A comparison of light-duty vehicle NOx emissions measured by remote sensing in Zurich and Europe

Remote sensing is one technique used to measure real-world NOx emissions in Europe. Remote sensing measurements conducted by the Canton of Zurich are unique in terms of how consistently they have been collected since 2000 and the steep road grade at the main remote sensing monitoring site. This paper compares the remote sensing measurements and emissions in Zurich to a large dataset of other European remote sensing measurements—the so-called CONOX database—focusing on the effect of estimated engine load on NOx emissions.

A comparison of the CONOX and Zurich datasets for diesel passenger cars shows that while Euro 6 diesel vehicles do show significant reductions in average real-world NOx emissions, some Euro 6 vehicle families still emit as much NOx as the worst Euro 5 families. The three manufacturer groups with the lowest average diesel NOx emissions had comparatively low emissions across a wide range of operating conditions. However, diesel vehicle manufacturers with higher emissions experienced large increases in fuel-specific NOx emissions as engine load increased. This is likely primarily related to poor emission control systems and calibration that are not robust as engine loads increase. Average gasoline NOx emissions were lower in Zurich than for the average of the other measurement sites, suggesting that gasoline vehicles control emissions better at higher engine load.

In terms of annual NOx emissions in Zurich, all high-emitting vehicle families were diesel-fueled, and the majority were Euro 5 vehicles. Out of all Euro standard and fuel type combinations, diesel Euro 5 vehicles were estimated to emit almost half of annual NOx emissions. Ten popular vehicle families, most of them Euro 5 vehicles, were estimated to account for more than one-third of passenger car NOx emissions in Zurich while they made up approximately one-eighth of the Zurich passenger car fleet.

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