Carbon dioxide and ozone in high school classrooms

High school classrooms are important places of learning and working for millions of students and teachers. Because small discomforts can cause losses in student productivity and achievement, ensuring a healthy working environment is vital. As the primary method of supplying outdoor air to classrooms, mechanical ventilation systems are an important component of the indoor space and have the power to affect concentrations of indoor pollutants. The objective of this research was to investigate mechanical ventilation systems and the concentrations of two specific indoor pollutants, carbon dioxide and ozone, in high school classrooms. As part of this study, a two-year field researching campaign was conducted in seven high schools. Carbon dioxide concentrations were measured in the supply airstream and the general room area of classrooms. Through use of steady-state and dynamic mass balance analyses, classroom ventilation rates were estimated. Ozone concentrations were monitored on school rooftops and in classrooms to investigate the influence of mechanical system operation on ozone concentrations indoors. Mechanical ventilation systems were found to be an important consideration when studying the indoor environment, with system operation affecting indoor carbon dioxide and ozone concentrations. When compared to the outdoor air recommendations provided by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) in Standard 62.1, it was found that many classrooms did not receive sufficient fresh air. Classrooms located in portable structures were found to receive large amounts of outdoor air through infiltration and natural ventilation when compared to classrooms in permanent structures. A relationship between average carbon dioxide concentrations and indoor-to-outdoor ozone concentrations was observed, indicating the influence of outdoor air on the concentrations of both pollutants indoors