Air Quality Monitoring
Air Quality Ventilation System
The ventilation stack is located between the Western Distributor viaducts near the north-western corner of the existing Harbour and Bathurst Street intersection.
The colour, cladding and architecture of the stack have been determined in consultation with the Roads and Traffic Authority (RTA), other Government Departments and stakeholders including the Sydney Harbour Foreshore Authority (SHFA), City of Sydney Council and the Air Quality Community Consultative Committee (AQCCC). The stack has been designed to blend in with the surrounding urban landscape. The preferred colour selection is a light grey colour similar to nearby buildings in Darling Harbour.
How the ventilation system works
Key features of the ventilation system for the Cross City Tunnel are:
- Jet fans along the ceiling of the tunnels and access ramps to control air flow.
- A main underground ventilation station at the western end near Druitt Street.
- A ventilation tunnel connecting the main ventilation station to a single ventilation stack near the Western Distributor in Darling Harbour.
- Ventilation of cross passage egress tunnels for pressurisation.
- A ventilation cross-over passage and ventilation station at the eastern end of the main tunnels.
- A bypass ventilation tunnel that runs beneath the main road tunnels connecting the eastern crossover and western ventilation stations.
- A bypass fan station at the western end that will generate airflow in the bypass ventilation tunnel.
In the event of traffic incidents or extreme adverse external environmental conditions, such as bushfires, contingency measures and traffic management will be deployed to manage air quality in the tunnel.
Normal operating conditions
At the Harbour Street (Darling Harbour) end of the eastbound tunnel, air is drawn into the tunnel by a combination of the piston effect of the traffic and the jet fans installed along the tunnel roof. The air then travels east, mixing with fresh air drawn from the portal at Bourke Street (where the Cross City Tunnel connects with the Eastern Distributor) and the eastbound exit portal in Rushcutters Bay. Air then flows in the westbound tunnel via the eastern ventilation cross-over passage.
Inside the main westbound tunnel, the air from the eastbound tunnel mixes with fresh air from the Rushcutters Bay portal, the entry portal from the Eastern Distributor and the exit portal at Sir John Young Crescent. The air then flows west under both the piston effect of the traffic and the jet fans attached to the tunnel roof. The main fan station, positioned near Druitt Street, extracts the air from the westbound tunnel and directs it to the ventilation stack where it is discharged into the atmosphere.
During times of heavy traffic or a blockage in the tunnel, air extracted from the eastbound tunnel at the eastern cross-over ventilation station is drawn into the separate ventilation tunnel not the westbound tunnel. The air in the ventilation tunnel is extracted via a separate bypass fan station adjacent to the main fan station (exhaust chamber) in the western end.
In the westbound tunnel, the air is extracted via the main fan station (exhaust chamber) and mixed with the exhaust air from the bypass ventilation duct (eastbound tunnel air) before being directed through the ventilation stack.
Air quality monitoring
Inside the tunnel
The Minister for Planning's Condition of Approval 257 requires carbon monoxide to be monitored inside the tunnel at locations including the stack, portals, ramp junctions and crossovers and exhaust in-take ducts.
An independent expert monitors compliance and ensures that the in-tunnel monitoring stations are maintained. In addition, the NSW Department of Environment and Conservation (DEC) has specified the Approved Methods for the Sampling and Analysis of Air Pollutants in NSW. These results will be made available to the Department of Infrastructure, Planning and Natural Resources, the Department of Environment and Conservation and the NSW Department of Health.
The Cross City Tunnel ventilation system is operated to ensure that the in-tunnel carbon monoxide (CO) levels meet the goals set by DIPNR under the Minister for Planning's Conditions of Approval. Condition 258 requires that the CO exposure of motorists is kept below 50 parts per million measured over a 30 minute rolling average and 87 parts per million measured over a 15 minute average.
In addition, Condition 259 requires that CO levels in the tunnel do not rise above 200 parts per million measured over a 3 minute rolling average at any point in the tunnel.
Ambient Air Quality - August 2005 ~ August 2008
Four separate monitoring stations were established at a number of ground level and elevated locations for air quality monitoring in accordance with the requirements of the Conditions of Approval 262 to 269.
The AQCCC oversighted monitoring of air quality at one Community Based Monitoring Station sited in Tumbalong Park. The results of all monitoring undertaken during August 2005 ~ August 2008 where made available on the Cross City Tunnel website and provided to the various parties including the AQCCC, the Department of Environment and Conservation and the Department of Infrastructure, Planning and Natural Resources.
Monitoring of ambient (or background) air quality and meteorological conditions at the monitoring stations was carried out by a NATA (National Association of Testing Authorities) accredited organisation. Independent auditing of the operating procedures and the monitoring data occurred every six months.
In-Tunnel CO data
CO data for a given hour will be available at 30 minutes after the following hour. For example, data for 09:00 to 10:00 is available at 10:30.
Monthly summaries of CO are also available on this site. To view the most recent data go to the In Tunnel Data.
Historical data is available in tabular form for the following time periods:
Hard copies of monthly validated reports (containing ambient and in-tunnel data) are available from the Customs House Branch of the City of Sydney Council Library.