Air quality Sydney

  • The air quality in Sydney is among the best in the world, and the NSW Government is committed to improving it by reducing emissions from industry, vehicles, businesses and residences.
  • In NSW air emissions are regulated by the NSW Environment Protection Authority (EPA), and compliance with ambient, or outdoor, air quality standards is an essential consideration during road project design and operation.
  • The M4-M5 Air Quality Assessment Report was developed in consultation with the NSW Advisory Committee on Tunnel Air Quality, chaired by the NSW Chief Scientist and Engineer and including representatives from the NSW Environment Protection Authority, NSW Health, Roads and Maritime, and the Department of Planning and Environment as well as world-leading air quality experts.


  • Air quality standards are established to protect our health. They typically define maximum concentration limits of pollutants in the air over a given timeframe, for example 24 hours.  The full range of pollutants assessed for the project, and their maximum recommended concentration levels, are detailed in Chapter 9, Section 9.2.3, of the EIS.
  • Of all the pollutants assessed, PM2.5 (tiny particles of matter, one-fortieth the width of a hair) is considered to present the greatest potential impact to our health, and accordingly NSW standards for PM2.5 are the most stringent in the world.
  • By far, the biggest source of human made PM2.5 is home heating, such as open fire places. This constitutes 50.6 per cent of all human made PM2.5 in Sydney. By contrast, petrol powered vehicles are a relatively minor source at only 0.75%.  

Air quality assessment and evaluation

  • Air pollutants originate from several sources, with variable impacts on air quality.
    • Background concentration refers to all sources other than road traffic, for example contributions from natural sources, industry and domestic activity, and has the biggest impact on air quality.
    • Surface road concentration describes the pollutants that emanate from the surface road network – this has the second biggest impact on air quality.
    • Ventilation outlet concentration describes the contribution of pollutants from tunnel ventilation outlets – this has the least impact on air quality.
  • Computer modelling was used to measure the potential impacts on air quality during construction and operation of the project. Extensive ambient (outdoor) monitoring around existing motorway tunnels demonstrates that emissions from the ventilation outlets do not have a measurable impact on local air quality.
  • Regional air quality would be impacted in some areas where there would be more traffic on the surface roads. However, air quality is set to improve in many locations as traffic moves from surface roads (where emissions are currently at surface level), into the underground motorway tunnels which produce less emissions due to the free-flowing traffic (avoiding up to 28 sets of traffic lights). On balance, regional air quality would improve overall, particularly in the Inner West Local Government Area.
  • The layout of construction sites would be planned to minimise dust emissions, by locating machinery and dust causing activities away from surrounding buildings where possible, and erecting barriers around site boundaries. There is the risk that buildings in the immediate vicinity of the construction zone may experience some occasional dust impacts, however construction dust is unlikely to represent a serious ongoing problem overall. SMC will continue to monitor this and implement dust mitigation strategies to minimise impacts on local properties.

Dust mitigation measures are addressed further in Chapter 9, Section 9.10.1, of the EIS. Chapter 9, Section 9.10.2, of the EIS outlines how traffic management measures can control exposure to vehicle-derived air pollution.

In-tunnel ventilation

  • Tunnel infrastructure is designed to minimise traffic emissions by avoiding large gradients and reducing traffic congestion within the tunnels. This is further improved using ventilation outlets.
  • WestConnex is constructing state-of-the-art ventilation facilities that meet the EPA air quality criteria outlined in Chapter 9 of the EIS, meaning they are safe for motorists and the community.
  • Ventilation facilities are needed to maintain air quality within the tunnels. They do this by diluting the emissions with fresh air and then dispersing them through an elevated ventilation system.
  • Our analysis of existing tunnels and ventilation systems across Australia and internationally indicates that air filtration would not provide any measurable improvement to the air quality in the surrounding area.
  • Our tunnels would use longitudinal ventilation systems, which relies on the movement of air through the tunnels in the same direction as traffic flow. The air from the tunnel is released through ventilation facilities, supported by fans, which control air movement within the tunnel.
  • The ventilation system is automatically controlled using real-time traffic data – considering traffic mix and speed, plus feedback from air quality sensors in the tunnel which allow the fans to be adjusted accordingly.

The longitudinal ventilation system is described further in Chapter 5, Section 5.8.2, of the EIS.