AERMOD View: When Numerical Values Are Outside AERMOD’s Default Threshold

AERMOD outputs numeric results with up to 13 significant figures. When emission rates are very high or very low, values may not fit within this default range. Concentration values at or above about 1E9 units can cause the output to render as a field of asterisks, indicating an overflow.

Concentrations near the default reporting threshold (1E-5) may yield repeating values such as 0.00000 or 0.00001, which reduces precision and can hinder contour generation in AERMOD View.

Approach 1: Adjust the model's unit labels

In the Source Pathway, the Emission Output Unit setting controls the emission label and concentration unit. By default, the model uses GRAMS/SECOND for emission rate and MICROGRAMS/M³ for concentration with a unit factor of 1E6. Selecting the User Defined option enables editing of the unit factor and labels.

Examples: a unit factor of 1 with a concentration label of GRAMS/M³ prints numeric values for high results; a unit factor of 1E12 with a concentration label of PICOGRAMS/M³ prints numeric values for very low results.

Approach 2: Write data in exponential format

In the Output Pathway under Output Settings, enable Use Exponential Format for Output Results. This reports all values in external output files (Contour Plot Files, PLOT-formatted Post-Processing Files, etc.) using scientific notation to ensure full numeric representation.

This approach maintains numeric precision across the result range and supports downstream processing that relies on consistent formatting.