Air Pollution

Atmospheric Emissions Photo: Owen Byrne

CONTENTS Introduction Causes     Fundamental Causes     Industries     Atmospheric Pollutants         Sulfur Dioxide         Nitrogen Oxides         Carbon Monoxide         Ammonia         Ozone         Other Atmospheric Pollutants Effects     Effects on Humans         Sulfur Dioxide         Nitrogen Dioxide         Carbon Monoxide         Ozone         Ammonia         Volatile Organic Compounds         Airborne Particles     Effects on Animals     Effects on Trees     Economic Losses Global Warming & Pollution

So what is air pollution?

Air pollution is a release into the atmosphere of any substances, ex. chemicals or airborne particles, which are harmful both to the human and animal health as well as the health of the wider environment.

Atmospheric pollution occurs because the release of air pollutants takes place at a rate much faster than they can be accommodated by the environment and removed from the atmosphere without causing serious harm.

Pollution had been known to exist for centuries, but it became an issue of serious concern only in the last 200 years or so, mostly due to the industrial revolution.

Atmospheric pollution originates from all the parts of the world and travels around knowing no borders.

Air Pollution Causes

There are natural and anthropogenic (human-made) causes of air pollution.

Natural causes of pollution may include forest fires and volcano eruptions as well as vegetation, oceans and decay processes in soil.

It is however the anthropogenic causes that we are mostly interested in, as they no doubt play the most important role in polluting the Earth’s atmosphere.

Fossil fuels (oil, gas & coal) are the largest anthropogenic sources of air pollution – they are widely used in industry and everyday life.

But they are not the only ones.

For example, industrial processes involving some chemical reactions may also release significant amounts of pollution into the air.

We discuss anthropogenic air pollution causes in more detail below.

Fundamental Causes of Air Pollution

During the last couple of centuries we witnessed an emergence of several fundamental trends that became the major forces behind the dramatic levels of air pollution worldwide.

Beijing Traffic
Photo: Aapo Haapanen

Industrialization set in motion the widespread use of fossil fuels which are now the main drivers of pollution as we know it.

Population growth causes the demand for food and other goods to go up, which is met by expanded production and use of natural resources. This then leads to higher levels of atmospheric pollution.

Globalization has in a way become a facilitator of air pollution. Big industry takes advantage of lax environmental controls in developing nations and moves its manufacturing facilities to such “pollution havens” from where air pollution travels around the world without any obstacles.

So industrialization, population growth and globalization become the fundamental drivers of pollution, the very roots of the gigantic pollution tree.

Industries as Sources of Air Pollution

Some of the major air polluting industries are:

• Biofuel Combustion
• Manufacturing Industry & Refineries
• Power Generation
• Residential & Commercial Sector
• Road, Rail & Air Transport

See the breakdown of other polluting sectors here.

Air Pollutants

There are many dangerous air pollutants emitted by virtually every industry.

Sulfur Dioxide (SO2)

Sulfur dioxide (SO2) is corrosive to organic materials and it irritates the eyes, nose and lungs; therefore it is quite a dangerous air pollutant.

Sulfur is contained within all fossil fuels, and is released in the form of sulfur dioxide during fossil fuel combustion.

The main sectors producing sulfur dioxide are:

Power Generation

Power generation is the largest industry for global SO2 emissions, which is mainly due to this industry’s use of vast amounts of fossil fuels, especially coal.

Industry

Just like power generation, manufacturing industry generates its own SO2 emissions through its use of fossil fuels.

Non-ferrous metals

Production of non-ferrous metals (ex. aluminium, copper, lead) generates SO2 emissions both through the use of fossil fuels and specificity of the industrial process involved. Learn more about it here.

Other Industries

Refineries and residential & commercial sector are another significant sources of sulfur dioxide emissions.

See the breakdown of global SO2 emissions for all sectors here.

Nitrogen Oxides (NOx)

There are two main nitrogen oxides together referred to as NOx: nitric oxide (NO) and nitrogen dioxide (NO2).

While fossil fuel combustion produces both NO2 and NO, almost 90% of the total NOx combustion product is released in the form of NO which is then converted to NO2 in the air. (4, 5)

Deforestation:
Amazon Rainforest on Fire
Photo: Leonardo F. Freitas

The main sectors producing nitrogen dioxide (NO2) are:

• Road Transport
• Power Generation
• Deforestation & Savannah Fires
• Industry (excl. refineries)
• Shipping

See the breakdown of global NOx emissions for all sectors here.

Carbon Monoxide (CO)

Carbon monoxide, a highly toxic gas, is a by-product of incomplete fossil fuel combustion.

The top sectors producing carbon monoxide are:

• Deforestation & Other Wildfires
• Biofuel Combustion
• Road Transport
• Residential & Commercial Sector
• Agriculture Waste Burning

See the breakdown of global CO emissions for all sectors here.

