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3 Sources and Composition of Indoor Particulate Matter
Pages 23-82

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From page 23...
... Outdoor sources of indoor PM2.5 are then discussed, followed by the individual indoor sources of PM2.5, which are grouped based on the mechanisms that generate or produce these particles. Five main generation mechanisms are covered: combustion processes, other non-combustion heating processes, mechanical particle resuspension, residual particles from liquid aerosol evaporation, and secondary particles formed through chemical reactions.
From page 24...
... INDOOR PM2.5 CONCENTRATIONS AND COMPOSITION Indoor PM2.5 of Outdoor Origin Ambient fine particulate matter (PM2.5) has been widely reported as an important cause of mortality, both worldwide and in the United States (Cohen et al., 2017; Di et al., 2017; Fann et al., 2012)
From page 25...
... The amount that outdoor pollution contributes to indoor air depends on a number of factors, including the proximity of a building to point and mobile sources, factors associated with boundary layer meteorology, urban and regional air pollution, and a number of building-related factors such as ventilation and infiltration rates, as well as location of air intakes (for nearby sources)
From page 26...
... Many of the studies presented in the sections below report indoor particle concentrations resulting from these sources, while others measure particle emissions rates (sometimes in terms of particle mass, sometimes particle number)
From page 27...
... 2 The following particle size cutoff definitions are used in this report: Ultrafine: <100 nm, Fine: <2.5 µm, Supermicron: particles >1 µm. 3 Although tobacco smoke products are not covered in this report, they are well-known indoor combustion sources.
From page 28...
... In each case, particle emissions to the indoor environment are dominated by ultrafine particles. Most combustion appliances are required by code to utilize exhaust vents to direct products of incomplete combustion to the outdoors.
From page 29...
... Where used, pilot lights are a continuous source of ultrafine particle emissions to indoor air. Patel et al.
From page 30...
... While the literature on natural gas combustion and its effects on indoor air quality is dominated by cooking appliances, several other sources exist, including unvented natural gas space heaters, unvented natural gas fireplaces, gas water heaters, and clothes dryers. Weichenthal et al.
From page 31...
... . There are two pathways for indoor exposure to fine particulate matter emitted by the residential combustion of wood.
From page 32...
... . Wood stoves are also major contributors to fine particulate matter in both outdoor and indoor air.
From page 33...
... This process was observed to release both fine and coarse particulate matter, with relatively high amounts of copper and manganese emitted to indoor air during ash removal from a pellet stove. A number of factors are associated with lower fine and ultrafine particle emissions from wood stoves.
From page 34...
... . These modes greatly influence the nature of emissions from candles, particularly particle size and composition (Pagels et al., 2009)
From page 35...
... Emission rates for ultrafine particles have been reported by several research teams. Salthammer et al.
From page 36...
... Aromatic materials include wood and bark, herbs, seeds, spices, essential oils, and synthetic substitute chemicals (Jetter et al., 2002)
From page 37...
... Emissions for incense sticks ranged from 7 to 108 mg/hr. The authors concluded that "incense emits fine particulate matter in large quantities compared to other indoor sources" and completed model simulations for a small room with predicted concentrations of PM2.5 that exceeded several thousand μg/m3.
From page 38...
... . Indoor PM from Other Heating Processes Other indoor heating processes beyond combustion can also contribute significant amounts of PM to indoor environments.
From page 39...
... . Even the mass concentration of ultrafine particles (PM <100 nm in diameter)
From page 40...
... Cookware and Other Appliances The process of heating cooking utensils and instruments themselves, even without food, has been found to lead to the formation of particles attributed to desorption of semi-volatile organic compounds (SVOCs) present on their surface, which then recondense in the indoor air and form ultrafine particles.
From page 41...
... (2009) demonstrated that the particles are formed during printing when the fuser unit heats the paper and the toner, volatilizing compounds that then recondense in the indoor air.
From page 42...
... A variety of scenting products employ heat to vaporize a mixture of fragrances or essential oils into the indoor air. These consumer products are commonly used to mask odors and to promote psychological well-being (e.g., aromatherapy)
From page 43...
... . In addition, e-cigarette aerosols can leave residue on indoor surfaces and particles, which can accumulate over time and potentially affect indoor air quality, commonly referred to as thirdhand exposure (Acuff et al., 2016; Goniewicz and Lee, 2015)
From page 44...
... Indoor Particle Resuspension and Shedding The movement of people or equipment indoors can detach and lift particulate matter previously deposited on surfaces. This phenomenon is called particle resuspension, and it can increase indoor particle concentrations significantly (Thatcher and Layton, 1995)
From page 45...
... (2021) performed a review of biological contaminants in the indoor air environment and stated that there is a "lack of awareness about biological contamination in the
From page 46...
... The same study determined that the resuspension rates for cat dander and dust mite allergen were higher than those for dog dander and bacterial endotoxins. Residual PM from Liquid Droplet Evaporation There are several indoor processes, such as cooking, showering, spray cleaning and personal care products, and using humidifiers or nebulizers, that, by accident or by design, emit liquid droplets into the indoor air.
