CMAQ-DDM unit problem

CMAQ-DDM-3D
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1

Hi everyone,

I have used DDM to calculate the sensitivity of NO₂ pollutant concentrations to NOx emissions and I noticed that the output units are “ppmV”. Could you confirm if this is reasonable for DDM sensitivity outputs?

Additionally, assuming I have an observed NO₂ value from observation data and a modeled NO₂ value from CMAQ, I calculated the difference between them. I attempted to estimate the emission adjustment using the formula:

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However, I found that the resulting emission adjustment is very small, showing almost no significant change. Interestingly, when I multiplied the result by the original emission inventory value, the adjusted emission difference became more reasonable. Could this issue be related to the units of the DDM sensitivity output? I would greatly appreciate your insights on whether this approach is correct and if the units of the sensitivity output might be affecting the calculation.

Thank you for your time and assistance. I look forward to your guidance.

Best regards,
Jimmy

2

The units in the output files are correctly labeled. They should be ppmV for gasses and ug/m3 for aerosols. The sensitivity coefficients are semi-normalized by the parameter used in their definition. Since you are calculating the sensitivity to emissions of NOx, the reported outputs have been normalized by those emissions. If you are interested in emissions adjustments, you can calculate the response by applying fractional adjustments directly to the DDM-3D outputs. For example, a 10% cut of NOx emissions would represented by 0.1 multiplied by the output field. Please, refer the DDM-3D publications for further explanation.

Sergey

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