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

                        November 28, 1984







MEMORANDUM

SUBJECT:  Correcting Atmospheric Dispersion Model Results to Standard
          Temperature and Pressure

FROM:     Richard G. Rhoads, Director /s/
          Monitoring and Data Analysis Division (MD-14)

TO:       Robert L. Duprey, Director
          Air and Waste Management Division, Region VIII (8AW-AP)

     We have considered your request on whether atmospheric dispersion model
estimates should be corrected to standard temperature and pressure conditions
(STP).  Given the manner in which the S02 ambient air quality standards are
written, and to be consistent with the handling of monitoring data, it could be
reasoned that the correction of model estimates to STP should be made.  

     From a historical standpoint, we can find no indication from our records
that we have provided written guidance on correcting model estimates to STP. To
provide additional background information, we contacted all the other Regional
Offices to find out what their current policies are. In most cases the possible
need to correct to STP has not arisen and in no case has a correction been
made, other than possibly in your Region.

     Considering the historical precedent and how other Regions are handling
the STP issue I do not believe it is wise to institute a new nationwide policy
at this time.  However, if a State wishes to make the STP correction, I would
have no objection, since they have the right to be more stringent than EPA.

     If you have any questions please contact me.

cc:  T. Helms
     R. Neligan
     M. Trutna
bcc:  Regional Modeling Contacts, Regions I-X