California enforcing NO₂ limits for diesel emission retrofits

6 November 2006

The California Air Resources Board (ARB) announced that all verified diesel emission control strategies used in California diesel retrofit programs must meet NO₂ emission limits effective January 1, 2007. Devices that exceed the NO₂ limits will no longer be considered verified after that date.

The first version of the California verification procedure for diesel emission control strategies included a post-control NO₂ limit (defined as 20% of the total baseline NOx emission) which was later suspended. In March 2006, the ARB introduced modified NO₂ requirements, with a two tier implementation schedule. Effective January 1, 2007, verified diesel emission control systems must not increase NO₂ emissions by more than 30% of the baseline NOx, and by no more than 20% from January 1, 2009.

The ARB has published a list of verified devices which meet the 30% NO₂ increase limit and, thus, will remain verified in 2007. All other currently verified systems will loose their verified status. Systems that already have been installed will remain in service as a valid compliance option, but no new devices that do not meet the NO₂ requirements can be installed from January 1^st.

The ARB issued a two month grace period (until February 28, 2007) for the installation of devices which loose their verification status, but had their sales contracts executed by October 26, 2006.

Emission control devices that meet the 20% NO₂ increase limit ahead of the 2009 deadline will receive a “Plus” designation, e.g., a “Level 3 Plus” system would provide an 85% PM emission reduction while meeting the 2009 NO₂ limit.

Many catalyst-based diesel emission controls—such as diesel particulate filters or diesel oxidation catalysts—promote the oxidation of nitric oxide (NO), the main component of NOx, to nitrogen dioxide (NO₂), thus increasing the NO₂ proportion in NOx emissions. Even though the total NOx is not increased, this may present a potential health and environmental issue, as NO₂ is a more reactive and toxic gas than NO.

Source: California ARB