Only Simulating Primary Particulate Matter (PPM) with CMAQ

CMAQ
1

Hi friends!
I’m trying to simulate spatial distribution of primary particulate matter (PPM) with CMAQ 5.2. However, I could only find some primary components of PM (including APOCI/J/K, APOMI/J/K, where I, J, K denotes different modes.) in the output files (COMBINE_ACONC_v52_gcc13.1_***_082016).

  1. Is it possible to simply simulate the distribution of primary particulate matter (without considering the chemical reactions)? If so, should I modify the chemical mechanism definition files and some other files? and what other steps should i take?
  2. Or, taking all the chemical reactions into consideration during simulation, can I separate the relative contribution of primary PM from secondary PM within the simulation results?

Any suggestions will be appreciated ^_^.

2

Dear Alpha_Su,

Thanks for your question. While quantifying the contribution of primary vs. secondary species to total PM is a highly valuable result, it can be a bit tricky to process it from CMAQ output. For some time, CMAQ has employed various chemical and mass transfer schemes to process aerosols that sort of blur the lines between primary and secondary – this is of course happening in the real atmosphere as well.

As you point out, APOC and APOM are nominally ‘primary organic aerosol’, but they are susceptible to aging chemistry within the CMAQ mechanism. Moreover, any particulate ammonium or nitrate emitted reaches equilibrium with gas-phase emissions and any secondarily formed mass as well.

All that said, I think a reasonable approximation of the total primary PM would be the following sum (in terms of variables created by the combine post-processing tool):

Primary PM = APOMIJ + AECIJ + AFEJ + AALJ + ASIJ + ATIJ + ACAJ + AMGJ + AKJ + AMNJ + AOTHRIJ + ASEACAT + ACORS

Secondary PM = ASOMIJ + ASO4JK + ANO3IJK + ANH4IJK + ACLIJK

You could try instead to add a tracer scaled o all primary PM emissions, but that will take a bit of work in CMAQv5.2 and I don’t know that it would give you exactly what you’re looking for.

Best regards,
Ben

2 Likes
3

Hi Ben! Thank you for your detailed and prompt response!
I will follow your instructions and try.