AIR AMD RADIATION

Dear Manufacturer or other Interested Party:

Subject: Nitrogen Dioxide Limits From Retrofit Technologies

       This is to inform you that the US Environmental Protection Agency's (EPA's)
National Clean Diesel Campaign (NCDC) is establishing a nitrogen dioxide (NOi) limit
for diesel retrofit technologies verified under the NCDC's Retrofit Technology
Verification Program. As you likely know, the California Air Resources Board (ARB)
has established limits for increases in NOi emissions for diese! emission control
strategies. In establishing an N>2 limit for NCDC verified technologies, EPA intends to
harmonize with ARB's limits, test procedures and requirements for technologies included
on the NCDC's Verified Technologies List,  It is appropriate to avoid potential increased
NO2 levels as greater numbers of engines are retrofitted, although the EPA does not have
an immediate pressing concern for NOi emissions from retrofit technologies. We
believe that harmonizing with ARB's NC2 limit is an appropriate action that will help
limit NOa emissions, and enable retrofit technology manufacturers to produce one
technology that can be marketed nationwide while meeting the same Nt>2 requirements.

       Effective January 1, 2009, the NCDC is implementing the limit for increases in
NC>2 that will also be required by the ARB for retrofit technologies.  This requirement
limits the increase  in NO? emissions associated with some types of retrofit technologies to
levels no greater than 20 percent above baseline engine levels. To evaluate compliance
with this requirement, we are adopting the ARB test procedures at Title 13 Chapter 14
Section 2706 of the California Code of Regulations. As a result, manufacturers must use
the same procedures for any new EPA and ARB verifications.

       For existing EPA  verified technologies, manufacturers must submit NC>2 data to
EPA prior to November 1, 2008 or those technologies will be removed from the NCDC
Verified Technologies List as of the effective date of this requirement. Data previously
submitted and approved by ARB  may also be submitted to EPA to demonstrate
compliance with these limits. Manufacturers shall work with EPA prior to conducting
any additional testing to demonstrate compliance with this limit.  In the meantime, EPA
intends to update the Verified Technology List to indicate which technologies have
demonstrated compliance with this limit.

       If you have any questions regarding this matter, please contact Dennis Johnson of
my staff at 202-343-9278 or by email at

Lori Stewart, Acting Director
Transportation and Regional Programs Division
Office of Transportation and Air Quality