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. University of California at Riverside, Regional Modeling Center (RMC)

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. University of California at Riverside, Regional Modeling Center (RMC)

4. JPROC – Calculate J-values • Photolysis rates (min-1), sometimes called J-values, are computed for photodissociation reaction (i) by: where: F(λ): is the actinic flux (photons cm-2 min-1 nm-1 ), σi(λ): the absorption cross section for the molecule undergoing photodissociation (cm2 molecule-1 ), i(λ): the quantum yield of the photolysis reaction (molecules photon-1 ), and λ: the wavelength (nm). University of California at Riverside, Regional Modeling Center (RMC)

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. University of California at Riverside, Regional Modeling Center (RMC)

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 (10N, 20N, 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. University of California at Riverside, Regional Modeling Center (RMC)

7. JPROC Input Files • The input files needed for JPROC are: • Extaterrestial radiation data • Absorption cross section data • Vertical ozone profile • Albedo data University of California at Riverside, Regional Modeling Center (RMC)

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. University of California at Riverside, Regional Modeling Center (RMC)

9. Hands-on ……. University of California at Riverside, Regional Modeling Center (RMC)