Air Pollution Causes

Cars & Buses: Major Causes of Air Pollution Photo: Doron Laor

AIR POLLUTION CAUSES Introduction Anthropogenic Causes     Fundamental Causes     Industries     Air Pollutants         Sulfur Dioxide         Nitrogen Oxides         Carbon Monoxide         Ammonia         Ozone         Other Air Pollutants Natural Causes

So what are the main causes of air pollution?

The largest amounts of air pollution come from human activity though there are some natural sources as well.

Fossil fuels are no doubt the most important source of harmful atmospheric emissions.

We cannot (just yet!) imagine our lives without fossil fuels.

They are used in virtually every area of human life starting from gasoline for our cars to a multitude of applications in industrial production, agriculture etc.

But fossil fuels are not the only culprits. There are other pollution sources, ex. processes used to produce non-ferrous metals, which also cause air pollution.

In one word, anthropogenic (human-induced) causes are far more important than natural ones in raising the current levels of atmospheric pollution dangerously high.

We discuss major air pollution causes below.

Anthropogenic Air Pollution Causes

Air Pollution Causes: Fundamental Causes (1)

The humanity had known air pollution, to some extent or another, at least since the times the fire had been invented.

But it was only with the onset of the industrial revolution in the 19 th century that people realized the seriousness of the problem of air pollution and its often devastating effects.

In the last 200 years or so there appeared several fundamental trends which became the major forces behind the surge in levels of air pollution throughout the globe.

Industrialization is the first fundamental pollution cause. Among other things, industrialization set in motion the widespread use of fossil fuels (oil, gas & coal) which are now the main pollution sources.

Population growth is the second fundamental pollution cause. With population numbers literally exploding around the world, the demand for food and other goods goes up. This demand is met by expanded production and use of natural resources, which in its turn leads to higher levels of environmental pollution in general, and air pollution in particular.

Globalization is the another major pollution cause. Globalization has become an effective facilitator of air pollution. Developing countries usually have much looser laws on environmental protection. With this “benefit” as well as the population growth and easy availability of cheap labor, big industry prefers to move its facilities to such “pollution havens” rather than work in more regulated markets.

So we won’t be wrong if we consider industrialization, population growth and globalization the fundamental drivers of pollution, the very roots of the gigantic pollution tree.

Air Pollution Causes: Industries

The global industrial development gave rise to a great number of economic sectors, with each generating air pollution to some degree or another.

So these economic sectors act as pollution causes in their own right.

Below we list some important sectors and types of air pollutants produced by each of them:

Sector	Air Pollutants Emitted
Biofuel Combustion	Mostly CO; also SO2 and NOx
Industry & Refineries	Mostly SO2 and NOx; also CO
Power Generation	Mostly SO2 and NOx; also CO
Residential and Commercial Sector	Mostly SO2 and CO; also NOx
Road, Rail, Air & Other Transport	Mostly NOx and CO; also SO2

See the breakdown of other polluting sectors here.

Air Pollution Causes: Air Pollutants

Air pollutants are basically the waste products generated by the above mentioned economic sectors.

They come in the form of gases and finely divided solid and liquid particles suspended in the air (aerosols).

Air pollutants can also be of primary or secondary nature.

Primary pollutants are the ones that are emitted directly into the atmosphere by the sources ( ex., power plants).

Secondary pollutants are the ones that are formed as a result of reactions between primary pollutants and other elements in the atmosphere.

Air pollutants are direct pollution causes, in other words they are the actual pollution agents which directly affect the health of living beings as well as the wider environment.

We discuss the most important air pollutants below.

Sulfur Dioxide (SO2)

Sulfur dioxide (SO2) is a colorless gas with a pungent, suffocating odor. SO2 is corrosive to organic materials and it irritates the eyes, nose and lungs; therefore it is quite a dangerous air pollutant. (3)

Sulfur is contained within all fossil fuels, and is released in the form of sulfur dioxide during fossil fuel combustion. Fossil fuel combustion accounts for almost all anthropogenic sulfur emissions. (4)

Sector	SO2 Emissions, Gg
Power Generation	53,592
Industry (excl. refineries)	24,347
Non-ferrous metals	21,283
Transformation Sector (incl. refineries)	10,212
Residential & Commercial Sector	8,117
Other	32,789
Total:	150,339

Power generation (public electricity & heat production) is by far the largest industry for global SO2 emissions.

Coal Burning
Photo: Marcus Vegas

Power plants require large amounts of energy for their operations.

This use of energy by power plants produces emissions of a whole cocktail of air pollutants including greenhouse gases (causing global warming) and non-greenhouse gases.

It is worth singling out coal as the dirtiest fossil fuel of all; it is still widely used as a source of energy by power plants.

Coal combustion is a very serious source of sulfur dioxide emissions.

But in addition to that, it produces a number of greenhouse gases and other waste products such as arsenic, lead, mercury etc.

Industry (manufacturing industries & construction) is the second biggest source of sulfur dioxide emissions globally.

