2017 Yes https://www.sciencedirect.com/science/article/pii/S0160412017306840 Morawska Europe Exposure Study Modeling Other the main origins of particle metrics differ from one type of indoor environment to another. For homes, outdoor air is the main origin of PM 10 and PM 2.5 but PN originate from indoor sources; for schools and day cares, outdoor air is the source of PN while PM 10 and PM 2.5 have indoor sources; and for offices, outdoor air is the source of all three particle size fractions.