Diesel Exhaust Fluid (DEF) is a chemical used to reduce the amount of nitrogen oxides (NOx) emitted into the air by diesel engines.  DEF is a high purity chemical, comprised of 32.5% urea and 67.5% de-ionized water.
    Diesel Exhaust Fluid is produced to an international standard (ISO 22241).  In order to meet the 2010 EPA Diesel Emission Standards to reduce the amount of NOx emitted by diesel engines, several engine manufactures employed Selective Catalytic Reduction (SCR) as an after-treatment technology combined with Exhaust Gas Recirculation (EGR).  
    As explained by the American Trucking Association, “To reduce NOx, a small amount of DEF is injected directly into the exhaust upstream of a catalyst.  The DEF vaporizes and decomposes to form ammonia (NH3), which in conjunction with the SCR catalyst, reacts with NOx to convert the pollutant into nitrogen (N2) and water (H2O).” 
    Automotive grade Diesel Exhaust Fluid must meet stringent purity standards.  The American Petroleum Institute (API), licenses manufacturers who consistently meet the quality standards set by the International Organization for Standardization.  API issues a seal to those manufactures who are committed to the quality investment and processes.  TerraCair® Ultrapure has been certified by the API and proudly displays the API seal.