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

On-road remote sensors can measure the emissions of motor vehicles under real-world conditions. The most sensitive remote sensing technique reported to date is tunable infrared laser differential absorption spectroscopy (TILDAS). A TILDAS remote sensor was used in this study to measure the NO, emissions of heavy-duty diesel trucks (HDDTs). The remote sensor could operate with 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 measurements with the on-board measurements of an instrumented HOOT. The distribution of NO emissions from HDDTs was found to be close to normal. Remote sensing of NO;, emissions was demonstrated for the first time. The NO, emission factor determined in this study is consistent with other recent measurements. These emissions are underestimated in the EPA inventory, although part of the discrepancy can be explained by the effect of a "defeat device" that increases NO, emissions.