EPA AirWatch uses air quality categories to show the level of air pollutants at our monitoring sites across Victoria.

To calculate an air quality category we measure the average concentration of a pollutant in the air over an hour. We then compare this measurement to the pollutant's air quality guideline or standard.

Concentration ranges for air quality categories


Measurement Good Fair Poor Very poor Extremely poor
Ozone ppb Less than 50
100–150 150–300
300 and above
Nitrogen dioxide ppb Less than 60
360 and above
Sulfur dioxide ppb Less than 100
200–300 300–600
600 and above
PM10 µg/m3 Less than 40 40–80
300 and above
PM2.5 µg/m3 Less than 25 25–50
100–300 300 and above
Carbon monoxide ppm Less than 30
70 and above

We determine the overall air quality category for a monitoring site  by looking at these pollutants:

  • PM2.5 particles
  •  PM10 particles
  • ozone
  • nitrogen dioxide
  • sulfur dioxide.

We compare the pollutants’ concentrations and use the highest one as the overall site category.

The results for each site show the pollutant used to determine the category.  

Screenshot of map

We've changed how we calculate air quality categories

Prior to November 2019, we calculated an air quality index for each station. Contact EPA for more information.

Read more about monitoring and forecasting air pollution

About EPA AirWatch

People sensitive to air pollution

Air quality categories

How we forecast air quality

Accreditation of EPA air quality monitoring

Your health and the environment: learn and take action

Reviewed 13 January 2021