Ammonia (NH3)

Ammonia is a pungent, hazardous caustic gas.

Agriculture, specifically livestock farming & animals waste, is the main source of ammonia emissions.

Ozone (O3)

Ozone (O3) is a poisonous gas which can be found in:

Smog, Mexico City
Photo: Alfredo Cottin

• the stratosphere (upper layer of the atmosphere) where it occurs naturally and protects the Earth from harmful ultraviolet sunlight, and
• the troposphere (lowest layer of the atmosphere) where it occurs both naturally and as a product of anthropogenic emissions.

Human-induced tropospheric ozone is a secondary pollutant produced by the reaction of primary pollutants – nitrogen oxides and hydrocarbons – In the presence of sunlight.

It is one of the main components of the photochemical smog which is damaging to human and animal health.

Other Air Pollutants

Other air pollutants include volatile organic compounds (VOCs), persistent organic pollutants (POPs) and airborne particles.

VOCs are organic compounds which easily evaporate and enter the atmosphere. They may affect human and animal health directly, or indirectly as contributors to the formation of tropospheric ozone.

POPs are compounds which are resistant to degradation and persistent in the environment. They may affect human and animal health through diet, environmental exposure or accidents.

Airborne particles are very small fragments of solid or liquid nature suspended in the air. Human and animal health may be affected by particles through inhalation.

Air Pollution Effects

Of course, atmospheric pollution would not be such a big problem if it weren’t for its harmful effects on humans, animals, trees and the wider environment.

We can distinguish between short-term acute effects and long-term chronic effects of air pollution.

Air pollutants enter the body primarily through the respiratory system which thus becomes their main victim.

Each air pollutant exerts their own specific adverse impacts, ranging from mild to really damaging.

We discuss this below.

Air Pollution Effects on Humans

Sulfur Dioxide Effects

Some effects of sulfur dioxide on human health include (6, 7, 8):

Asthma Sufferer, Cambodia
Photo: Masaru Goto / World Bank

• Irritation of eyes, nose, throat; damage to lungs when inhaled
• Acute and chronic asthma
• Bronchitis and emphysema (as a result of synergy between SO2 and airborne particles)
• Lung cancer

Sulfur dioxide may often act in synergy with other pollutants (ex., airborne particles) to produce certain air pollution effects.

Nitrogen Dioxide Effects

Depending on its different concentrations in the air, effects of nitrogen dioxide on human health include (9, 10):

• Increased incidence of respiratory illness
• Increased airway resistance (due to inflammation)
• Damage to lung tissue
• Chronic obstructive pulmonary disease, or COPD (narrowing of the airways)
• Emphysema (as part of COPD)
• Pulmonary edema (accumulation of excessive fluid in the lungs)
• Infant and cardiovascular death

Exposure to high concentrations of nitrogen dioxide can make living organisms more susceptible to bacterial infections and lung cancer. (11)

Nitrogen dioxide affects people with existing medical conditions more severely than healthy people. Children are affected easier than adults.

It is also a major component of the photochemical smog which brings its own negative effects on.

Carbon Monoxide Effects

Exposure to carbon monoxide may lead to (12, 13, 14):

Extreme Pollution, Delhi
Photo: Dave Morris

• Toxicity of the central nervous system and heart
• Headaches, dizziness, nausea and unconsciousness
• Loss of vision
• Decreased muscular coordination
• Abdominal pain
• Severe effects on the baby of a pregnant woman
• Impaired performance on simple psychological tests and arithmetic; loss of judgment of time
• In cases of prolonged exposure to high CO concentrations, unconsciousness, convulsions and death would occur

Carbon monoxide is the most common type of fatal poisoning in many countries around the world. (15)

Again, effects of carbon monoxide are exacerbated in people with pre-existing conditions.

Ozone Effects

Exposure to the tropospheric ozone may cause (16, 17, 18):

• Burning nose and watering eyes
• Tightening of the chest
• Coughing, wheezing and throat irritation
• Rapid, shallow, painful breathing
• Susceptibility to respiratory infections
• Inflammation and damage to the lining of the lungs
• Aggravation of asthma
• Fatigue
• Cancer

Children are more susceptible to the negative effects of ozone than adults.

