American Petroleum Institute (API) - The API is a trade body responsible for certifying Diesel Exhaust Fluid (DEF) producers and distributors through its Diesel Exhaust Fluid Certification Program. Suppliers which have been approved by the API display its Diesel Exhaust Fluid Certification Mark on their products. All DEF suppliers listed on are API certified.

Diesel particulate filter (DPF) - A diesel particulate filter traps and stores solid particles, removing these dangerous emissions from the exhaust stream. All vehicle manufacturers use DPFs in their 2010 model heavy-trucks to meet the EPA's emissions standards.

Exhaust gas recirculation (EGR) - Exhaust gas recirculation is a technology that reduces emissions by lowering combustion temperature, this works by cooling and returning some of the exhaust gas to the engine inlet.

ISO 22241 - Is an international standard that defines the quality requirements for DEF including production, storage and distribution. View more information here.

Nitrogen oxides (NOx) - Nitrogen oxides (NOx) is the term used for a group of highly reactive gases which contain nitrogen and oxygen as NO or NO2. NOx cause of a range of environmental and health problems.

On-Board Diagnostics - An electronic telemetry system built into a vehicle which measures operating parameters and reports these to the driver. The system is responsible for applying torque penalties to vehicles operating without DEF, and ensuring the emissions control system (SCR or EGR) is working correctly.

Particulate matter - A harmful pollutant made up of small particles of unburned fuel and other solid particles. Particulate matter can penetrate deep into the lungs and over time can cause serious respiratory and cardiac problems. Smaller particle (less than 10 μm) are more dangerous than larger particles and DPF units are designed to remove these particles.

Selective Catalytic Reduction (SCR) - An emissions aftertreatment technology that reduces NOx emissions by breaking them down into harmless nitrogen and water. For more information on how SCR works see the Selective Catalytic Reduction page.

Tote - A standardized method of transporting and storing 275 or 330 gallons of a liquid chemical. In this context totes are used to store and distribute DEF. For more information see the Supply Formats section. Totes are also called Intermediate Bulk Containers (IBCs).

California Air Resources Board (CARB) - The state of California has the authority to develop its own emission regulations through CARB. Other states must either adhere to federal standards or adopt the Californian requirements (often more stringent than federal ones). However, they may not create their own.

Environmental Protection Agency (EPA) - The EPA sets the emissions standards for vehicles sold in the US. Manufacturers have to seek model approval from the government body.