Clarification on variables required to calculate total black carbon deposition from MERRA-2 and globally zero BCWT001 va

[pritijadhav]

I am working with NASA MERRA-2 aerosol diagnostic data to calculate long-term black carbon (BC) deposition over the Hindu Kush Himalaya (HKH) region. I would appreciate clarification regarding which MERRA-2 variables should be combined to calculate total BC deposition.

Data product:
MERRA-2 tavgM_2d_adg_Nx – 2D Monthly Mean, Time-Averaged, Single-Level, Aerosol Diagnostics (extended)
Short name: M2TMNXADG
Version: V5.12.4
DOI: 10.5067/RZIK2TV7PP38

Variables currently being used:

BCDP001 – Black Carbon Dry Deposition Bin 001
BCDP002 – Black Carbon Dry Deposition Bin 002
BCWT001 – Black Carbon Wet Deposition Bin 001
BCWT002 – Black Carbon Wet Deposition Bin 002

Units for these variables are kg m⁻² s⁻¹.

My main questions are:

1. Which variables should be used to calculate total black carbon deposition?

Is it correct to calculate:

BC Dry Deposition = BCDP001 + BCDP002

BC Wet Deposition = BCWT001 + BCWT002

and therefore:

Total BC Deposition = BCDP001 + BCDP002 + BCWT001 + BCWT002?

Or are additional MERRA-2 BC diagnostics required for a complete estimate of deposition to the surface?

For example, the tavgM_2d_adg_Nx product also contains variables such as:

BCSD001 – Black Carbon Sedimentation Bin 001
BCSD002 – Black Carbon Sedimentation Bin 002
BCSV001 – Black Carbon Convective Scavenging Bin 001
BCSV002 – Black Carbon Convective Scavenging Bin 002

Should BC sedimentation (BCSD001 and BCSD002) also be added when estimating total surface deposition?

Similarly, is convective scavenging represented within the BCWT wet-deposition variables, or would BCSV001/002 need to be considered separately?

In other words, I would like to confirm the recommended MERRA-2 formulation for:

Total BC deposition to the Earth's surface = Dry deposition + Wet deposition [+ Sedimentation?]

and which exact diagnostic variables should be used without either omitting a deposition pathway or double-counting one.