Evidence of outdoor air quality events in classroom IAQ, RoomVent 2024

The impact of a period of unusually high outdoor particulate matter (PM) levels resulting from Saharan dust was seen on schools in the UK. Almost all measured schools across the UK showed significantly elevated PM measurements over this period, with classroom PM levels being more than seven times larger during this event than in a typical period, and indoor PM levels were often higher than those outdoors. Levels of inferred ventilation (based on classroom CO2) did not significantly correlate with indoor PMs during this event, likely because of the role of ventilation in both transporting PM into the classroom, and of dilution. Classroom PM levels remained elevated for some time even as outdoor PM levels fell, possibly due to increased particulate settling in classrooms and later re-suspension.