Indoor air quality in classrooms: Environmental measures and effective ventilation rate modeling in urban elementary schools

Associations have been shown between poor classroom indoor air quality (IAQ) and schoolchildren's risk of asthma, increased absenteeism, and impaired performance on standardized tests. Mechanically ventilated classrooms often lack an adequate fresh air supply. There is also concern that outdoor pollutants, particularly vehicle exhaust products, may penetrate classrooms. The purpose of this work was to characterize IAQ in elementary school classrooms and estimate average effective fresh air ventilation rates under cold, mild, and warm season conditions. IAQ measures were made in third-grade classrooms of 12 elementary schools. Particulate matter, CO₂, CO, NO₂, total VOCs, and formaldehyde concentrations, as well as relative humidity and temperature, were measured for 24-h periods in each season. Effective fresh air ventilation rates were estimated using a transient mass balance modeling approach. The schools measured had generally adequate temperature and humidity control, extremely low non-occupant related pollutants, and little to no incursion of outdoor vehicle-related pollutants. However, there was a lack of adequate fresh air ventilation in many cases. Ventilation adequacy varied within the schools across seasons but with no consistent pattern, perhaps reflecting variations in class size as well as seasonal demands on the HVAC systems and/or HVAC seasonal operating mode. Transient mass balance method effective fresh air ventilation estimates near or above ASHRAE-recommended fresh air ventilation rates for people-related pollutants corresponded well with good CO₂ control in the classrooms.