Quoted from: https://ncar.github.io/CAM/doc/build/html/cam5_scientific_guide/introduction.html#the-cam-chemistry-model-cam-chem 

Chemistry in CAM is now fully interactive and implemented in CESM (Section sec-chem_sub_cam); in particular, emissions of biogenic compounds and deposition of aerosols to snow, ice, ocean and vegetation are handled through the coupler. The released version of CAM-chem in CESM is using the recently-developed superfast chemistry (Section Superfast Chemistry), in collaboration with P. Cameron-Smith from LLNL and M. Prather from UCI) to perform centennial scale simulations at a minor cost increase over the base CAM4. These simulations use the recently developed 1850-2005 emissions created in support of CMIP5.