Is deposition rate of ammonium nitrate (NH4NO3) calculated by CMAQ?

CMAQ Chemistry and Aerosols
1

Hello,

I want to look at deposition rates of ammonium nitrate (NH4NO3). I checked DRYDEP and WETDEP files and I could not find it in those files.

Is the deposition rates of this species included in CMAQ output files, or I have to calculate/estimate it?

Thanks.

2

Hi Ehsan,

You likely need to use the post-processing tool called combine that is provided with CMAQ.
Use combine to “combine species from raw CMAQ output files or wrfout input files into a new IOAPI output file. Species can be aggregated or transformed into variables of interest”
https://github.com/USEPA/CMAQ/tree/5.3.b2/POST

Liz

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3

Thank you, Liz, for your response. I was looking at spec_def file in the following link and I could not find the NH4NO3 name there. I am not sure if I am looking at the right spec_def file. Can you please advise or point me to the formula for calculating NH4NO3?

Also, I was wondering why NH4NO3 is not calculated as an independent species in deposition module?

Thanks.

4

Ammonium in the particle phase can be paired with various anions and thus in the form of ammonium nitrate, ammonium sulfate, ammonium bisulfate, or ammonium chloride. While the thermodynamic routines for the accumulation mode (ISORROPIA II) calculate each of these species, CMAQ only tracks total particulate ammonium, not the specific form. Thus, you can obtain ammonium and nitrate deposition. If you want to estimate ammonium nitrate, you could make assumptions/estimate it from stoichiometry. The accuracy of the approach will depend on the abundance of other aerosol species.

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