AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Spatiotemporal Trends in Concentrations of Ozone and Ozone-Skin Oil Oxidation Products in an Occupied Office and HVAC System
JINGLIN JIANG, Tianren Wu, Danielle Wagner, Philip Stevens, Heinz Huber, Antonios Tasoglou, Brandon E. Boor, Purdue University
Abstract Number: 777 Working Group: The Air We Breathe: Indoor Aerosol Sources and Chemistry
Abstract Ozone is an important driver of indoor oxidative reactive chemistry. Ozone can initiate the formation of indoor secondary organic aerosols through the oxidation of monoterpenes. Ozone oxidation of human skin lipids can produce volatile organic compounds (VOCs), such as 6-methyl-5-hepten-2-one (6-MHO), acetone, 4-oxopentanal (4-OPA), and decanal. HVAC systems in office buildings can deliver outdoor ozone to the indoor environment and serve as a site for heterogenous reactions of ozone with ventilation duct surfaces and HVAC filters. The objective of this study is to explore spatiotemporal trends in the concentrations of ozone and ozone-skin oil oxidation products in an occupied office and HVAC system.
A four-month measurement campaign was performed from February-May 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 ozone were measured with a UV photometric ozone analyzer. Ozone-skin oil oxidation products were measured via proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) for a portion of the campaign. An automated multi-point sampling system was built to sample ozone and volatile reaction products at eight locations throughout the HVAC system. More than ten ventilation modes with variable outdoor air exchange rates from 0 to 6 h-1 were implemented, including natural ventilation via a double-skin façade.
Outdoor ozone delivered to the occupied office was found to be an important participant in indoor oxidative reactive chemistry. Prominent spatial variations in ozone concentrations were observed throughout the HVAC system. Typical ranges in ozone concentrations were: 20 to 50 ppb for outdoor air, 10 to 30 ppb for supply air, and 5 to 20 ppb for return air. Negligible ozone loss occurred across the HVAC filter bank. Indoor concentrations of ozone were found to be strongly related to the fractional amount of outdoor air supplied to the office and increased with increasing outdoor air exchange rates. Human occupants and indoor surfaces were found to be a major ozone sink in the office. Ozone concentrations decreased by ~20 to 50% from the supply to return duct, depending on the ventilation mode. Concentrations of primary (e.g. 6-MHO) and secondary (e.g. 4-OPA) ozone-squalene oxidation products exhibited diel patterns and generally correlated with carbon dioxide concentrations. 6-MHO and 4-OPA reached peak concentrations of ~0.3-0.5 ppb in mid-afternoon, with I/O ratios often exceeding 10.