AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Secondary Aerosol Mass Contributions from Human Occupants in a Classroom
ANITA AVERY, Michael Waring, Peter DeCarlo, Drexel University
Abstract Number: 603 Working Group: The Air We Breathe: Indoor Aerosol Sources and Chemistry
Abstract Humans can impact the composition of indoor air via heterogeneous reactions of gas-phase oxidants with skin constituents on an occupant or skin that has been shed (desquamation), as well as by direct emissions from people themselves (bioeffluents) and the personal care products they use. However, separating the influence of the many emissions and their oxidation products from the influence of outdoor-originated aerosols has been a challenge. Indoor and outdoor aerosols were alternatively sampled at 4-minute time resolution with a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) in a classroom with student occupants at regular intervals. Mass spectral analysis showed aerosol enhancements of oxidized and unoxidized hydrocarbon ion families during occupied periods, especially at ion fragments larger than m/z 100 and double bond equivalents consistent with squalene (C30H50) and its oxidized products from reaction with ozone, indicative of the secondary nature of the aerosol mass. Individual hydrocarbon mass fragments consistent with squalene fragmentation, including C5H9+ , and C6H9+ were especially enhanced with room occupancy. Other oxidized fragments related to oxidation products of squalene and ozone were also enhanced. Emissions of individual organic fragment ions were estimated using a model accounting for outdoor aerosols and air exchange. This showed occupancy related emissions at smaller fragments from occupants indoors. Ozone losses (β) were used to parameterize emissions to relate to other environments, such that total emission of all fragments was 17.6 μg β-1 h-1 above unoccupied levels. This translates to approximately 25% increase in organic aerosol mass concentration in the classroom during an occupied hour with a median occupied ozone loss. Human occupants, therefore, represent an additional mass burden of organic aerosol, especially in poorly ventilated or highly occupied indoor spaces.