Valvoline Premium Blue Diesel Exhaust Fluid Enables On-Highway Diesel Engines To Meet The EPA'sNear-Zero NOx Initrogen Oxide) Emissions Levels Required For 2010 & Later. The Environmental Protection Agency Requires All 2010 & Later On-Highway Diesel Engines To Meet NOx (Nitrogen Oxide) Emission Standards. In Order To Meet These Lower Standards, Most Engine Manufacturers Are Using Selective Catalytic Reduction (SCR) Exhaust After-Treatment. These Systems Mix Diesel Exhaust Fluid (DEF) w/ Exhaust Gas & Use A Catalytic Converter To Change The NOx Emissions Into Nitrogen & Water.