An on-board version of a fast response chemiluminescence analyzer with a 3 millisecond response time enables the recording of high temporal resolution transient NOx emissions during cold start and pull-away, gear changes, speed bumps and other real world transient conditions. Tests were performed on a 1.6 litre turbo GDI vehicle. The data has been correlated with on-board engine data available from the vehicle’s electronic control unit to study the underlying causes of these short-duration events. Exhaust gas was sampled from after the catalyst but before the silencer (muffler) to preserve all high frequency detail and to allow accurate integration of pollutant concentration and engine exhaust mass flow. Various aspects of the vehicle’s calibration are seen to contribute to the short-duration bursts of tailpipe emissions which would not be visible with slower response analyzers.