Air Pollutants: Examples, Types, Sources and Effects

What are Air Pollutants?

Air pollutants are those substances emitted into the air that can cause adverse effects on the ecosystem and the organisms inhabiting it. They cause harm to humans and the environment and exist as solid particles, gases, or liquid droplets. These pollutants can be from a natural or man-made source of pollution.

Air pollutants, because of their hazardous nature are monitored and controlled in many countries. For instance, these four air pollutants in India namely oxides of nitrogen (NOx), sulfur dioxide (SO2), respirate particulate (PM10), and suspended particulate matter (SPM) are now routinely monitored by India’s Central Pollution Control Board.

Air pollutants are substances that contaminate the air

Air pollutants are the elements of air pollution. This means that air pollution is the contamination of the environment (indoor and outdoor) by any physical, biological, or chemical agent that ends up altering the natural condition of the atmosphere. Air pollution causes respiratory diseases and other health conditions. According to WHO, almost all the population worldwide breathes air that exceeds the WHO guidelines limits containing high levels of pollutants. The data shows that low-income and middle-income countries suffer the highest exposure and as a result WHO is supporting countries to address air pollution.

There are several effects of air pollutants on human health, climate, and plants. Polluted air causes global warming and increases the risk of heart disease, respiratory infections, and lung cancer. Short-term and long-term exposure to these pollutants always results in health impacts in humans. Severe impacts are seen in ill people, and children, as well as elderly people, are also susceptible. An air pollutant can also enter through the plant’s stomata and destroy the chlorophyll of the plant. This stoma is what plants use for transpiration and are usually wide open during the day to facilitate photosynthesis. Therefore, as these pollutants destroy the chlorophyll in the chloroplast, photosynthesis is affected.

Air pollutants can be grouped into two types based on the process of their production. An air pollutant could be a primary pollutant or secondary pollutant. Primary pollutants are usually emitted directly and produced by processes as in ash from a volcanic eruption. Sulfur dioxide emitted from factories and carbon monoxide gas released from motor vehicles are also examples of primary air pollutants.

Secondary pollutants, on the other hand, are formed when primary pollutants react in the air. This means they are not emitted directly. A secondary pollutant example is the ground-level ozone. However, there are some pollutants that can be both primary and secondary because they can be emitted directly and can still be formed from other primary pollutants.

It is actually sad that air pollutants can find their way eventually to water when polluted air settles onto lakes and oceans. Also, during precipitation, air pollutants can get dissolved in water drops and acidify them which later falls as acid rain. This means that emitting toxic gases can indirectly pollute a water supply and it doesn’t just happen one day, it is the result of a cumulative effect over time. Hence, water pollution can take place too as a result of polluting the air. Once, our water bodies are contaminated, there is a lot of disadvantaged repercussion to this. Humans and other organisms need water for survival and it is a fact that supplying clean drinking water is one of the essential ecosystem services that many freshwater systems offer.

What are Criteria air pollutants?

There are six major air pollutants that their concentrations in the atmosphere are useful as indicators of overall air quality. In regard to this, The US Environmental protection Agency (EPA) has designated these pollutants as “criteria” pollutants. These criteria air pollutants are found all over the U.S and the EPA is required by the Clean Air Act to set National Ambient Air Quality Standards (NAAQS) for them.

However, regardless of the progress made in the last 30 years, there are still millions of people that live in counties with monitored concentration data that shows unhealthy air for one or more of these six EPA criteria air pollutants.

The six EPA criteria air pollutants

  1. Ground-level ozone
  2. Particulate matter
  3. Carbon monoxide
  4. Lead
  5. Sulfur dioxide
  6. Nitrogen dioxide

EPA refers to these named pollutants as criteria air pollutants because it regulates them. Hence, EPA develops environmentally-based and human-based criteria for setting permissible levels. The primary standards are the limits based on human health whereas secondary standards are the limits based on the prevention of environmental and property damage.

These six criteria air pollutants and their sources vary in the environment. For instance, in urban settings, the criteria air pollutants of main concern are sulfur dioxide, nitrogen dioxide, and carbon monoxide which are emitted directly from fossil fuels into the air. They are emitted from gasoline, fuel oil, and natural gas that is burned in automobiles, power plants, and other combustion sources.

The ozone is another of the gaseous criteria air pollutants. It is formed through complex chemical reactions in the atmosphere. The chemical reaction that forms ozone occurs between nitrogen dioxide and several volatile organic compounds like gasoline vapors. In fact, ozone and particulate matter are the most widespread health threats of the six criteria pollutants.

