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4 Particle Dynamics and Building Characteristics that Influence Indoor PM
Pages 83-108

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From page 83...
... , and what types of practical mitigation measures can be implemented effectively (e.g., can central air cleaning be used?
From page 84...
... , which affects the types of indoor PM mitigation measures that can be deployed and the effects they can have. Some differences in building characteristics that can affect the fate, transport, and transformation of indoor PM are also associated with differences in geographic and socioeconomic factors that may contribute to disparities in exposure to indoor PM and associated health effects.
From page 85...
... For example, a building with open windows will generally have diminished marginal benefit on reducing indoor particle concentrations from the use of air cleaning because of competition by the additional ventilation and high rates of delivery of outdoor fine PM. The extent of the impact of these factors depends on parameters such as the inside–outside temperature difference, the wind speed and direction, the number, extent, and location of open windows, and the concentration of ambient fine PM.
From page 86...
... Surface area, material properties (e.g., material, roughness) , and Deposition to surfaces orientation, particle deposition velocity, space and surface air flow characteristics In-duct: Flow rate through air cleaner/filter relative to space volume, installed removal/filtration efficiency, system runtime, mixing Air cleaning In-room: Flow rate through air cleaner relative to space volume, installed removal/filtration efficiency, air cleaner runtime, location relative to source Transformations Intra-zonal transport (mixing)
From page 87...
... For example, measurements of indoor and outdoor concentrations in buildings under relatively tightly controlled conditions, such as air cleaner on versus air cleaner off conditions, can yield insights into the effectiveness of an intervention while not necessarily yielding direct measurements of the magnitude of individual sinks or transformation processes. Also worth noting is that recent advancements in low-cost PM sensors that provide real-time displays of indoor PM concentrations to building occupants may also be useful in promoting behavioral interventions that affect indoor PM concentrations (Klepeis et al., 2013)
From page 88...
... over a certain time period, which may vary by the nature of ventilation air, the magnitude of air change rate, ambient particle size distributions, or other building characteristics. Once the infiltration factor is known and applied to calculate the fraction of indoor PM originating from outdoors, the remaining fraction of indoor PM can be estimated to be generated from indoor sources (Özkaynak et al., 1996; Wilson et al., 2000)
From page 89...
... , which in turn suggests that ambient PM2.5 infiltration factors may also range in magnitude depending on the same factors. A 2017 study used targeted measurements in an unoccupied apartment unit to estimate size-resolved penetration factors for particles approximately 0.01–2.5 μm in size with doors and windows closed, which were then used to estimate penetration factors for an integral measure of PM2.5 by scaling to concurrent outdoor size distributions, resulting in a mean estimated PM2.5 penetration factor of ~0.73 (Zhao and Stephens, 2017)
From page 90...
... . Similar test approaches in controlled chambers and smaller-scale field studies have also been useful in quantifying the effectiveness and demonstrating some of the potential consequences of air cleaning technologies that rely on the addition of reactive constituents to air, such as the formation of secondary organic aerosols and gas-phase oxidation byproducts from the operation of ozone-generating ionizing and other oxidizing air cleaners in the presence of unsaturated organic compounds (Joo et al., 2021; Waring et al., 2008; Ye et al., 2021; Zeng et al., 2022)
From page 91...
... For example, comparing loss rates between different in-duct filter or portable air cleaner configurations can make it possible to quantify the impact that higher efficiency filtration or stand-alone air cleaning has on loss rates in a space, which also allows for estimating the in-situ clean air delivery rate (CADR) of the filter or air cleaning system (Alavy and Siegel, 2020; MacIntosh et al., 2008; Stephens and Siegel, 2012, 2013)
From page 92...
... Measuring Indoor PM Transformations Indoor PM of both indoor and outdoor origin is subject to a number of transformation processes as particles interact with each other and the environment. Transformation processes can act as a source or a sink, or lead to changes in aerosol properties such as size distribution or toxicological profile, depending on a number of factors and conditions.
From page 93...
... . Such phase changes can lead to losses of PM mass as it transports from cooler outdoor air to warmer indoor air and, conversely, gains of PM mass as warmer outdoor air transports into cooler indoor environments (humidity, and thus total enthalpy, as well as PM composition, also interact to influence the magnitude and direction of partitioning, but the above simplification is useful for illustration)
From page 94...
... SOCIOECONOMIC DISPARITIES IN INDOOR PARTICLE DYNAMICS The extent to which socioeconomic disparities in individual source, sink, and transformation processes contribute to disparities in indoor PM exposure has not been explored in much depth in the literature, but there are several logical ways in which known socioeconomic differences in buildings and their occupants and their activities likely contribute to such disparities. First, the concentration and composition of outdoor PM varies geographically, and such differences have been shown to be associated with socioeconomic status, age, and race/ethnicity.
From page 95...
... . Similarly, one 2021 study observed that renters in multifamily housing units experienced a higher proportion of indoor PM2.5 concentrations from indoor sources than homeowners in either single-family or multi-family housing, suggesting that differences in indoor sources had less to do with housing type and more to do with socioeconomic factors (Chu et al., 2021)
From page 96...
... However, the lack of impact would be due to competition from ventilation or the introduction of non-monitored outdoor air pollutants. To overcome such limitations, the research community needs to adopt a more "building-aware" epidemiological approach whereby research characterizing the effects of a practical mitigation approach provides the context of the mechanisms that affect fate, transport, and transformations of indoor PM (e.g., if an air cleaner intervention is done in homes/locations with other competing mechanisms like high air change rates/windows wide open, was that characterized and how?
From page 97...
... In order to enable this contextualization, research should explore what minimal information on indoor PM dynamics is needed to meaningfully improve understanding of practical mitigation measures for indoor PM. To do so, there is a specific need for clear, practical, and relatively low-cost monitoring approaches to identify and quantify important parameters that potentially affect the effectiveness of practical mitigation strategies.
From page 98...
... 2005. Characterization of indoor sources of fine and ultrafine particles: a study conducted in a full-scale chamber.
From page 99...
... 2022. Phase state of organic aerosols may limit temperature-driven thermodynamic repartitioning following outdoor-to-indoor transport.
From page 100...
... 2004. Source strengths for indoor human activities that resuspend particulate matter.
From page 101...
... 2021. Formation of oxidized gases and secondary organic aerosol from a commercial oxidant-generating electronic air cleaner.
From page 102...
... 2020. High-efficiency air cleaning reduces indoor traffic-related air pollution and alters indoor air chemistry in a near-roadway school.
From page 103...
... 2018. Spatiotemporal distribution of indoor particulate matter concentration with a low-cost sensor network.
From page 104...
... Nazaroff, W.W., 2004. Indoor particle dynamics.
From page 105...
... 2018. Effect of model spatial resolution on estimates of fine particulate matter exposure and exposure disparities in the United States.
From page 106...
... 2015. Building design and operational choices that impact indoor exposures to outdoor particulate matter inside residences.
From page 107...
... 2014. Transient secondary organic aerosol formation from limonene ozonolysis in indoor environments: Impacts of air exchange rates and initial concentration ratios.
From page 108...
... 2017. Using portable particle sizing instrumentation to rapidly measure the penetration of fine and ultrafine particles in unoccupied residences.


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