For diesel buses, this study has demonstrated that in-use emissions of NO measured in real traffic roughly correlates with the certification levels for NOx for Euro 2, Euro 3 and Euro 4. The NO2/NOx fraction for DPF equipped Euro 2 and Euro 3 diesel buses was estimated to approximately 25 %. The effect of vehicle age as regards NO-emissions was studied for Euro 3 EGR diesel buses and Euro 2 diesel buses equipped with DPF. For the EGR buses there was no evidence of ageing effects. For the DPF buses there seemed to be a tendency for increased NO emissions with increasing vehicle age. However, this does not necessarily imply that NOx emissions have increased an equal amount, since the reason for increased NO may be a deterioration in the NO to NO2 conversion that takes place in the DPF. It is not known whether a decrease in NO2 concentration will have any effect on the efficiency of the particle filter. CNG buses certified according to the EEV standard and equipped with catalysts displayed for NO emissions a statistical distribution that was similar to what is normally observed for modern gasoline passenger cars. Most buses in the data set had quite low emissions, but there were also 'high-emitters' which were few in number but had a clear influence on average emissions. The average NO emission was significantly higher (in relation to e.g. Euro 3) than was expected from the certification levels. This result indicates that the emissions of CNG buses need to be checked at regular intervals in order to maintain the environmental benefits associated with CNG technology. Further on, this study has demonstrated that remote sensing is a viable and cost-efficient alternative to more costly laboratory methods as regards emission measurements on in-use buses. If future development of remote sensing systems could allow for measurement of NO2, particles and NH3 (for SCR applications), the method would be further strengthened.
On-road optical remote sensing measurements of in-use bus emissions
Optische Fernmessung von Omnibusemissionen im Straßenverkehr
incl. COST 346 - Final Conference, Transport and Air Pollution, International Symposium, 14 ; 241-248
2005
8 Seiten, 4 Bilder, 3 Tabellen, 12 Quellen
Conference paper
English
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