Sources of air pollutants

  1. Anthropogenic sources
  2. Natural sources

The substances that pollute the air definitely come from somewhere. Therefore, the various location, activities, or factors that are responsible for the presence of pollutants in the atmosphere are the sources of air pollutants. For instance, the most common source of carbon monoxide is vehicle exhaust. Air pollutants sources can be grouped into two main categories:

Anthropogenic sources

  • Landfills
  • Stationary sources
  • Military source
  • Agricultural and forestry management
  • Fumes from man-made products
  • Mining operations
  • Mobile sources

Anthropogenic sources are based on human activities and are mostly related to the burning of different sorts of fuels. Let’s look at some of these common anthropogenic sources of air pollutants:

Landfills

Landfill is an anthropogenic source of air pollutants

The waste deposited in landfills generates methane into the atmosphere. Even though methane is not toxic, it is highly flammable and can form explosive mixtures with air. In an enclosed space, methane as an asphyxiate can displace oxygen. Once, the oxygen concentration is lower than 19.5% by displacement, suffocation or asphyxia can take place.

Stationary sources

This involves the smokestacks of manufacturing industries, waste incinerators, furnaces, and power plants. Other types of fuel-burning heating devices are sources of air pollution as well.

Industrial emissions is an example of stationary source of pollution

These stationary sources emit large amounts of pollution from a single location which is referred to as point sources of pollution.

Military source

Weapons used by the military such as toxic gases, nuclear weapons, rocketry, and germ warfare are also a source of air pollutants.

Agricultural and forestry management

This is also a source of air pollution as chemicals, dust, and controlled burn practices are implemented in this field. Sometimes, in forest management, the controlled or prescribed technique is used. This technique is also used in farming, greenhouse gas abatement, or prairie restoration.

Fumes from man-made products

There are fumes that emit from manmade products that pollute the air. These fumes can be air pollutants and their sources are products like paints, aerosol sprays, hair spray, varnish, and other solvents.

Mining operations

During the process of mining, minerals that are below the earth are extracted using large equipment which releases chemicals and dust into the air. Thereby causing air pollution which is one of the reasons why there is deterioration in the health conditions of most of the workers as well as the neighboring residents.

Mobile sources

Vehicle exhaust is a source of Carbon monoxide

This source accounts for more than half of all the air pollution. According to the Environmental Protection Agency, the automobile is the primary mobile source of air pollution. Other mobile sources include buses, trucks, aircraft, trains, marine vessels, etc.

Natural sources

  • Radioactive decay
  • Dust
  • Digestion of food
  • Volcanoes
  • Forest fire/wildfires

This source is based on natural occurrences. These natural sources can be significant sometimes but do not normally create as many air pollution problems as anthropogenic sources.

Radioactive decay

The radioactive decay that takes place within the crust of the earth emits a colorless, odorless, and naturally occurring gas known as radon gas. This radioactive noble gas is formed from the decay of radium and is said to be a health hazard. The radon gas from this natural source can accumulate in building, most especially in confined spaces. It is said that after cigarette smoking, this gas is considered to be the second most frequent cause of lung cancer.

Dust

Dust is a natural source of air pollutants

Dust from large land areas with little or no vegetation can naturally pollute the atmosphere.

Digestion of food

Food digestion is a natural phenomenon but can also be one of the natural sources of air pollutants. As food is digested by animals such as cattle, methane is emitted into the atmosphere. Cattle, sheep, deer, buffalo, elk, camels, giraffes, goats, etc as ruminant animals, have a specialized digestive system that enables them to digest and break down food that cannot be easily digested by nonruminants like humans.

These animals have four stomach compartments where one of the compartments (rumen) allows them to store partially digested food and let the food ferment. These animals later regurgitate the food and complete the digestive process. The greenhouse gas, methane as well as other by-product is produced as the food (grass and other vegetation) ferments in the rumen. The cattle eventually expel the methane gas as they belch. Hence, as ruminant animals digest their food, they naturally contribute to the amount of methane gas in the atmosphere.

Volcanoes

Volcanoes contribute to air pollution

During volcanic activity, sulfur, ash particulates, and chlorine are produced and released into the atmosphere.

Forest fire/wildfires

Forest fire is a natural source of air pollutants

Wildfire contributes as a source of air pollution as smoke and carbon monoxide are emitted in the process of burning.

Types of air pollutants

  • Primary air pollutants
  • Secondary air pollutants

Primary air pollutants

Primary pollutants are usually emitted directly and are a result of a process. Typical examples of primary air pollutants are the ash from a volcanic eruption, Sulfur dioxide emitted from factories, and carbon monoxide gas released from motor vehicles.

