Simulation of photochemical smog in the melbourne airshed: Worst case studies

Abstract

The impact of a large NO_x point source on photochemical smog in Melbourne is examined through the use of a numerical model described by Hess. Over most of the Melbourne Airshed the NMHC/NO_x ratio is found to be less than 10, in agreement with the results of Evans et al. For these cases trajectories passing through the Newport Power Station exhibit a decrease in ozone (compared to background values) of about 0.02 ppm and an increase in nitrogen dioxide of about the same amount due to Newport's emissions. This result confirms a preliminary finding by Form and Substance (1982).

However, worst case scenarios have not been previously studied. Measurements indicate that any trajectory that links the high NO_x from Newport and the high NMHC from Pt Cook will result in a worst case. The windfield observations reported here show the existence of a topographically generated mesoscale eddy in the airshed, as proposed by Spillane (1978, Clean Air12, 50–56.), and its location tends to link Newport and Pt Cook. Simulation of two cases indicates that under worst case conditions Newport's emissions increase the ozone concentration by 0.01–0.04 ppm. These conditions are estimated to occur on one day in four to one day in three of high oxidant days in Melbourne.