How to convert mass emission (kg/m2/s) to emission (molecules/cm3/s)?

[xnnzka]

Hi, everyone. I have 1 question about the unit convertion.

I want to use CEDS emission data to simulate. I want to use the emission from aircraft so I think I must convert its unit (kg/m2/s) to molecules/cm3/s. I try to calculate but I do not know if my calculation is right.

My calculation is:
y (molecules/cm^3/s)= Emissions (kg/m^2/s) × N_Av (molecules/mol) ÷ MW (g/mol) × 1000 (g/kg) ÷ 1000000 (cm^2/m^2) ÷ altitude interface (km, I found the altitude interface=0.61km, so here I fix it to be 0.61) ÷ 1000 (km/m)
(ps:the level (i.e., altitude) of CEDS data is:level = 0.305, 0.915, 1.525, 2.135, 2.745, 3.355, 3.965, 4.575, 5.185, 5.795, 6.405, 7.015, 7.625, 8.235, 8.845, 9.455, 10.065, 10.675, 11.285, 11.895, 12.505, 13.115, 13.725, 14.335, 14.945 km)

But compared with emissions-cmip6_SO2_aircraft_vertical_1750-2015_0.9x1.25_c20170608.nc, I found my results was about 10^1 times smaller.
I suspect there might be wrong with my calculation process but I do not know how I can solve it.

I need your help!

 

[erik]

This topic is specific to the atmosphere model CAM and the atmosphere chemistry model CAM-CHEM, so I'm moving it there.

 

[Danny Leung]

Hi xnnzka-
I rewrote your equation below to make it clear to myself. I changed the conversion factors in bold. I didn't see big issues in your conversion. I am not familiar with CEDS emissions, but I think emission files can be reasonably different (by an order of magnitude).
y (molecules/cm^3/s)= Emissions (kg/m^2/s) × N_Av (molecules/mol) × 1/MW (mol/g) × 1000 (g/kg) × 1/10000 (m^2/cm^2) × 0.61km × 1/1000 (km/m) × 1/100 (m/cm)
One thing is that CAM's lowest level grid is less than 610 m and so you might want to compare the two emission files at the same height. Check these history variables: HEIGHT and Z3, for CAM vertical grid interface and for grid mid-point height.
I suppose you have checked through these already, but you can double check if the year of concerns from both datasets are the same, or if they provide S or SO2 emissions (in which case the molecular weight MW can be different).
Danny

 

[xnnzka]

Hi xnnzka-
I rewrote your equation below to make it clear to myself. I changed the conversion factors in bold. I didn't see big issues in your conversion. I am not familiar with CEDS emissions, but I think emission files can be reasonably different (by an order of magnitude).
y (molecules/cm^3/s)= Emissions (kg/m^2/s) × N_Av (molecules/mol) × 1/MW (mol/g) × 1000 (g/kg) × 1/10000 (m^2/cm^2) × 0.61km × 1/1000 (km/m) × 1/100 (m/cm)
One thing is that CAM's lowest level grid is less than 610 m and so you might want to compare the two emission files at the same height. Check these history variables: HEIGHT and Z3, for CAM vertical grid interface and for grid mid-point height.
I suppose you have checked through these already, but you can double check if the year of concerns from both datasets are the same, or if they provide S or SO2 emissions (in which case the molecular weight MW can be different).
Danny

Hi, Danny.
Very thanks for your suggestion and work!
The emission file I compared with: emissions-cmip6_SO2_aircraft_vertical_1750-2015_0.9x1.25_c20170608.nc is originated from CEDS version 2017 and mine is CEDS version 2024 (so I am not sure if they have so big difference).
And I also checked the height and height interface, they are the same. I compared the same year (1990) data between both.
About the MW, I use the CESM official MW excel form.
You are very careful because you think about many probable reason. I think after I double check, I might email to official to ask this question. Your calculation give me confidence because I think there must calculation error in my conversion equation these days.If there are any developments, I will update here.

 

[Danny Leung]

Great! Do post it here if you get a resolution and find it helpful for others!

 

[xnnzka]

Great! Do post it here if you get a resolution and find it helpful for others!

Hi, Danny

I just spent Chinese New Year holidy so I've been a little slow in updating the news. I have emailed to Jean-Francois and he gives similar comments with you. I plan to discuss it with my supervisor next week and also welcome any suggestions and comments from whom sees this thread.

 

[xnnzka]

My equation has a typo: 1000000 (cm^2/m^2) should be 1000000 (cm^3/m^3).

Corrected as here:
y (molecules/cm^3/s)= Emissions (kg/m^2/s) × N_Av (molecules/mol) ÷ MW (g/mol) × 1000 (g/kg) ÷ 1000000 (cm^3/m^3) ÷ altitude interface (km, I found the altitude interface=0.61km, so here I fix it to be 0.61) ÷ 1000 (km/m)

 

[Danny Leung]

Hi xnnzka-
Thanks for updating! Let us know if you have updates with your unit conversion after discussing with others.
Danny

 

[xnnzka]

Hi xnnzka-
Thanks for updating! Let us know if you have updates with your unit conversion after discussing with others.
Danny

Hi, Danny

After asking my my supervisor, he kindly provided me a website (cesm-cmip6-emissions/historical_emissions/make_emis_cmip6_aircraft.pro at main · lkemmons/cesm-cmip6-emissions). I recently have something else to do so I have not yet carefully compared my calculations with those in this code. But I think I would write a new code to calculate my emission file with reference to this github.

I hope this website could give some help for whom recently prepare for their own emission files.

Thanks for your help and ongoing attention.

 

[Danny Leung]

Hi xnnzka, thanks for the update and the information! The page will be helpful to those who are working on the same problem.
Danny