Why Indoor Chemistry Matters (2022) / Chapter Skim
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Next, it summarizes the main classes of compounds emitted from primary sources and reservoirs, their typical concentration ranges if they have been reported in indoor air or dust, and key physicochemical properties that dictate their behavior and lifetime indoors within and across these matrices. The chapter continues by introducing various 19 NAS-A00426-Indoor_Chemistry.indd 19 01/10/2022 7:25 AM
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approaches to chemical inventories, which are important because they enable more accurate chemical exposure estimates, followed by a discussion of the wide range of analytical approaches that can be used to measure the chemical contents of an indoor space. Finally, the chapter con cludes by highlighting emerging chemicals of concern indoors, current sampling and measure ment capabilities and limitations, and areas of research gaps and future directions.
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Emission rates can be highly variable and are driven or influenced by multiple factors, including human activities, building characteristics, physical parameters, environmental conditions, and spa tial and/or temporal factors. We define continuous sources as those constantly emitting chemicals into indoor environments at rates that may vary due to environmental conditions (e.g., temperature, humidity, and ventila tion)
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Emphasis is placed on newer sources or source categories of relevance to indoor chemical concentrations and human exposures and on emerging science within each category. Continuous Sources and Reservoirs Building materials are continuous sources of gas-phase emissions in indoor environments.
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combustion, concrete Nazaroff and Weschler, 2020 containing urea, cleaning agents, cooking Nitric Acid 111–541e Outdoor air, 10−2–101 Nazaroff and Weschler, 2020 Nitrous Acid combustion (HNO3, HONO) Other Inorganics Nitrogen Dioxide −152–21 Outdoor air, 100–101 Mullen et al., 2016; Nazaroff Nitric Oxide combustion, gas and Weschler, 2020; Zhou (NO2, NO)
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products, natural gas 2003; Hodgson et al., 2000 Carboxylic Acids 4.9* 10−2– 122–269 2.62–7.71e Outdoor air, breath, 10−2–102 Duncan et al., 2019; Nazaroff (CH2O2–CH3(CH2)
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Chemical class properties generally represent the straight chain structures of the class, with ranges shown to represent what has been historically measured in indoor environments. b Most chemical class properties are taken from EPA's CompTox Chemicals Dashboard with noted values (a)
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<10 μm (PM10) abrasion, paint chipping, Vardoulakis et al., 2020; Zwoz´ dziak skin flakes et al., 2013 ELEMENTAL COMPOSITION OF PM2.5 GROUPED BY TYPICAL SOURCE Concentration Range Chemical Component Example Primary Sources in Indoor Air References for Concentration Ranges Organic Carbon (OC)
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can be elevated in indoor air in kindergartens and certain retail or commercial spaces like carpeting stores, suggesting that inhalation may be a more important exposure route than previously thought for PFAS and their breakdown products (Morales-McDevitt et al., 2021)
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. The need to quantify the diversity of microbial species that influence indoor air across a variety of indoor environments and materials remains (Bekö et al., 2020; Prussin and Marr, 2015)
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. In 2021, California issued new draft vapor screening guidance in an effort to provide more consistency in evaluating exposure and health risks despite the challenges of significant spatial and temporal vari ability in subsurface and indoor air concentrations.
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and its decay products, like lead and polonium, are widely recognized as an indoor air concern and a risk factor for lung cancer (Darby et al., 2005; Krewski et al., 2006)
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HVAC operation may appear like a periodic source impacting indoor air chemical composition. Dust coated heating coils can act as a reservoir of SVOCs, taking up and releasing them as a function of temperature or moisture.
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. As shown by the information presented in Table 2-1, concentrations of some chemicals are abundant in indoor air, while others are abundant on surfaces and in indoor dust and airborne particles (refer to Table 2-2 for aerosol phase)
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, or particles with an aerodynamic diameter ≤2.5 μm, are usually emitted from primary sources like combustion and secondary formation indoors and reported in mass concentrations (μg/m3)
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. Thousands of chemicals are present in indoor environments that potentially can be released into indoor air.
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. Today, significant research has focused on the toxicity and health effects of EHTBB and BEHTBP, while they and other flame retardants continue to be commonly detected in indoor air, dust, and other environmental samples.
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However, recent analytical and instrumental advances have led to greater sensitivity for detecting chemicals at lower concentrations (i.e., lower detection limits) , and the increasing use of non-targeted analyses is revealing the presence of chemicals in indoor air, particulates, and dust that were unknown until recently.
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analytical techniques. Recent advances in analytical techniques and application of outdoor measurement technologies and methods to indoor air quality have decreased detection limits of known indoor compounds, increased the number of different chemicals detected in the indoor environment, and increased the time resolution of samples.
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Facilitating the greater application of these instruments to a wide range of indoor spaces and environmental conditions could make top-down approaches to the inventory of indoor gas-phase constituents more robust and give a greater understanding of the dynamic nature of indoor sources. Particulate Matter Sampling Traditional Techniques Indoor airborne PM has been commonly analyzed using techniques that quantify total mass, particle count, surface area, size distribution, and chemical composition.
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and change after cook ing (Katz et al., 2021a) , as well as the impact of particles on third-hand smoke transport in indoor air (DeCarlo et al., 2018)
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. These methods provide more insight into the complex and diverse suite of chemicals that are present in indoor environments, yet they are not currently at a point where every chemical in the thousands in a mass spectrum of an indoor air or dust sample can be identified -- let alone quantified.
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Surface Sampling Traditional Techniques Surfaces in indoor environments, including windows, countertops, and walls, accumulate organic films and act as sinks, reaction sites, and reservoirs for SVOCs (Weschler and Nazaroff, 2008)
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New research also suggests that clothing mediates our exposure to chemicals in the indoor environment, acting as a sink for chemicals present in indoor air (Licina et al., 2019)
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The vast majority of the information presented in this chapter refers to research conducted in residential settings and in high-income countries. However, people spend time in other indoor environments, which may have different sources and emission rates.
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2020. The past, present, and future of indoor air chemistry.
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2017. Significant OH production under surface cleaning and air cleaning conditions: Impact on indoor air quality.
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2011. Chlorinated paraffins in indoor air and dust: concentrations, congener patterns, and human exposure.
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2003. Volatile organic compounds in indoor air: A review of concentrations measured in North America since 1990.
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Indoor Air 27:79–802. https://doi.org/10.1111/ina.12365.
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in the indoor environment: occurrence in consumer products, indoor air and dust. Chemosphere 201:466–482.
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2017. Investigation of the Best Approach for Assess ing Human Exposure to Poly- and Perfluoroalkyl Substances through Indoor Air.
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2014. Application of proton-transfer-reaction mass-spectrometry for Indoor Air Quality research.
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Indoor Air 26:6–24. Weschler, C
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Indoor Air 25(1)
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While chemical transformations can subsequently occur, as discussed in Chapter 4, this chapter will focus on the role of partitioning of chemicals in indoor environments as it relates to indoor chemistry and indoor air quality. Chemicals can have a greater affinity for one reservoir than another, and this is characterized by a "partition coefficient" defined later in this chapter.
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Other useful reservoirs include paint films; the surfaces of glass, wood, dust, and indoor air; and even the volume of air surrounding a building. Important points to consider in the partitioning of chemicals are the fact that the physicochemical properties of these different materials are quite varied and the surfaces (see Box 3-1)
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In this region, thin films of organics can become surfaces themselves. Thus, there are complexities in understanding these surfaces, from clean to dirty, that are part of indoor environments.
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