EPA measures a range of pollutants at each of its monitoring stations. Each pollutant has a different impact on human beings or the environment. Two policies, the State Environment Protection Policy (Ambient Air Quality) and State Environment Protection Policy (Air Quality Management) set objectives for these pollutants.

The National Environment Protection (Ambient Air Quality) Measure sets nationally agreed air quality standards for a range of pollutants. There is one exception: visibility – where the current SEPP objectives will continue to apply.

Data in EPA air quality bulletins are expressed in terms of an air quality index. EPA has also adopted five-colour coded air quality categories. Data is assigned to a category based on the index value as listed in the table below.

A grey background indicates that the monitoring station is not instrumented for the pollutant or data is temporarily unavailable.

The station summary is determined after a check to see whether or not enough data have been measured to form a useful summary of air quality. This check involves ensuring at least one pollutant of major concern has been measured. In Victoria:

• Particles (PM₁₀) and visibility reduction are the pollutants of major concern from May to September.
• Ozone, particles (PM₁₀), and visibility reduction are the pollutants of major concern from October to April.

Guidance

• A station summary of good or very good can only be formed if at least one of the pollutants of major concern is being actively recorded. However, if any pollutant (either major or not) is found to cause air quality to be fair, poor or very poor then a station summary will be generated.
• Some stations may not record enough data to form a valid summary because they are designated for special purposes, or because of instrument failures.
• If the check shows enough data are present, then a summary (very good, good, fair, poor or very poor) will be shown according to air quality category (see table).
• If a useful summary cannot be formed, the words not available will appear in the summary column.
• If no data at all are present for the station, the word off-line will appear.

Currently EPA 24-hour summary air quality bulletins are issued twice daily (approximately 9.45 am and 3.45 pm) from Monday to Friday and daily (3.45 pm) on weekends. 

Hourly data (via interactive map, data table) is available 24 hours a day, seven days a week on this website.

An index for any given pollutant is its concentration expressed as a percentage of the relevant standard, or:

It is therefore easy to interpret the pollutant index; that is, assess whether the pollutant is at a level which may cause harm.

An index value of 100 means the pollutant is currently at a concentration equal to an environmental standard level. These standards are designed to protect human health and the visual quality of the air environment, and are taken from either:

• the National Environment Protection (Ambient Air Quality) Measure (Air NEPM), or
• the State Environment Protection Policy (Ambient Air Quality) (SEPP AAQ), or
• standards derived from the above levels.

Expressing air quality as an index makes it easier to compare at a glance pollutant levels and air quality at different monitoring stations. The raw data (actual measurements/concentrations) are also available on our website - select 'data readings' as an option - for more detail.

* How calculated

A: For daily and weekly reports: Uses the maximum of the preceeding 24 one-hour averages. For hourly updates: Uses the selected hourly average (defaults to the latest available reading).

B: For daily and weekly reports: Uses the maximum of the preceding 16 rolling 8-hour averages. For hourly updates: Uses the 8 hours up to the selected hour (defaults to the latest 8-hour average).

C: For daily and weekly reports: Uses an average of the preceeding 24 hours of PM₁₀ readings, divided by the 24-hour Air NEPM standard of 50 µg/m3. For hourly updates: Uses the selected hourly average PM₁₀ (defaults to the latest available reading), divided by a derived 1-hour standard of 80 µg/m3.

The data obtained from EPA's monitoring stations are averaged over various averaging times depending on pollutant, as listed in the 'Pollutants, standard levels and calculation averaging times' table. These averages are calculated every hour by EPA.

The calculation is done separately for each station. There are two stages in the calculation. First, each pollutant measurement is converted into a pollutant index, and second, all the pollutant index values are combined together to form a station index.

Station index

In order to get an overall appreciation of air quality at a particular EPA monitoring station, the index for each pollutant is calculated. The maximum of these figures is taken to be the index for that monitoring station.

See also 'Determination of an overall station summary'.

Example

Assume the values listed in the table below have been measured at an EPA monitoring station, and that EPA is preparing the 9 am bulletin on 2/2/98.

Smoke from bushfires can lead to significant deterioration in air quality, with high concentrations of fine particles and reduced visibility being the main concerns. View the bushfires and air quality page.