Abstract: The health and academic performance of children are significantly impacted by air quality in classrooms. However, there is a lack of understanding of the relationship between classroom air pollutants and contextual factors such as physical characteristics of the classroom, ventilation and occupancy. As a part of EPSRC-funded COTRACE/SAMHE project, we monitored concentrations of particulate matter (PM), CO2 and thermal comfort (relative humidity and temperature) across ten schools in London. Results were compared between occupied and unoccupied hours to assess the impact of occupants and their activities, different floor coverings and the locations of the classrooms. In-classroom CO2 concentrations varied between 500 and 1500 ppm during occupancy; average CO2 (955±365 ppm) during occupancy was ∼150% higher than non-occupancy. Average PM10 (23±15 μgm-3 ), PM2.5 (10±4 μgm-3 ) and PM1 (6±3 μg m-3 ) during the occupancy were 230, 125 and 120% higher than non-occupancy. Average RH (29±6%) was below the 40–60% comfort range in all classrooms. Average temperature (24±2 °C) was >23 °C in 60% of classrooms. Reduction in PM10 concentration (50%) by dual ventilation (mechanical + natural) was higher than for PM2.5 (40%) and PM1 (33%) compared with natural ventilation (door + window). PM10 was higher in classrooms with wooden (33 ± 19 μgm-3 ) and vinyl (25±20 μgm-3 ) floors compared with carpet (17±12 μgm-3 ). The average CO2 levels for smaller children (reception and year one) was ~190% higher than older children (year eight and nine) due to higher levels of activity. Air change rate (ACH) and CO2 did not vary appreciably between the different floor levels and types. PM2.5/PM10 was influenced by different occupancy periods; the highest value (∼0.87) was during non-occupancy compared with occupancy (∼0.56). Classrooms located on the ground floor had PM2.5/PM10 > 0.5, indicating an outdoor PM2.5 ingress compared with those located on the first and third floors (<0.5). The large-volume (>300 m3 ) classroom showed ∼33% lower ACH compared with small-volume (100–200 m3 ). Low PM10 events coincided with low CO2 events in classrooms across all schools. These findings provide guidance for taking appropriate measures to improve classroom air quality.

Keywords: Classroom air quality, Thermal comfort, CO2, PM10, Ventilation rates, UK schools