Examples of primary air pollutants and their sources

  • Sulfur oxides (SOx) are emitted as a result of volcanoes and several industrial activities.
  • Nitrogen oxides (NOx) are produced from high-temperature combustion.
  • Carbon monoxide is emitted as a result of the incomplete combustion of fuel.
  • Carbon dioxide is a greenhouse gas produced from combustion.
  • Volatile organic compounds such as methane.
  • Particulate matter can occur from dust storms, fire, volcanoes, sea spray, and the burning of fossil fuel.
  • Persistent free radicals
  • Chlorofluorocarbons (CFCs) are emitted from products that are currently banned from use.
  • Toxic metals
  • Ammonia (NH3) is produced from agricultural processes.
  • Odors are emitted from industrial processes, sewage, and garbage.
  • Radioactive pollutants are produced from the radioactive decay of radon as well as from nuclear explosions, and war explosives.

Secondary air pollutants

The reaction of primary pollutants in the atmosphere produces secondary pollutants. This means secondary air pollutants are not emitted directly, e.g ground-level ozone which is one of the pollutants that make up photochemical smog.

These air pollutants types are caused by the reaction and intermingling of primary pollutants. Hence, smog is known as a secondary pollutant as it is created by the reactions of many primary pollutants. However, there are some pollutants that can be both primary and secondary because they can be emitted directly and can still be formed from other primary pollutants.

Examples of secondary air pollutants and their sources

  • Particulates are formed from the gaseous primary pollutants and compounds in photochemical smog.
  • Ground-level ozone (O3) is formed from the reaction of Nitrogen oxides and Volatile Organic Compounds (NOx and VOCs).
  • Peroxyacetyl nitrate PAN (C2H3NO5) is formed from nitrogen oxides and Volatile Organic Compounds (NOx and VOCs).

Other types of air pollutants

  • Hazardous air pollutants
  • Greenhouse gasses
  • Pollen and mold

Hazardous air pollutants

These are the pollutants that pose severe health risks. Sometimes, even in small amounts, they can be fatal. Common hazardous air pollutants types include lead, mercury, benzene, dioxins, etc, and about 200 of these types of air pollutants are regulated by law. These pollutants are usually released during incinerating, coal/gas combustion, or are found in gasoline such as benzene.

  • EPA classifies benzene as a carcinogen and this pollutant is known to cause skin, eye, and lung irritation in short term as well as blood disorders in long term.
  • Dioxins are present in small amounts in the air and are known to affect the liver in short term. In long term, it can harm the nervous, immune, reproductive, and endocrine systems.
  • Mercury can attack the central nervous system.
  • Lead in large amounts tends to damage the kidneys and brains of children. A child’s IQ and ability to learn can be affected even by minimal exposure to lead.
  • Polycyclic aromatic hydrocarbons (PAHs) are another group of toxic compounds. They are by-products of wildfire smoke and traffic exhaust. They are cancerous and tend to cause lung irritation, liver issues, eye irritation, and blood issues when in large amounts. A study conducted showed that the children of the pregnant mothers that were exposed to PAHs exhibited slower brain-processing speeds and more conspicuous symptoms of ADHD (attention deficit hyperactivity disorder).

Greenhouse gases

These air pollutants types are gases that trap the earth’s heat in the atmosphere which leads to warmer temperatures. As the planet warms up, climate change (see causes of climate change) takes place which results in rising sea levels, heat-related deaths, more extreme weather, and an increase in the transmission of infectious disease (see the effects of climate change on food security).

Greenhouse gases include fluorinated gases which are synthetic and other gases like carbon dioxide, methane, nitrous oxide, and water vapor that occur naturally. Methane is released from natural and industrial sources and carbon dioxide is released during the combustion of fossil fuels. A larger amount of carbon dioxide is emitted compared to methane but methane is significantly more potent and destructive.

The hydrofluorocarbons (HFCs) are far more powerful than carbon dioxide in their ability to trap heat. As a result, more than 140 countries in October 2016 reached an agreement to reduce the use of HFCs which are found in refrigerators and air conditioners.

Pollen and mold

The mold and allergens from trees, grass, and weeds that are carried in the air can be hazardous to health when aggravated by climate change. They can be considered a form of air pollution even though they are not regulated and are less directly connected to anthropogenic activities.

In a school, business, or home, mold can grow when there is water damage and can produce allergenic airborne pollutants. Some molds can even produce toxins that are hazardous for humans to inhale. Moreso, mold exposure can bring about an allergic response or asthma attacks.

