Remote sensing of NO and NO2 emissions from heavy-duty diesel trucks usingtunable diode lasers

On-road remote sensors can measure the emissions of motor vehicles under re al-world conditions. The most sensitive remote sensing technique reported t o date is tunable infrared laser differential absorption spectroscopy (TILD AS). A TILDAS remote sensor was used in this study to measure the NO, emiss ions of heavy-duty diesel trucks (HDDTs). The remote sensor could operate w ith an optical path length of 88 m or more than five times that of NDIR-UV instruments. Good agreement was obtained when comparing the TILDAS measurem ents with the on-board measurements of an instrumented HOOT. The distributi on of NO emissions from HDDTs was found to be close to normal. Remote sensi ng of NO;, emissions was demonstrated for the first time. The NO, emission factor determined in this study is consistent with other recent measurement s. These emissions are underestimated in the EPA inventory, although part o f the discrepancy can be explained by the effect of a "defeat device" that increases NO, emissions.