Conference Agenda

Sub-3 nm nanocluster aerosol (NCA) represent a critically important, yet understudied, class of atmospheric aerosol particles. They can originate from primary processes, such as combustion, or secondary processes, such as the oxidation of volatile organic compounds (VOCs). NCA can efficiently deposit in the human respiratory system and subsequently translocate to vital organs. Given their high surface area-to-mass ratios, NCA exhibit a greater likelihood of bioactivity and toxicity. Notably, the indoor atmosphere differs significantly from the outdoors. The behavior and prevalence of indoor atmospheric NCA are likely to be influenced by a variety of building and occupant characteristics. Given the nature of human activities in indoor spaces, NCA sources are likely to be highly transient, resulting in rapidly changing concentrations over short time-scales. However, a complete mechanistic understanding of the formation, transformation, and exposure of indoor atmospheric NCA down to 1 nm in residential buildings is presently lacking.

Field measurements of the formation and growth of indoor atmospheric NCA during common household activities were conducted in a mechanically ventilated residential building – the Purdue zero Energy Design Guidance for Engineers (zEDGE) Tiny House. These activities included cooking, cleaning, and the use of scented volatile chemical products. Particle number size distributions from 1.18 to 30,000 nm were measured using a suite of aerosol instrumentation, including a Particle Size Magnifier – Scanning Mobility Particle Sizer (PSMPS), a SMPS with a long-DMA, and a Wideband Integrated Bioaerosol Sensor (WIBS). Additionally, a comprehensive mass balance model was developed, integrating complex physical transformation processes such as nucleation, intermodal and intramodal coagulation, condensation, deposition, and ventilation, to understand the transformation of indoor atmospheric NCA.

The results reveal unique dynamics and heightened inhalation exposure to indoor atmospheric NCA during common household activities. First, during indoor combustion activities such as cooking and using scented candles, NCA persisted throughout the active combustion period despite their tendency to coagulate and diffuse to surfaces. This resulted in indoor atmospheric NCA respiratory tract deposited dose rates that greatly surpass those linked to outdoor traffic-related NCA. Additionally, the use of scented volatile chemical products indoors was found to trigger the rapid secondary formation of NCA, even under low ozone levels (below 25 ppb). Remarkably, these particles grew over ten-fold in size within minutes. Comparatively, the formation and growth rates of indoor atmospheric NCA were substantially higher than those reported in outdoor environments during secondary NCA formation.

The primary mechanisms driving the loss of indoor atmospheric NCA are coagulation, followed by condensation, deposition, and ventilation. Interestingly, the presence of larger particles was observed to suppress the persistence of indoor atmospheric NCA through coagulation scavenging, impacting both primary and secondary indoor atmospheric NCA formation processes. Furthermore, indoor atmospheric NCA could not be adequately modeled using conventional indoor air pollution markers, such as PM_2.5 and NO_x. Considering that people spend approximately 90% of their time indoors, understanding the unique behaviors and transformations of indoor atmospheric NCA is vital for assessing and mitigating potential human health risks in residential buildings.

During the key motor development stages for infants that occur between the ages of 6 and 18 months, the act of crawling over a surface disturbs settled dust particles by the impact of the infant’s hands and limbs. The disturbed settled dust can then either be resuspended and inhaled by the infant or contact transferred and then ingested during mouthing events, entering their system regardless. The contents of settled dust in a given environment are reflective of the socioeconomic disparities of services in cities. Settled dust in indoor environments can contain health-relevant materials, such as per- and polyfluoroalkyl substances (PFAS), metals, microplastics, flame retardants, plasticizers, allergens, and microorganisms. Given the significant potential for ingestion and inhalation of disturbed settled dust, it is critical to understand the size-dependent fate and transport of these particles during crawling events. Doing so will help identify how to mitigate health risks for infants during their key motor development stages. Infant contact dynamics will be simulated with a linear stage motor to perform impact tests between samples of simulated skin and indoor surfaces of interest. Simulated skin will be used to model infant limbs, with artificial saliva and skin oil being added to simulate different conditions. Information about the velocity and forces of infant crawling styles and their associated development stages will be determined through the New York University Databrary database of laboratory and home recordings of infant locomotion. This data can then be replicated with the linear stage motor through specified contact impulses on surfaces to mimic infant locomotion.

