• Nitrogen Dioxide NO2
• Ozone O3
• Particles PM10
• Sulphur Dioxide SO2

For more information on the sources and health effects of each pollutant, follow its link or scroll down this page.

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 (see 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.
For completeness' sake: 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 NOx 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 NOx and the resulting concentrations of NO2.

The main sources of NOx 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 as examples, 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.

Select this link for results and conclusions of NO2 monitoring in Ashfield

Ozone

Pure ozone 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 (03) 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. In these reactions oxides of nitrogen and hydrocarbons, derived mainly from traffic, react to produce ozone. The more nitrogen dioxide and volatile organic compounds (VOCs) that there are in the air, the more ozone will be produced in the presence of sunlight.

Chemical reactions take place over several hours or days and once formed 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.

Select this link for results and conclusions of O3 monitoring in Ashfield

Particles

Health Effects
Particles known as PM1O have a diameter less than 10um and when inhaled would penetrate beyond the larynx.

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 PM1O the greater effect on health.

Main Sources
'Primary PM1O' 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 PM1O arises from the formation of particulate sulphates and nitrates in the atmosphere, known as 'secondary PM1O'. There are also natural or semi-natural sources of PM1O 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 PM1O concentrations in urban background locations. The fine particle fraction is composed predominantly of primary and secondary particles.

Select this link for results and conclusions of PM10 monitoring in Ashfield

Sulphur Dioxide

SO2 is a colourless gas. It 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
Sulphur Dioxide (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%).

Select this link for results and conclusions of SO2 monitoring in Ashfield.