How to run with diagnostic CO2?

[jiamenglai]

Hello, I am trying to run a case with diagnostic CO2, by setting:
./xmlchange DATM_CO2_TSERIES=20tr
./xmlchange ELM_CO2_TYPE=diagnostic

However, I got an error message: ENDRUN:lnd_import_mct ERROR: must have nonzero index_x2l_Sa_co2diag for co2_type equal to diagnostic

I wonder where can I find description of this 'index_x2l_Sa_co2diag', and how (and what value) should I change it?