CMAQv5.0.2 ACONC bug fix
CMAQ's CONC file includes instantaneous values of chemical species. Values written to the ACONC file are species concentrations averaged over the model synchronization steps subdividing each output time step. Typically, we use a one hour output time step, but this is not required. For example, for debugging purposes it is sometimes useful to set the output time step equal to the model synchronization time step. However, the logic in computing the normalization factor for ACONC was flawed, such that if using a subhourly output time step (e.g., 12 or 30 minutes), the AGRID and CGRID arrays diverged wildly on a periodic basis.
Significance and Impact
ACONC values are now correctly normalized regardless of the output time step. No impact on model run time.
Chris Nolte, Atmospheric Modeling and Analysis Division, U.S. EPA