About air quality monitoring
See monitoring sites.
In June 1998, there were two major changes in relation to air quality and how it is reported:
- national standards were set for how air quality is measured (using five criteria air pollutants)
- national reporting process was introduced.
The five pollutants to be measured under the 1998 national standards are ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide and air particles.
In 2002 the NSW DECC began reporting on these pollutants to the national body. The NSW DECC updated the old Regional Pollution Index (RPI) in 2008. This new index, the Regional Air Quality Index (RAQI), is based on the five criteria pollutants (as per national standards) plus visibility (as per a standard set by NSW) at all sites in the NSW DECC air quality monitoring network.
In 1993, following a major review of monitoring needs, the NSW Government upgraded the monitoring network and extended it to the lower Hunter, Illawarra and western area of Sydney.
As a consequence of the expansion of the network, daily reporting of air quality was also reviewed, resulting in the reporting of a Regional pollution index (RPI). The RPI was produced for three regions in Sydney (Eastern Sydney, North Western Sydney and South Western Sydney) three sites in the lower Hunter (Newcastle, Wallsend and Beresfield) and three sites in the Illawarra (Wollongong, Kembla Grange and Albion Park).
Sydney's air has been monitored for a range of pollutants since the 1960s. By the early 1980s, daily air quality reports were being released, based specifically on concentrations of ozone and fine particles. These Sydney Pollution Index (SPI) reports used a simple linear scale that reported pollution levels as low, medium or high. The SPI measured ozone and fine particles from 6am to 3pm. This reflected an emphasis on visible pollution and focused on daytime visibility as a measure of air quality.
At that time Sydney's population lived mainly east of Parramatta and in the south-western areas of Liverpool/Campbelltown. Monitoring was therefore concentrated in these areas.
Back to top
AQI values are derived from air quality data readings, which allows for more meaningful comparison of pollutants affecting air quality. The index is derived using the following formula:
Data readings are translated on to a linear scale based on relevant NEPM standards (for Ozone, Nitrogen Dioxide, Carbon monoxide, Sulfur dioxide and PM10) and the DECC standard for Visibility to derive the AQI values for the hourly AQI and daily AQI.
The AQI (air quality index) is updated hourly on DECC's air quality index web page and provided to the electronic media and published in newspapers serving Sydney, the lower Hunter and Illawarra.
This information is also available by calling the NSW DECC Environment Line:
More about the AQI and how it is calculated
In order to provide more detailed information than is available in the AQI (air quality index), measurements are also published as hourly data readings, and daily data readings, in scientific units rather than the derived values provided in the AQI.
Data readings are the actual scientific measurements for each air pollutant. The data readings are recorded in different units of measure, depending on the type of pollutant.
|Pollutant||Units used for air quality data|
|Ozone||pphm (parts per hundred million)|
|Nitrogen dioxide||pphm (parts per hundred million)|
|Visibility (as Bsp)||10-4 m-1|
|Carbon monoxide||ppm (parts per million)|
|Sulfur dioxide||pphm (parts per hundred million)|
|Particles||µg/m3 (micrograms per cubic metre)|
Back to top
Data is collected from each site where these parameters are measured in the DECC network and reported as hourly AQI values and hourly data readings in scientific units.
The air quality daily summary is published daily at 9.30 am. It lists maximum pollutant values measured from 01.00am to 12.00 midnight the previous day and presents them as a daily AQI values and as daily data readings in scientific units.
| ||Hourly||Daily |
01.00am to 12.00 midnight
|1-hour average||Maximum 1-hour average of the 24 1-hour average between 01.00am and 12.00 midnight|
Rolling 4-hour average: is an average of the previous 4 hours for each hour of the day. For example, for the hour ending 05:00, the 4-hour rolling average is calculated from the values for hours 02:00 to 05:00, for the hour ending 06:00 the next 4-hour rolling average is calculated as the average of values for hours 03:00 to 06:00.
