AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Indoor Measurements of Nanocluster Aerosols and New Particle Formation
TIANREN WU, Philip Stevens, Heinz Huber, Antonios Tasoglou, Brandon E. Boor, Purdue University
Abstract Number: 775 Working Group: The Air We Breathe: Indoor Aerosol Sources and Chemistry
Abstract A major source of atmospheric aerosol is new particle formation (NPF). NPF proceeds by the nucleation of molecular clusters as small as a single nanometer and their subsequent growth into larger sizes. Direct observations of atmospheric NPF necessitate the measurement of sub-3 nm nanocluster aerosol (NCA). While numerous studies have been conducted on atmospheric NCA, there have been no systematic investigations into NCA nucleation in occupied indoor environments. The objectives of this study are to investigate temporal trends in the concentrations and size distributions of NCA in an office and HVAC system and to characterize indoor NPF events down to ~1 nm.
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. NCA size distributions were measured with a nano Condensation Nucleus Counter operating in scanning mode and inverted by the expectation-maximization algorithm from the raw data. Size distributions beyond the NCA mode were measured with two scanning mobility particle sizers. Indoor and outdoor NCA was sampled from the office supply/return air ducts and outdoor air duct, respectively, using a core sampling probe. Measurements of ozone and volatile organic compounds (VOCs), via proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS), were also conducted for a portion of the campaign.
The peeling of mandarins was found to initiate rapid indoor NPF in an occupied office. NPF was likely initiated by the ozonolysis of monoterpenes as supply air ozone concentrations were typically between 10 to 30 ppb and monoterpene concentrations often peaked at ~10 ppb during mandarin peeling. The time-scale for such indoor NPF events is much shorter than atmospheric NPF. The modal diameter of the indoor aerosol size distribution increased from 1.4 nm to 55 nm within one hour and NCA concentrations exceeded 40,000 cm-3 at the inception of the nucleation process. During non-NPF event periods, concentrations of indoor NCA in the office were much lower than outdoors. Mean daytime and evening indoor NCA concentrations were ~170 cm-3 and ~20 cm-3, respectively. The daily maximum in indoor NCA concentrations (~270 cm-3) appeared between 10:00 and 15:00. Measurements of outdoor NCA found a daily mean NCA concentration of ~14,000 cm-3. Frequent atmospheric NPF events were detected in the outdoor air duct of the HVAC system. NCA measurements in the office supply air duct suggest a small fraction of the outdoor NCA may penetrate the HVAC filter bank.