December 19, 2003



Dear Air Quality Modeler:



     Select the method to download the files.  You may download each file

individually (~ 360 separate files and ~200 MB total).  Alternatively all the

files may be downloaded in three separate compressed files (< ~18 MB each).

You will need PKUNZIP to uncompress the compressed data.  Choose to download

by one method or the other only.



Filename convention:



  *.met  - Meteorlogical data files for use with ISCST3

  *.emf  - Enhanced Meta Files of wind rose for import to Word and Powerpoint



     This is the "readme" file for the processed hourly meteorological data

available from the Planning and Technical Support Division of the California Air

Resources Board.  The ASCII data are in the format specified by ISCST3 for

standard ASCII input.  The data have NOT been processed for use with the

deposition algorithms in the  ISCST3 model.  To determine the mixing height, the

surface data are processed with upper air data, a constant value, or Holzworth

seasonal mixing height data (Holzworth, G.C., Mixing Heights, Wind Speeds,

and Potential for Urban Air Pollution Throughout the Contiguous United States,

USEPA, 1972).  Users of these data should understand how the mixing heights and

final plume rise interact within the model and use these data accordingly especially

in the case of elevated plumes.



     As a reminder, the US-EPA Guideline on Air Quality Models recommend that

the most recent five years of consecutive meteorological data should be used

for air quality modeling studies.  The OEHHA Air Toxics Hot Spots Program Guidance

Manual for HRAs (www.oehha.ca.gov/air/hot_spots/HRSguide.html) recommend that

the most recent five years of consecutive meteorological data should be used

for risk assessment analysis.  A single year may be used if it is the most

conservative year.



     These data are made available for your convenience.  We will update these

data on an "as needed" basis.  This means where we have a specific application

to include additional processed data for individual projects, the data will also

be available at this location.  If you have processed data specific to California

that you would like to make available to the general public, please notify the

contact person below.



Standard CARB Disclaimer

-----------------------

The fact that the California Air Resources Board (CARB) has supplied you with

these data does not mean that the CARB will place its approval on subsequent

applications.  We must emphasize that the models must be applied properly with

appropriate input data which is consistent with their formulation, testing,

and assumptions.



     Should you have any questions, please contact Tony Servin at (916)

323-5122 or aservin@arb.ca.gov.



Sincerely,

Planning and Technical Support Division

California Air Resources Board