June 23, 1992


MEMORANDUM

SUBJECT:  Ozone Modeling Requirements for the Lewiston-Auburn,
          and Knox-Lincoln Counties Moderate Ozone Nonattainment
          Areas in Maine

From:     Edwin L. Meyer, Acting Chief  
          Source Receptor Analysis Branch

To:       David B. Conroy, Acting Chief
          State Air Programs Branch, Region I


     In response to your request, the Model Clearinghouse has
reviewed your proposal to clarify modeling requirements for the
subject areas.  We agree with your position number (4) stating
that existing Urban Airshed Modeling (UAM) planned for eastern
Massachusetts can be used to satisfy attainment demonstration
requirements for Lewiston-Auburn counties.  The ozone monitor
location used to set the design value for Lewiston-Auburn
counties is located within the proposed eastern New England
domain.  Thus, the domain clearly is sufficient for attainment
demonstration purposes.  

     Modeling requirements for Knox-Lincoln counties are less
clear.  Those counties likely would qualify as a rural transport
area under section 182(h) of the CAA.  However, Maine is not
pursuing rural transport status in the interest of achieving
emissions reduction benefits imposed by the current nonattainment
designation.  Furthermore, portions of the contiguous Knox-
Lincoln counties are located within the eastern New England
boundary.  As you have pointed out, emissions from these counties
are minimal relative to other areas of the eastern New England
UAM domain.  All trajectories leading from the boundaries of the
eastern New England UAM domain to the nonattainment monitor
located on Isle au Haut do not cross significant emission
sources.  Consequently, the probability that ozone would increase
on any trajectory leading from the domain boundary to the Isle au
Haut location is near zero.  Furthermore, historical UAM modeling
conducted on the eastern New England domain shows a decreasing
ozone concentration gradient near the downwind boundaries of the
domain.  Therefore, a demonstration of attainment based on the
eastern New England UAM domain is sufficient for demonstrating
attainment for Knox and Lincoln counties.

     Your memorandum mentions the use of Regional Oxidant Model
(ROM) simulations as a basis for demonstrating attainment.  An
explicit use of ROM results for demonstrating attainment is not
acceptable.  The eastern New England UAM application, as
discussed above, is acceptable for demonstrating attainment for
the subject nonattainment areas.

     If you have any questions please contact me at 919-541-5562.


cc:  Ian Cohen, Region I
     Doug Grano, MD-15
     Richard Scheffe
     Dean Wilson