Step 1: Recall the purpose of the Gaussian plume model.
The Gaussian plume model is a mathematical model used to predict the dispersion of pollutants released into the atmosphere from continuous point sources such as chimneys and stacks.
Step 2: Identify the correct application.
Therefore, it is primarily used for estimating
\[
\boxed{\text{Air pollutant dispersion}.}
\]
Hence,
\[
\boxed{(C)}
\]
is the correct answer.