While air pollution causes may be both natural and human-made, it is undoubtedly the human activity that is the largest source of atmospheric pollution.
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
Table of Contents
Air Pollution Causes: Fundamental Causes (Ref. 1)
Some experts now draw our attention to several global trends such as industrialization, population growth & globalization – which form the basis of all pollution including air pollution.
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. (Ref. 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. (Ref. 4)
Table 2: Top 5 Sectors for Global SO2 Emissions in Gg, Year 2000 based on EDGAR Data (Ref. 5)
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.
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
the 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 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.
(Ref. 6)
Nitrogen Oxides (NOx)
Nitrogen oxides (NOx) are produced by combustion of all fossil fuels including coal- and gas-fired power stations and motor vehicles. (Ref. 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. (Ref. 8, 9)
Table 3: Top 5 Sectors for Global NOx Emissions in Gg NO2, Year 2000 based on EDGAR Data (Ref. 10)
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. (Ref. 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. (Ref. 12)
While rainforest destruction 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 the deforestation is now taking place in tropical countries where rainforests are routinely cleared for a number of reasons, ex. cattle ranching, crop plantations, etc.
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. (Ref. 13)
Table 4: Top 5 Sectors for Global CO Emissions in Gg, Year 2000 based on EDGAR Data (Ref. 14)
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. (Ref. 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. (Ref. 16)
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. (Ref. 17)
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. (Ref. 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).
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.
