United States Environmental Protection Agency
          Office of Air Quality Planning and Standards
          Research Triangle Park, North Carolina 27711




Date:     Oct. 21, l982

SUBJECT:  Level II Bubble Analyses

FROM:     Joseph A. Tikvart, Chief  /s/
          Source Receptor Analysis Branch (MD-14)

TO:       Steven Rothblatt, Chief
          Air Programs Branch, Region V


     Questions have been raised by you and by other Regional
Offices as to how one should perform modeling analyses for Level
II bubbles.  Included in the definition of a Level II bubble are
the conditions that (1) there is no net emissions increase and (2)
there is no significant degradation of air quality as a result of
the emissions trade.  A screening type of modeling analysis is
intended for the Level II bubbles.  An examination relative to the
NAAQS is not required.  

     A problem at the present time is that screening techniques
that can be generally applied to Level II bubbles are not yet
available.  OAQPS has a contract with PEDCO to consider several
potential techniques and to report on their findings by early 1983. 
In the meantime, you may wish to follow one of the following
procedures in dealing with the ambient analysis for Level II
bubbles:

     (1)  Develop in-house screening techniques that address the
worst-case incremental concentration for the specific sources,
climate and terrain under consideration; this may initially require
a resource intensive effort, but it could have long-term dividends
for your future.

     (2)  Follow procedures recommended in the Guideline on Air
Quality Models and use a refined model with at least one year of
meteorological data.  

     If you have any questions or comments concerning these
suggestions, please contact Dean Wilson of my staff at FTS 629-
5681.

cc:  Modeling Contact, Regions I-X
     R. Cunningham
     L. Deal
     T. Helms
     R. Rhoads
     D. Wilson