CMAQ DDM for point source

CMAQ-DDM-3D
1

Hello, CMAQ users
I am wondering how to calculate surface ozone response to NOx and VOC emissions from point sources. Use surface layer (the first layer) sensitivities is appropriate for surface-based emission sources like on-road and area sources, but not directly for elevated point sources.

Surface sources (e.g., on-road mobile and area sources) emit ozone precursors exclusively into the lowest model layer. Therefore, estimating the surface ozone response (ΔO₃ at layer 1) using only first-layer sensitivities is physically consistent. In this case, applying CCTM_ASENS sensitivities from layer 1 alone is sufficient to quantify the surface ozone response to these emissions.

Point sources are fundamentally different. Stack emissions can be injected at multiple vertical levels depending on plume rise, stack parameters, and meteorology. As a result, precursor perturbations from point sources influence ozone formation throughout the vertical column, not just in the surface layer.

Because of vertical distribution of emissions, using only layer-1 sensitivities for point source emissions seems not completed. This explains why surface ozone responses (ΔO₃) calculated using only first-layer sensitivities for point source emissions are systematically underestimated compared with our results from CMAQ/ISAM source apportionment and brute-force emission perturbation simulations.

My question is

For point sources, should CCTM_ASENS sensitivities from all vertical layers be included when estimating surface ozone response?

How should surface-layer ozone response to point-source NOₓ and VOC emissions be calculated using first-order sensitivities, second-order sensitivities, and cross sensitivities (NOₓ–VOC interactions) across all vertical layers? How do we use mixing ratio sensitivity results for multiple layers as mentioned by Christian Hogrefe? Total VOC from CB6 - CMAQ-DDM-3D - CMAS CENTER FORUM

Thank you very much for any inputs and comments

Feng

2

Dear Feng,

It is not clear to me what you are asking. DDM-3D does account for processes in the full modeling domain including the upper layers. If you set the run script to output upper layers, you will also get sensitivities for these in the output files, but they are always calculated internally. How you use these would be up to you and will depend on you application.

Sergey

3

Hi Sergey,
Thank you for your response. Could you please provide an example of how sensitivities are applied to the upper layers? Specifically, in what types of situations would it be necessary or appropriate to use sensitivities for the upper layers?

For instance, would this be required when evaluating how much ozone is produced aloft from point sources, lightning, or aircraft emissions?

Thank you,
Feng