U.S. Environmental Protection Agency
Office of Mobile Sources

May 21, 1999
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NONROAD Model Status Update

We have now released a second Draft version of NONROAD in
conjunction with the signing of the Tier 2/Gasoline Sulfur Notice
of Proposed Rulemaking.  It is available on our web site at
http://www.epa.gov/oms/nonrdmdl.htm, and it will be available
shortly on CD for anyone unable to easily get the files from the
web.  

This release includes further updates to the input data files
(such as equipment populations, average horsepowers, growth, and
geographic allocation), additional functionality in the Core
Model and Reporting Utility (such as separate outputs for
refueling spillage and vapor displacement), as well as
corresponding enhancements to the Graphic User Interface (such as
the ability to set Stage II refueling effectiveness). 

Users should understand that NONROAD is still draft and that all
the usual caveats and restrictions apply to its use in SIP
submittals.  We are currently addressing major comments on the
draft model and have yet to go through peer review.  As a result,
the current draft of NONROAD is likely to undergo revision before
it is released for general use.  Some of the revisions may be
major.

In our prior notice (March 12, 1999), we stated that, "Until it
is officially released, the NONROAD model is not to be used for
State Implementation Plans (SIPs) or other official submittals to
EPA."  We received some questions on that. 

To clarify the current situation, we would still encourage states
to take a cautious approach to use of the Draft NONROAD for SIP
submittals of any kind, especially for ozone transport SIP
revisions.  The NOx budgets in the SIP call were established
based on a different method of estimating nonroad emissions.  A
shift to the draft NONROAD model by any state will raise
complications in comparing budgets and submissions, possibly
requiring the budget itself to be revised. 

States which choose to use the draft NONROAD model in other SIP
submissions do so at their own risk, but all SIP submissions will
be considered on their merits. The draft NONROAD model is not EPA
guidance and does not carry any presumptive weight when EPA
reviews a SIP submission, but neither will it lead to any
automatic rejection by EPA.

We have learned that some states had been told to use the draft
NONROAD model for their 1996 Periodic Emission Inventory
submittals.  States which have proceeded on that advice should not
expend extra resources or delay their submissions to return to an
earlier inventory approach.  Also, states that have used an
earlier inventory approach should not expend effort or incur
delay to change to the NONROAD model. 

We are considering the use of this second draft, or a subsequent
revision to it, in one or more national analyses we will be
initiating very soon.  We will keep interested parties informed of
our plans in this regard.  If we do use the model in this way, we
will likely be able to share county-level inventory results from
the model with any interested state, in a standard inventory
format.  This possibility argues against any state expending
substantial effort on its own to generate such results, for now.

At this time EPA efforts are concentrated on testing, improving,
and finalizing the model.  We are not able to direct resources
toward support or assistance in its use beyond what is needed for
purposes of testing and evaluation.  Situations may arise where
the use of a draft model in a state submittal may affect EPA's
action on the submittal; furthermore, subsequent revisions to the
model may necessitate revisions to the submittal when the model
is officially released as final.  

We certainly encourage everyone testing the NONROAD model to
continue your analyses and let us know of any questions or
problems you experience.  We look forward to working with you in
the coming months as we move toward the release of a final
version of NONROAD.  Thank you for your comments and your
continued interest in NONROAD. 

          Email: nonroad@epa.gov  (preferred method)

          Fax:  (734) 214-4939

          U.S. mail:
          *NONROAD Comments*
          US EPA Assessment and Modeling Division
          2000 Traverwood Drive
          Ann Arbor MI 48105

Sincerely,

NONROAD Engine Emission Modeling Team
Assessment and Modeling Division, US EPA