How to add a choice of tracer in the code

[Lin Lu]

Hello all,

I wish to use the tracer option in WRF-Chem. I am using the default tracers for now using option tracer_opt = 3.
But I am confused does this option also include CO Tracer as seen here ACOM Forecasts for FIREX-AQ: Tracers ?

I can see tr17_1 to tr17_8 but how to get CO tracer from biomass burning or aerosol like organic carbon ?
How to modify the code to output this? Please help.

Also, what is meant by the output 'fire_smoke' in the wrfout file? How can I find more info about this output?

Thanks
Lin

[Gabriele Pfister]

Hello Lin

the WRF-Chem released versions do not include CO tracers, for this you would have to modify the code. You can find more information in these two papers  (https://agupubs.onlinelibrary.wiley.com/doi/10.1002/jgrd.50134; https://acp.copernicus.org/articles/11/7515/2011/acp-11-7515-2011.pdf). 

Given the near-linear CO chemistry, you have to add CO tracers that undergo the same chemistry as the standard CO but do not have them impact the chemistry of the standard species. E.g. for biomass burning you would have to add a CO biomass burning tracer that has emissions from biomass burning only and add the tracer also to the chemical scheme. You would add the tracer into the parameter list, and in the eqn file you have to add the reaction of the CO tracer with OH  in a way that the total OH concentrations are not impacted by the tracer such as: 

CO_FIRE+OH=OH : usr_CO_OH_a( temp, c_m ) ;

So basically the parts in the code that need to be modified for the addition of a CO biomass burning are the Registry (you have to add the tracer as additional species and also the tracer emissions), the reading of emissions (following the example of that is done for total CO) and the chemical scheme.

We can share our code as an example if needed. 

Tracking of aerosols is more complex but see here for tracking of black carbon aerosols. 

Gabi

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Gabriele Pfister

Atmospheric Chemistry Observations & Modeling (ACOM) Lab

National Center for Atmospheric Research (NCAR)

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[Lin Lu]

Hi Gabi,

Thank you so much.

I can use help from your code as an example. That would be great.

Now as I understand, I need to make changes in registry.chem  (adding a new array of variable species and in the emissions package for tracer_opt).

In the subroutine chem_driver.F and convert_emiss.F (not sure what changes here).

1. Do I also need to add a new namelist option with a new stream number and auxhist everytime I output a new variable via iofields.txt ? or is just +h:00: is enough?

2. Also, I get fire_smoke as an output in wrfout. I am wondering how to find more about it? Is it a fire smoke tracer? I am currently trying tracer_opt =3 without any code changes. 

Thank you for your help

Lin

[Mary Barth]

Hi,

I can answer your 2nd question. 

With tracer_opt > 0 the smoke tracer (or biomass burning tracer) marks where air from biomass burning goes. It's based on CO emissions from fires. Please read section 4.3.4 in the User's Guide for more information. 

There is a module, module_tracer_input.F (I think) where the tracer options are defined. You can create your own tracers there.

- Mary

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National Center for Atmospheric Research

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[Lin Lu]

Dear all, 

Thanks for your help. 

I am outputting the tracer opt = 3 and I see 'fire_smoke' in all my wrfout files. 

However, even though my domain has large fires, the fire smoke variable looks empty. Is there a post-processing involved to plot this output?

I appreciate any help.