Due to climate change, pollen allergies are worsening. It is seen in lab and field studies that pollen-producing plants like ragweed tend to grow larger and produce more pollen when there is an increase in the carbon dioxide that they grow in. Also, climate change extends the pollen production season. Some studies are even beginning to suggest that ragweed pollen might become a more potent allergen. This means that if this is true, more people will suffer fevers, runny noses, itchy eyes, and other symptoms.

Examples of air pollutants

  • Sulfur dioxide
  • Carbon monoxide
  • Carbon dioxide
  • Nitrogen oxides
  • Volatile organic compounds (VOCs)
  • Particulates
  • Ozone
  • Chlorofluorocarbons (CFCs)
  • Ammonia
  • Persistent organic pollutants (POPs)
  • Lead and heavy metals

Sulfur dioxide

This gas is colorless and has a choking odor. The chemical formula of this chemical compound is SO2. Petroleum and coal usually contain sulfur compounds and that is why the gas is formed when coal or oil that has sulfur as an impurity is combusted. Most of the sulfur dioxide emitted is generated from power generating plants, volcanoes and very little comes from mobile sources. Sulfur dioxide can cause throat and eye irritation and when inhaled can harm the lung tissue.

This gas is also a component of acid rain. In the air, it reacts with oxygen and water vapor to form a mist of sulfuric acid that falls to the ground as acid rain. Sulfur oxide is usually oxidized in the presence of a catalyst such as NO2 to form H2SO4 (acid rain).  Acid rain can harm and destroy fish and plant life as well as cause corrosion of metals. It deteriorates the exposed surfaces of public monuments and buildings. It is literally one of the concerns for the environmental impact of using fuels as sources of power.

Carbon monoxide

This gas is colorless and toxic. It is generated from incomplete combustion of fuel (natural gas, wood, or coal) and is the most abundant of the criteria pollutants. The sources of carbon monoxide include industrial processes, residential heating systems, and gasoline-powered highway vehicles (primary source). It is fact that vehicle exhaust is the major contributor of the carbon monoxides emitted into the atmosphere. A little amount of carbon monoxide is emitted from power plants because they are carefully designed and operated to maximize combustion efficiency.

Carbon monoxide can replace oxygen in the bloodstream and this is why exposure to it can be acutely harmful. High exposure time and concentration can lead to asphyxiation (the process of being deprived of oxygen, which can result in unconsciousness or death; suffocation). Carbon monoxide forms a kind of smog in the atmosphere that has been linked to several lung diseases. Also, it disrupts the natural ecosystem and animals.

Carbon dioxide

This gas CO2 as a greenhouse gas is one of the air pollutants examples and plays a role in climate change. Even though carbon dioxide is a natural essential component for plant life, it has been described as the leading pollutant and worst climate pollutant. CO2 is emitted by burning fossil fuels and its increase in the atmosphere has been accelerating. Currently, this gas forms about 410 ppm of the earth’s atmosphere. This figure as compared to about 280 ppm in pre-industrial times proves that billions of metric tons of carbon dioxide are emitted annually.

Nitrogen dioxide

This gas (NO2) is a pungent irritating gas that reacts in the atmosphere to form nitric acid which contributes to acid rain. Nitrogen dioxide is the most concern of all the several forms of nitrogen oxides. Nitrogen oxides are produced from high-temperature combustion. This combustion causes molecular nitrogen in the air to react with oxygen.

Coal-burning power plants are the primary source of NO2, followed by gasoline engines and other mobile sources. In addition, nitrogen oxides are also produced by electric discharge during thunderstorms. This gas causes pulmonary edema (a condition due to excess fluid in the lungs) and contributes to the formation of photochemical smog. Photochemical smog is a reddish-brown haze that is usually seen in a lot of urban areas. It is created by sunlight promoted reactions in the lower atmosphere.

Volatile Organic Compounds

These compounds (VOC) are well-known outdoor air pollutants examples that are grouped as either methane (CH4) or nonmethane ( NMVOCs). Methane is known as an extremely efficient greenhouse gas that contributes to the enhancement of global warming.

Whereas other hydrocarbons VOCs as greenhouse gases create ozone and prolong the life of methane in the atmosphere. However, this effect would vary based on the local air quality. The aromatic NMVOCs such as benzene, xylene, and toluene are suspected to cause leukemia and cancer with prolonged exposure. Another hazardous compound associated with industrial use is the 1,3-butadiene.

