Influence of Human Activities and Occupancy on the Emission of Indoor Particles from Respiratory and Nonrespiratory Sources

Abstract

In this study, we examined the relationship between human activities and emission characteristics of CO 2 and particles in three indoor settings: a clean environmental chamber, a cafe, and a musical club. We determined CO 2 and particle emission rates (CER and PER) across various human activities (sitting, reading, and exercise) in both masked (N-95) and unmasked scenarios, as well as scenarios involving normal and clean-room clothing (CRC) in the clean environmental chamber. Masking reduced PER only during the exercise (∼11%), indicating that respiratory sources constitute a tiny fraction of the total particle emissions during passive activities (e.g., sitting and reading). In contrast, wearing CRC reduced the PER by over 55% for all activities, demonstrating that clothing and skin-shedding constitute a dominant fraction of particle emissions from humans. Results from the caféand club measurements showed that the CO 2 and particle number concentrations were mostly driven by human occupancy. Collectively, the results from the controlled lab and field environments demonstrate that nonrespiratory emissions (e.g., clothing and skin-shedding) from humans outnumber respiratory emissions in an indoor environment, emphasizing the need to better quantify the contribution and evaluate the potential role of nonrespiratory emissions from humans in the airborne transmission of infectious diseases.