Goals and limits

Monitoring types

The air quality goals and criteria for pollutants monitored at the Transurban M4 tunnel ambient monitoring sites are based on the Conditions of Approval. The air quality goals and criteria are shown in the table below:

Monitoring type Pollutant / parameter Averaging period Units of measurement Limit / goal
External ambient CO 8 hours (rolling) PPM 9
External ambient NO2 1 hour PPM 0.12
External ambient PM2.5 24 hours µg/m³ 25
External ambient PM10 24 hours µg/m³ 50
External ambient Sigma Theta 1 hour º N/A
External ambient Temperature at 10 metres 1 hour K N/A
External ambient Temperature at 2 metres 1 hour K N/A
External ambient Wind direction 1 hour º N/A
External ambient Wind speed 1 hour m/s N/A
In-tunnel CO 3 minutes (maximum value) PPM 200
In-tunnel CO 15 minutes (maximum value) PPM 87
In-tunnel CO 30 minutes (maximum value) PPM 50
In-tunnel NO2 15 minutes (maximum value) PPM 0.5
In-tunnel Visibility 15 minutes (maximum value) m-1 0.005
Ventilation outlet CO 1 hour mg/m³ 40
Ventilation outlet NO2 1 hour mg/m³ 2
Ventilation outlet NOX 1 hour mg/m³ 20
Ventilation outlet Solid particles 1 hour mg/m³ 1.1
Ventilation outlet VOC 1 hour mg/m³ 4

Traffic light status

We have developed a traffic light status for air quality based on the same values the Office of Environment and Heritage (OEH) use to display their Air Quality Index (AQI). The AQI is a scale of air pollution that helps people understand air quality and modify any activities if pollution levels are high. For further detailed description and explanation of the OEH AQI visit Understanding air quality for the Office of Environment and Heritage.

The traffic light status of each pollutant is shown in the 'Current snapshot' table for External Ambient, In-tunnel and Ventilation Outlet and it is based on the hourly reading relative to the limit or goal.

Percentage of goal Traffic light status
If reading is less than 67% of limit/goal Good
If reading is greater than or equal to 67% and less than 100% of limit/goal Fair
If reading is greater than or equal to 100% of limit/goal Poor