Particulate

This particulate is an example of air pollutants and can be called fine particulate, particulate matter (PM), atmospheric particulate matter, or fine particles.  They are very small fragments of liquid droplets or solid material suspended in gas or air. Aerosol, in contrast, is the combination of particles and gas which is generated from anthropogenic activities such as the burning of fossil fuels in power plants, vehicles, and several industrial processes.  Globally on average, anthropogenic aerosols currently account for approximately 10% of our atmosphere.

Particulates are characterized based on their size or phase (solid or liquid) instead of chemical composition. For instance, airborne solids with a diameter less than 1μm are referred to as fumes while solid particulates with diameters between 1-100 μm are referred to as dust particles. The primary source of particulate emissions is manufacturing processes, fossil-fuel power plants, gasoline-powered vehicles, and fossil-fuel residential heating systems. However, there are some natural sources of particulates which are volcanoes, dust storms, sea spray, forest fires, living vegetation, and grassland fires.

In regard to the effect of particulates on human health, solids with a diameter less than 10 μm are the particulates of most concern because they can be inhaled deep into the lungs. They get trapped in the lower respiratory system of humans once they are inhaled deep. Hence, an increase in the level of fine particles in the air is associated with health hazards like altered lung function, heart disease, and lung cancer. Some particulate matter like asbestos fibers is known as cancer-causing agents. Many carbonaceous particulates such as soot are suspected to be carcinogens as well. Since particulates are related to respiratory infections, they can cause harm to people with conditions like asthma.

Particulates are also created from gaseous primary pollutants and compounds in photochemical smog. Smog is a type of air pollution which is of two kinds; classic smog and modern smog. The burning of a large number of coal results in a mixture of sulfur dioxide and smoke, therefore, producing classic smog. Whereas, modern smog results from industrial and vehicular emissions which are reacted upon by ultraviolet light in the atmosphere. The ultraviolet light from the sun acts on these emissions to form secondary pollutants which also react with the primary emissions to form photochemical smog.

Ozone

In the presence of sunlight, this pollutant is formed by a complex reaction of nitrogen dioxide and hydrocarbons. Ground-level ozone (O3) is therefore a product of NOx and VOCs reaction. Ozone is a major component of photochemical smog and is said to be a criteria pollutant in the lowermost layer of the atmosphere (troposphere). However, in the upper atmosphere, ozone occurs naturally to block harmful ultraviolet rays from the sun.

It is an essential component of the ozone layer in the stratosphere and is involved in the photochemical and chemical reactions that drive many of the processes that take place in the atmosphere day and night. However, ozone at abnormally high concentrations becomes a pollutant and constituent of smog due to human activities that involve the combustion of fossil fuels.

In cities where sunshine is ample and highway traffic is heavy e.g Los Angeles, photochemical smog tends to be common. This is because nitrogen dioxide and hydrocarbons that form ozone are emitted in significant quantities by motor vehicles.

Chlorofluorocarbons (CFCs)

CFCs are emitted from products that are currently banned from use as well as aerosol sprays, refrigerator, and air conditioners. They rise to the stratosphere when released into the air and harm the ozone layer as they come in contact with other gases. Once, the ozone layer is damaged, harmful ultraviolet rays reach the earth’s surface which can lead to eye disease, skin cancer, and even damage our plants.

Ammonia

This compound (NH3) has a pungent odor and is emitted basically from agricultural waste and processes. The synthesis of many pharmaceuticals involves ammonia directly or indirectly. Despite, being used widely, it can be hazardous and caustic. Ammonia can react in the atmosphere with oxides of nitrogen and sulfur to form secondary particles.

Persistent Organic Pollutants

These organic compounds (POPs) are examples of air pollutants that are resistant to environmental degradation, be it through biodegradation, chemical, or photolytic processes. As a result of this characteristic, they tend to be persistent in the environment and are capable of biomagnifying in food chains (see biomagnification), bioaccumulating in human and animal tissue (see bioaccumulation), and long-range transport. Hence, they have significant impacts on the environment and human health. Moreso, there are a variety of persistent organic pollutants that can attach to particulates.

Lead and Heavy metals

Toxic metals like mercury, lead and their compounds are examples of air pollutants. Oil refining, smelting, and other industrial activities are the main sources of airborne lead particulate. In the past, gasoline contained tetraethyl, a lead-based antiknock additive. Hence, when this gasoline is combusted, it releases lead particulates and was a major source.

There is, however, a complete ban on the use of lead in gasoline in many countries. Hence, there was a more than 90% decrease in the lead concentration in outdoor air in the United States. This was after the use of leaded gasoline was restricted in the mid-1970s and completely banned later on in 1996. Lead particulates, when inhaled in form of dust and fumes, can be harmful especially to children. In children, slightly elevated levels of lead in the blood can cause seizures, learning disabilities, and even death.

