Evaluation of Vehicle Exhaust Gas Odor Intensity Using Natural Dilution 700105
Although exhaust gas odorants are generally a product of engine and fuel parameters, it is the vehicle that the public associates with exhaust odor. The vehicle and its movements have a large influence on the dispersion of exhaust odorants and, therefore, on the actual public exposure to exhaust odor. A considerable amount of public exposure to vehicle exhaust odor results from municipal operation of diesel-powered buses, especially during the bus-stop sequence. Panel test procedures were developed for field evaluation of full-scale vehicle exhaust odor intensity during the idle and acceleration portions of a simulated bus-stop sequence.
Odor tests, based on natural dilution of the vehicle exhaust to the odor threshold, were conducted in a controlled environment, indoors in large buildings. Different degrees of exhaust dilution were achieved by randomly varying the distance from the test vehicle to the panelists. Panelists were required to make yes-or-no decisions on whether or not they could detect an odor above the background level.
Exhaust odor intensity was expressed in terms of the threshold response distance, with greater threshold response distances indicating greater exhaust odor intensity. The test procedures gave adequate repeatability. Six repeat idle tests with one bus gave threshold response distances ranging from 27 - 32 ft, averaging 29 ft. Four repeat acceleration tests with another bus gave threshold response distances ranging from 32 - 41 ft, averaging 36 ft.
Idle tests with two different buses in two different test facilities showed repeatable differences in the exhaust odor intensity, indicating that the procedure was capable of discriminating between two odor sources of differing intensity.