What is the smallest horizontal resolution allowed by the code, e.g., 10×10 meters, or 1×1 km?

The concentration grid size is a single precision variable and therefore can have any value within that range. However, from a computational perspective, the model’s minimum integration time step is 1 minute, and therefore if you assume an average wind speed of say 5 m/s, the minimum grid size would be 300 m.

Roland Draxler