The effect of ventilation on air particulate matter in school classrooms

Health problems and respiratory diseases are associated with indoor air particulate matter (PM) mass. This is specially a concern in schools as children spend most of their time indoors. Understanding factors that affect PM mass such as occupant activities, ventilation and the infiltrating outdoor environment are important to safeguard occupant health. We investigated the air quality inside and outside two low decile primary school classrooms (children ages 7–9) over a three-week period during the southern hemisphere winter season in Palmerston North, New Zealand. Both classrooms were heated with wall mounted inverter heat pumps and in addition one classroom roof was fitted with a solar air heated ventilation unit (treatment). Particulate matter was continuously sampled and monitored to identify particles less than 10 µm in aerodynamic diameter (PM10) both outside and inside both classrooms to compare their indoor air quality. Significantly higher PM10 concentrations occurred within both classrooms during school hours (0845–1500), but the ventilated treatment classroom had PM10 concentrations on average 66% lower than those measured in the unventilated control classroom. Elemental composition and source apportionment of hourly samples showed that outdoor sources of PM10 infiltrated indoors, with similar contributions in both classrooms to those measured outdoors. However, the increased PM10 in the classrooms was predominantly from crustal sources, thought to be soil tracked in from outside on children's footwear and re-suspended during activities within the classrooms. Our results indicate that ventilation plays an important role in the quality of indoor air of classrooms and will contribute to the wellbeing of the students. In addition, there is a need to improve dust exposure mitigation strategies (carpet cleaning regime, dust reducing carpet) in classrooms fitted with carpets.