num_a4 unit

[nattanan]

I have a question regarding the actual unit of the num_a4 parameter.

From what I’ve observed, num_a4 typically has a unit of
(particles/cm²/s) × (molecules/mole) × (g/kg).
However, when I looked into the source code used to generate BC emissions—such as the script at:
https://svn.code.sf.net/p/codescripts/code/trunk/ncl/emission/createBC_US-Russia.ncl —I noticed it uses the "smoke" parameter, which has units of molec/cm³/s. This value is then multiplied by "(MW_bc / mass_particle)", where the units are (g/mole) × (particles/kg). This results in a final unit of
(particles/cm³/s) × (molecules/mole) × (g/kg).

The discrepancy I’m concerned about is the volume versus area component—cm³ versus cm²—between the derived unit and the expected unit. I’d really appreciate any clarification you can provide on this issue.

Best regards,
Nattanan

 

[peverley]

Moving this to the CAM-Chem forum

 

[rrbuchholz]

Hi Nattanan,

The units of num_particle should be (particles/cm2/s)(molecules/mole)(g/kg), see this line in your linked script:
smokeNum = smoke * MWbc /mass_particle ;(particles/cm2/s)(molecules/mole)(g/kg)
There is a depth unit in your linked script that seems to be converting cm3 to cm2.

This script shows an example of preparing num_*

hires-qfed-process/redistribute_emiss_hires.ncl at main · rrbuchholz/hires-qfed-process

Processing QFED fire emissions for use in CESM. Contribute to rrbuchholz/hires-qfed-process development by creating an account on GitHub.

github.com

Best,
Rebecca