Why Indoor Chemistry Matters (2022) / Chapter Skim
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5 Management of Chemicals in Indoor Environments
5 Management of Chemicals in Indoor Environments
Pages 97-120
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From page 97... ...
The chapter provides an overview of the hierarchy of controls as a framework for considering risk-reduction strategies. With this framework in mind, the committee first considers management approaches that result in minimal changes in indoor chemistry, followed by management approaches that rely on chemical transformations.
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From page 98... ...
NOTE: HEPA = high-efficiency particulate air; HVAC = heating, ventilation, and air conditioning; PPE = personal protective equipment; VOC = volatile organic compound. FIGURE 5-1 Hierarchy of controls.
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From page 99... ...
. Engineering controls, such as mechanical ventilation or general exhaust systems that bring in outdoor air, filtration of gas-phase and particulate contaminants, and other types of air clean ers, further reduce the risk when elimination or substitution of a chemical hazard is not practical or incompletely mitigates the risk.
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From page 100... ...
This may have an effect on indoor chemistry because ozone-containing outdoor air mixes with and can react with recirculated indoor air in the HVAC system before the mixture is supplied to occupied spaces. NAS-A00426-Indoor_Chemistry.indd 100 01/10/2022 7:25 AM
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From page 101... ...
Our understanding of the influence of these ventilation approaches on exposure that results from indoor chemistry is still developing. Ventilation rates are set by building codes that rely on consensus standards, such as ASHRAE Standard 62.1, to achieve "acceptable" indoor air quality.
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From page 102... ...
, an international nonprofit technical society that develops standards and educational programs and materials, and supports its own research program. ASHRAE ventilation standards, either by reference or by excerpt, are the basis for ventilation rates, air filtration efficiency, and air cleaner requirements in U.S.
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From page 103... ...
From the critical rebreathed air fraction, the necessary ventilation rate can be determined, as well as the resulting indoor carbon dioxide concentration that can be used in ventilation system control. Outdoor air is a source of contaminants to the indoor environment, creating caveats for ventila tion.
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From page 104... ...
. A widely used standard for high performance filters is published by the Institute of Environmental Sciences and Technology (IEST Contamination Control Division, 2016)
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From page 105... ...
Activated carbon can be used to remove ozone and is recommended by ASHRAE Standard 62.1 in circumstances where outdoor ozone levels exceed specified thresholds (Aldred et al., 2016a,b)
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From page 106... ...
Removal of pollutants at indoor surfaces is an attractive option because of passive transport of pollutants to the large available surface area. The effective clean air delivery rate for small molecules in an indoor environment is typically ~2.5 m3/h per square meter of engineered surface based on reported deposition velocities of ozone to passive removal materials (Darling et al., 2016)
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From page 107... ...
Saturation, re-emission, and reactive chemistry all play roles that require consid eration before passive surfaces are implemented to remove indoor air pollutants. MANAGEMENT THROUGH CHEMICAL TRANSFORMATIONS Chemically modifying air pollutants to transform them into benign species or increase their removal rates is an increasingly used approach to improve indoor air quality.
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From page 108... ...
, which can undergo a series of reactions resulting in complex products, including peroxides, carbonyls, and carboxylic acids. Hydroxyl radical oxidation is not yet widely used in indoor environments to intentionally degrade VOCs but raises many of the same concerns as ozone, including the potential for production of secondary organic aerosol and other unintended byproducts due to its rapid oxidation chemistry (Friedman and Farmer, 2018; Lee et al., 2006)
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From page 109... ...
The physical and chemical mechanisms responsible for byproduct formation -- and the health effects of those byproducts in real-world indoor environments -- warrants further study. Ultraviolet Light Photolysis, the decomposition of molecules due to interaction with light, can also be used to control chemical air contaminants and inactivate or kill microorganisms.
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From page 110... ...
. UV-C air disinfection using 254 nm sources is applied in a number of ways in indoor environments (Kowalski, 2010)
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From page 111... ...
. While PCO efficiency and byproduct formation have been investigated extensively in controlled laboratory environments, more studies of effectiveness, longevity, and byproducts in real-world indoor environments are needed to understand the potential for subsequent chemical transforma tions.
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From page 112... ...
Given the possible presence of a much larger number of compounds in indoor environments, however, there is a clear need for advances in both analytical instrumentation and our understanding of indoor chemistry to move such efforts forward. Applied research on energy-optimal use of combinations of control technologies is also needed.
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From page 113... ...
With the exception of ventilation, particle filtration, and sorption, few air-cleaning approaches are tested in real-world environments, which contain a far more complicated mixture of compounds than most laboratory studies. As outlined in previous chapters, chemical reactions in indoor environments can follow complex mechanisms and result in numerous different products.
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From page 114... ...
2013. HVAC filtration for controlling infectious airborne disease transmission in indoor environments: Predicting risk reductions and operational costs.
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From page 115... ...
2019. Impact of outdoor air quality on the natural ventilation usage of commercial buildings in the US.
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From page 116... ...
1997. The effects of human behavior on natural ventilation rate and indoor air environ ment in summer -- A field study in southern Japan.
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From page 117... ...
2019. Prediction of VOC adsorption performance for estimation of service life of activated carbon based filter media for indoor air purification.
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From page 118... ...
2017. Efficiency of ionizers in removing airborne particles in indoor environments.
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From page 119... ...
Environmental Science & Technology Letters 2(11)
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From page 120... ...
2021. Real-time laboratory measurements of VOC emis sions, removal rates, and byproduct formation from consumer-grade oxidation-based air cleaners.
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