Factors influencing variability in the infiltration of PM2.5 mass and its components

► This is one of the few papers to describe and model Finf and Fpex on a daily basis. ► Finf and Fpex can be lower and less seasonally variable where heating and cooling systems are used. ► Air cleaners and electrostatic precipitators may provide a mechanism of reducing exposures. ► Ambient and Non-ambient contributions can be quantified using Finf and Fpex.