Experimental data collection will distinguish between resuspended and contact transferred particles from each event of interest. The Wideband Integrated Bioaerosol Sensor (WIBS) utilizes single particle fluorescence spectrometry to count and measure the equivalent diameter of airborne particles, which will be used to determine the size-resolved (i) dust resuspension fraction, r_i, of each event of interest using a single-zone mass balance model. For the dust particles that underwent surface transfer during the event of interest, microscopic imagery will be used for identifying the particle count of dust that transferred from the experimental surface at impact, and a Laser Diffraction Particle Sizer (LDPS) will be used to develop particle diameter distribution curves. These processes will be used to determine the size-resolved surface contact transfer fraction, c_i, of each event of interest. In the existing literature, the factors for dust inhalation and ingestion, as well as the processes themselves, have been studied and examined individually and exclusively of each other. The aforementioned dust resuspension and surface transfer fractions will provide insights into the dust inhalation and dust ingestion potential of our interactions of interest, respectively. This novel examination of both fractions simultaneously allows for new mechanistic insights into the size-resolved behavior of settled indoor dust particles, removing the limited perspective of analyzing these processes individually.

This study focuses on the development of an inert controlled environmental chamber (ICEC) that will be able to isolate chemical emissions from scented volatile chemical products (sVCPs) by housing them within the completely pollutant resistant environment. The two overarching goals of this instrument are to: (1) utilize these chemical emissions in conjunction with human participants to evaluate their associated psychological and emotional response and to (2) isolate samples from sVCPs that are uncontaminated by outside air for high-resolution online mass spectrometry analysis.

Personal care and household products are potent sources of indoor air pollution as they contain volatile organic compounds (VOCs) that interact and transform within the indoor atmospheric environment. Scented products that individuals bring into their homes, cars, and workplaces are of particular interest in this study as their value is rooted in creating smellscapes that appeal to the emotional perceptions of the consumer rather than a discernible function that are offered by skin products that moisturize skin or hair care products that add shine to hair, for example.

This study utilizes the ICEC with mainstream and widely available sVCPs by housing them and supplying zero air to ensure that the sVCP emissions are not altered by influences like excess ozone and particulate matter. Emission concentrations are then diluted with zero air with a specialized system of mass flow controllers and delivered to a human participant through a stainless steel sniffing port. The participant’s heart rate (HR) and blood oxygen saturation (SpO₂) are monitored using non-invasive measures to evaluate any changes in breathing and HR patterns through each dilution phase. For odor and emotional assessment, this study utilizes the Geneva Odor and Emotional Scale (GEOS). This scale is an effective tool in measuring the subjective experience triggered by commonly experienced odors and scents using a series of Likert scales in six dimensions including disgust, happiness-well-being, sensuality-desire, energy, soothing-peacefulness, and hunger-thirst. This tool aids in understanding the motivation to incorporate certain products into one’s personal smellscapes. Starting at the highest dilution setting, the participant will inhale at the top of the sniffing port and respond to a series of questions on the GEOS regarding their perception of the odor they are asked to perceive. This will occur in 7 stages as the emission concentration increases and dilution decreases, using an online mass spectrometer to concurrently track the VOC concentrations.

This study is expected to find a relationship between the increased concentration of VOCs introduced from the sVCPs and stress-response factors reflected in the olfactory assessment and biometric data. The incorporation of the ICEC with human participants, odor and emotional assessment, and biometric data will contribute a well-rounded perspective to the literature expanding on relationships between sVCPs in the curated indoor environment and human olfaction perception with emotional and physiological responses. This study is approved by Purdue University’s Institutional Review Board Committee #IRB 2022-343.

Heat-based hair styling activities are a daily routine that can release large quantities of gas-phase chemical contaminants into the indoor atmosphere. Such activities involve the use of hair care products (HCPs) that emit a variety of volatile organic compounds, such as cyclic and linear volatile methyl siloxanes, monoterpenes, monoterpenoids, and glycols. During hair styling, HCPs are often used with heat-based appliances, such as hair straighteners, hair curlers, hair wavers, and blow dryers. The combination of chemically complex HCPs and heat may generate particle-phase contaminants that can be subsequently inhaled into the respiratory system. The aim of this study is to evaluate indoor nanoparticle emissions and exposures during heat-based hair styling activities in residential buildings. Realistic hair care routines were conducted in a mechanically ventilated residential building – the Purdue zero Energy Design Guidance for Engineers (zEDGE) Tiny House. Nanoparticle concentrations and size distributions from 6 to 500 nm were measured in real-time (1 Hz) with a high-resolution electrical low pressure impactor (HR-ELPI+) with sintered collection plates. During the measurement campaign, a variety of HCPs were used in tandem with heated appliances, including hair straighteners, curlers, and wavers. Occupant exposure was evaluated through size-resolved respiratory tract deposited dose rates.

