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Impacts of air pollution

Many human activities and natural processes release substances or chemical compounds into the atmosphere: for example particulate matter, oxides of nitrogen, sulphur dioxide and volatile organic compounds. These can result in air pollution. Once in the atmosphere, these chemical compounds are subjected to various atmospheric processes that control their transport, and can alter their chemical and physical form. The eventual environmental impact of substances released to the atmosphere is therefore greatly influenced by these processes.

The impacts of air pollution can range from poor air quality in the close vicinity of a source, to the disruption of natural chemical cycles and physical processes that occur on a global scale. The table below shows some of the environmental impacts that the most important air pollutants may have, on a local, regional and global scale.

Local Impacts

Pollutant Pollutant Properties Environmental Impacts

Nitrogen oxides, particulate matter, sulphur dioxide, volatile organic compounds, carbon monoxide, benzene, 1,3-butadiene, lead and metallic pollutants

Most of these are "primary" pollutants – meaning that they are emitted directly into the atmosphere from a source (such as an industrial process, domestic boiler or vehicle engine).

The exceptions are:

*Particulate matter, which may be "primary" (such as smoke from a chimney) or "secondary", formed in the atmosphere from reactions involving other pollutants.
*nitrogen dioxide (NO2) which has a primary component (directly emitted NO2), and a secondary pollutant, formed when nitric oxide (NO) is released to the atmosphere and undergoes oxidation.

Reduction of local air quality: affecting human health, affecting vegetation growth, and causing damage to materials and buildings.

Regional Impacts

Pollutant Pollutant Properties Environmental Impacts

Sulphur dioxide, nitrogen oxides, hydrochloric acid.

Once released, these compounds can be deposited close to their source. Alternatively chemical reactions can convert them into other acidic compounds that may be transported long distances (possibly across national boundaries) before deposition to the surface.

Acid deposition, which leads to degradation of the terrestrial environment.

Ozone, peroxyacetylnitrate.

These compounds are "secondary" pollutants, that is, formed by reactions involving primary pollutants.

They are formed from reactions involving volatile organic compounds and nitrogen oxides, in the presence of sunlight and especially in warm weather.

Impacts generally occur at a distance from the source of the original pollutants, due to the time needed for the chemical reactions to take place.

These "photochemical oxidant" pollutants cause poor air quality (particularly in summer). Ozone in particular is a respiratory irritant. It can affect human health and (in high concentrations) damage vegetation.

Fine particles (generally <2.5m in diameter)

Secondary particles, formed in the atmosphere from chemical reactions mainly involving SO2 and NOx, can have effects on a regional scale as they may be transported long distances.

Human health impacts

Global Impacts

Pollutant Pollutant Properties Environmental Impacts

Carbon dioxide, methane, nitrous oxide, halocarbons, black carbon.

These compounds and substances contribute to climate change, by absorbing long wave radiation, which results in a warming of the atmosphere.

Most of these substances are only slowly removed from the atmosphere and therefore their concentrations are continually increasing because their emission rate is greater than their removal rate. (The exception is black carbon which is removed relatively quickly).

Contribution to climate change.

Halocarbons

These compounds can be transported to the stratosphere (an upper part of the atmosphere), where the protective 'ozone layer' is concentrated. They can disrupt natural chemical reactions, leading to ozone destruction. Most are very stable and may persist in the environment for many years.

Destruction of stratospheric ozone - causing increased UV radiation at the earth's surface.