Diesel Retrofits

Download the Diesel Retrofits – What You Need to Know PDF.


When diesel engines burn fuel, they leave behind a dangerous stew of emissions. Because diesel vehicles and equipment often operate on the street level, this pollution is emitted exactly where people breathe. Diesel exhaust is one of the most dangerous pollutants, and can be the cause of asthma attacks, heart attacks, strokes and early deaths. To help save the lives and health of many people, technology and regulations can make diesel engines less pollutant. Clean diesel advocates have a goal of reducing direct diesel fine particulate matter emissions by 70 percent by 2020.

What is the technology?

While there are several varieties of diesel pollution controls, the two most common are:

  • Diesel Particulate Filters (DPFs)
    DPFs are installed in the engine exhaust system and physically trap particles in the engine exhaust before they leave the tailpipe. Particles trapped in the filter are oxidized to carbon dioxide and water.
  • Diesel Oxidation Catalysts (DOCs)
    DOCs are stainless steel canisters installed in the exhaust system. They use a chemical process to break down pollutants in the exhaust stream into less harmful components. As exhaust gases pass through a DOC’s honeycomb structure, pollutants and particulate matter are chemically oxidized to harmless gases.

Testing indicates that these filters are so effective that they can eliminate nearly all harmful soot emissions. DPFs are most effective, and when used with Ultra Low Sulfur Diesel fuel, can reduce at least 90 percent of soot emissions.

What are the impacts and benefits?

All new diesel engines in trucks and buses, model year 2007 or newer, are federally mandated to be 90 percent cleaner. New offroad equipment, such as construction equipment, also began meeting similar federal requirements during a 2008-15 phase-in period. For every dollar spent on reducing particulate matter pollution from diesel engines, $12 will be avoided in health damages. 100% battery powered electric trucks and buses are also commercially available.

What about engines built before 2007?

Diesel engines have a very long lifespan. As a result, there are still approximately 11 million old, dirty diesels in use in the United States. Fortunately the same pollution control technology can be retrofitted onto existing older engines in use today. The U.S. Environmental Protection Agency estimates that retrofitting 10,000 engines would eliminate roughly 15,000 tons of harmful pollution each year.

How can I take action?

You can help Respiratory Health Association advocate for diesel retrofits and other clean air policies. Become an RHA  e-advocate today. {Add advocacy boilerplate language}