Atmosphere Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Lead Author: Dr Peter Manins, Environmental Consulting and Research Unit, CSIRO Atmospheric Research, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06746 9
Urban Air Quality (continued)
Indicators of the condition of air quality (continued)
Carbon monoxide in urban areas [A Indicator 3.1]
High carbon monoxide concentrations may occur in poorly ventilated urban canyons or tunnels, but sporadically and only then during the morning and evening rush hours. There have been exceedences of the eight-hour NEPM Standard of 9 ppm in the centres of Sydney and Adelaide (Figure 90). These are areas of high traffic density and low traffic flow, so that there is a tendency for vehicles to sit under idling conditions for extended periods.
Figure 90: Number of days in Sydney and number of exceedences in Adelaide central business districts when eight-hour averaged carbon monoxide was above the NEPM Standard of 9 ppm.
Negative values indicate zero exceedences. Zero values indicate no data.
Source: State environmental authorities
In Sydney, the data record is not complete because of building works near the monitoring station. In Adelaide, high concentrations have occurred particularly on weekends, when there is an influx of patrons to cinemas and clubs. The monitoring station, in Hindley Street, is in an area that is enclosed by tall buildings, creating a canyon effect. Hence, the station has a historical pattern of carbon monoxide concentrations which exceed the National Environment Protection Standard of 9 ppm averaged over eight hours. The pattern is highly seasonal in both cities. The highest eight-hour averaged concentrations of carbon monoxide for selected Australian cities are shown in Figure 91.
Figure 91: Highest eight-hour averaged carbon monoxide concentrations for selected Australian cities.
Source: State and territory environmental authorities
Because urban CO is so strongly associated with motor vehicles, the declines shown in Figures 90 and 91 must reflect the response to the exhaust emission standards that were successively applied under ADRs for new vehicles (see Table 24). The first controls on carbon monoxide emissions were instituted under ADR27A in 1976, which set a limit of 24.2 g/km. In 1981, this was reduced to 18.6 g/km as part of ADR27C and then reduced to 9.3 g/km in 1986 as part of ADR37/00.
The sudden changes in ADR standards show up in the concentrations as a steady decline from new vehicles with lower emissions replacing older, more polluting vehicles. It takes about 10 years for most of the vehicle fleet to comply with an ADR as a result of this replacement. Thus, the present situation, which indicates overall compliance with the NEPM standard for carbon monoxide (see Figure 91), results from the imposition of the ADR37/00 rules in 1986.