Some of the major findings from this study include:
• Reversible sulfur poisoning is occurring in the in-use fleet of Tier 2 vehicles and has a
measureable effect on emissions of NOx, HCs, and other pollutants of interest.
• The effectiveness of high speed/load procedures in restoring catalyst efficiency is limited
when operating on higher sulfur fuel.
• Reducing fuel sulfur levels from 28 ppm to 5 ppm produces significant reductions in
emissions of NOx, HCs, and other pollutants of interest from a broad range of in-use Tier
2 vehicles.
• Bag 2 NOx effects, which are relatively large but based on low emission levels, were
found to be robust to sensitivity analyses related to influential vehicles and measurement uncertainty at low emission levels.