Measurement of Polycyclic Aromatic Hydrocarbons (PAHs) on Indoor Materials: Method Development

Wildfire smoke penetrates indoors, and polycyclic aromatic hydrocarbons (PAHs) in smoke may accumulate on indoor materials. We developed two approaches for measuring PAHs on common indoor materials: (1) solvent-soaked wiping of solid materials (glass and drywall) and (2) direct extraction of porous/fleecy materials (mechanical air filter media and cotton sheets). Samples are extracted by sonication in dichloromethane and analyzed with gas chromatography–mass spectrometry. Extraction recoveries range from 50–83% for surrogate standards and for PAHs recovered from direct application to isopropanol-soaked wipes, in line with prior studies. We evaluate our methods with a total recovery metric, defined as the sampling and extraction recovery of PAHs from a test material spiked with known PAH mass. Total recovery is higher for “heavy” PAHs (HPAHs, 4 or more aromatic rings) than for “light” PAHs (LPAHs, 2–3 aromatic rings). For glass, the total recovery range is 44–77% for HPAHs and 0–30% for LPAHs. Total recoveries from painted drywall ar

Experimental and Modeled Assessment of Interventions to Reduce PM2.5 in a Residence during aWildfire Event

Increasingly large and frequent wildfires affect air quality even indoors by emitting and dispersing fine/ultrafine particulate matter known to pose health risks to residents. With this health threat, we are working to help the building science community develop simplified tools that may be used to estimate impacts to large numbers of homes based on high-level housing characteristics. In addition to reviewing literature sources, we performed an experiment to evaluate interventions to mitigate degraded indoor air quality. We instrumented one residence for one week during an extreme wildfire event in the Pacific Northwest. Outdoor ambient concentrations of PM2.5 reached historic levels, sustained at over 200 μg/m3 for multiple days. Outdoor and indoor PM2.5 were monitored, and data regarding building characteristics, infiltration, and mechanical system operation were gathered to be consistent with the type of information commonly known for residential energy models. Two conditions were studied: a high-capture minimum efficiency rated value (MERV 13) filter integrated into a central forced air (CFA) system, and a CFA with MERV 13 filtration operating with a portable air cleaner (PAC). With intermittent CFA operation and no PAC, indoor corrected concentrations of PM2.5 reached 280 μg/m3, and indoor/outdoor (I/O) ratios reached a mean of 0.55. The measured I/O ratio was reduced to a mean of 0.22 when both intermittent CFA and the PAC were in operation. Data gathered from the test home were used in a modeling exercise to assess expected I/O ratios from both interventions. The mean modeled I/O ratio for the CFA with an MERV 13 filter was 0.48, and 0.28 when the PAC was added. The model overpredicted the MERV 13 performance and underpredicted the CFA with an MERV 13 filter plus a PAC, though both conditions were predicted within 0.15 standard deviation. The results illustrate the ways that models can be used to estimate indoor PM2.5 concentrations in residences during extreme wildfire smoke events

Investigating CO2 Removal by Ca- and Mg-based Sorbents with Application to Indoor Air Treatment

Indoor carbon dioxide (CO 2 ) levels serve as an indicator of ventilation sufficiency in relation to metabolic effluents. Recent evidence suggests that elevated CO 2 exposure (with or without other bioeffluents) may cause adverse cognitive effects. In shelter-in-place (SIP) facilities, indoor CO 2 levels may become particularly elevated. This study evaluates four low-cost alkaline earth metal oxides and hydroxides as CO 2 sorbents for potential use in indoor air cleaning applications. Sorbents studied were MgO, Mg(OH) 2 , Ca(OH) 2 and commercially available soda lime. Uncarbonated sorbents characterized with nitrogen adsorption porosimetry showed BET surface areas in the 5.6–27 m 2 /g range. Microstructural analyses, including X-ray diffraction, thermogravimetric analysis and scanning electron microscopy confirmed the carbonation mechanisms and extent of sorption under environmental conditions typical of indoor spaces. Ca-based sorbents demonstrated higher extent of carbonation than Mg-based sorbents. Laboratory parameterizations, including rate constants ( k ) and carbonation yields ( y ), were applied in material balance models to assess the CO 2 removal potential of Ca-based sorbents in three types of indoor environments. Soda lime ( k = [2.2–3.6] × 10 −3 m 3 mol CO 2 −1 h −1 , y = 0.49–0.51) showed potential for effective use in SIP facilities. For example, CO 2 exposure in a modeled SIP facility could be reduced by 80% for an 8-h sheltering interval and to levels below 5000 ppm for an 8-h period with a practically sized air cleaner. Predicted effectiveness was more modest for bedrooms and classroom

