SAChE Source Models (ELA965 ) Practice Test

Instantaneous releases are extremely brief events that deliver mass in a negligible amount of time, effectively an impulse or puff. Quasi-steady releases, on the other hand, extend over a finite duration and have a mass flow rate that remains roughly constant during that time. This means the instantaneous release is a sharp, short surge, while a quasi-steady release is a sustained, near-constant flow. The other descriptions mix up duration and rate: an instantaneous event isn’t a constant-rate process, and a quasi-steady release isn’t just a brief impulse. Consequently, the described contrast—a puff-like, negligible duration versus a finite-duration, nearly constant flow—best captures the difference.