Updating the DMS oxidation chemistry

[kamingfung]

Based on previous laboratory studies, we expand the simplified DMS oxidation scheme used in CAM6-chem to capture the OH-addition pathway as well as the H-abstraction pathway and the associated isomerization branch.

The expanded DMS oxidation scheme has shown some important chemical and climate implications, which are detailed in this recent paper.

We would like to share our modified CAM6-chem codes with the community, which can be found here.

Summary of our code development:

• developed based on the codebase located in /glade/work/fvitt/cesm/cesm2.1.0_mosaic07/
• added API with MOSAIC and OASISS
• added expanded DMS oxidation scheme (both gas- and aqueous-phases)

Thank you in advance to @lkemmons and @fvitt for helping with reviewing our changes.

[cacraigucar]

@andrewgettelman - You asked to review when it is ready

[lkemmons]

This depends on MOSAIC (gas-aerosol exchange scheme), which has not yet been implemented.
#69