an R2 value>90% to be acceptable. Note that particle decay due to air
change is the same for all particle sizes while particle deposition and
coagulation are size-dependent processes in which smaller particles
generally have higher loss rates. Particle coagulation loss is larger
with higher UFP concentrations due to increased collision rates;
therefore, comparing the exhaust fan on and off cases, coagulation
losses are expected to be higher with the fan off than with the fan on