AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Dynamics of Volatile Organic Compounds in a Living Laboratory Office and HVAC System
TIANREN WU, Danielle Wagner, Jinglin Jiang, Philip Stevens, Heinz Huber, Antonios Tasoglou, Brandon E. Boor, Purdue University
Abstract Number: 771 Working Group: The Air We Breathe: Indoor Aerosol Sources and Chemistry
Abstract Indoor emissions of volatile organic compounds (VOCs) and their subsequent transformations in HVAC systems can strongly influence the composition and chemistry of indoor air. Humans are an important indoor VOC source. Human-associated VOC emissions include exhaled breath, skin secretions, personal care products, ozone-skin oil reaction products, clothing, and microorganisms. Selected VOCs, such as monoterpenes, can be precursors for indoor secondary organic aerosol formation. The use of proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) enables for characterization of time-dependent VOC dynamics driven by transient occupancy and building system operation. The objective of this study is to understand how occupancy and ventilation mode influence spatiotemporal variations in the composition and concentrations of VOCs in an office and HVAC system.
A one-month measurement campaign was performed from February-March 2019 at the Herrick Living Laboratories at Purdue University, which are four modern open-plan offices with precisely controlled HVAC systems. Time-resolved concentrations of VOCs were measured via PTR-TOF-MS for one office housing twenty graduate students. An automated multi-point sampling system was built to sample VOCs at eight locations throughout the HVAC system: office return air (x2), supply air (x2), pre-/post-filter bank, common area return air, and outdoor air. Seven ventilation modes were implemented.
Preliminary results demonstrate that humans are a prominent source of VOCs in an occupied office and concentrations of human-associated VOCs exhibit diel variations driven by occupancy. VOCs related to metabolic activity reached peak concentrations in mid-afternoon (e.g. methanol: ~25 ppb; acetone: ~10 ppb), while those related to personal care products present daily maxima in the morning (e.g. decamethylcyclopentasiloxane (D5): ~0.2 to 2 ppb) and then decay throughout the day. I/O ratios exhibited variations among the many VOCs detected, ranging from ~1 for benzene to > 10 for isoprene. Spatial variations in VOC concentrations throughout the HVAC system were observed for all VOCs. Concentrations of some VOCs were found to decrease by ~5 to 20% across the HVAC filter bank, suggesting VOC removal via partitioning to deposited particles. The primary loss mechanism for indoor VOCs is ventilation, and the rate increased with increasing outdoor air exchange rate. VOC emission factors (μg h-1 person-1) and deposition rates to indoor and ventilation duct surfaces will be reported, along with results from positive matrix factorization (PMF) analysis. To evaluate the impact of indoor VOC emissions on atmospheric chemistry, office- and building-normalized VOC emission factors to the urban atmosphere will be estimated.