November 7, 1988



SUBJ:  Compilation of Most Recent, Available Five-Year 
       Meteorological Data by Texas

FROM:  Dean A. Wilson, Meteorologist,
       Source Receptor Analysis Branch (MD-14)

TO:    James W. Yarbrough
       SIP New Source Section (6T-AN), Region VI

The Model Clearinghouse has reviewed your position with respect
to the appropriate meteorological data bases to be used by the
State of Texas for regulatory modeling.  For the most part we
agree with your position but do have a couple of
comments/clarifications.

Our understanding of the State's position is that they would like
to model both short-term and long-term using four individual
years (1982-1985) of recent, readily available meteorological
data and then, for the fifth year, use 1964 data for the short-
term, or existing historical multiple year composite STAR data
for the long-term.  Their reasoning is that it is important in
permitting, from an equity standpoint, to use the same years of
meteorological data, regardless of the data station.

Our understanding of the Region VI position is that the State
need not specify the same meteorological data bases across the
State and five years of recent readily available meteorological
data be used.  The data bases would be 1981-1985 or 1982-1986,
depending on the station.  Furthermore, you recommend that, for
modifications of existing emission limits that were originally
based on earlier meteorological data, these data bases be
included in any remodeling.  The historical data bases would be
1964 for the short-term and the existing composite STAR data for
the long-term.

The Guideline on Air Quality Models (Revised) indicates that
consecutive years from the most recent readily available 5-year
period be used when estimating concentrations with an air quality
model.  This statement supports the Region VI position to use
1981-1985 or 1982-1986 data, depending on which 5-year period is
readily available for a given NWS station.  The Clearinghouse
agrees with the Region VI position.  However, it should be noted
that the data bases identified in Attachments 2 and 3 to your
memorandum only represent the current readily available data.  At
some point in the future it may be necessary to update the data
base to something more current. 

 The Guideline on Air Quality Models (Revised) also indicates
that for permitted sources whose emission limits are based on a
specific year of meteorological data, that year should be added
to any longer period being used (e.g. 5 years of NWS data) when
modeling the facility at a later time.  Thus, since previous
Texas modeling was done using data bases from an earlier time
period, e.g. 1964, it would seem logical to retain these data
bases for future remodeling of existing facilities.  The Model
Clearinghouse agrees with your position that the 1964 data base
should be included in any modeling done that would potentially
modify existing emission limits.

Regarding the use of historical multiple year STAR data, the
Model Clearinghouse has long held the position that composite
STARS are not appropriate for use in analyzing the annual mean
for most pollutants.  (It is possible that such data could be
used for making estimates for standards that written in
statistical form, e.g. PM10.)  Thus from a regulatory standpoint
we do not believe that it is useful to require any modeling using
historical composite STAR data bases, since we would not be able
to defend emission limits based on these data.

In summary, the Model Clearinghouse agrees with your position
with respect to use of the data bases identified in Attachments 2
and 3 to your October 26, 1988 memorandum.  We also agree that,
for the short -term analyses for existing sources it is 
appropriate to add the 1964 data base to the most recent,
available 5-year data bases (currently those data bases
identified in Attachments 2 and 3).  However, for the long term
analyses, emission limits should be based solely on the STAR data
bases from the most recent readily available 5-year period.


If your have any further questions, please contact me.

cc:  D. Grano
     D. deRoeck
     S. Reinders
     Regional Modeling Contact, Regions I-V, VII-X (with incoming
     memo and list of FY89 Clearinghouse memos)