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• Nitrogen dioxide (NO₂)
• Ozone (O₃)
• Particles (PM₁₀)
• Sulphur dioxide (SO₂)

For more information on the sources and health effects of each pollutant please see the detailed descriptions below.

Nitrogen Dioxide

Nitrogen dioxide (NO₂) is a reddish-brown gas with a pungent and irritating odour. It transforms in the air to form gaseous nitric acid and toxic organic nitrates. This contributes to the production of acid rain that can kill trees, fish and animal life (as does sulphur dioxide).

NO₂ also plays a major role in atmospheric reactions that produce ground-level ozone, a major component of smog. It is a precursor to nitrates, which contribute to increased respirable particle levels in the atmosphere.

Health Effects

Nitrogen Dioxide (NO₂) can have both acute (short-term) and chronic (long-term) effects on health, particularly in people with asthma.

At relatively high concentrations NO₂ causes inflammation of the airways. Studies suggest that long-term exposure to NO₂ may affect lung function and may increase the level of respiratory infections in children and enhance the response to allergens in sensitised individuals.

Main Sources

Whenever anything is burnt in air, nitrogen oxides are formed. This is because the air we breathe is mostly made up of nitrogen (78%) and oxygen (21%) and these combine when energy (from burning material) is available. The other two main constituents of air are argon (0.94%) and carbon dioxide (0.04%).

Nitrogen dioxide (NO₂) and nitric oxide (NO) are both oxides of nitrogen and are together referred to as NO_x, although it is only NO₂ that is associated with adverse health effects. However, NO₂ is produced by the further oxidation of NO and there is a complex relationship between emissions for NO_x and the resulting concentrations of NO₂.

The main sources of NO_x are:

• Road transport (approximately 47%, rising in urban areas)
• Power generation (22%) – Nuclear, solar, wind and wave power do not produce NO₂
• Domestic sources (4%) – Coal fires, home heaters and gas cookers can produce nitrogen dioxide inside homes

There are several natural sources of oxides of nitrogen (such as lightning), but these are far outweighed by human activity.

Results and conclusions of nitrogen dioxide monitoring in Ashfield

Ozone

Pure ozone (O₃) is an unstable, faintly bluish gas with a characteristic fresh, penetrating odor. The smell is noticeable after thunder storms, where the energy from the flashes of lightning has created short-lived ozone from the oxygen in the atmosphere. The Victorians spoke of taking the ozone at the seaside for health reasons, but what they smelled is more likely to have been rotting seaweed.

Atmospheric ozone exists in the stratosphere, which surrounds the earth at a height of 6 to 30 miles, the so-called ozone layer. There it plays a vital role in absorbing harmful ultraviolet radiation from the sun. Over recent years there has been growing concern over the depletion of the ozone layer, increasing the risk of skin cancer in areas where it is thinning (e.g. Australia). However, at ground level increased ozone is a problem, and is a major factor in the formation of photochemical smog.

Health Effects

Ozone has an irritant effect on the delicate surface tissues of the body such as the eyes, nose and lungs if present in the air at high concentrations.

Main Sources

Ozone is not emitted directly from any man-made source in significant quantities. At ground level it is primarily generated by a complicated series of chemical reactions driven by sunlight. Oxides of nitrogen and hydrocarbons (derived mainly from traffic), react in the presence of sunlight to produce ozone. These chemical reactions take place over several hours or days and, once formed, the ozone is stable and can persist for several days.

Maximum ozone concentrations usually occur away from sources of the primary pollutants, nitrogen dioxide and volatile organic compounds. Conversely, in urban areas nitric oxide also from traffic may react to reduce ozone concentrations here.

Ozone occurs more in summer than winter, more in southern areas than northern areas and more in the country than in cities. The problem is an international one.

Results and conclusions of ozone monitoring in Ashfield

Particles

Particles known as PM₁₀ have a diameter less than 10μm and when inhaled would penetrate beyond the larynx.

Health Effects

Particulate air pollution is associated with a range of effects on health including effects on the respiratory and cardiovascular systems, asthma and mortality. It is known that particulate air pollution episodes are responsible for causing excess deaths among people with pre-existing lung and heart disease and that the higher the concentration of PM₁₀ the greater effect on health.

Main Sources

"Primary PM₁₀" arises mainly from combustion associated with:

• Road transport (24%)
• Industrial sources (38%)
• Power stations (16%)
• Domestic/low power combustion (17%)

However, a significant proportion of PM₁₀ arises from the formation of particulate sulphates and nitrates in the atmosphere, known as "secondary PM₁₀". There are also natural or semi-natural sources of PM₁₀ such as wind-blown dust and sea salt particles referred to as "coarse particulates". In general these three sources make up one third of total long-term PM₁₀ concentrations in urban background locations. The fine particle fraction is composed predominantly of primary and secondary particles.

Results and conclusions of particles monitoring in Ashfield

Sulphur Dioxide

Sulphur dioxide (SO₂) is a colourless gas that smells like burnt matches. It can be oxidized to sulphur trioxide, which in the presence of water vapour is readily transformed to sulphuric acid mist. SO₂ can be oxidized to form acid aerosols. SO₂ is a precursor to sulphates, which are one of the main components of respirable (breathable) particles in the atmosphere.

Health Effects

SO₂ is an irritant when it is inhaled, because of its acidic nature, and high concentrations may cause breathing difficulties in people exposed to it.

Recent studies have shown that people suffering from asthma may be especially susceptible to the adverse effects of sulphur dioxide and that it may provoke attacks of asthma.

SO₂ reacts with water in the atmosphere to from a weak solution of sulphuric acid, which then falls as environmentally-destructive acid rain.

• Lakes become acidic and plants and fishes die as a result
• Tree growth is damaged; whole forests can die as a result
• Acid rain attacks metal structures and also buildings made of limestone

Main Sources

SO₂ air pollution is caused by the combustion of coal and oil. Fossil fuels often contain a lot of sulphur impurities which burn to give sulphur dioxide.

The major sources are:

• Power generation (65%)
• Industry (24%)
• Commercial and domestic heating (6%)
• Road transport, mainly diesel engines (2%)

Results and conclusions of sulphur dioxide monitoring in Ashfield

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