Issue: A new rule from EPA this spring could reduce diesel-engine emissions by 90%. What does it mean for your fleet?

While the Clean Air debate over whether or not diesel exhaust emissions pose a significant health risk continues, no one disputes the fact that diesel trucks emit thousands of tons of smog-forming nitrogen oxides (NOx) and particulate matter (PM) each year. Consequently, regulations to decrease air pollution are increasingly targeting diesel vehicles.

This spring, EPA is expected to propose even stricter emissions standards for trucks manufactured after 2007. Designed to reduce emissions by 75% to 90%, the new rules present a hefty challenge to an industry that's already cut emissions from new trucks by more than 85% during the past 15 years.

In order to meet the new emissions requirements, engine OEMs must develop new technologies to further reduce the amount of NOx and particulates spewed into the air. Most of the methods currently under development, however, involve the use of catalysts that are sensitive to sulfur. In other words, sulfur in the fuel "poisons" the catalyst and prevents it from doing its job, which is to eliminate NOx and/or particulates.

According to engine manufacturers, the only way around this seems to be to reduce the amount of sulfur in the fuel. Without a reduction in the sulfur content of diesel fuel it will be impossible for new vehicles to meet EPA's proposed standards.

Consequently, EPA is proposing that the sulfur content of fuel be lowered from its current maximum of 500 parts per million (ppm). Engine manufacturers have suggested a maximum of 5 ppm, while the American Institute of Petroleum Engineers advocates an average level of 30 ppm, with a cap of 50 ppm. The group warns that anything less than 20 ppm could be extremely expensive to make and distribute.

EPA is currently considering a maximum sulfur content of 5 to 40 ppm, which would mean an estimated cost increase of 4 cents to 9 cents/gal. of fuel.

If that sounds like a lot to swallow, consider that some of the emissions-control technologies under development could also double the cost of new engines. Not to mention changes in maintenance requirements such as frequent catalyst replacement and filter cleanings, as well as separate 30-gal. tanks of urea that would have to be refilled just like the fuel tanks.

There's also some concern over the properties and performance of lower-sulfur diesel. For example, removing the sulfur can affect fuel lubricity.

None of us will forget what happened the last time EPA changed the makeup of diesel fuel. After years of preparation and negotiations among oil and engine manufacturers, a proposed rule was issued in 1993 that was embraced by all parties, including the trucking industry.

Lower-sulfur diesel (no more than 500 ppm sulfur) was introduced to help reduce particulate matter emissions from heavy-duty vehicles. But fleets soon experienced equipment breakdowns, fuel leaks, price spikes, and persistent supply shortages over the course of a six-week period from October to November of that year. Hopefully, EPA can avoid a repeat of this frustrating and costly experience.

As we learned in 1993, tinkering with the cost, performance, and distribution of diesel fuel can create a severe disruption to trucking. Such a move must be handled carefully.

At the same time, however, we need to keep in mind the potential benefits of using cleaner lower-sulfur diesel fuel. When combined with new engine technology, lower-sulfur diesel fuel has the potential to cut diesel engine emissions in half, leading to a cleaner environment for all of us.

In addition, cleaner diesel engines could lead to a wider acceptance of them by the general public and an end to the anti-diesel campaigns that have been springing up throughout the country.