Tier 4 off-highway rules set: it starts in 2008, with new standards phased in through 2015; the age of aftertreatment dawns

The diesel emissions box is now officially small; make that very, very small. On May 11, the U.S. Environmental Protection Agency (EPA) officially announced the Clean Air Nonroad Diesel Rule, or Tier 4 off-highway to the rest of us. It also, almost officially, inaugurates the age of aftertreatment since most engine manufacturers, as it stands today, said it will require some sort of device after combustion to meet these new and very stringent standards (see accompanying tables).

Standards for new diesel engines will be phased in starting with the engines under 25 hp in 2008, and move up the horsepower charts until all but engines over 750 hp have to meet both N[O.sub.x] and PM standards in 2014. Off-highway engines over 750 hp will have one additional year to meet these new emissions standards.

Tier 4, said EPA, is expected to cut emission levels from construction, agricultural and industrial diesel-powered equipment by more than 90%. The rule, EPA said, complements the Clean Diesel Truck and Bus Rule announced December 21, 2000, which will place a fleet of heavy-duty trucks and buses on American highways that will be 95% cleaner than today's trucks and buses. On-highway compliance requirements take effect with the 2007 model year.

Maybe most importantly to the engine community, EPA also said the new rule will also remove 99% of the sulfur in diesel fuel by 2010, resulting in dramatic reductions in particulate matter from all diesel engines. By EPA's estimate, diesel fuel currently contains about 3000 ppm sulfur. The new rule will cut that to 500 ppm in 2007 and 15 ppm by 2010.

"We are going to make that burst of black smoke that erupts from diesels a thing of the past," EPA Administrator Mike Leavitt said. "We're able to accomplish this in large part because of a masterful collaboration with engine and equipment manufacturers, the oil industry, state officials, and the public health and environmental communities."

EPA's release announcing Tier 4 noted that, "the non-road rule represents an unprecedented commitment and collaboration that included the White House, EPA, the Office of Management and Budget, the environmental community, states and local governments, engine and equipment manufacturers, refiners, technology companies, and other groups and associations."

And in fact, most of the responding press releases from engine manufacturers acknowledged this cooperation.