R. A. Wright
| The accumulation of vehicle emissions from valley
freeways
In 1984 it was recognised that major roads in valleys may cause a build up of motor vehicle pollutants. Since that time numerous studies have been undertaken to evaluate this risk. From the evidence obtained over the last sixteen years it is now possible to provide a more complete understanding of what happens and why. Still air conditions occur on a regular basis in Melbourne. These may
last one or two days and sometimes up to four days. During these events
wind speeds are low and air pollution levels are high. Visiblity is reduced
as motor vehicle pollutants build up around the city. Valleys are affected
when the weak general wind does not flush out the pollution in the valley.
On these occasions air flow can be up and down the valley. Evidence of
this type of flow was found during a 1984 VicRoads study in the Gardiners
Creek valley. The study monitored wind and the motor vehicle pollutant
nitrogen dioxide over a three-month period. At the same time the nearby
Environment Protection Authority (EPA) station at Camberwell monitored
both wind and nitrogen dioxide above the valley. The results indicated
that the low strength wind at Camberwell was not always sufficient to flush
out the traffic pollution in the valley.
Over a three month period valley pollution exceeded normal pollution on a significant number of days (see graph above). Over a period of 92 days, 27 days showed high nitrogen dioxide pollution in both locations. Of these 27 days, 3 days recorded normal pollution noticeably higher than valley pollution. The graph shows the 9 highest differences. The most significant feature of this graph, apart from the obvious extra pollution which occurred in the valley, was that it was prepared in 1994, some ten years after both EPA Victoria and VicRoads had concluded that the new road in the Gardiners Creek valley would have only a minor effect on pollution in the valley. At that time the new road was to be a four-lane arterial. However, the road reserve made provision for a six-lane freeway. This latter option had the capacity to double the 1984 traffic emissions in the valley which caused the extra pollution shown in the graph. Computer modelling Computer modelling was used to establish the air quality effects of the Gardiners Creek valley arterial road link in 1984, the Eastern Arterial Road and Ringwood Bypass in 1987, the upgrading of the South Eastern Arterial Road to the City Link freeway in 1994 and an in-house study, also in 1994, for the Mullum Mullum Creek valley. None of these studies indicated the level of valley pollution shown in the graph above. Valley pollution was always predicted to be similar to normal pollution. The graph shows the real answer. The problem is not new When the proposal to build the Eastern Freeway to Ringwood was released for public review in 1987, the air quality study was found to contain errors. A second Review Panel, in 1990, recommended that “Vicroads should conduct further investigations into air quality modelling techniques in relation to the effects of topography on predictions and with particular respect to creek valleys”. In 1994, a Review Panel approved the VicRoads study for the City Link project, including the Gardiners Creek valley freeway, without seriously addressing and resolving the issues raised in the 1990 Review Panel recommendations. In 1998, a Review Panel for the Scoresby Freeway extension was requested to review all of the above issues. This Panel regarded the issues raised by KMFA as “a matter for serious consideration” and indicated “support” for the 1990 Panel recommendations. PM10 fine particle pollution The above pollutant has now replaced nitrogen dioxide as the pollutant of primary concern. Levels of nitrogen dioxide are falling and the 24-hour EPA limit of 6.0 pphm is no longer considered to be critical. Now fine particle pollution, measured as a daily average, is regarded with more concern and is linked with significant adverse health effects. Fine particle pollution may be emitted by motor vehicles in similar quantities to nitrogen dioxide. The current EPA objective of 50 micrograms per cubic metre averaged over a 24-hour period is currently exceeded, on an average, one percent of days annually. Clearly additional fine particle pollution, such as may occur in a valley containing a major freeway, needs new careful study. What is required now A new air quality study is required for the Mullum Mullum valley. This study should recognise the previous critical comment and address the issues of model suitability and validation. Ideally the model should be able to predict the differences noted in the preceding graph. The new study report should be submitted for peer review by a committee equivalent to that provided by the Standards Association of Australia. The results of this peer review should be made publicly available. Conclusions It is evident that air quality matters relating to major roads in valleys have attracted justified public criticism. This situation would seem to require a combined effort from both VicRoads and EPA Victoria. There is uncertainty associated with fine particle pollution—both in terms of how much comes from the various sources and vehicle emission rates. These issues have not been comprehensively addressed in any study by VicRoads for a major road in a valley. Without a sound verified answer to the question: “How often and by how much” for fine particle pollution in the Mullum Mullum valley, the Victorian Government should not proceed with the proposed freeway extension. |