Legislation

Since the passing of the Clean Air Act in the 1970s, the Environmental Protection Agency (EPA) has regulated emissions of NOx, particulate matter and other pollutants from road vehicles, electric utilities, and off-road equipment.

Heavy-duty trucks

The EPA adopted emissions standards for heavy-duty vehicles in 2001 which would govern models manufactured from 2007 onwards and required manufacturers to reduce particle matter emissions to 0.01 g/bhp-hr and NOx emissions to 0.20 g/bhp-hr. Between 2007 and 2009 there was a phase-in period for which allowed NOx emissions of 1.2 g/bhp-hr, but from 2010 all medium and heavy duty diesel vehicles have had to meet the standards. Manufacturers that exceeded requirements before 2010 such as Cummins and Navistar are allowed NOx emissions up to 0.5 g/bhp-hr under a bank and trade system.

Off-road vehicles

In 2004 the EPA issued its final program to reduce emissions from off-road diesel engines, to be phased-in from 2008 to 2015. The Tier 4 off-road rule established new emissions standards and test procedures and led to the implementation of Selective Catalytic Reduction (SCR) technology by a number of manufacturers.

The exhaust standards require emissions of particle matter and NOx be further reduced by about 90% from Tier 1-3 standards. Beginning in 2008, the new Tier 4 engine standards for five power categories of engines from under 25 hp to above 750 hp have been phased in.

Cars, pickup trucks and SUVs

The Clean Air Act first set out emissions rules for cars as part of a set of amendments in 1990. Tier 2 standards were adopted in December 1999, with an implementation schedule of 2004 to 2009. Under Tier 2 federal regulations emissions limits were made more stringent and the same emission standards were applied to all non-commercial vehicles under 10,000 lbs and commercial vehicles under 8,500 lbs.

This meant passenger cars, pickup trucks and SUVs all become subject to the same rules and, because the standards are expressed in terms of emissions per mile, larger vehicles require more advanced engine and aftertreatment technology than smaller vehicles.

Tier 2 limits the average NOx emissions of all vehicles sold by a manufacturer to 0.07 g/mile. The Environmental Protection Agency allows emissions from vehicles which are under this limit to be offset with those above it in a complex system which divides vehicles into different 'Bins' based on whether they are above or below this limit.

American Petroleum Institute

The American Petroleum Institute (API) runs a voluntary program for certifying DEF producers and distributors through its Diesel Exhaust Fluid Certification Program. Suppliers who have been approved by the API display its logo on their DEF products, guaranteeing the quality of your purchase and its suitability for proper SCR operation. All DEF marketers listed on www.discoverDEF.com are API certified.

ISO standard

The production, handling and transportation of Diesel Exhaust Fluid (DEF) is governed by the ISO 22241 standards. The key points are:

Diesel Exhaust Fluid (DEF) must have a urea concentration of 32.5% by weight. This concentration was chosen because it is has the lowest freezing temperature, 12°F.
The maximum level of impurities such as calcium and various metals such as iron, copper, zinc and aluminum are clearly specified. These limits are very low, to ensure reliable operation of the SCR system.
This definition excludes the use of urea grades used in agriculture, and requires water purified by distillation or deionization or similar.
Materials which are safe for the storage and handling of Diesel Exhaust Fluid (DEF). Carbon steel and aluminium are not allowed.
Handling guidelines.

The ISO standards are available for purchase for a small fee from the ISO website.