# How can I specifiy a substance in AERMOD?

Since I use OTHER as a pollutant ID, are there some parameters I could specify in order to get better results for dispersion of substance I am trying to model? eg. molecular weight or density?

The POLLUTID key is used to specify some regular options.
• PM2.5 can only evaluate averages greater than 24 hours (if you try to generate hourly averages it throws an error).
• NO2 forces the use of options to simulate the conversion of NOx to NO2.
• SO2 triggers the use of a 4-hour half-life for SO2 decay in urban zones.