What is air pollution?

Air pollution is poor air quality and harms people and the environment. It is a health concern in Australia and around the world.

Clean air is fundamental to our health and wellbeing. Poor air quality can be particularly critical to the health of children, older people, pregnant women and people with pre-existing health conditions. It also affects the natural environment and liveability of our communities.

Air pollutants and their effects

An air pollutant is any substance in the air that can harm people or the environment. Pollutants arise from natural processes, such as bushfires, and human activities, such as transport. They can be solid particles, liquid droplets or gases. Some (called 'secondary pollutants') form in the air when (primary) pollutants react with other substances or each other.

Research shows air pollution is a risk for health. An increasing range of health effects has been linked to air pollution, especially fine particles.

Air quality standards that allow for protecting human health and wellbeing are outlined in the National Environment Protection (Ambient Air Quality) Measure (Ambient Air Quality NEPM).

In 1998, ambient air quality standards and goals for six common pollutants (carbon monoxide, lead, nitrogen dioxide, ozone, PM10 particles and sulfur dioxide) were included. NSW Office of Environment and Heritage (OEH) also measures and reports on visibility. In 2006, OEH stopped monitoring lead as levels became undetectable. 

Today, our air quality monitoring focuses on the following six pollution indicators.


  • symbol: O3
  • when near the ground, ozone is a colourless, gaseous secondary pollutant formed by chemical reactions between reactive organic gases and oxides of nitrogen on sunny days. 
  • is one of the irritant secondary pollutants in photochemical smog and is often used to measure it.
  • is also formed  in the upper atmosphere or 'stratosphere' (the ozone layer) but isn't a pollutant there because it is produced naturally and is important in absorbing harmful UV radiation, preventing it from reaching the Earth's surface.
  • is strongly oxidising
  • forms more readily in summer and reaches its highest concentrations in the afternoon or early evening.
  • can irritate human eyes and airways and damage plants. Breathing ozone can affect lung function and worsen asthma. You may notice difficulty in breathing, coughing, and throat irritation if you are exercising outdoors when ozone levels are high.

Nitrogen dioxide

  • symbol: NO2
  • nitrogen dioxide is one of the main oxides of nitrogen in the atmosphere along with nitric oxide (NO) and nitrous oxide (N2O). Nitrous oxide occurs in much smaller quantities than the other two but is a powerful greenhouse gas and so contributes to global warming.
  • with respect to human sources, is mostly produced by fuel combustion, especially in motor vehicle. Mostly this is nitric oxide with less than 10% nitrogen dioxide.
  • is further formed when nitric oxide combines with oxygen ('oxidises'), especially in warm, sunny conditions.
  • may, along with other oxides of nitrogen, remain in the atmosphere for several days, during which time chemical processes may generate nitric acid, and nitrates and nitrites as particles.
  • plays a major role in the chemical reactions which generate photochemical smog, along with other oxides of nitrogen.
  • is at highest concentrations near busy roads.
  • irritates the lungs, making people with asthma more susceptible to lung infections and to asthma-triggers like pollen and exercise.


  • symbol: NEPH
  • this provides an indication of the reduction in visibility caused by fine particles in the air  
  • is measured using a technique is called nephelometry (NEPH) by shining light through an air sample and determining how much is scattered. The greater the concentration of particles, the greater the light scattering and the higher the reading, indicating lower visibility in the atmosphere.

Carbon monoxide

  • symbol: CO
  • carbon monoxide is an odourless, colourless gas produced by incomplete oxidation (burning).
  • is produced naturally by bushfires and by oxidation in the oceans and air of methane produced from organic decomposition
  • is produced by humans from combustion processes. In cities, the motor vehicle is by far the largest human source
  • usually remains in the atmosphere for a month or two.
  • is removed by oxidation to form carbon dioxide, absorption by some plants and micro-organisms, and rain
  • reduces oxygen transport in the body when inhaled, binding to the oxygen-carrying site on the blood's haemoglobin. At high concentrations it is very toxic, causing headaches, dizziness, reduced ability to think, and nausea.
  • most affects people suffering from heart disease. They may experience chest pain if exposed to carbon monoxide, particularly while exercising.

Sulfur dioxide

  • symbol: SO2
  • comes from both natural and human activities. Natural processes include decomposition and combustion of organic matter; sea spray and volcanic eruptions. The main human activities are smelting sulfur-containing mineral ores and fossil fuel combustion
  • dissolves in water to form sulfuric acid, a corrosive substance that damages materials and plant and animal tissue. Acid rain, a serious environmental issue worldwide, can harm historic buildings, forests and lakes.
  • irritates airways of the lungs - people with asthma who are physically active outdoors are most vulnerable. Effects may include wheezing, chest tightness, and shortness of breath.


  • symobols: PM10 for large particles, PM2.5 for small
  • particles (or 'particulates') are solid or liquid particles that may be suspended in the air 
  • may reduce visibility and harm health.
  • are measured as PM10 (particles less than 10 micrometers diameter) and PM2.5 (particles less than 2.5 micrometers diameter)
  • include dust, smoke, plant spores, bacteria and salt.
  • may be a primary pollutant, such as smoke particles, or a secondary pollutant formed from the chemical reaction of gaseous pollutants.
  • may result from human activities like mining; burning fossil fuels; transportation; agricultural and hazard reduction burning; the use of incinerators; and the use of solid fuel for cooking and heating.
  • can be classified by size. Large particles usually settle out of the air quickly but smaller ones can remain suspended for days or months. Rain is important for removing particles from the air.
  • have potential impact on human health depending on size. Larger particles are usually trapped in the nose and throat and swallowed. Smaller particles may reach the lungs and irritate them. Fine particles can be carried deep into the lungs and irritate the airways.
  • may cause people with heart disease to experience symptoms like chest pain, and shortness of breath. Particle pollution can aggravate existing respiratory diseases such as asthma and chronic bronchitis.
  • in the case of  PM10 particles, was measured using two different methods, using a high-volume sampler and a tapered element oscillating microbalance (TEOM) both measuring particles continuously. PM10 measurements using high volume samplers was stopped in 2004.


Page last updated: 10 February 2016