A model for determination of motor vehicle emission factors from on-road measurements with a focus on submicrometer particles

The multiplicity of parameters that influence traffic-related emissions and that are often very difficult to measure or predict, makes the assessment of traffic emissions a very complicated process, strongly dependent on loca l conditions and usually associated with a high degree of error. The aim of this paper was to develop, calibrate and test a simple model for 'on-road' measurements of traffic emission factors as part of a major program focuss ed on the assessment of traffic contribution to fine and ultrafine emission s to the whole air shed and to local areas in south-east Queensland, Austra lia. A mathematical model developed was based on the mass balance concept f or on-road assessment of traffic-related emission rates. The model requires fewer experimental data points as input and is more applicable to the comm on on-road testing situation, when no more than two monitors of a specific pollutant can be used. The model was tested and calibrated using experiment al data on particle number concentration collected at a road-monitoring sit e using the scanning mobility particle sizer, and was applied to assess the emission factors of submicrometer particles emitted by traffic. The averag e emission factor obtained using the box model and the experimental data fr om road measurements was 1.75 x 10(14) particles km(-1) vehicle(-1), with a standard error of 67.6%. While the emission factor obtained was comparable with some results obtained from dynamometer studies and applied to the veh icle mix at the sampling site, they were significantly higher than the fact ors reported by other studies. (C) 2001 Elsevier Science B.V. All rights re served.