Question about vertical levels for air pollution dispersion modeling over the Alps

[Alice Burton]

Dear all,

I am planning to study air pollutant dispersion over a mountainous region in the Alps using WRF/WRF-Chem or a coupled meteorology air-quality modeling setup.

Since the study area has complex terrain and strong near-surface gradients, I would like to ask for your advice regarding the vertical resolution. In particular, I am interested in the appropriate number of eta levels for this type of application.

My main question is about the lowest part of the atmosphere, especially the first 1 km above ground level, where most of the pollutants are expected to accumulate and where boundary-layer processes are very important.

Would it be reasonable to use around 10 vertical levels below 1 km AGL for an air pollution dispersion study over complex mountainous terrain? Or would you recommend using more levels in this layer?

I would also appreciate any suggestions on how to define the eta levels in WRF so that approximately 10 levels are placed below 1 km AGL while keeping a smooth vertical stretching above that height.

More specifically, I would like to know:

1. How many total vertical eta levels would you recommend for a mountainous air pollution dispersion study over the Alps?
2. How many levels should ideally be placed below 1 km AGL?
3. Is 10 levels below 1 km AGL sufficient, or should I consider a finer near-surface vertical resolution?
4. Are there any recommended values or examples for eta_levels in the WRF namelist for this type of application?

Any guidance, experience, or references would be greatly appreciated.

Best regards,

[Will H]

https://www2.mmm.ucar.edu/wrf/users/tutorial/presentation_pdfs/201901/gill_real.pdf