Eco-Efficient Coatings for Healthy Indoors: Ozone Deposition Velocities, Primary and Secondary Emissions

Volatile organic compounds (VOCs) and ozone (O3) are harmful pollutants present in indoor air. Indoor concentrations of VOCs are typically higher than outdoors, due to the presence of indoor sources like building materials and ozone-surface reactions. The study aims to identify and quantify the ozone reactivity and primary and secondary emissions of different indoor coatings. The coatings selected for the study were three gypsum-based plastering mortar, with and without the addition of a bio-waste from Acacia dealbata (raw bark, BA, and bark heated at 250°C, BA250), two clay plasters (one with sand and the other with seashells as additional aggregate), applied both as basecoat and topcoat (on drywall), and one un-coated drywall. All the products tested had ozone deposition velocities that would reduce the indoor ozone concentration meaningfully if implemented in a real indoors, contributing to the improvement of indoor air quality. The gypsum-based plaster shows the lowest ozone deposition velocity, but also the lowest primary and secondary emissions. The addition of bark, either BA or BA250, increased by 50% the ozone deposition velocity of the coating but also increased primary and secondary emissions by 80% (BA) and 200% (BA250), with methanol (m/z 33.030) accounting for about 60% of the increase. The addition of crushed seashells to the formulation of the clay-based plasters lowered the secondary emission yields (102% and 120% respectively, when applied as base and topcoat)

Experimental Evaluations of the Impact of an Additive Oxidizing Electronic Air Cleaner on Particles and Gases

Electronic air cleaning (EAC) technologies have garnered significant attention for use in buildings. Many EAC technologies rely on the addition of reactive constituents to indoor air to react with gas-phase compounds, enhance particle deposition, and/or inactivate microorganisms. However, limited data are available on the efficacy of many EAC technologies and their potential to form chemical byproducts during operation. Here we experimentally evaluate the indoor air quality impacts, specifically targeting particles and gases but not microbial constituents, of a commercially available additive oxidizing EAC that generates positive and negative ions and hydrogen peroxide (H2O2). Tests were conducted in a large unoccupied test chamber in Chicago, IL and an unoccupied laboratory in Portland, OR under a combination of natural conditions (i.e., without pollutant injection) and perturbation conditions (i.e., with pollutant injection and decay). A combination of integrated and time-resolved measurements was used across both test locations. Chamber tests at lower airflow rates demonstrated that operation of the EAC: (i) had no discernible impact on particle concentrations or particle loss rates, with estimated clean air delivery rates (CADRs) for various particle measures less than ±10 m3/h, (ii) was associated with apparent decreases in some volatile organic compounds (VOCs) and increases in other VOCs and aldehydes, especially acetaldehyde, although a combination of high propagated uncertainty, limitations in test methods (e.g., lack of replicates), and variability between repeated tests limit what quantitative conclusions can be drawn regarding gas-phase organics; (iii) did generate H2O2, assessed using a crude measure, and (iv) did not generate ozone (O3). Laboratory tests at higher airflow rates, which involved injection and decay of particles and a single VOC (limonene), both simultaneously and separately, demonstrated that: (i) pollutant loss rates for both particles and limonene were slightly lower with the EAC on compared to off, yielding slightly negative pollutant removal efficiencies (albeit largely within propagated uncertainty) and (ii) there was a change in observed concentrations of one potential limonene degradation product, m/z 59 (putatively identified as acetone), with steady-state levels increasing from 10 ppb (air cleaner off) to 15 ppb (air cleaner on). No increases or decreases beyond measurement uncertainty were observed for other analyzed gaseous limonene degradation products. Overall, both chamber and laboratory tests demonstrated negligible effectiveness of this device at the test conditions described herein for removing particles and mixed results for VOCs, including decreases in some VOCs, no discernible differences in other VOCs, and apparent increases in other compounds, especially lower molecular weight aldehydes including acetaldehyde