(note: the time of the average refers to the last hour of the averaging period - therefore averages for 0:01 to 03:00 includes data from the day prior to the reported day)
|Maximum rolling 4-hour average between 01.00am and 12.00 midnight|
|Carbon monoxide||Rolling 8-hour average: is an average of the previous 8 hours for each hour of the day. |
(note: the time of the average refers to the last hour of the averaging period - therefore averages for 0:01 to 07:00 includes data from the day prior to the reported day)
|Maximum rolling 8-hour average between 01.00am and 12.00 midnight|
Rolling 24-hour average: is an average of the previous 24 hours for each hour of the day.
(note: the time of the average refers to the last hour of the averaging period - therefore averages for 0:01 to 23:00 includes data from the day prior to the reported day)
|The arithmetic mean of the 24 1-hour averages between 01.00am and 12.00 midnight|
|Note: 75% of the data must be available to calculate the 1-hour, 8-hour and 24-hour averages.|
More about air quality sampling
Back to top
A new categorisation scheme is now used to indicate how an AQI relates to relevant NSW standards: NEPM or NSW standards:
|VERY GOOD||GOOD||FAIR||POOR||VERY POOR||HAZARDOUS|
An AQI of 100 corresponds to the relevant NEPM standard for criteria pollutants or the relevant NSW standard for visibility. Hence, when the AQI is reported as POOR, VERY POOR or HAZARDOUS it indicates that the determining pollutant levels have reached or exceeded the relevant standard or goal.
|Standards/goals for AQI|
|Pollutant|| Averaging period|| Maximum concentration|
|Carbon monoxide||8 hours||9.0 ppm|
|Nitrogen dioxide||1 hour ||0.12 ppm|
|Ozone ||1 hour|
|Sulfur dioxide||1 hour||0.20 ppm |
|PM10||1 day||50 µg/m3|
|Visibility (as Bsp)||1 hour||2.1 10-4 m-1|
- ppm = parts per million by volume, i.e. parts of pollutant per million parts of air.
- PM10 = particles less than 10 micrometers in diameter.
- PM2.5 = particles less than 2.5 micrometers in diameter.
- µg/m3 = micrograms per cubic metre, i.e. mass of pollutant per volume of air.
- Bsp = coefficient of light scattering due to particles. The lower the Bsp value, the lower the level of suspended particles and the better the visibility. The DECC one-hour visibility goal, 2.1 10-4 m-1, corresponds to a visual distance of approximately 9 kilometres.
Back to top
Ozone - 03
Near the ground, ozone is a colourless, gaseous secondary pollutant. It is formed by chemical reactions between reactive organic gases and oxides of nitrogen in the presence of sunlight. Ozone is one of the irritant secondary pollutants in photochemical smog and is often used as a measure of it.
The formation of ozone in the upper levels of the atmosphere or 'stratosphere' is by a different process. Ozone there is not regarded as a pollutant because it is produced naturally. It is important in absorbing harmful ultraviolet radiation and preventing it from reaching the earth.
Ozone is strongly oxidising and can irritate the eyes and the respiratory tract. It also damages plants.
Ozone is more readily formed during the summer months and reaches its highest concentrations in the afternoon or early evening. If we breathe in too much ozone, it can irritate the lungs. 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.
Back to top
Nitrogen dioxide - NO2
The main oxides of nitrogen present in the atmosphere are nitric oxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O). Nitrous oxide occurs in much smaller quantities than the other two, but is of interest as it is a powerful greenhouse gas and thus contributes to global warming.
The major human activity which generates oxides of nitrogen is fuel combustion, especially in motor vehicles. Oxides of nitrogen form in the air when fuel is burnt at high temperatures. This is mostly in the form of nitric oxide with usually less than 10% as nitrogen dioxide. Once emitted, nitric oxide combines with oxygen ('oxidises') to form nitrogen dioxide, especially in warm sunny conditions.
These oxides of nitrogen may remain in the atmosphere for several days and during this time chemical processes may generate nitric acid, and nitrates and nitrites as particles. These oxides of nitrogen play a major role in the chemical reactions which generate photochemical smog.