It involves the use of energy for the manufacture of industrial products (ex., iron, steel etc) as well as consumer goods, which releases SO2 into the atmosphere.

Non-ferrous metals’ production is the third largest source of SO2 emissions. Some examples of non-ferrous metals are aluminium, copper, lead, zinc, gold.

The manufacture of non-ferrous metals generates SO2 emissions via:

• the use of fossil fuels, and
• specificity of the industrial process involved

The industrial process we are talking about involves the heating of sulfide ores in the air and results in the separation of a non-ferrous metal and the sulfur from the ore.

The separated sulfur combines with oxygen in the air, turns into sulfur dioxide and thus becomes a source of SO2 emissions. (6)

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

Nitrogen Oxides (NOx)

Nitrogen oxides (NOx) are produced by combustion of all fossil fuels including coal- and gas-fired power stations and motor vehicles. (7)

There are two main nitrogen oxides: nitric oxide (NO) and nitrogen dioxide (NO2).

While NO is a colorless gas, NO2 is a gas of reddish-brown color with a distinct sharp, biting odor.

Fossil fuel combustion produces both NO2 and NO.

But almost 90% of the total NOx combustion product is released in the form of NO which is then converted to NO2 in the air. (8, 9)

Sector	NOx Emissions, Gg NO2
Road	28,471
Power Generation	24,792
Deforestation & Savannah Fires	21,450
Industry (excl. refineries)	9,630
Shipping	9,574
Other	32,692
Total:	126,610

Road transport is the biggest global contributor of nitrogen emissions produced by motor fuel combustion.

US, China, Brazil, India and Russia are the largest producers of global nitrogen emissions. (11)

Power generation is indeed another top producer of nitrogen emissions.

For example, in the US power plants are responsible for about a quarter of all nitrogen oxides emitted in the country every year. (12)

Deforestation in Burma
Photo: Isabel Esterman

While deforestation is much better known for being one of the largest causes of carbon dioxide emissions, it (alongside savannah fires) is also a significant source of nitrogen dioxide.

Most of deforestation is now taking place in tropical countries where rainforests are routinely cleared for a number of reasons, ex. cattle ranching, crop plantations etc.

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

Carbon Monoxide (CO)

Carbon monoxide is a highly toxic gas which has no color, odor or taste.

Fossil fuel combustion normally produces carbon dioxide (CO2) but sometimes, when such combustion is incomplete it also becomes a source of carbon monoxide. (13)

Sector	CO Emissions, Gg
Deforestation & Other Wildfires	527,064
Biofuel Combustion	250,758
Road	185,813
Residential & Commercial Sector	27,413
Agriculture Waste Burning	16,397
Other	68,882
Total:	1,076,327

Deforestation by means of fires (plus other wildfires) has become such a serious global problem that it is now the biggest source of carbon monoxide emissions.

The way biofuel combustion causes CO emissions is similar to that of wildfires’.

Biofuel is used by some power plants and road transport in developed countries, but mostly as a source of energy for residential purposes in developing regions of the world, with Africa and Asia being the biggest biofuel users. (15)

Road transport is another major source of carbon monoxide both in developed and developing countries.

It is the largest producer of carbon monoxide emissions in developed countries. (16)

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 colorless, poisonous gas with a sharp, cold, irritating odor. (17)

It can be found in: (18, 19)

Los Angeles Smog
Photo: Brooke Ganz

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

Stratospheric ozone protects the Earth by keeping harmful ultraviolet sunlight from reaching the planet’s surface.

However, human-induced tropospheric ozone is a secondary pollutant produced by the reaction of primary pollutants, nitrogen oxides and hydrocarbons, in the presence of sunlight. (20)

Tropospheric ozone is one of the main components of the photochemical smog which is harmful to human and animal health.

Other Air Pollutants

Airborne Particles are tiny fragments of solid or liquid nature suspended in the air (aerosols).

Particulate Pollution: Coal Dust
Photo: Paul Vitucci

They may be primary – when emitted directly into the atmosphere by sources (ex., road transport & power plants), or secondary – when particles are formed in the atmosphere through the interaction of primary pollutants.

Inhalation of airborne particles may lead to asthma, lung cancer and other problems.

Volatile Organic Compounds (VOCs) may include a wide range of organic air pollutants, from pure hydrocarbons to partially oxidized hydrocarbons to organic compounds containing chlorine, sulfur, or nitrogen.

VOCs may affect human health directly (ex., leukemia) or indirectly as contributors to the formation of tropospheric ozone, with all the negative effects of ozone on human health and the environment.

Persistent Organic Pollutants (POPs) are compounds which are resistant to degradation and persistent in the environment, and may include dioxins, furans, polychlorinated biphenyls (PCBs) and organochlorine pesticides such as DDT.

Exposure to POPs takes place through diet (ex., animal fat consumption), environmental exposure or accidents and may lead to cancers, neurobehavioral disorders and other illnesses.

Natural Air Pollution Causes

Natural air pollution causes are mostly forest fires and volcano eruptions but may also include vegetation (ex., forests), oceans and decay processes in soil.

Last Update: November 2008