AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Size Distributions and Emissions of Fluorescent Biological Aerosol Particles in an Office
TIANREN WU, Brandon E. Boor, Purdue University
Abstract Number: 794 Working Group: Bioaerosols
Abstract Human occupants are a major source of bioaerosols in indoor environments. Many processes that influence the emissions and removal of bioaerosols in buildings are dynamic and change over time. Human-driven particle resuspension from flooring, furniture, and clothing is very much linked to human movement and occupancy patterns, which can change throughout the day. The transient operation of HVAC systems affects the delivery of outdoor bioaerosols to indoor spaces and bioaerosol removal via ventilation and filtration. Real-time detection of fluorescent biological aerosol particles (FBAPs) via laser-induced fluorescence (LIF) offers a foundation to probe time-dependent indoor bioaerosol dynamics. The objective of this study is to investigate how occupancy patterns influence the size distributions and emissions of FBAPs in an occupied office.
A four-month measurement campaign was performed from February-May 2019 at the Herrick Living Laboratories at Purdue University, which are four open-plan offices with precisely controlled HVAC systems. Time-resolved size distributions of FBAPs from 0.5 to 20 μm were measured via a LIF-based instrument, the Wideband Integrated Bioaerosol Sensor (WIBS), for one office with hard vinyl flooring and a maximum occupancy of twenty graduate students. The WIBS was enclosed in a fan-cooled soundproof box and sampled indoor air via a vertical copper tube at an inlet height of 1.3 m. Supply air was delivered to the office via an underfloor air distribution system with floor swirl diffusers. Occupancy was monitored via chair-embedded thermocouples and carbon dioxide concentrations. Supplemental measurements of outdoor FBAPs were made via an isokinetic probe directed to the outdoor air duct of the HVAC system.
Size-integrated number concentrations of FBAPs and total particles increased with increasing occupancy in the office. The mean number concentrations of FBAPs and total particles during high occupancy periods (09:00-18:00) on weekdays were 2,700 and 8,000 m-3, respectively, while those during low occupancy periods (18:00-09:00) were 1,000 and 4,700 m-3, respectively. The peak of the mean number size distribution of indoor FBAPs was not fully captured by the WIBS as the modal diameter was < 0.5 μm. This peak is likely caused by sub-micron non-biological fluorescent interferents. A sub-mode in the mean number size distribution of indoor FBAPs was observed at ~2.6 μm, which is likely associated with bacterial cell agglomerates and fungal spores. The ratio of FBAPs to total particles (NF/NT) increased with increasing particle size. Size-resolved FBAP emission factors (no. h-1 person-1) will be determined via integration of a material balance model and time-resolved occupancy data. Hierarchical agglomerative clustering (HAC) analysis will also be conducted to differentiate non-biological fluorescent particles from bioaerosols and to improve the classification of FBAPs.