Lumped chemical mechanism
From AMS Glossary
lumped chemical mechanism
A simplified atmospheric chemical model, most commonly used for urban airshed models.
In a lumped mechanism, organic compounds of similar chemical formula are grouped or "lumped" together and treated as a single representative species. For example, all aldehydes (acetaldehyde, propionaldehyde, etc.) might be treated as a single molecule of formula RCHO, which undergoes chemical reactions representative of the aldehydes.