catalyst survival as I recall. Here:
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"The new ULSD standards finalized by the EPA are crucial to the successful development of emission control equipment for heavy-duty diesel engines. The catalysts to be used in meeting the emission standards can be severely damaged by sulfur contamination. For example, catalyst-based particulate filters for diesel engines have shown significant losses of conversion efficiency with fuel containing 30 ppm sulfur, particularly in colder climates. With respect to NOx adsorbers, researchers have found that at fuel sulfur levels above 10 ppm, the heavy truck emission standard may not be attainable."
Happy now?