Photolysis Rates Processor (JPROC)

1
Photolysis Rates Processor (JPROC)

• Gail Tonnesen
• UCR Regional Modeling Center Training
• January 16, 2002

2
JPROC Purpose

• JPROC processor calculates a table of clear-sky
  photolysis rates (or J-values) for a specific
  date.
• The look-up table consists of photolysis rates at
  various altitudes, latitudes, and hour angles.
• The look-up table is recalculated for each
  simulation day and is dependent upon the chemical
  mechanism.

3
JPROC Overview

• Many chemical reactions in the atmosphere are
  initiated by the photodissociation of numerous
  trace gases.
• These photodissociative reactions are responsible
  for most of the smog buildup.
• Good photodissociation reaction rate (or
  photolysis rate) estimates must be made to
  accurately model and predict the effects of air
  pollution.
• Photodissociation is the conversion of solar
  radiation into chemical energy to activate and
  dissociate chemical species.

4
JPROC Calculate J-values

• Photolysis rates (min-1), sometimes called
  J-values, are computed for photodissociation
  reaction (i) by
• where
• F(?) is the actinic flux (photons cm-2 min-1
  nm-1 ),
• si(?) the absorption cross section for the
  molecule undergoing photodissociation
  (cm2 molecule-1 ),
• ?i(?) the quantum yield of the photolysis
  reaction
• (molecules photon-1 ), and
• ? the wavelength (nm).

5
JPROC Calculating J-values

• The current approach for setting photolysis rates
  in the Models-3/CMAQ framework follows that of
  RADM.
• It includes two stages of processing
• a table of clear-sky photolysis rates is
  calculated by the JPROC processor for specified
  heights, latitudes, and hours from local noon
  and
• photolysis rates are interpolated from the table
  within the CMAQ Chemistry Transport Model (CCTM)
  based on grid cell location and the model time,
  and are corrected for cloud cover.
• This approach is computationally efficient and
  gives clear-sky photolysis rates within the
  uncertainty of the surface-based measurements.

6
Clear-Sky Photolysis Rate Table

• Preprocessor JPROC calculates a table of
  clear-sky photolysis rates (or J-values) for a
  specific date.
• The table is dimensioned by latitude, altitude,
  and time.
• Currently, J-values are calculated for
• 6 latitudinal bands (10 N, 20 N, 30 N, 40 N, 50
  N, and 60 N),
• 7 altitudes (0, 1, 2, 3, 4, 5, and 10 km), and
• 9 hours from local noon (0 h, 1 h, 2 h, 3 h, 4
  h, 5 h, 6 h, 7 h, and 8 h).
• There is a separate table for each photolysis
  reaction.

7
JPROC Input Files

• The input files needed for JPROC are
• Extaterrestial radiation data
• Absorption cross section data
• Vertical ozone profile
• Albedo data

8
How to run JPROC?

• Verify that the CMAQ distribution tar file is
  downloaded from the RMC website
  www.cert.ucr.edu/rmc/download/.
• Gunzip and untar the files into the desired
  directories.
• Go to the JPROC run scripts directory, modify and
  execute the bldit and run job scripts.
• bldit script choose the compilation options
  and compiling the code.
• run script modify the run-time options and
  execute JPROC processor
• Check the log file for possible compile and
  runtime errors.

9
Hands-on .