Did you know that today's diesel-powered light-duty vehicles must meet the same stringent emission requirements as gasoline-powered models?API helped those diesel vehicles meet the same air quality standards as gasoline vehicles in two ways. First, by producing Ultra-Low Sulfur Diesel (ULSD) fuel, which burns more cleanly than earlier forms of diesel fuel. And second, by developing a certification program for Diesel Exhaust Fluid (DEF). DEF is a liquid that is injected into the exhaust system of diesel vehicles from a container located under the hood in most cars. The DEF hydrolyzes into ammonia when injected into the exhaust, and the ammonia reacts with the nitrogen oxide (NOX, which is a precursor to ground-level ozone formation) in the catalyst and converts it to pure nitrogen and water. The process is called Selective Catalytic Reduction, or SCR, and it has been used for years in coal-burning power plants. It is new to diesel cars in model year 2009 and is being applied to heavy duty trucks in the 2010 model year.

API developed the certification program at the request of the diesel vehicle and engine makers, who needed to demonstrate to the U.S. Environmental Protection Agency (EPA) that their vehicles would meet the emissions requirements over the lifetime of the engines. This meant the quality of the DEF needed to be assured by a certifying entity. EPA specifically cited API's Engine Oil Licensing and Certification Program as a model.

Adding a new supply of API-certified DEF to a diesel vehicle is as easy as adding windshield-washing fluid. And EPA says DEF, when combined with ULSD and new diesel engines, will help to reduce NOX emissions from diesel vehicles by 90 percent.