Conversion between cm3 and cm2 emissions

[Jakub_Sypek]

What version of the code are you using?
CESM v2.1.5


Have you made any changes to files in the source tree?
xml files updated for porting to lab workstation


Describe every step you took leading up to the problem:
I have run a case f19_f19_mg17.FW2000climo and would like to create a new aerosol emissions file. I would like to create a dust emission in Aitken mode between 60 and 80 km altitude. To do this, I have attempted to modify the the aircraft emissions files from /atm/cam/chem/emis/CMIP6_emissions_2000climo to provide an additional emission. I have changed the 25 altitude and 26 altitude_int levels (in km) to a uniform distribution between 60 and 80 km. I have then replaced all matrix values with a uniform emission of around 1.5 molecules/cm3/s.


Describe your problem or question:
It is my understanding that emissions must be inputted both as molecular emissions and particular emissions. In the aircraft emissions files, the units were:
emiss_aircraft:units = "molecules/cm3/s"
num_bc_a4_aircraft:units = "(particles/cm2/s)(molecules/mole)(g/kg)"

I understand the conversion between molecules and particles includes using the diameter of Aitken mode particles and the (molecules/mole)(g/kg) factor is just an idiosyncrasy of CESM. However, I am confused as to how I am to convert between cm2 and cm3. My understanding is that cm2 should be for surface emissions, not vertical emissions but somehow the molecular emission must be converted to a particular emission with a different emission.

I am quite confused and would really appreciate any help that could be provided!

Files used:
/atm/cam/chem/emis/CMIP6_emissions_2000climo/emissions-cmip6_bc_a4_aircraft_vertical_2000climo_0.9x1.25_c20170322.nc
/atm/cam/chem/emis/CMIP6_emissions_2000climo/emissions-cmip6_num_bc_a4_aircraft_vertical_2000climo_0.9x1.25_c20170322.nc

 

[Jakub_Sypek]

Small typo: I meant "the molecular emission seemingly must be converted to a particular emission with a different dimensionality"

 

[peverley]

Moving this to the CAM-Chem forum - hopefully they can help!

Courtney

 

[Jakub_Sypek]

Thank you Courtney :)

Update:

I have found that cesm-cmip6-emissions/historical_emissions/make_emis_cmip6_mam4num.pro at main · lkemmons/cesm-cmip6-emissions has been used previously to convert surface emissions (molecules/cm2/s) to number emissions (particles/cm2/s)(molecules/mole)(g/kg). Is there a similar code for vertical emissions? Or should I first convert my vertical emissions (molecules/cm3/s) to (molecules/cm2/s) by integrating over a vertical level?

For the conversion between the aforementioned aircraft files, by trial and error I found that the number file was simply the molecular emissions file multiplied by mw / M_particle, where M_particle = (math.pi/6 * rho * d**3) and rho = 1700.0, d = 0.134e-6, mw = 12.0. Should I be using this conversion for my own emissions files? I am confused as to how the vertical dimension conversion was accounted for; if the molecular emissions file is truly in (molecules/cm3/s), as is written in the metadata, then this calculation would result in a number file with units (particles/cm3/s)(molecules/mole)(g/kg). However, the metadata states that the number file is in units of (particles/cm2/s)(molecules/mole)(g/kg). Since delta_z in this file is 0.61, integrating over this altitude would result in a different result to what is found in the input data.