Nitrogen dioxide is found at highest concentrations near busy roads and can also be high indoors when unflued gas appliances are used. Nitrogen dioxide irritates the lungs and makes people with asthma more susceptible to lung infections and asthma triggers like pollen and exercise.
Back to top
Visibility - NEPH
Visibility is a measure which indicates the presence of fine particles in the air from sources such as motor vehicles, wood fires and industry.
When fine particles are trapped in cold still air, they cause the brown haze that typically appears over cities in winter.
Visibility is measured by shining a light through a sample of air and determining the amount of light scattered by fine particles. The greater the concentration of particles, the greater the extent of light scattering and the higher the visibility reading in units of 10-4 m-1. A high visibility reading indicates lower visibility in the atmosphere due to light scattering. The measurement technique is called nephelometry (NEPH).
Back to top
Carbon monoxide - CO
Carbon monoxide is an odourless, colourless gas produced by incomplete oxidation (burning). As well as wildfires, carbon monoxide is produced naturally by oxidation in the oceans and air of methane produced from organic decomposition. In cities, the motor vehicle is by far the largest human source, although any combustion process may produce it.
Carbon monoxide usually remains in the atmosphere for a month or two. It is removed by oxidation to form carbon dioxide, absorption by some plants and micro-organisms, and rain.
When inhaled, carbon monoxide binds to the oxygen-carrying site on the blood's haemoglobin, which reduces oxygen transport in the body. At high concentrations it is very toxic, causing headaches, dizziness, reduced ability to think, and nausea.
Carbon monoxide enters the bloodstream through the lungs and prevents the normal transport of oxygen by blood. This can reduce the amount of oxygen reaching the body's organs and tissues, especially the heart. People suffering from heart disease are most at risk. They may experience chest pain if they are exposed to carbon monoxide, particularly while exercising.
Back to top
Sulfur dioxide - SO2
Sulfur dioxide in the atmosphere arises from both natural and human activities. Natural processes which release sulfur compounds include decomposition and combustion of organic matter; spray from the sea; and volcanic eruptions. The main human activities producing sulfur dioxide are the smelting of mineral ores containing sulfur and the combustion of fossil fuels.
Sulfur dioxide dissolves in water to form sulfuric acid. This is a corrosive substance that damages materials and the tissue of plants and animals.
Sulfur dioxide irritates the airways of the lungs. People with asthma who are physically active outdoors are most likely to experience the health effects of sulfur dioxide. This may include wheezing, chest tightness, and shortness of breath.
Back to top
Not only are there gaseous pollutants, there are also solid or liquid particles that may be suspended in the air and may reduce visual amenity and adversely impact health.
NSW DECC measures particles as PM10 (particles less than 10 micrometers in diameter) and PM2.5 (particles less than 2.5 micrometers in diameter) .
Examples of particles in the air include dust, smoke, plant spores, bacteria and salt. Particulate matter may be a primary pollutant, such as smoke particles, or a secondary pollutant formed from the chemical reaction of gaseous pollutants.
Human activities resulting in particulate matter in the air include mining; burning of fossil fuels; transportation; agricultural and hazard reduction burning; the use of incinerators; and the use of solid fuel for cooking and heating.
Particulate matter can be usefully classified by size. Large particles usually settle out of the air quickly while smaller particles may remain suspended for days or months. Rainfall is an important mechanism for removing particles from the air.
The size of a particle also determines its potential impact on human health. Larger particles are usually trapped in the nose and throat and swallowed. Smaller particles may reach the lungs and cause irritation there. Fine particles can be carried deep into the lungs and irritate the airways. When exposed to particle pollution, people suffering from heart disease may experience symptoms such as chest pain, and shortness of breath. Particle pollution can aggravate existing respiratory diseases such as asthma and chronic bronchitis.
Prior to 2004, PM10was measured using two different methods, one requiring a high-volume sampler running for 24 hours and the other using a tapered element oscillating microbalance (TEOM) which measures particles continuously. The NSW DECC stopped PM10 measurements using high volume samplers in 2004.
Back to top
See: Principal air pollutants, About the AQI and how it is calculated, Air quality sampling
Back to top
Page last updated: 17 August 2012