ?

Air pollutants are substances that can contaminate the air and are hazardous to human and other living species’ health. They can be either primary pollutants like dust, smoke, ammonia etc that are emitted directly from their sources or secondary pollutants.

Secondary Pollutants are formed in the atmosphere by chemical reactions between primary pollutants and the other atmospheric constituents. The common examples include ozone, sulphur trioxide, Peroxy Acetyl Nitrate (PAN), ketones etc.

Air Pollutants Types

The Environmental Protection Agency regulates three types of pollutants:

  • Criteria air pollutants
  • Air Toxics
  • Greenhouse Gases

Criteria air pollutants

Criteria Air pollutants include Particulate matter (PM), photochemical oxidants (e.g., ozone), carbon monoxide, sulphur oxide, nitrogen oxide, and lead. They can have a significant impact on public health and wellbeing, the atmosphere and environment, and neighbouring structures.

Air Toxics

The term “air toxics” consists of a list of over 180 air pollutants such as organic chemicals, volatile organic compounds (VOCs), metals, metal compounds, solvents, mercury, arsenic, asbestos, and benzene etc. Even when existent in trace amounts and emitted by fewer sources than criteria pollutants, they have harmful health and environmental impacts.

Greenhouse Gases

Greenhouse gases (GHGs) are gases such as carbon dioxide, chlorofluorocarbons (CFCs), methane, and ozone. They can harm human health. In addition, they contribute to the acceleration of the greenhouse effect on Earth and the resulting impact on global climate.

Major Air Pollutants – Sources and Effects

The sources of air pollutants can be natural or anthropogenic. Check out our previous blog Air Pollution Causes – A Comprehensive Guide for detailed information on various sources of pollutants. Let me describe each of the air pollutants in detail.

Nitrogen Oxides

  • Nitrogen oxides, notably nitrogen dioxide, are ejected from high-temperature combustion and created by electric discharge during thunderstorms.
  • This reddish-brown poisonous gas has a distinctive sharp, biting stench.
  • They appear as a brown haze above cities or as a plume downwind.
  • High levels of NO2 can irritate and inflame the lining of your airways.
  • This results in asthma or COPD flare-up, as well as symptoms like coughing and difficulty in breathing.

Carbon Monoxide

  • CO is a poisonous gas that is colourless and odourless.
  • It causes a smog-like buildup in the air.
  • CO reacts with haemoglobin in the blood to generate carboxyhaemoglobin when inhaled.
  • CO has a 200-fold higher affinity for haemoglobin than oxygen.
  • The tissues are deprived of oxygen as a result of this situation.
  • When carboxyhaemoglobin saturation levels are about 20%, it affects the heart and destroys tissues by preventing oxygen from reaching them.
  • This has been related to a variety of pulmonary ailments as well as environmental problems.

Sulphur Oxides

  • Sulphur compounds are common in coal and petroleum, and their combustion produces sulphur dioxide.
  • Further oxidation of SO2, usually in the presence of a catalyst like NO2, produces H2SO4, which results in acid rain.
  • It also arises from chemical, paper, and fuel manufacturing plants.
  • People with asthma or emphysema may find it more difficult to breathe after being exposed to sulphur dioxide.
  • It can also irritate the eyes, noses, and throats of people exposed to it.
  • Sulphur dioxide can injure trees and crops, cause structural damage, and impair people’s ability to see over long distances.
sulphur dioxide Pollution- Petroleum refinery
sulphur dioxide Pollution- Petroleum refinery

Volatile Organic Compounds

  • Compounds with high vapour pressure and low water solubility are known as volatile organic compounds.
  • VOCs are man-made substances that are utilised and created in the production of paints, medicines, and refrigerants.
  • Industrial solvents, such as trichloroethylene; fuel oxygenates, such as methyl tert-butyl ether (MTBE); or chlorination by-products, such as chloroform, are examples of VOCs.
  • The aromatic non-methane VOCs such as benzene, toluene, and xylene are suspected carcinogens. They can cause leukaemia in those who are exposed to them for a long time. 

