How to get the aerosol's number concentration corresponding to each diameter? Aerosol distribution

Hi everyone, Merry Christmas.
I want to draw a plot of the aerosol number concentration distribution for accumulation modes. The vertical coordinate is dN/dlogDp and the horizontal coordinate is the diameter of the aerosol. But I can’t seem to find the number concentration corresponding to each diameter.

I’m using CMAQ 5.0.2, and I’ve so far found the variables DGACC_DRY, DGACC_WET in the CCTM_AERODIAM file, which represent the wet and dry diameters of the aerosol. In the CCTM_CONC file I found NUMACC in units of number/m3,this should be the number of accumulation mode aerosol. The NUMACC was found in the CCTM_SSEMIS file in units of number/s. (I’m actually more interested in the distribution of the sea salt aerosols.)
These variables do not seem to be able to plot the number concentration corresponding to each diameter. Is there any output for such variables in CMAQ? Or what should be done with these variables?
Thank you all and have a Merry Christmas!

NUMATKN, NUMACC, and NUMCOR are the modal total number concentrations Nt. To calculate number distributions dN/dlogDp, refer to equation 8.34 in Seinfeld and Pandis (2016) and then 8.18 to convert to log space. You’ll need the geometric mean diameter and standard deviation as well as number concentration.

For the sea spray particles, I’m not sure if the information in the SSEMIS file is enough to plot a number distribution. The output variables NUMFINE and NUMCOARSE are a flux calculated in the SSEMIS module by multiplying the mode-specific emission rates by the air volume of the gridcell, hence the /s units rather than /cm3/s. To convert this back to number you’d have to calculate average number concentration of emitted sea spray particles for each hour timestep within each grid cell volume by using ZF (layer height) from the METCRO3D files. Then, to plot the distribution, you’d have to use RH to figure out the diameter and standard deviation from the look-up tables in SSEMIS.F.

That’s my best guess, anyways! Hopefully someone else has more guidance on how to handle SSEMIS number distributions.


Thank you for these good questions, and thanks to abhoffman for good advice. There are two ways to get the parameters you need to input to the equations in Seinfeld and Pandis (i.e. the diameter and standard deviation for each mode).

(1) The AERODIAM file has the STDEVACC and STDEVCOR variables on it. These are the standard deviation of the accumulation and coarse modes that would be used to populate the number distribution along with the diameter variables you have already found. Note the Standard deviation is mathematically the same for wet and dry populations according to Seinfeld and Pandis and other literature. You can use the NUMACC and NUMCOR variables from the CONC or ACONC files to give you the number concentration in space and time.

(2) You may use the NUMACC and NUMCOR variables in the CONC/ACONC files along with the SRFACC and SRFCOR variables to calculate the diameter and standard deviation parameters. Use equations 5a and 5b from Binkowski and Roselle (2003) Note that 5a has a typo in it. I believe the -ln(M2) term should not be multiplied by 1/3. I’ll confirm this, but in the meantime, I recommend option 1 above.

If you are more concerned with sea spray particles then you will want to focus on the coarse mode variables. This is where the majority of the mass from sea spray emissions ends up.

Best wishes and Happy New Year,
Ben Murphy


Thanks for your suggestion! I checked out the corresponding equations and chapters and I believe that’s what I need, thank you very much.
Best wishes. Happy New Year!

Thank you very much for your reply, I preferred the first approach after trying it. Best wishes and Happy New Year!