Concentrations of NOx and NO2 in urban atmospheres have remained stubbornly high in recent years. The principal reason for the lack of decrease in concentrations is that vehicle emissions of NOx and NO2 have not decreased as much as expected.
To address this issue King’s has undertaken work sponsored by Defra to investigate vehicle emissions in considerable detail using a remote sensing technique. In earlier work (Carslaw et al, 2011, with the University of Leeds) one of the main findings was that diesel NO emissions from passenger cars had not decreased as much as expected.
In more recent work, using a vehicle emission remote sensing instrument developed by the University of Denver, USA that measures both NO and NO 2 as well as ammonia, many new insights were made.
One of the most important discoveries was the large range in NO 2 emissions due to different vehicle emission after-treatment technologies (Carslaw and Rhys-Tyler, 2013) available here:
New insights from comprehensive on-road measurements of NOx, NO2 and NH3 from vehicle emission remote sensing in London, UK
Also, as shown in Carslaw et al (2013) more recent diesel engine technologies are shown to emit higher emissions of NO x compared with older technologies for increased engine loads.