Bugfix/allow zero buffer elems

[laestrada]

Name and Institution (Required)

Name: Lucas Estrad Institution: Harvard ACMG

Describe the update

Previously the IMI required use of buffer elements in the state vector when making a rectilinear state vector. THis update allows specification of 0 buffer elements by setting the buffer region == -9999. Note that users should still leave enough buffer region to account for the geoschem "buffer zone". @djvaron @msulprizio how much buffer zone is required? Perhaps I should enforce at least that amount in make_state_vector_file.py?

[msulprizio]

how much buffer zone is required?

GEOS-Chem nested-grid simulations use a default buffer zone of 3 grid cells on each edge, so the actual extent depends on the model resolution. We tell users to exclude those boxes from their analysis.

[laestrada]

Thanks @msulprizio! That is very helpful -- I will add some logic to add 3 grid boxes to each side based on the resolution