This document provides a test methodology for collecting comparable emissions test data for different light duty vehicle makes and models, to allow the comparative rating of vehicles. It covers topics around the technical conducting of tests and reporting results, which includes equipment, calibration, test boundaries and outputs.
The scope has been defined in order to achieve two priorities. First, the data shall be most relevant to the pressing problem of poor air quality caused by nitrogen oxide emissions from light-duty vehicles – hence the focus on diesel vehicles. Second, factors are excluded that are relatively less important in the characterisation of the vehicles, in order to reduce variability and help facilitate comparable test data. For example, the highly variable cold start emissions are excluded as they make up a smaller proportion of total emissions from pre-RDE vehicles due to the typically high emissions levels during warm start.
Particle number emissions are excluded due to their variability and lower levels from diesel vehicles with particle filters. These areas could be included in future work, beyond the scope of this CWA.
The methodology in this CWA focuses on the collective nitrogen oxide emissions as this is what is regulated at the tailpipe. However, nitrogen dioxide emissions shall also be reported where available, as this is relevant for ambient air quality compliance.
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