You have likely encountered the term “Clean Diesel” in recent years. It’s a term that sounds relatively new but which in reality is based on technology in place for decades. The concept at the heart of “Clean Diesel” is Selective Catalytic Reduction (SCR) which has long been used to reduce stationary source emissions. The U.S. EPA updated diesel engine standards back in 2010 and SCR became the technology used to meet these new standards.