Emission control, vehicle tailpipe standards

There is currently no air quality regulation in Europe or any other part of the world to control the ambient concentrations of particles on a number basis. However, particle numbers are currently being regulated at vehicle tailpipe exhausts through Euro-5 and Euro-6 emission standards [103]. These are the first ever limits of this kind, though only applicable in Europe, to control the emissions of particle numbers at source. These standards include a lower size limit of 23 nm for minimising the... 

The composition and quantity of the particles emitted from motor vehicles could be determined by direct and indirect methods. The most widely used methods for evaluating vehicle tailpipe emissions are dynamometer tests, which involve measurements of emissions from selected vehicles using standardized driving cycles under controlled conditions. However, a key concern with these tests is that they do not fully represent real-world driving conditions and emissions. A number of studies reported that particulate emissions from motor vehicles operated under real-world conditions can be significantly different from the results obtained from dynamometer-based studies conducted in the laboratory (Fraser et al. 1999). 

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