HR-ELPI+ measurements revealed that heat-based hair styling activities produce significant amounts of airborne nanoparticles, with number concentrations often in the range of 10⁴ to 10⁵ particles/cm³. Indoor nanoparticle number size distributions were generally bi-modal in shape. The peak particle diameter was between 10 to 100 nm for styling activities using hair straighteners and curlers, while it was shifted to larger sizes (100 to 200 nm) for activities using hair wavers. The emitted nanoparticles are likely formed during heat-based processes involving the evaporation and thermal decomposition of chemical constituents in the HCPs. Total respiratory tract deposited doses during hair care routines were in the range of 10¹⁰ to 10¹¹ deposited particles across the head airways, tracheobronchial region, and pulmonary region. Our results demonstrate that heat-based hair styling activities represent an important source of airborne nanoparticles in bathrooms and bedrooms of residential buildings.

Understanding occupant comfort in compact residential spaces is important as people spend about 90% of their time indoors. This study aims to bridge the gap between occupants' perceived comfort and the actual indoor environmental quality (IEQ) in these spaces. The motivation behind this research is the growing need to optimize living conditions in compact residences, which are becoming more prevalent in urban areas. The study employs objective measurements and subjective surveys of full-scale living experiments in the Purdue zero Energy Design Guidance for Engineers (zEDGE) Tiny House. The objective component involves monitoring energy and water consumption, along with key IEQ parameters such as air and mean radiant temperature, relative humidity, sound level, lighting intensity, and indoor air quality. These measurements provide a quantitative assessment of the indoor environment and were enabled through an IoT-based sensing platform. Simultaneously, subjective surveys gather occupants' perceptions and comfort evaluations. This aspect is crucial as it reflects the actual lived experience of the residents, which may not always align with the objective data. By combining these two approaches, the study offers a comprehensive understanding of comfort in compact living spaces.

The current phase of the research has successfully integrated objective data with subjective comfort evaluations following twenty full-scale living experiments in the Purdue zEDGE Tiny House during the heating season. This integration is a significant step towards understanding the complex interplay between the physical environment and occupant perception. The anticipated findings of this study are multifold. Firstly, it is expected to reveal patterns in IEQ, energy, and water usage that impact occupant comfort. Secondly, by highlighting these patterns, the study aims to contribute to the enhancement of indoor living conditions. The expected benefits include improved design and management strategies for compact residential spaces, leading to more sustainable and comfortable urban living environments. This study not only contributes to the understanding of indoor comfort, but also has practical implications for urban residential design and policy-making. By addressing both the objective and subjective aspects of indoor comfort, it aims to foster indoor environments that are both efficient and comfortable for their occupants.

Air filters installed in residential and commercial HVAC systems encounter a complex mixture of aerosols of outdoor and indoor origin during their service life. Standardized laboratory test methodologies are important for evaluating the loading behavior of HVAC filters. Loading aerosols commonly used to age HVAC filters include various test dusts (ISO-12103-1-A2, ISO-12103-1-A4, ASHRAE Test Dust) that are primarily composed of coarse mode particles (1 to 100 µm). However, urban aerosol mass size distributions often feature a prominent accumulation mode between 0.1 and 1 µm that is not well represented by traditional loading aerosols. The aim of this study is to develop a new laboratory test methodology for rapid ageing of HVAC filters with a representative urban aerosol mass size distribution at a high concentration to better predict long-term changes in HVAC filter performance. A HVAC filter test rig was custom designed and built following ASHRAE 52.2 specifications to artificially age HVAC filters with sub-micron potassium chloride (KCl) aerosol produced by a thermal aerosol generator. The KCl aerosol is formed by burning KCl sticks in a high temperature oxygen-propane flame and is delivered to the test rig via a damper-controlled intake duct.

The loading behavior of a collection of air filters of variable design and efficiency (pleated MERV8, electrostatic bag MERV13, V-cell MERV14) was evaluated using the new experimental protocol. KCl aerosol size distributions were measured across the test filter using a scanning mobility particle sizer (SMPS) and a high-resolution electrical low pressure impactor (HR-ELPI+). Artificial ageing experiments were conducted until the filter pressure drop reached 1.5 in. H₂O. The new test methodology successfully aged MERV8, MERV13, and MERV14 filters to 1.5 in. H₂O in several hours. Loading curves were sensitive to the MERV rating, volumetric airflow rate, relative humidity, and KCl stick feed rate. The results demonstrate that the new sub-micron KCl loading aerosol is a time- and cost-effective technique to artificially age HVAC filters with a particle mass size distribution representative of that found in HVAC installations in buildings.