Comparing CMAQv5.2 and CMAQv5.3 results for same emission and meteorology inputs

I am trying to understand if it is possible to compare the performance (ozone, PM) of CMAQv5.2 and CMAQv5.3 for same emission and meteorology inputs. I believe CMAQ v5.3 has aero7 and v5.2 has aero6 modules, but I presume I would also have to make some changes to the SMOKE emission files and MCIP files to feed into both CMAQ versions?

Hi @skunwar,
Here is a good starting place to answer your question in terms of emissions and chemical mechanism choice:

In terms of meteorology inputs, CMAQv5.3 requires the use of MCIPv5.0+ which is described in the release notes and changes file here:

Hope this helps!

Thanks @foley.kristen - it is very useful link.

Do you happen to know if it is possible to integrate the new aero7 module within the older CMAQv5.2?

Hi @skunwar,

That’s a tough question. We made quite a few structural changes going from CMAQv5.2 to v5.3 including how the emissions are scaled, how SOA properties are stored and selected, and more. Going back to CMAQv5.2 would require introducing some new species for SOA from anthropogenic VOCs and new species for SOA from monoterpenes. It would also require some scaling of TERP and alpha-pinene emissions because we apply chemistry to those systems separately now. There are also some updates to heterogeneous chemistry that will be hard to implement quickly.

Going back to your original question, if you want to compare v5.2 to v5.3 with as little change as possible, I would recommend using meteorology that is as similar as possible, keeping in mind that it must be updated to be compatible with v5.3. Then you could use emissions built for aero6_svPOA in v5.2, which is essentially aero6 in v5.3.

We have worked really hard to make sure that older mechanisms are easy to introduce in the current and future versions of CMAQ. Unfortunately, this doesn’t really go the other way around. It’s pretty hard to take an old version of CMAQ and bring in a newer mechanism.

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