Why Indoor Chemistry Matters (2022) / Chapter Skim
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3 Partitioning of Chemicals in Indoor Environments
3 Partitioning of Chemicals in Indoor Environments
Pages 55-74
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From page 55... ...
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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From page 56... ...
INDOOR ENVIRONMENTAL RESERVOIRS AND SURFACES The indoor environment is often characterized by its different reservoirs. For the purposes of this report, reservoirs are defined as any surface or volume present in indoor environments to which chemicals can partition.
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From page 57... ...
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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From page 58... ...
Partition coefficients are specific to the contaminant and the material it partitions to, but they can be influenced by environmental conditions, such as relative humidity (as discussed later in this chapter)
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From page 59... ...
This excludes the area associated with internal porosity and therefore represents a lower-bound value for all accessible surface area. Note that organic and aqueous films can exist on all indoor surfaces, not only on paint as shown in the figure.
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From page 60... ...
As the amount of sorbed water on indoor surfaces increases with increasing relative humidity, the sorbed chemicals are displaced from the surface into the gas phase. The extent of this displacement depends on the relative energies of the specific molecular interactions that occur for water com pared to the sorbed chemical (Frank et al., 2020; Huang et al., 2021)
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From page 61... ...
CURRENT SCIENCE ON PARTITIONING OF CHEMICALS IN INDOOR ENVIRONMENTS Impermeable Surfaces Impermeable indoor surfaces, to which chemicals can adsorb but not penetrate, include win dows and mirrors, glazed tiles, ceramic-top stoves, polished stone counters, stainless steel, copper pipes, and enameled appliances. High-density plastics may sometimes be considered effectively impermeable to large organic chemicals.
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From page 62... ...
. Clear evidence has been found for the heterogeneity of glass surfaces in indoor environments using new microspectroscopic methods to analyze surface films and deposited particles on glass surfaces.
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From page 63... ...
For example, increasing ventilation by opening a window is usually expected to improve air quality by diluting chemicals that have indoor sources; however, in response to the disruption of equilibrium, near-instantaneous increased emissions of SVOCs stored in surface reservoirs will recharge the air phase, limiting the ability of a temporary increase in ventilation to decrease levels. Consistently high ventilation can eventually deplete these reservoirs, but the time required to lower indoor air concentrations can range from days to years.
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From page 64... ...
Glass slides in other indoor environments, including a garage, a copier room, and an office, also showed particle deposition. The greatest number of particles were less than 500 nm in diameter, with the copier room having the greatest number of particles deposited on the glass surface after 6 months.
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From page 65... ...
This highlights the importance of probing the physicochemical properties and interactions between particles and common indoor surfaces that influence deposition in more detail. Dust Deposited particles eventually accumulate, collectively forming dust.
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From page 66... ...
Experiments conducted at HOMEChem demonstrated that moderately strong acids (e.g., formic acid and HONO) present in indoor surfaces could be re-partitioned to the gas phase via acidification of the aqueous surface reservoirs, via application of acetic acid in a vinegar cleaner (Wang et al., 2020b)
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From page 67... ...
(2017, 2018) observed dermal uptake of nicotine from air for the first time and concluded that partitioning to the primarily organic component of skin lipids was more important than aqueous partitioning to skin surface reservoirs.
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From page 68... ...
Models to predict thermodynamic parameters exist, but their applica tion to real indoor materials has not been widely demonstrated. Furthermore, models have not yet successfully been applied to many chemical classes important in indoor environments, such as surfactants.
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From page 69... ...
Given that most chemicals are predominantly partitioned to indoor surfaces, it is important for exposure modeling to consider carefully the distribution of chemi cals among these surface reservoirs, the gas phase, and aerosol particles. Compositional changes occurring due to partitioning to airborne particles remains an important research topic.
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From page 70... ...
2018. A high throughput method for measuring cloth-air equilibrium distribution ratios for SVOCs present in indoor environments.
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2019a. Modeling the formation and growth of organic films on indoor surfaces.
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2014. The impact of mass transfer limitations on size distributions of particle associated SVOCs in outdoor and indoor environments.
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From page 73... ...
2019. Predicting the gas/particle distribution of SVOCs in the indoor environment using poly parameter linear free energy relationships.
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From page 74... ...
2008. Semivolatile organic compounds in indoor environments.
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