Diesel exhaust fluid (DEF; also known as AUS 32 and sometimes marketed as AdBlue[3]) is a liquid used to reduce the amount of air pollution created by a diesel engine. Specifically, DEF is an aqueous urea solution made with 32.5% urea and 67.5% deionized water. DEF is consumed in a selective catalytic reduction (SCR) that lowers the concentration of nitrogen oxides (NO
x) in the diesel exhaust emissions from a diesel engine.[4]