Ammonia Effects

Effects of ammonia inhalation are (19, 20, 21):

On the respiratory system :

• Nose & throat irritation and burns (their severity increasing with the increased ammonia concentrations)
• Swelling of the throat and airways; airways destruction
• Pulmonary edema
• Chronic lung disease
• Cough
• Asthma
• Lung fibrosis
• Inhaling large amounts of ammonia can be fatal

On the skin & eyes :

• Skin burns
• Skin conditions, ex. dermatitis
• Burning sensation in the eyes
• Ulceration & perforation of the cornea (can occur months after exposure); blindness
• Cataracts & glaucoma

Effects of Volatile Organic Compounds

Effects of VOCs on human health may include (22, 23, 24, 25, 26):

Vertigo
Photo: Nima Sa

• Tiredness, vertigo, drowsiness, dizziness, nausea, confusion, unconsciousness
• Anemia
• Bone marrow damage
• Liver damage
• Dysfunction of the central nervous system:
  
  
  • Behavioral problems
  • Memory loss
  • Disturbance of the circadian rhythm
• Cardiovascular diseases
• Cancer; specifically leukemia
• Abnormal changes in fetus development, birth defects
• VOCs also contribute to sick building syndrome indoors
• As facilitators in ozone formation, VOCs may indirectly contribute to respiratory problems

Effects of Airborne Particles

Short-term acute effects of exposure to airborne particles may include (27):

Construction Dust
Photo: NIOSH

• Stuffy noses, sinusitis
• Sore throats
• Wet cough, dry cough, phlegm
• Head colds
• Burning eyes
• Wheezing; shortness of breath
• Chest discomfort or pain

Children are of course more susceptible to particulate pollution.

Specific children’s disorders caused by airborne particles may include (28, 29, 30):

• Infant death
• Low birth weight
• Reduced lung function

General effects of exposure to airborne particles are (31):

• Increased respiratory symptoms (ex. irritation of the airways, coughing, difficulty breathing)
• Decreased lung function
• Aggravated asthma
• Chronic bronchitis
• Irregular heartbeat
• Nonfatal heart attacks
• Premature death in people with heart or lung disease

Air Pollution Effects on Animals

• Acid rain (as a by-product of atmospheric pollution) may acidify lakes and streams and kill fish and aquatic plants

• Pollution may affect animals through plants on which they feed.

For example, if a certain plant is negatively affected by air pollutants, this will also affect the animals that depend on this particular plant for food.

• Tropospheric ozone may damage animal lung tissue.

Air Pollution Effects on Trees & Plants

• Physical effects on trees & plants through exposure to specific air pollutants are (32):

• Ozone produces a speckle of brown spots, which appear on the flat areas of leaf between the veins
• Sulfur dioxide: larger bleached-looking areas
• Nitrogen dioxide: irregular brown or white collapsed lesions on intercostal tissue and near the leaf edge
• Ammonia: unnatural green appearance with tissue drying out

• Sulfur dioxide has been historically known to produce destructive effects on vegetation and forests.

Here is how sulfur dioxide may affect trees & plants (33):

• Cell metabolism disruption (membrane damage, respiration and photosynthetic effects)
• Leaf injury and loss
• Reduced growth and reproduction
• Increase in susceptibility of plants to attacks by insect herbivores

Nitrogen dioxide may also act in synergy with sulfur dioxide to produce a negative effect on plants’ photosynthesis. (34)

• Tropospheric ozone can have a negative impact on plants’ photosynthesis rates which will stunt their growth; it can also decay plant cells directly by entering stomata. (35)

• Particulate air pollution effects on plants & trees may include (36):
  
  • Blocked stomata
  • Increased leaf temperature
  • Reduced photosynthesis
  • Reduced fruit set, leaf growth, pollen growth
  • Reduced tree growth
  • Leaf necrosis and chlorosis, bark peeling
• Acid rain (as a product of sulfur and nitrogen pollution) can kill trees, destroy the leaves of plants, can infiltrate soil by making it unsuitable for purposes of nutrition and habitation. (37)

It is also associated with the reduction in forest and agricultural yields. (38)

Air Pollution Effects – Economic Losses

In addition to health-related problems, atmospheric pollution brings with it economic losses as well.

Some of these economic effects are (39):

• Direct medical losses
• Lost income from being absent from work
• Decreased productivity
• Travel time losses due to reduced visibility
• Losses from repair of damage to buildings
• Increased costs of cleaning
• Losses due to damage to crops & plants

Global Warming and Air Pollution

Global warming is a major international problem caused mostly by human actions.

In a way, global warming is part of air pollution.

Global warming is a result of greenhouse gas emissions such as carbon dioxide, methane and nitrous oxide.

Greenhouse gases are air pollutants as well, just like other gases that we’ve discussed in this article.

Because global warming has become a huge issue in its own right, greenhouse gases as air pollutants are usually discussed separately from air pollution.

It is interesting to note that some air pollutants are actually precursors to greenhouse gases.

For example, carbon monoxide (CO) is a precursor to the most powerful greenhouse gas carbon dioxide (CO2).

Both global warming and air pollution are very serious issues that can only be tackled collectively by all the nations working together for one common purpose.

Last Update: November 2008