Using indoor CO2 concentration thresholds to understand and improve the air quality of public buildings: A practical approach
Henry P. Oswin, Lucien Glachant, Savinda Arambawatta Lekamge, Behnaz Alinaghipour, Saima Bukhat Khan, Lídia Morawska
Abstract
New strategies for assessing and improving indoor air quality, particularly in a manner reducing exposure to airborne pathogens, are required. Monitoring CO 2 concentrations within indoor spaces provides a relatively simple means of achieving this. We aimed to develop a simple approach to tracking CO 2 concentrations within a variety of indoor spaces, relating this to the number of occupants within the space, and then using the data to provide recommendations, improving the air quality within the space. Portable CO 2 monitors were used to collect data across an inner-city educational facility. Occupancy data was collected for each space using several methods and then data was processed to extract the steady-state CO 2 concentration for each space and level of occupancy. To allow clearer comparison between different spaces we calculated a parameter we term the ‘OC800’ or occupants per square meter before 800 ppm of CO 2 is exceeded. Of the 25 spaces studied, 12 were observed to exceed our desired CO 2 threshold of 800 ppm. For each space it was possible to determine the exact level of occupancy which would result in the CO 2 exceeding 800 ppm, allowing the assignment of occupancy limits to each space. If a higher level of occupancy was required, it was possible to calculate the relative increase in ventilation needed to achieve this. The average OC800 across the spaces was 0.3, with an OC800 below 0.2 appearing to indicate problematic spaces. This approach can be tailored to different locations and CO 2 thresholds, providing clear actionable solutions to poor indoor air quality.