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Edit WRF dust emission and transportation scheme.

ChurnM

New member
Dear reader,

For my MSc thesis i'm using WRF to model the emission and transport of dust polluted with microplastics. I'm using the AFWA dust emission scheme and the GOCART dust transportation scheme. Due to the microplastics having a different shape, size and density when compared to the dust, I want to edit the existing 5 size bins used in the model but i'm not sure how to correctly do this. The microplastics emitted would be a set fraction of the total dust emitted and once the microplastics are airborne they are deposited only through gravitational settling. My idea is that I would add a few particle size bins (representing the microplastics) and include the effect of the shape factor in the dry deposition using Stoke's law.

This thread also talks about adding dust tracers but is does not mention how to do the emissions as I would like them. Please let me know what I would need to edit to achieve my goals or if it is even possible. Thanks in advance.

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Changing the distribution of what percentage of the bulk emitted dust flux gets assigned to each size bin in the AFWA dust emission module (dust_opt = 3) is pretty easy (prescribed; set with the distr_dust parameter). However, changing the number or effective diameter of the suspended dust size bins will require modifying multiple components of the GOCART suite in addition to the emission module. It's possible, but I'm not sure if that's the best option if you're not planning to use WRF-Chem's aerosol feedback functionality. Adding a microplastic emission module to WRF-ARW and using the passive tracer functionality might give you more flexibility to shape your experimental design the way you want it. Either option could work though.

Keep in mind - all three of the dust emission modules that work with the GOCART suite include a lot of assumptions about emitted dust flux particle size distribution and where/when to loft dust. They tend to work well when the dust production is being driven by abrasion (i.e., sand-blasting) from steady state saltation under strong wind forcing in areas with minimal vegetation and dust sources associated with holocene era mega lakes. These assumptions tend to work well for large-scale atmospheric dust weather patterns and climatological applications. Accuracy for finer-scale phenomena and specific regional areas will vary.

For the chem_opt=401 setting, I'd suggest referencing the WRF-Chem Users Guide instead of the LeGrand et al. 2019 paper. Georg Grell and Steve Peckham added the dust only option shortly after the WRF-Chem framework was released.
 
Super thanks for taking the time to reply, currently my MSc thesis is coming to an and and I managed to edit the code to include even a simple form of wet deposition. In the end it was just following all the routines and subroutines carefully and adding the 5 MP bins. I Indeed used the distr_dust to distribute dust along the new bins with Microplastic density and sizes.
 
That's great! When you finish your research, please consider releasing your code modifications through NCAR, github, or websites that host enduring code (e.g., zenodo). Microplastic transport modeling has been a hot topic lately.
 
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