Carbon Dioxide

  • The major greenhouse gas emitted by human activity is carbon dioxide.
  • Fossil fuel combustion, industrial emissions, wildfire etc. are the main sources of CO2 emissions.
  • It traps the solar radiations reflecting from Earth and increases the average temperature of Earth.
  • Due to its contribution to the greenhouse effect and climate change, it is often called the worst climate pollutant
  • It reaches the Earth’s surface as acid rain.

Particulate Matter

Fine particles, also known as atmospheric particulate matter, are microscopic solid or liquid particles suspended in a gas. Volcanoes, dust storms, forest and grassland fires, and sea spray are all sources of particulate matter. Particulate pollution comprises the following:

PM10:  inhalable particles with a diameter of 10 micrometres or less.

Can you imagine how small is 2.5 micrometre? Consider a single hair on your head. The average human hair is 70 micrometres in diameter, which is 30 times the size of the smallest microscopic particle. I hope this makes it clear how they penetrate deep into our lungs.


Aerosols are produced by human activities such as the combustion of fossil fuels in automobiles, power plants, and numerous industrial processes. Anthropogenic aerosols, or those produced by human activity, currently make up around 10% of our atmosphere. Increased fine particle levels in the air have been related to health risks such as heart disease.


  • CFCs are gases emitted by air conditioners, freezers, aerosol sprays, and other similar devices.
  • CFCs reach the stratosphere after being released into the atmosphere.
  • They interact with other gases here, causing harm to the ozone layer.
  • This allows UV radiation to reach the earth’s surface, which are hazardous.
  • This can result in skin cancer, eye problems etc.
  • As a result, they are currently restricted from usage in products.
Air Conditioners - Source of Chlorofluorocarbons
Air Conditioners – Source of Chlorofluorocarbons


Ammonia is a gas that is emitted primarily by agricultural waste. As a precursor to foodstuffs and fertilisers, it contributes considerably to the nutritional demands of terrestrial species. It is both corrosive and toxic, despite its widespread use. Ammonia combines with nitrogen and sulphur oxides in the atmosphere to generate secondary pollutants.


  • Carbon monoxide (CO), methane (CH4), or other volatile organic compounds (VOCs) are oxidised in the presence of nitrogen oxides (NOx) and sunlight to form ozone.
  • As a result, ozone is most abundant in the summer.
  • Ground-level ozone is a primary component of photochemical smog.
  • It is a significant health hazard connected to breathing issues, asthma, deterioration of lung function, and respiratory disorders.
  • People with asthma may experience more frequent asthma attacks as a result of ozone exposure, as well as sore throats, coughing, and breathing difficulties.
  • It could potentially result in premature death. Plants and crops can be harmed by ozone.


Lead is a neurotoxin. It was earlier used in petrol as an antiknocking agent. The fine particles emitted through automobile exhausts reaches the lungs and settles down there. At higher levels in the blood, it interferes with haemoglobin production. This results in oxygen starvation and anaemia. Higher levels lead to behavioural disorders.


Cigarette smoking is the main contributor to cadmium in the atmosphere. It can cause hypertension, cardiovascular diseases, kidney and liver damage.

 Cigarette Smoke - Source of Cadmium
Cigarette Smoke – Source of Cadmium


Finely divided nickel can react with carbon monoxide and forms Nickel Carbonyl. It is also formed in cigarette smoke. When it reaches our lungs it breaks down and deposits finely divided nickel inside our lungs. This is the main cause of lung cancer.


Mercury enters the aquatic systems and soil from the atmosphere through acid rain. The adverse effects of mercury poisoning include chromosomal aberrations, neurological damage and even death. It can damage the cerebellum and cortex of brain by penetrating the membranes separating bloodstream from the brain.

So, we had taken a quick trip understanding all the major air pollutants. In case of any doubts, feel free to ask in the comments.

Happy Learning!