William T. Hutzell, U.S. Environmental Protection Agency
The create_ebi utility has been updated to accomplish two tasks. First, a run-time option was added to set the maximum integration time step. The utility writes the setting to hrdata_mod.F as the value for DELTAT. The default value of 2.5 minutes is used for DELTAT when the run-script does not set the option. Second, these updates are a step toward fully incorporating ISAM into CMAQ by changing the EBI solver for a photochemical mechanism and the utility that creates an EBI solver. The changes add FORTRAN processing statements to subroutines and modify subroutines that compute analytical solutions for O(1D), HNO4, NO3, and N2O5. The former changes do not affect model predictions. This preprocessing option is not operational because additional files are needed and future pull requests will add these files. The latter changes affect results from the solver. The analytical solutions were modified; Changes were introduced into the hrg[1,2,3].F in the EBI solvers to improve performance for calculating source apportionment. The change also produced better agreement between the concentration of photochemical species and the sum of their source contributions.
To determine how these changes alter model predictions, sensitivity tests were conducted over hemispheric, 12‑km continental U.S., and 4‑km California domains using the cb6r3_ae6_aq and saprc07tic_ae7i_aq mechanisms. Differences in the absolute value of the hourly maximum ozone and fine-mode sulfate are less than 0.5 ppbV and 0.5 μg m‑3, respectively. The only species with differences greater than 1 ppbV was HNO3, which occurred for wintertime cases or VOC-limiting areas. The noticeable differences occurred in isolated locations and at sporadic times so the mean differences were equal to or more than two orders of magnitude lower than grid-cell averages for HNO3.
All EBI solvers for all photochemical mechanisms under CCTM/src/gas.