Anthropogenic activities like fossil fuel combustion and mining have contributed to the widespread mercury pollution in the world. Even though mercury occurs naturally in the earth’s crust, it is one of the heavy metals that are hazardous. The mercury emitted into the air due to human activities settles on land where it is washed into water or the mercury can settle into water directly.

This mercury deposited in water can be changed into methylmercury by certain microbes which is a highly toxic form that builds up in aquatic animals like shellfish, and fish. It can also build up in carnivorous animals that feed on fish. In the U.S and globally, the majority of human exposure to mercury is as a result of the consumption of fish and shellfish that is contaminated with methylmercury.

Effects of air pollutants

The effect of air pollutants on human health and plants is numerous. Humans being exposed to high levels of air pollution can cause several adverse health conditions. Polluted air increases the risk of heart disease, respiratory infections, and lung cancer. Short-term and long-term exposure to these pollutants always results in health impacts in humans.

Severe impacts are seen in ill people and children as well as elderly people are also susceptible. Fine particulate matter that usually penetrates deep into the lung passageways is the most health-harmful pollutants that are closely associated with excessive premature deaths.

Not only humans and animals are affected by polluted air, plants too are not excluded. An air pollutant enters through the plant’s stomata and destroys the chlorophyll of the plant. This stoma is what plants use for transpiration and are usually wide open during the day to facilitate photosynthesis. Hence, these pollutants enter the leaf of the plants during the daytime more than at night. Therefore, as these pollutants destroy the chlorophyll, photosynthesis is affected.

The cuticle (waxy coating of the leaves) of the plant is usually affected by these pollutants. The function of the cuticle is to prevent excessive water loss and damage from pests, diseases, frost, and drought. As a result of the damage done to the leaf structure by air pollutants, conditions such as abscission (dropping of leaves), necrosis (dead areas of the leaf), epinasty (downward curling of leaf), or chlorosis (loss or reduction of chlorophyll causing yellowing of leaf) takes place in the plant. For instance, necrosis of leaf-tip in plants is caused by fluoride. Moreso, leaf abscission, epinasty, and dropping off flowers can occur in plants due to the pollutant- ethylene.

Below is a summary table of the major air pollutants and their effects on human health:

A table showing air pollutants and their effects

Air pollutants
Sources
Effects
Carbon monoxide
  1. Automobile exhaust
  2. Photochemical reactions in the atmosphere
  3. Biological oxidation by marine organisms

CO affects respiratory activity.

Since hemoglobin has more affinity for CO than for oxygen, CO combines with HB and reduces the oxygen-carrying capacity of the blood.

This eventually leads to blurred vision, headache, unconsciousness, and death due to asphyxiation (lack of oxygen).

Carbon dioxide
  1. Carbon burning of fossil fuels
  2. Deforestation (depleting the forest trees that remove excess carbon dioxide) These trees usually help in maintaining the oxygen-carbon dioxide ratio)

It causes global warming.

As ozone concentration increases due to hot temperatures, lungs tissue can get damaged.

Also, this can cause complications for people with lung diseases and asthma patients.

Chloro-fluorocarbons (CFCs)
  1. Refrigerators
  2. Air conditioners
  3. Foam shaving cream
  4. Spray cans
  5. Cleaning solvents

This pollutant can destroy the ozone layer that protects the earth from the ultraviolet rays sent down by the sun.

Without the ozone layer for protection, the ultraviolet rays can cause adverse effects such as eye disease, skin cancer, and even damage our plants.

 Sulfur dioxide
  1. Industrial activities
  2. Burning of fossil fuels
  3. Forest fires
  4. Electric generation plants
  5. Smelting plants
  6. Industrial boilers
  7. Petroleum refineries
  8. Volcanic eruptions

It causes respiratory problems and severe headaches.

Reduces the productivity of plants.

Causes yellowing and damage to limestone and marble.

Damages leather and increases the rate of corrosion of steel, iron, aluminum, and zinc.

It causes bleaching of leaves.

Chlorosis and necrosis of leaves.

Poly-nuclear Aromatic Hydrocarbons(PAH)
  1. Automobile exhaust
  2. Industrial activities
  3. Leaking fuel tanks
  4. Leaching from toxic waste dumping sites
  5. Coal tar lining of pipes for water supply

They are carcinogenic and may cause leukemia.

In large amounts, they can cause lung irritation, liver issues, eye irritation, and blood issues.

