Many indoor air pollutants have been demonstrated to have a negative impact on occupants and due to physiological and behavioural differences, young children are more vulnerable to these effects than adults. Millions of children in the UK spend large parts of the day in nurseries, where occupant density is high, and indoor air quality can be poor. Therefore, it is imperative to understand the quality of indoor air in nurseries and how to improve it. The aims of the research presented here were to explore the indoor air quality (IAQ) in nurseries and the impact of both the use of air purifiers and window operations on IAQ. Three nurseries in London were selected and monitored via both continuous air quality sensors and passive sampling covering a total of 21 pollutants. Key findings include that mean reduction rate of PM2.5 by using air purifier was 63% with window closed, and 46% with window open. The results also highlight the impacts of operational changes implemented during the Covid-19 pandemic. Windows were operated more frequently for ventilation needs rather than being driven by temperature alone. The increased ventilation in the monitored nurseries in London led to low levels of VOCs and aldehydes (except for formaldehyde and 2-ethylhexanol) but could bring thermal discomfort to occupants. Both temperature and noise levels were shown to be relevant factors impacting the operation of air purifiers. Air purifiers can be effective at reducing PM2.5 when combined with proper window operation and have potential to bring substantial health benefits
