For CMAQ, the photolysis rate model, JPROC, is used to generate clear sky photo-dissociation reaction rates. JPROC requires temperature profiles from the U.S. Standard Atmosphere (NOAA, 1976), a profile of the aerosol extinction coefficients, (Elterman et al., 1969) and can optionally use ozone column totals from the NASA Total Ozone Mapping Spectrometer (TOMS) satellite to produce the photolysis rates for CCTM (Figure 2-5).

JPROC uses this information in a radiative transfer model to calculate the actinic flux (photons cm^-2 min^-1) needed for calculating photolysis rates. Currently, JPROC calculates the actinic flux for clear-sky conditions (no clouds present), and CCTM then attenuates for cloudiness when clouds are present. JPROC computes the rate for each photolysis reaction at various latitudes, altitudes, and zenith angles. Within CCTM, the subroutine PHOT interpolates the data generated by JPROC to individual grid cells, and adjusts for the presence of clouds.