January 10, 1990  
  
  
  
  
  
  
MEMORANDUM  
  
SUBJECT:  Utah PM-10, Secondary Sulfate and Nitrate Projections  
  
FROM:     Joseph A. Tikvart, Chief  
          Source Receptor Analysis Branch (MD-14)  
  
TO:       Marius Gedgaudas, Chief  
          Compliance Section and Utah PM-10, Region VIII (8AT-AP)  
  
  
     In response to your request to Dean Wilson, the Model Clearinghouse
has  reviewed your proposed procedure for calculating the effects of the
reduction of precursor emissions on ambient levels of secondary
particulate.  We agree  that your approach is logical.  Given the
limitations in information and tools (e.g. models) available to use for
assessing effects of controlling precursors to secondary particulates, the
approach is a reasonable one.  
  
     Our only comment relates to your suggestion in the next to last
paragraph that a box type of dispersion model could be used in conjunction
with the "up and down" procedure.  We do not fully understand what is being
proposed here  but, as we have previously agreed with John Notar and others
in your Region,  we do not feel that a box type of dispersion model is
technically supportable in this area.  
  
     If you have any questions, please contact Dean Wilson (FTS 629-5683)
or  Quang Nguyen (FTS 629-0832) of my staff.  
  
cc:  N. Frank  
     L. Hanley  
     T. Pace  
     M. Smith  
     D. Wells  
     D. Wilson