# How to apply DDM results to estimate ozone/PM2.5 changes?

Hi, I want to know how to apply DDM results to calculate ozone/PM2.5 changes with a certain emission reduction rate. I am OK with getting the DDM results but am not 100% sure about how to apply these results. I understand that DDM basically calculates the changes in ozone/PM2.5 concentration in response to changes of precursors emissions (i.e., the slope in the following figure from EPA’s website). I want to know, for instance, when the SO2 emissions are reduced by 10%, what’s change in PM2.5 concentration. Should I multiply the DDM result (sulfate to SO2 sensitivity) by 10% (i.e. 0.1, unitless) or 10% of the total SO2 emissions (i.e., unit is mass)? In other words, does DDM calculates the pollutant response to relative changes (i.e. 1%, 5%) or absolute changes (e.g., 100 kg, 200kg)?

Thank you very much!
Ling

DDM-3D output is semi-normalized by the parameter in question. The answer is this one from your choices:

“DDM calculates the pollutant response to relative changes (i.e. 1%, 5%)”

Sergey

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Thanks, Dr. Sergey. I am still not unsure about this. Say if I got the DDM results with the base emissions and now I want to calculate the response to the reduction by 10%, should I multiply by 0.1 with the DDM results or should I multiply by 10 (assuming the DDM results responds to 1% change)? To more be specific, if the DDM result gives sulfate to SO2 sensitivity of 1.5 ug/m3. For a reduction by 10%, the changes of sulfate concentration is 0.15 ug/m3 or 15 ug/m3?

Ling

Ling,

If sulfate sensitivity to SO2 is 1.5 ug/m3 at some hypothetical time/space composite, then a 10% reduction in the input parameter leading to that sensitivity would indicate 0.15 ug/m3 reduction in sulfate.

Sergey

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Much appreciated, Dr. Sergey!