From page 47...
... Age may also play a role in respiratory particle emission rates, with emissions increasing with age (Archer, 2022; Bagheri, 2023)
From page 48...
... investigated aerosol emissions by three indoor air freshener sprays from pressurized canisters in a ventilated test chamber and found that >90 percent of particles emitted were <0.3 μm in size. A number of studies have investigated particle emissions from the use of consumer spray products that contain engineered nanoparticles as part of their formulation, with silver particles and ions as well as titanium dioxide particles as common ingredients.
From page 49...
... (2020) subsequently showed that using tap water that meets water quality standards in ultrasonic humidifiers can result in substandard indoor air quality.
From page 50...
... , are present in indoor air, they can react with these VOCs and form particles called secondary organic aerosols (SOAs)
From page 51...
... Indoor particles can also be formed as an unintended consequence of using some devices that are nominally intended to clean the air. Indoor air cleaning devices encompass a broad category of products used to reduce the concentration of particles, VOCs, odors, pathogens, etc., in indoor air.
From page 52...
... Moreover, variability in the types of indoor sources present in buildings is broadly expected to contribute to variability in indoor PM2.5 concentrations and compositions across spatial, temporal, socioeconomic, and even cultural dimensions, even if robust characterizations of the presence, types, and frequency of indoor emission sources for specific populations do not yet exist. For example, it is understood that there are obvious differences across regions, buildings, and populations in factors such as the predominant heating and cooking fuel types that can affect combustion emissions, the presence and use of appliances and activities that contribute to emissions from combustion and heating processes (e.g., cooking, burning incense or candles)
From page 53...
... A more detailed discussion on PM2.5 exposure is presented in Chapter 5 of this report. FINDINGS AND CONCLUSIONS This chapter describes in detail numerous indoor sources of fine and ultrafine particulate matter and their indoor concentrations and compositions.
From page 54...
... Discoveries related to the production of infectious aerosols during the COVID-19 pandemic indicate that aerosol particles are emitted from humans doing natural activities such as speaking and singing. These discoveries have shifted thinking on appropriate types of personal respiratory protection as well as highlighted the importance of indoor air quality in all settings.
From page 55...
... There is an opportunity to educate the general public on indoor sources of fine particulate matter, including UFP, to enable more informed decision making when choosing indoor products and activities to minimize exposure. Ambient air pollution as a source of indoor particles.
From page 56...
... Indoor Air, 15(2)
From page 57...
... 2021. Emissions of soot, PAHs, ultrafine particles, NOx, and other health relevant compounds from stressed burning of candles in indoor air.
From page 58...
... Indoor Air, 26(2)
From page 59...
... 2015. Characterization of indoor aerosol temporal variations for the real-time management of indoor air quality.
From page 60...
... 2016. Discontinuous and continuous indoor air quality monitoring in homes with fireplaces or wood stoves as heating system.
From page 61...
... 2023. Environmental risks from consumer products: Acceptable drinking water quality can produce unacceptable Indoor Air quality with ultrasonic humidifier use.
From page 62...
... 2018. Influence of advanced wood-fired appliances for residential heating on indoor air quality.
From page 63...
... 2023. Unwanted indoor air Quality effects from using ultraviolet C lamps for disinfection.
From page 64...
... Indoor Air, 32(9)
From page 65...
... Indoor Air, 30(2)
From page 66...
... Indoor Air, 25(4)
From page 67...
... 2021. Particulate matter emitted from ultrasonic humidifiers -- Chemical composition and implication to indoor air.
From page 68...
... 2020. Effects of electronic cigarettes on indoor air quality and health.
From page 69...
... Indoor Air, 27(1)
From page 70...
... 2020. Multiphase chemistry controls inorganic chlorinated and nitrogenated compounds in Indoor Air during bleach cleaning.
From page 71...
... 2016. Results of the California Healthy Homes Indoor Air Quality Study of 2011–2013: Impact of natural gas appliances on air pollutant concentrations.
From page 72...
... Indoor Air, 32(8)
From page 73...
... 2014. Walking-induced particle resuspension in indoor environments.
From page 74...
... 2010. Effect of gas and kerosene space heaters on indoor air quality: A study in homes of Santiago, Chile.
From page 75...
... Indoor Air, 23(1)
From page 76...
... 2015. Evaluation of nanoparticles emitted from printers in a lean chamber, a copy center and office rooms: Health risks of indoor air quality.
From page 77...
... 2012. Fine and ultrafine particles emitted from laser printers as indoor air contaminants in German offices.
From page 78...
... Indoor Air, 22(6)
From page 79...
... Indoor Air, 32(9)
From page 80...
... 2015. Volatile organic compound conversion by ozone, hydroxyl radicals, and nitrate radicals in residential indoor air: Magnitudes and impacts of oxidant sources.
From page 81...
... 2020. Human exposure to particles at the air-water interface: Influence of water quality on indoor air quality from use of ultrasonic humidifiers.
From page 82...
... Indoor Air, 22(1)


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