Gas-phase chemistry is described in detail in the CAM6 Scientific guide https://ncar.github.io/CAM/doc/build/html/cam6_scientific_guide/extensions.html#chemistry.
Default Chemical Mechanism used in CESM 2.0 and CESM 2.1
All CAM-Chem compsets default to the TS1 chemical mechanism, which includes all chemistry relevant to the troposphere and stratosphere. All WACCM compsets default to TSMLT1 chemical mechanism, which includes all chemistry relevant to the troposphere, stratosphere, mesosphere, and lower thermosphere. The TS1 and TSMLT1 chemical mechanisms are described in Emmons et al., 2019 (in review). Both are updated versions of the MOZART-4 chemistry described in Emmons et al., 2010. These updates include speciated aromatics, updated isoprene and terpenes oxidation, new organic nitrates, and updated JPL rate constants (Evaluation No. 18, 2015).
Current gas-phase chemical mechanism development:
Tagged NOx scheme (Louisa Emmons, NCAR)
A tagged NOx scheme is under development, which will be useful for tracking NOx emissions in CAM-chem. This scheme will allow the user to tag NOx emissions from certain sectors or regions. The tagged NOx will be chemically processed in the same manner as untagged NOx and the O3 production from the tagged NOx will be tracked.
MOZART-TS2: Improved isoprene and terpene oxidation (Rebecca Schwantes, NCAR)
The isoprene chemical mechanism was updated to include the most recent advances in our theoretical/experimental understanding of isoprene OH, NO3, and O3 oxidation (e.g., Wennberg et al. 2018). The terpene (monoterpenes and sesquiterpenes) chemistry was expanded to include 5 surrogate species (APIN, BPIN, LIMON, MYRC, and BCARY) rather than 2 (MTERP and BCARY) with terpenes grouped according to their chemical structure and oxidation products. These terpene chemistry updates are based on the most recent theoretical/experimental understanding of terpene OH, NO3, and O3 oxidation. A description and evaluation of the MOZART-TS2 chemical mechanism is provided in Schwantes et al., 2019 (in review). MOZART-TS2 is completed and will be implemented as a new compset into CESM 2.2.
Speciated alkane oxidation (Rebecca Schwantes, NCAR)
The alkane chemical mechanism is expanded from one surrogate species (BIGALK) to 5 surrogate species (NBUTANE, ISOBUTANE, NPENTANE, IPENTANE, and C6ALKANES).
If you are working on updating certain aspects of the gas-phase chemistry in CAM-Chem, please complete the form on Users and Projects page. We will add your project to this list, and ensure your updates are contributed back to the main code.