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The air we like to breathe is mainly made up of Nitrogen and Oxygen -
- 78.09% Nitrogen
- 20.95% Oxygen
- 0.92% Trace gases
- 0.04% Carbon Dioxide
Polluted air is air that is contaminated with other noxious materials.
Particulate Matter : WHO uses Particulate Matter (PM) as a proxy indicator for air pollution as the particulates lead to significant health problems. The major components of PM are sulphates, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water. They consists of a complex mixture of solid and liquid particles of organic and inorganic substances suspended in the air.
Size of Particulates : The particulate matter varies in size. Large particles can be caught by the hairs in the nostrils and so never reach the lungs. The more damaging particles are those with a diameter of 2.5 microns or less. These can penetrate the lung barrier entering the blood system to cause more widespread problems.
Distribution of Particulates : The distribution of particulates in the atmosphere is not evenly distributed across the globe. They tend to be more in low and middle income countries and there is a band across Africa extending to China where particulate levels (P<2.5) are high. (Map 1)
Deaths attributable to air pollution (Indoor and Outdoor)
Air pollution kills an estimated 7 million people worldwide every year. Globally it is calculated to be the 4th most important risk factor for death. (Figure 1)
Where does the pollution come from?
Both outdoor (ambient) and indoor air pollution come mainly from the burning of fossil fuels. The types of fuel are different for outdoor and indoor air pollution.
a) Outdoor Air Pollution
Human activities that are major sources of outdoor air pollution include:
- Fuel combustion from motor vehicles (e.g. cars and heavy duty vehicles)
- Heat and power generation (e.g. oil and coal power plants and boilers)
- Industrial facilities (e.g. manufacturing factories, mines, and oil refineries)
- Municipal and agricultural waste sites and waste incineration/burning
More than 80% of people living in urban areas that monitor air pollution are exposed to air quality levels that exceed WHO guideline limits. Low- and middle-income countries suffer from the highest exposures.
Outdoor air pollution is estimated to have contributed to 4.2 million premature deaths/year, and this is particularly due to the small particulate matter of 2.5 microns or less in diameter. The burden is experienced disproportionately in LIMCs where around 90% of these deaths take place (Map 2).
Chronic exposure to particles contributes to the risk of developing cardiovascular and respiratory diseases, as well as lung cancer.
Indoor Air Pollution
Indoor air pollution comes mainly from residential cooking, heating, and lighting with polluting fuels. Some fuels are relatively clean, but not everyone has access to these.
Fuels used by those without access to ones that are clean include dung, wood and coal in inefficient stoves or open hearths and they produce a variety of damaging pollutants. These types of fuels are those used by low-income groups. The pattern of access to clean fuels across the world reflects this. (Figure 2)
Fuel for Life : Household energy and health (WHO)
Our World in Data :
Exposure to indoor air pollutants leads to a variety of health problems, ranging from respiratory illness, to cancer to eye problems. Smoke from cooking fires is estimated to contribute to 3.8 million premature deaths each year. Indoor open fires are also a cause of burns, particularly in children.
As might be expected the pattern of mortality across the world from indoor air pollution (Map 4) is similar to that for lack of access to clean fuels for cooking (Map 3).
What is being done to reduce air pollution?
Many countries have agreed to work towards certain air quality standards and WHO has an Air Quality Health unit that takes the lead in various initiatives and provides technical support to member states.
Progress has been made in reducing death rates from indoor air pollution, but there has been no change in mortality from outdoor air pollution (Figure 3), so efforts need in particular to be focused on reducing outdoor air pollution.
"Air pollution : A major global public health issue" : You Tube overview of the topic (7.75 min).
WHO landing page website on Air pollution
WHO Factsheet on Ambient (Outdoor) Air Pollution
WHO Factsheet on Household air pollution and health
WHO Air Quality and Health Team
Natural History Museum
The museum has produced a series of YouTube presentations entitle "Our Broken Planet" that examine a variety of topics related to sustainability and pollution.
See clip the Great London Smog : BBC Archive