Definitions

Air pollutant

The air pollutants monitored by the Office of Environment and Heritage and used in the AQI are ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide and air particles. Visibility is also measured and reported. For other pollutants monitored see the monitoring site tables.

Air quality alerts

An air quality alert may be raised when pollutant concentrations reach levels which exceed national air quality standards for gaseous pollutants (ozone, carbon monoxide, nitrogen dioxide and sulfur dioxide), fine particles (PM10 and PM2.5) for a rolling 24-hour average and/or the NSW OEH standard for visibility. During an air quality alert, people sensitive to the effects of air pollution are likely to feel its impacts (POOR and VERY POOR categories) or during extreme episodes of air pollution such as during prolonged bushfires (HAZARDOUS category) which can affect everyone's health.

There are two types of air quality alerts:

  1. Hourly: An air quality alert may be raised on an hourly basis at any site whenever national air quality standards and/or NSW OEH standard for visibility are exceeded. This type of air quality alert may be raised by any site within the NSW air quality monitoring network.

  2. Forecast: A Sydney only air quality forecast alert may be included with the next day forecast for Sydney at 4.00pm if it is predicted that the AQI is likely to be above 100 the next day in any of the three regions within Sydney. In the case of an alert due to ozone, the predicted elevated levels of ozone may not occur until the afternoon as production of ozone is related to temperature among other variables (as temperature goes up, ozone concentrations increase).

Air Quality Index (AQI)

A value 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:

AQ+ = pollutant data reading divided by the standard for that pollutant and multiplied by 100

More about the AQI and how it is calculated

AQI

See air quality index

BAM-PM2.5

Particles less than 2.5 micrometres in diameter measured using a Beta Attenuation Monitor (BAM).
See also particles (PM10, PM2.5)

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 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.

More about carbon monoxide

Cd

Cadmium. Measured at certain monitoring sites, but not used in reporting the air quality index (AQI).

CO

See carbon monoxide

Data readings

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.

More about the AQI

Goal

See standard

O3

See ozone

NEPH

Suspended fine particles as measured by a nephelometer

NEPM

National Environment Protection Measure

Nitrogen dioxide (NO2)

Nitrogen dioxide is found at its highest concentrations near busy roads and can also be high indoors when unflued gas appliances are used. Nitrogen dioxide is also a respiratory irritant which may worsen the symptoms of existing respiratory illness. Nitrogen dioxide makes people with asthma more susceptible to lung infections and asthma triggers like pollen and exercise.

More about nitrogen dioxide

NO

Nitrogen oxide. Measured at certain monitoring sites, but not used in reporting the air quality index (AQI).

NO2

See nitrogen dioxide

NOx

Oxides of nitrogen. Measured at certain monitoring sites, but not used in reporting the air quality index (AQI).

O3

See ozone

Ozone (O3)

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. 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.

More about ozone

Particles (PM10, PM2.5)

Solid or liquid particles may be suspended in the air and reduce visual amenity and adversely impact health. The size of a particle 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. Particles less than 10 micrometres in diameter are measured using a Tapered Element Oscillating Microbalance (TEOM). See TEOM-PM10. Particles less than 2.5 micrometres in diameter are measured using a Tapered Element Oscillating Microbalance (TEOM) - see TEOM-PM2.5 or a Beta Attenuation Monitor (BAM) - see BAM-PM2.5.

More about particles

Pb

Lead. Measured at certain monitoring sites, but not used in reporting the air quality index (AQI).

PM10

See particles

Pollutant

See air pollutant

Regional AQI

See site AQI

Rolling average

Is an average of the previous N 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  and so on. Rolling 4, 8 and 24-hour averages can include values from the previous day

More about averaging

SO2

See sulfur dioxide

Site AQI

For each site, the highest AQI is used as the Site AQI. For each region, the highest Site AQI is used as the Regional AQI for that region.

More about the AQI and how it is calculated

Sulfur dioxide (SO2)

The main human activities producing sulfur dioxide are the smelting of mineral ores containing sulfur and the combustion of fossil fuels. Sulfur dioxide is a respiratory irritant and may worsen existing respiratory illness.

More about sulfur dioxide

Standard

The standards for ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide and air particles were set in 1998 by the National Environment Protection Council. The standard for visibility is set by NSW.

More about the standards

TEOM-PM10

Particles less than 10 micrometres in diameter measured using a Tapered Element Oscillating Microbalance (TEOM).
See also particles (PM10, PM2.5)

TEOM-PM2.5

Particles less than 2.5 micrometres in diameter measured using a Tapered Element Oscillating Microbalance (TEOM).
See also particles (PM10, PM2.5)

TSP

Total suspended particulates

Unhealthy, unhealthy for sensitive people, very unhealthy

See air quality alerts

Page last updated: 13 November 2015