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Technology Solutions

Diesel Filters Can Virtually Eliminate the Problem

photo of DPF installation

Unlike many of today’s complex environmental problems, diesel pollution is a problem with a readily available solution that can virtually eliminate particulate matter soot from diesel exhaust. Retrofitting diesel engines with tailpipe filters can provide immediate reductions in pollution exposure as well as near-term climate benefits, complementing long-term efforts to reduce CO2 emissions. Diesel particulate filters (DPFs) routinely reduce particulate matter by more than 90%. Recent federal regulations require these filters in all newly manufactured on-road and off-road diesel engines, but not in the millions of engines already in use that dominate the fleets, and which could operate for decades to come.

Additional Possibilities

dpf diagram

For engines that cannot be retrofitted with DPFs, flow through filters (FTFs) also offer the potential to cut diesel particulate matter and black carbon soot by approximately half. Numerous state and local agencies have begun to retrofit diesel fleets built in the 1990s and early 2000s with diesel filters (for example, transit buses, school buses, port trucks, and other fleets). One of the least effective retrofit options is the diesel oxidation catalyst (DOC), which reduces particulate matter by approximately 20%. DOCs do not remove black carbon, the climate-forcing component of diesel particulate matter.

Another way to clean up the fleet of existing diesel engines is to accelerate their replacement with new, cleaner engines through financial incentives and other means. It is important that any diesel engine that is replaced with a new engine is then “scrapped,” otherwise there will be no net improvement in emissions. Other options for reducing diesel exhaust exposure include: anti-idling measures and use of ultralow sulfur diesel fuel, especially useful for off-road applications such as construction, locomotives, and marine vessels.

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This comparison of particulate matter emissions from two nearly identical wheel loaders shows clearly the benefits of diesel particulate filter retrofits. See CATF's Diesel Videos for more on this example and others.