I am using CMAQ v5.5 with the Windblown Dust module.
I’m reviewing the DUSTEMIS diagnostic output from my model results, which reports dust emission rates in units of g m⁻³ s⁻¹ but does not include any information about the vertical layer into which these emissions are injected.
I have two questions:
Vertical layer placement: When DUSTEMIS adds emissions, into which model layer(s) are they injected?
Converting to g s⁻¹: If I want to express the emissions as g s⁻¹ per grid cell, should I multiply the DUSTEMIS values by the horizontal grid area and the layer thickness (i.e., the cell volume)?
yes, all windblown dust emissions are injected into the first model layer. And to convert these emissions from g m⁻³ s⁻¹ to g s⁻¹, you would indeed multiply them by the cell volume. In this calculation, my understanding is that you should account for the map scale factor by dividing the product of emissions, dx, dy, and dz by the squared map scale factor MSFX2 from METCRO2D GRIDCRO2D.
I can confirm what Christian is saying. You need to calculate volume using 1st layer thickness (ZF from METCRO3D) and divide by MSFX2 (from your GRIDCRO2D file).
Thank you for your response, I have an additional question.
When the emissions generated by the windblown dust module appear as PM concentrations in the CONC file, they are not only reflected in the 1st layer but also affect the upper layers.
I’m curious about the mechanism behind this result.
It seems that DUST_EMIS.F is only responsible for calculating the emissions, so I would like to understand how these emissions are distributed throughout the vertical column and lead to changes in concentration in the upper layers.
If I manually add the PMC to the 1st layer of my emissions file in the same regions where windblown dust emissions are generated by the module, would the PMC be transported through the atmosphere in the same way as dust?
I don’t see why not. “Dust” is 93% PMC and 7% PMF in CMAQ, and the PMC is made up of different species. If you wanted it to look exactly like dust you would need to speciate the PMC, either offline or using DESID, to match the speciation of the inline dust module. Otherwise there will be slight differences across species as a function of things like settling and deposition.