The traditional on-road emissions remote sensing technique has been enhanced with the ability to monitor not only CO, CO 2 , HC and NO, but also SO 2 , NH 3 and NO 2 . Modern diesel powered vehicles, particularly in Japan and Europe are equipped with diesel particle filters (DPFs). These traps are frequently designed to be self regenerating by means of a prior catalytic oxidation of the exhaust NO to NO 2 . Because of this intentional conversion to NO 2 , the ratio of NO 2 to NO in modern

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... vehicles is very different from older vehicles. The detailed results of measurements from several thousand vehicles measured in Japan, Austria and Sweden in 2006 and 2007 will be compared to results from the USA where there are very few vehicles equipped with DPFs. The overall picture is vehicles without DPFs in the USA emit between 5 and 10% NO 2 while vehicles with DPFs are often observed at 50% NO 2 by moles. This, together with the overall NO x reductions has strong negative implications for local photochemical ozone production.