What is difference between O3_OTHR and O3_GR1

In the ISAM control file:


We also get O3_OTHR as default output according to Users’ Guide
O3_OTHR is defined as ozone contribution from all emissions not tagged
O3_GR1 is Gridded Emissions from everywhere.

What is difference between O3_OTHR and O3_GR1 in output file CCTM_SA_ACON* ?

Thanks you very much.


The difference is just what the Users Guide says. “O3_GR1” is the concentrations attributed to the “GRIDDED_EMIS” emissions stream as specified the user generated ISAM control file. “O3_OTHR” is the concentrations attributed to all other emissions streams and other processes in the model. The sum of all differently named O3_??? species should closely resemble the regular O3 output from the concentration file.

Also, we want to make sure you are aware of this Known Issue with CMAQ-ISAMv5.3.1 predictions of secondary gas species 1. A bugfix release (v5.3.2) is planned for release shortly will address this issue. It’s fine to proceed with setting up and testing CMAQ-ISAM for your application, but you would want to switch to the updated version of the code before moving to the stage of analyzing/interpreting your simulation results.

Thank you very much for your response.
I really need to understand the definition of those two terms.
All of our emissions are processed and gridded by SMOKE even biogenic emissions and lightning NOx. If I have only one emission stream: GRIDDED_EMIS and the tag name is GR1 in my control file, I think, O3_OTHR should be the same as O3_GR1 because all emissions are gridded emissions and all emissions are not tagged (NO remaining unspecified emissions).
I did a sensitivity analysis run (see the control file at the end attached) and the model results show that O3_OTHR and O3_GR1 indeed are different. I don not know how to explain the difference.

In another case, O3_OTHR should be zero if I have all emissions tagged theoretically. Am I right?

BTW, I am using CMAQ v3.5. I am sure to be moving to the updated version.


isam control file


This may be source of your confusion. No - its not correct that if you tag all emissions, O3_OTHR should be zero.

As I wrote above: “O3_OTHER” is concentrations attributed to all other emissions streams and other processes in the model.

First, there are internally calculated emissions that you can tag, but didn’t in your control file. These are things like inline biogenics, inline lightning, dust, etc.

Second, there are processes in the model that create O3 not just from user specified emissions streams like your “GRIDDED_EMIS” and also not just from inline emissions I listed above. The most obvious examples are actually tracked - these are ICON and BCON. Additionally, there ozone that comes from background methane that is specified in the model as a constant.

Finally, ISAM is an approximation for attribution. In the formulation, assumptions are made about which species are most important in ozone formation. However, pretty much ALL species in the gas-phase chemical mechanism of your choice contribute to some degree to ozone formation. Their contribution will go into “OTHER” even though you specified their source emissions stream. Now, this gets into the Known Issue thing I posted. There is currently a problem where “OTHER” from such sources is actually over-estimated and we are working on this issue.

There is a test you can do to illustrate all this stuff if you really want. You can zero out all of the emissions in your input files and lower the values in your ICON/BCON files to close to zero. When you run the model, you will still get ozone. This is a very rough approximation of the “OTHER” ozone.