Real-driving emissions from cars and light commercial vehicles - Results from 13 years remote sensing at Zurich/CH

We report on long-term remote sensing measurements of light duty vehicle emissions at one site close to Zurich/Switzerland. The time series of annual measurements at the same site between 2000 and 2012, the same season, and virtually the same instrument is unique, probably worldwide. We analyze the development of unit exhaust emissions from model years 1985 until 2012, covering all five Euro emission limit stages in force. NOx emissions from both diesel cars and light commercial vehicles have actually increased in real-driving over time although emission limits have been progressively tightened. This behavior is explained mostly by a significant discrepancy between engine conditions during real-driving and the homologation test procedure. This discrepancy is not important for the other pollutants or for gasoline light duty vehicles, for which the emission control equipment is found working over a wide range of engine conditions. Our results confirm emission factors from the latest HBEFA model when deterioration and engine load are accounted for. Recent remote sensing measurements of diesel cars and light commercial vehicles in London are at the same or higher levels. However, given that engine load is much lower in London, this coincidence is rather puzzling. A key uncertainty is the amount of primary NO2 in the exhaust, and potential systematic differences between dominant brands in European countries. Both needs further investigation