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How to convert emissions (molecules/cm2/s) to mass emission (kg/m2/s)?

penguin77

ranqi
New Member
Hello, I have the input data for B2000CAM5CN (e.g. ar5_mam3_oc_surf_2000_c090726.nc). The unit for OC emission is molecules/cm2/s. I want to compare the emissions from EDAGR (emission unit is [kg/m2/s]) and that from CESM input data. So, how can I convert [molecules/cm2/s] to [kg/m2/s]? I think the calculation needs the molecular weight (MW), and I know that MW of SO2 is 64. But what is the WM for BC, OC and SOAG?
I'm stuck with this issue, I really appreciate any help!
 

nusbaume

Jesse Nusbaumer
CSEG and Liaisons
Staff member
Hi Ranqi,

I am moving this thread to the CAM-Chem forum, so that experts in CAM's chemistry routines can provide the information you need, at least with regards to the molecular weights.

Hope that helps, and have a great day!

Jesse
 

penguin77

ranqi
New Member
Hi Ranqi,

I am moving this thread to the CAM-Chem forum, so that experts in CAM's chemistry routines can provide the information you need, at least with regards to the molecular weights.

Hope that helps, and have a great day!

Jesse
Thank you, Jesse. It's so nice of you.
 

rrbuchholz

Rebecca
New Member
Hi Ranqi,

Users can find the chemical formula used for each compound in ./CaseDocs/chem_mech.in or chem_mech.doc
We have added a file of molecular weights used in CAM-chem to the CAM-chem Wiki: https://wiki.ucar.edu/display/camchem/Using+CAM-chem+Output
The direct link to that file is here:
https://wiki.ucar.edu/download/attachments/372834728/species_molwts_2021-05-07.csv

The process of converting units:
  • There are 6.022e23 (Avogadro's number, N_Av) molecules in one mole of a particular species, so divide by N_Av to calculate the number of moles.
  • The MW of a species defines the number of grams per mole, so multiply my the MW.
  • To convert grams to kilograms, divide by 1000.
  • One meter squared is 100 cm x 100 cm so converting cm^2 to m^2, multiply by 10000.
In an equation:

Emissions (kg/m2/s) = y (molecules/cm^2/s) ÷ N_Av (molecules/mol) × MW (g/mol) ÷ 1000 (g/kg) × 10000 (cm^2/m^2)

Note that we are developing a python tool to also help with this:
Python Resources for CAM-chem

Hope that helps!
Best,
Rebecca
 

penguin77

ranqi
New Member
Hi Ranqi,

Users can find the chemical formula used for each compound in ./CaseDocs/chem_mech.in or chem_mech.doc
We have added a file of molecular weights used in CAM-chem to the CAM-chem Wiki: https://wiki.ucar.edu/display/camchem/Using+CAM-chem+Output
The direct link to that file is here:
https://wiki.ucar.edu/download/attachments/372834728/species_molwts_2021-05-07.csv

The process of converting units:
  • There are 6.022e23 (Avogadro's number, N_Av) molecules in one mole of a particular species, so divide by N_Av to calculate the number of moles.
  • The MW of a species defines the number of grams per mole, so multiply my the MW.
  • To convert grams to kilograms, divide by 1000.
  • One meter squared is 100 cm x 100 cm so converting cm^2 to m^2, multiply by 10000.
In an equation:

Emissions (kg/m2/s) = y (molecules/cm^2/s) ÷ N_Av (molecules/mol) × MW (g/mol) ÷ 1000 (g/kg) × 10000 (cm^2/m^2)

Note that we are developing a python tool to also help with this:
Python Resources for CAM-chem

Hope that helps!
Best,
Rebecca
Thank you so much, Rebecca. Your reply is very helpful and detailed. Now I know how to do the unit conversion!
 
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