A study carried out for the Roads and Traffic Authority (RTA) in October and November 1994 looked at the composition of exhaust gas emissions from the NSW motor vehicle fleet. The data gained from this study was to be used to validate the motor vehicle component of the Metropolitan Air Quality Study emissions inventory as well as information on the mass emission rates to enable models to be established for road side pollutant concentration estimations.

The ventilation exhaust system of the harbour tunnel enabled pollutant concentrations of carbon monoxide, sulphur dioxide, oxides of nitrogen, benzene, total hydrocarbons and other air toxins to be measured while the breakdown bays of each tunnel were used to measure total suspended particles (TSP), particles contributing to PM IO, lead in TSP and dioxins.

An average of 128 µg/M³ was recorded for PM 2.5 (a range of 73-197 µg/M³ This corresponded to a range of 0.19-0.46 for the ratio of PM 2.5 to TSP concentration. High particle concentrations were observed with peak morning traffic and continued to vary with changing traffic volumes.