Why Indoor Chemistry Matters (2022) / Chapter Skim
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4 Chemical Transformations
4 Chemical Transformations
Pages 75-96
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From page 75... ...
These chemical processes are complex and extensive, with numerous species involved as precursors, intermediates, or products. As outlined in Chapter 3, indoor chemical compounds partition into a variety of compartments that may contain a variety of phases; hence, chemical transformations occur at different locations indoors, including the gas phase, airborne particles, and indoor surfaces, as well as hidden places such as ducts and the heating, ventilation, and air-conditioning (HVAC)
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. The spatial, tem poral, and spectral variability need to be taken into account when considering the role of photochem istry in indoor environments (Kowal et al., 2017; Weschler and Carslaw, 2018; Zhou et al., 2020)
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From page 77... ...
, indoor air constituents often have been treated as well mixed and homogeneously distributed in ventilated indoor environ ments. Hence, indoor measurements are mostly conducted at a single location in a room and at a fixed height, and indoor chemistry models often employ a box model assuming homogeneous mix ing.
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. This section explores common oxidation reactions occurring on indoor surfaces.
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Environmental Science & Technology 50(21)
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The formation of organic surface films described in Chapter 3 may occur not only through gas-to-surface partitioning of semivolatile molecules but also through contributions of such high molecular weight oxidation products and deposition of particles. An additional class of ozonolysis reactions long explored to understand outdoor chemistry is the reaction of polycyclic aromatic hydrocarbons (PAHs)
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Indoor surfaces are sufficiently acidic to form HOCl when bleach washing occurs (Mattila et al., 2020b; Wong et al., 2017)
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. A major challenge in understanding aqueous-phase reac tions in indoor environments is that, besides macroscopic thick films of water and bulk water reser voirs, thin water films and water adsorbed in small pores may be present; the concept of "pH" breaks down in these confined-space environments, as pH, defined as −log[H+]
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However, there have been studies of some reactions involving water that are relevant to indoor environments. A few cases are discussed in more detail below.
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, play an important role in photochemical reactions in outdoor chemistry (Chen et al., 2012) as well as indoor environments (Gligorovski, 2016)
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ROS can also readily react with organic compounds to yield more oxygenated, less volatile organic compounds that will have a higher affinity for indoor surfaces. MODELING INDOOR CHEMISTRY Indoor chemistry models are essential for quantifying chemical transformations and partition ing by treating a variety of highly complex chemical and physical processes.
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From page 86... ...
. Molecular dynamics simula tions were applied to simulate ozone interactions with squalene, determining key kinetic parameters that can be used directly in a kinetic process model to resolve mass transport and chemical reactions in the gas phase, in clothing, and on skin (Lakey et al., 2019)
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From page 87... ...
have been shown to affect the mechanisms and kinetics. Without a better understanding of the identities and amounts of many indoor chemicals, especially in surface reservoirs, an accurate toxicological and epidemiological evaluation of chemical dose and health outcomes is not yet possible in indoor environments.
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It is possible that important, yet slow, photochemistry occurs elsewhere on indoor surfaces that are not exposed to direct sunlight, but this has yet to be confirmed. Water is an important molecule indoors for facilitating chemical transformations.
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Models are also limited due to uncertainties regarding the parameterization of surface interactions, the propagation of light through indoor environments, and the concentrations and identity of a suite of secondary pollutants formed through indoor chemical reactions. REFERENCES Abbass, O
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residences: Impacts of relative humidity, aerosol mass and composition, and mechanical system operation. Environmental Science: Processes & Impacts 22(10)
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2019. The impact of clothing on ozone and squalene ozonolysis products in indoor environments.
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Environmental Science & Technology Letters 7(11)
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: Integrat ing chemical processes from molecular to room scales. Environmental Science: Processes & Impacts 21(8)
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2008. Partitioning of phthalates among the gas phase, airborne par ticles and settled dust in indoor environments.
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Environmental Science & Technology Letters 3(4)
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NAS-A00426-Indoor_Chemistry.indd 96 01/10/2022 7:25 AM
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