Exposure to PAH can cause slower brain-processing speeds and ADHD (attention deficit hyperactivity disorder) in children.

Peroxyacetyl nitrate (PAN) 
The reaction of nitrogen oxides and Volatile Organic Compounds(In the presence of sunlight)

It causes silvering of the lower surfaces of leaves.

In humans, PAN at its lowest level can cause eye irritation.

It causes damage to young and more sensitive leaves.

PAN suppresses growth in plants.

Nitrogen Oxides
  1. Automobile exhausts
  2. Burning of fossil fuels
  3. Forest fires
  4. Electric generation plants
  5. Smelting plants
  6. Industrial boilers
  7. Petroleum refineries
  8. Volcanic eruptions

They form photochemical smog.

These pollutants at higher concentrations can cause respiratory problems in mammals.

It damages plant leaves at higher concentrations and affects the photosynthetic activities of plants.

N02 in plants causes increased abscission and suppressed growth.

Pulmonary edema in humans

Hydrocarbons Poly-nuclear Aromatic Compounds(PAC)
  1. Automobile exhaust
  2. Leaching from toxic waste dumping sites
  3. Industries
  4. Coal tar lining of pipes for water supply
  5. Leaking fuel tanks
They can be carcinogenic and cause leukemia.
Asbestos particles
Mining activities
It causes Asbestosis which is a chronic lung disease.
Particulate matter(Lead halides)
  1. Combustion of leaded gasoline products
  2. Oil refining
  3. Smelting
  4. Industrial activities

Lead pollution causes a toxic effect on man.

Minimal exposure to lead can affect a child’s IQ and ability to learn.

In large amounts, lead can cause damage to the kidneys and brains of children.

Ozone

Ozone forms from nitrogen dioxide reacting with hydrocarbons in the presence of sunlight.

Nitrogen dioxide and hydrocarbons are emitted by motor vehicles

It causes flecks on the leaf surface.

Premature aging, necrosis, and bleaching of the leaves of plants.

It becomes a constituent of smog at high concentrations.

As ozone concentration increases, lungs tissue can get damaged.

Complications for people with lung diseases and asthma patients.

Mercury
  1. Combustion of fossil fuel
  2. Artisanal and small scale mining
  3. Stationary combustion of coal
  4. Ferrous and nonferrous metals production
  5. Cement production
  6. Waste from products
  7. Biomass burning
  8. Chlor-alkali production
  9. Waste incineration
  10. Oil refining
  11. Cremation

It causes brain and kidney damage.

Mercury concentration in the body can attack the central nervous system.

Silicon dioxide
  1. Stone cutting
  2. Pottery
  3. Glass manufacturing
  4. Cement industries
It causes silicosis, a chronic lung disease.
Particulates
  1. Manufacturing processes
  2. Fossil-fuel power plants
  3. Gasoline-powered vehicles
  4. Fossil-fuel residential heating systems
  5. Volcanoes
  6. Dust storms
  7. Sea spray
  8. Forest fires
  9. Living vegetation
  10. Grassland fires

The presence of particulates on the leaves of plants can form encrustation that plugs the stomata.

This reduces the plant’s availability to sunlight and the damage can lead to the plant’s death.

It alters lung function and causes lung cancer.

Heart disease

Respiratory infections

Carcinogenic

They can cause harm to people with conditions like asthma.

How can we control air pollutants?

  1. Use of pollution control devices
  2. Minimize vehicle usage and use public transport
  3. Conserve energy
  4. Recycle and Reuse
  5. Forest fires and smoking should be reduced
  6. Filters should be used for chimney
  7. Using crackers should be avoided
  8. Usage of environmentally safe products
  9. Practice afforestation
  10. Usage of clean energy resources
  11. Treatment and control of industrial emissions

In order to control air pollutants, some regulations, devices, and practices can be implemented.

Use of pollution control devices

There are some pollution control devices that are used by industries or transportation devices. These control devices can either remove pollutants or destroy them. They can remove an air pollutant from an exhaust stream before it is emitted into the atmosphere. Examples of such devices include:

Mechanical collectors

Dust cyclones and multi-cyclones are examples of such collectors. This device makes use of the cyclonic separation mechanism. It is a method whereby without using filters, particulates are removed from the air, water stream, or gas through vortex separation. In this device, rotational effects and gravity are utilized to separate mixtures of solids and fluids.

Electrostatic Precipitators

An electrostatic precipitator (ESP) is also called an electrostatic air cleaner. This device, as a particulate collection device, makes use of the force of an induced electrostatic charge to remove particles from a flowing gas (such as air). They can easily remove fine particulate matter like smoke and dust from the air stream. These pollution control devices are highly efficient filtration devices. This is because, through the device, the flow of gases is minimally prevented.

