AERMOD View – Customize Output Units
July 2016
The AERMOD model features default units for emission inputs and concentration or deposition outputs. Emissions are presented as grams per second (g/s)*, and concentrations are calculated as micrograms per cubic meter (µg/m3). However, there may come a time when one or both of these default units needs to be changed to better represent project data. This change can be easily made via the Source Pathway options.
Under the Source Pathway, look under Source Options and select the Emission Output Unit heading.
Under the Source Pathway, look under Source Options and select the Emission Output Unit heading.
To modify the parameters, select the User Defined radio button. The user can then supply their own values for each of the three fields:
One time where adjusting the unit labels can help is when the default units produce numeric values that are too large or too small for the model to accurately write. For example, if the emissions for a given source were very small (e.g., 1E-6 g/s), the output concentrations may be too small for the model to write (<1E-5 µg/m3). In this situation, you could input a unit factor of 1 and change the Emission Unit Label to MICROGRAMS/SEC so that the results are not excessively-lowered to the point of not writing them. Making such an adjustment will help produce more detailed contour plots since the numeric data will be more precise and easier to work with.
- Unit Factor: The factor used to convert the emission rate input units to the output units. The default factor of 1000000 is used to get micrograms as output from the input of grams.
- Emission Unit Label: The label applied to the emission unit. This may be up to 40 characters in length.
- Concentration Unit Label: The output unit label. This may be up to 40 characters in length.
One time where adjusting the unit labels can help is when the default units produce numeric values that are too large or too small for the model to accurately write. For example, if the emissions for a given source were very small (e.g., 1E-6 g/s), the output concentrations may be too small for the model to write (<1E-5 µg/m3). In this situation, you could input a unit factor of 1 and change the Emission Unit Label to MICROGRAMS/SEC so that the results are not excessively-lowered to the point of not writing them. Making such an adjustment will help produce more detailed contour plots since the numeric data will be more precise and easier to work with.
