Title

Utah Wintertime Measurements of Heavy-Duty Vehicle Nitrogen Oxide Emission Factors

Document Type

Article

Publication Date

2-1-2022

Organizational Units

Chemistry and Biochemistry

Abstract

There have only been a few wintertime studies of heavy-duty vehicle (HDV) NOx emissions in the U.S., and while they have observed increased emissions, fleet characterization to identify the cause has been lacking. We have collected wintertime measurements of NOx emission factors from 1,591 HDV at a Utah Port of Entry in December 2020 that includes individual vehicle identification. In general, the NOx emission factors for 2011 & newer chassis model year HDV are significantly higher than 2017 spring measurements from California. The newest chassis model year HDV (2017 - 2021) NOx emission factors are similar indicating no significant emissions deterioration over the five year period though they are still approximately a factor of 3 higher than the Portable Emissions Measurement on-road enforcement standard. We estimate that ambient temperature increases NOx emissions no more than 25% in these newer HDV likely through reductions in catalyst efficiencies. NOx emissions rise to a significantly higher level for the 2011 - 2013 chassis model year vehicles, where within the uncertainties they have emissions similar to older pre-control vehicles indicating they have lost their NOx control capabilities within eight years. MOVES3 modeling of the Utah fleet under predicted mean NOx emissions by a factor of 1.8 but the MOVES3 estimate is helped by including a larger fraction of high emitting Glider Kit trucks (new chassis with pre-emission control engines) than found in the observations.

Publication Statement

Copyright held by the American Chemical Society.

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