Particulate Scrubbers

Wet scrubbers are pollution control devices. They function in the removal of pollutants from furnace flue gas or from other gas streams. The mechanism of a wet scrubber involves a polluted gas stream coming in contact with the scrubbing liquid. In order to remove the pollutant, this contact is done by either spraying it with the liquid, forcing it through a pool of liquid, or via some other contact method.

The nature of the air pollutant and the industrial processes involved is the basis for the design of wet scrubbers or any air pollution control device. Dust properties and inlet gas characteristics are of primary importance. Scrubbers can be designed to remove gaseous pollutants or particulate matter. They remove dust particles by capturing them in liquid droplets and remove pollutant gases by absorbing or dissolving them into the liquid.

Minimize vehicle usage and use public transport

Using public transport, carpool and minimizing vehicle usage is a sure way of controlling air pollution. This is because less gas and energy would be utilized. Since the vehicular exhaust is one of the main sources of air pollution, minimizing its usage will help control the release of air pollutants into the atmosphere.

People should walk or make use of bikes if possible, especially for shorter distances, and make use of public modes of transportation when traveling far. Furthermore, pollution from vehicles can be checked by the following:

  • A regular tune-up of engines
  • Installing catalytic converters
  • Engine modifications to have fuel-efficient mixtures to reduce hydrocarbon and carbon monoxide emissions
  • Replacement of more polluting old vehicles
  • Slow and cooler burning of fuels to reduce nitrogen oxides emission

Conserve energy

Energy should be conserved at home, work, and everywhere. Fans should be used instead of air conditioners because AC’s takes a lot of energy compared to fans and emit a lot of heat. This is bad for the environment. In order to generate electricity, a large number of fossil fuels are burnt, this is why you should turn off every electrical appliance when not in use.

Switch off your lights when you’re not using them to conserve energy. It is advisable to use energy-saving fluorescent lights and when buying a home or office equipment look for the ENERGY STAR label. Using energy-efficient devices such as the CFLs will help control pollution to a great extent. The religious practice of conserving energy will definitely help save the environment at the individual level.

Recycle and Reuse

Manufacturing industries are sources of some air pollutants and this is why the concept of recycling and reuse will help control air pollution. Conserving resources for reuse will help reduce pollution emissions and recycled products would take less energy and power when making other products. Hence, with this practice emissions from this source would be reduced to a great extent.

Forest fires and smoking should be reduced

Fire is a huge contributor to air pollution. The collection of garbage or dry leaves to set on fire in dry seasons should be reduced. Smoking too should be reduced because it worsens the air quality and causes air pollution along with the damage it causes to one’s health. Even the gas emitted from fireplaces in factories and homes affects the air quality. Hence, it is advisable for filters to be used for chimneys to help reduce the rate of pollution in the air.

Usage of environmentally safe products

People should use less of or totally avoid products with chemicals such as paints or perfumes. Usage of products with low chemicals and organic properties should be implemented more. It is advisable to make use of environmentally safe paints or cleaning products if possible.

Practice Afforestation

Afforestation (planting of trees) should be practiced globally. Planting and growing as many trees as possible will help the environment because plants release oxygen. Afforestation is one of the best ways to reduce the adverse effects of air pollution. Tree plantation reduces a large number of air pollutants and planting trees in places with high pollution levels would be very effective.

Usage of clean energy resources

Clean energy resources such as solar, wind, and geothermal energies should be used more than fuel-powered sources. This will reduce and control the air pollutants emitted to the atmosphere at a larger level. This is why various countries in an attempt for a cleaner environment have implemented the use of these resources e.g India. The major air pollutants in India are oxides of nitrogen (NOx), sulfur dioxide (SO2), respirate particulate (PM10), and suspended particulate matter (SPM).

Another way of controlling the emission of pollutants is fuel substitution. For instance, petrol and diesel have been replaced by CNG (Compressed Natural Gas) in many parts of India. Vehicles are running on this CNG, especially those vehicles that are not fully operating with ideal emission engines.

Treatment and control of industrial emissions

Industrial emissions are one of the major contributors to air pollution. Hence, it would be better if the pollutants can be controlled or treated at the source itself in order to reduce its effects. Industries should make use of pollution control devices.

Also, if the reactions of a certain raw material produce a pollutant, then a less polluting material can substitute this raw material. Industries should use low sulfur coal as well as maintain their existing pieces of equipment in order to minimize the emission of pollutants.

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