Questions about emissions scaling with DESID

Hello everyone,

I’m a little comfused about the comment in CMAQ run script :
setenv EMISDIAG T #> Print Emission Rates at the output time step after they have been
#> scaled and modified by the user Rules
Is that means the emission rates in are 1 hour later than those in original emission files?
For example the emission rates at 1st time step in equal 2nd in original emission files.
Do I understand correctly?
I compared the rates in the two files at same time step and found that they are not scaled by the factor i gave.


Hi Yunqing,

The emissions diagnostic files in CMAQv5.3 and recent versions have some limitations in terms of time stepping.

  1. They do not begin at hour 0 like the emissions input files do. This is because emissions are called after the initialization time.
  2. The data is not written out at precisely the same time as the input time step. This is because the emissions in DESID are calculated at the midpoint of each time step. The diagnostic algorithm checks to see if the end of the time step matches the output time step, and if so, writes to the diagnostic files. Thus, the data written to the diagnostic files is interpolated to 2.5 mins before the hour if there are 5 min time steps and hourly output steps.

In CMAQv5.4 (expected release September 2022), both of these issues are solved. We have reconfigured DESID so that it can run in standard mode or diagnostic mode. This way, emissions are calculated and written out for the initial time step and for each output time step exactly at the output time. This should facilitate the comparisons you are trying to make.

For your current case, the hours should match up with the original input files, except that the first hour is missing. The data should generally match, with deviations for the interpolation issue.

Kind regards,