Monitoring the environment

Hourly air quality data table

This bulletin is updated hourly with information calculated on data readings averaged over 8 hours for carbon monoxide, 24 hours for PM2.5 and 1 hour for PM10, ozone, nitrogen dioxide, sulfur dioxide and visibility reduction. Detailed information on the calculation of the index is available below.

Data for a given hour are available at 30 minutes after the following hour. For example, data for 9 am-10 am is available at 10.30 am. See below for more information about station summaries, 'not available' and 'offline' reports.

Update 28 February 2014: EPA has changed the way some of our data (including CO and SO2) is displayed in the air quality table. It is possible for CO concentrations to be reported by our equipment as a negative. To avoid any confusion, EPA is now rounding all readings back to 0. The raw data in our systems will remain as originally collected.

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FAQs about air quality bulletins and index + Expand all Collapse all

  • Why do we monitor air quality?

    EPA measures a range of pollutants at each of its monitoring stations. Each pollutant has a different impact on human beings or the environment. The relevant environmental policy is the State Environment Protection Policy (Ambient Air Quality), or SEPP (AAQ).

    Another policy the National Environment Protection (Ambient Air Quality) Measure sets nationally agreed air quality standards for a range of pollutants. All national standards have been incorporated into the State policy, with one addition, visibility reduction. This extra standard relates to the need to be able to see clearly through the atmosphere for a range of reasons including transport safety and tourism. 

  • Air quality categories

    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.

    Category Index range
    Very good air quality 0–33
    Good air quality 34–66
    Fair air quality 67–99
    Poor air quality 100–149
    Very poor air quality 150 or greater

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

  • Determination of an overall station summary

    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 PM2.5 ) and visibility reduction are the pollutants of major concern from May to September.
    • Ozone, particles (PM10 and PM2.5 ), and visibility reduction are the pollutants of major concern from October to April.


    • 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 outages.
    • 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.
  • Bulletin issue

    Currently EPA 24-hour summary air quality bulletins are issued twice daily from Monday to Friday.

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

  • Conversion of a pollutant concentration into an index

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

    Index equals pollution concentration divided by pollutant standard level, multiplied by 100

    This calculation is used so that the impacts of several pollutants can be compared. 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:

    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.

  • Pollutants, standard levels and calculation averaging times
    Pollutant Standard level Source Averaging time How calculated*
    Ozone 100ppb Air NEPM 1-hour Note A
    Nitrogen dioxide 120ppb Air NEPM 1-hour Note A
    Sulfur dioxide 200ppb Air NEPM 1-hour Note A
    Carbon monoxide 9ppm Air NEPM 8-hour Note B
    Particles (PM10) Note C Note C Note C Note C
    Particles (PM2.5)  25 µg/m3  Air NEPM 24-hour  Note D 
    Visibility reduction 2.35 SEPP AAQ 1-hour Note A

    * 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 quality 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.

    D: Hourly updates for PM2.5  are provided as the latest rolling 24-hour average. For daily and weekly reports PM2.5  is not yet included, however this will be added in the near future using the same rolling 24-hour average method as for PM10.

  • Calculation of the index

    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'.


    Assume the values listed in the table below have been measured at an EPA monitoring station and reported on the hourly air quality update web pages (table and map) at 9.30am.

    Pollutant Maximum measured level Averaging time Standard level* Calculated index
    Ozone 15ppb 1-hour 100ppb 15
    Nitrogen dioxide 46ppb 1-hour 120ppb 38
    Sulfur dioxide 30ppb 1-hour 200ppb 15
    Carbon monoxide 0.9ppm 8-hour 9ppm 10
    Particles (PM10) 20µg/m3 1-hour 80µg/m3 25
    Particles (PM2.5) 15µg/m3  24-hour  25µg/m3   60
    Visibility reduction 1.20 1-hour 2.35 51
    Overall station index (the maximum of the figures is taken to be the index) 60
  • About bushfires and air quality

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

Page last updated on 3 Jun 2014