De-hardcode chemical tracers work in prepare_data for ICON

[efmkoene]

If I want to do a prepare_data job for ICON with, say, CO2 instead of CH4, I would have to change this code. It would be good if this was something I could specify in the job instead.

processing-chain/jobs/prepare_data.py

Line 445 in bfaaee4

ds_chem['TRCH4_chemtr'] = ds_chem['CH4_BG']

[mjaehn]

@efmkoene Thanks and good catch! Would you be willing to implement this and make a PR into https://github.com/C2SM/processing-chain/tree/v3.0-rc?

[mjaehn]

This is now part of the prepare_art_oem.py job.