A Novel VOC Breath Tracer Method to Evaluate Indoor Respiratory Exposures in the Near- and far-fields; implications for the spread of respiratory viruses

Background Several studies suggest that far-field transmission (\u3e6 ft) explains a significant number of COVID-19 superspreading outbreaks. Objective Therefore, quantifying the ratio of near- and far-field exposure to emissions from a source is key to better understanding human-to-human airborne infectious disease transmission and associated risks. Methods In this study, we used an environmentally-controlled chamber to measure volatile organic compounds (VOCs) released from a healthy participant who consumed breath mints, which contained unique tracer compounds. Tracer measurements were made at 0.76 m (2.5 ft), 1.52 m (5 ft), 2.28 m (7.5 ft) from the participant, as well as in the exhaust plenum of the chamber. Results We observed that 0.76 m (2.5 ft) trials had ~36–44% higher concentrations than other distances during the first 20 minutes of experiments, highlighting the importance of the near-field exposure relative to the far-field before virus-laden respiratory aerosol plumes are continuously mixed into the far-field. However, for the conditions studied, the concentrations of human-sourced tracers after 20 minutes and approaching the end of the 60-minute trials at 0.76 m, 1.52 m, and 2.28 m were only ~18%, ~11%, and ~7.5% higher than volume-averaged concentrations, respectively. Significance This study suggests that for rooms with similar airflow parameters disease transmission risk is dominated by near-field exposures for shorter event durations (e.g., initial 20–25-minutes of event) whereas far-field exposures are critical throughout the entire event and are increasingly more important for longer event durations

Bioaerosol Deposition on an Air-Conditioning Cooling Coil

This study is concerned with the role of a fin-and-tube heat exchanger in modifying microbial indoor air quality. Specifically, depositional losses of ambient bioaerosols and particles onto dry (not cooled) and wet (cool) coil surfaces were measured for different airspeeds passing through the test coil. Total, bacterial and fungal DNA concentrations in condensate water produced by a wet coil were also quantified by means of fluorescent dsDNA-binding dye and qPCR assays. Results revealed that the deposition of bioaerosols and total particles is substantial on coil surfaces, especially when wet and cool. The average deposition fraction was 0.14 for total DNA, 0.18 for bacterial DNA and 0.22 for fungal DNA on the dry coil, increasing to 0.51 for total DNA, 0.50 for bacterial DNA and 0.68 for fungal DNA on the wet coil. Overall, as expected, deposition fractions increased with increasing particle size and increasing airspeed. Deposited DNA was removed from the cooling coil surfaces through the flow of condensing water at a rate comparable to the rate of direct deposition from air. A downward trend of bacterial and fungal DNA measured in condensate water over time provides suggestive evidence of biological growth on heat exchangers during nonoperational times of a ventilation system. This investigation provides new information about bioaerosol deposition onto a conventional fin-and-tube cooling coil, a potentially important factor influencing indoor exposure to microbial aerosols in air-conditioned buildings

Monitored Indoor Environmental Quality of a Mass Timber Office Building: A Case Study

A broad range of building performance monitoring, sampling, and evaluation was conducted periodically after construction and spanning more than a year, for an occupied office building constructed using mass timber elements such as cross-laminated timber (CLT) floor and roof panels, as well as glue-laminated timber (GLT) beams and columns. This case study contributes research on monitoring indoor environmental quality in buildings, describing one of the few studies of an occupied mass timber building, and analyzing data in three areas that impact occupant experience: indoor air quality, bacterial community composition, and floor vibration. As a whole, the building was found to perform well. Volatile organic compounds (VOCs), including formaldehyde, were analyzed using multiple methods. Formaldehyde was found to be present in the building, though levels were below most recommended exposure limits. The source of formaldehyde was not able to be identified in this study. The richness of the bacterial community was affected by the height of sampling with respect to the floor, and richness and composition was aected by the location within the building. Floor vibration was observed to be below recognized human comfort thresholds