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Suggested Citation:"2 Background." National Academies of Sciences, Engineering, and Medicine. 2024. Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions. Washington, DC: The National Academies Press. doi: 10.17226/27341.
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2
Background

This chapter provides a background for the committee’s evaluation of the health effects of indoor exposure to fine particulate matter (PM2.5) and practical mitigation solutions by briefly summarizing information on two issues of relevance to the analysis: the U.S. Environmental Protection Agency’s interests and responsibilities regarding the indoor environment, and earlier reports produced by the National Academies of Sciences, Engineering and Medicine (National Academies; NASEM) related to the indoor environment and health.

THE US EPA’S ROLE IN INDOOR ENVIRONMENTAL QUALITY

The U.S. Environmental Protection Agency (EPA) manages activities related to indoor environmental quality in its Indoor Environments Division (IED), an organization that resides within EPA’s Office of Air and Radiation. IED’s website states that its main objective is “to improve indoor air quality in buildings where people live, learn and work.”7 Toward this end, it implements non-regulatory programs to reduce public health risks from poor indoor air quality with the goal of reducing or preventing human exposure to harmful indoor contaminants including particulate matter (PM), indoor asthma triggers, mold, environmental tobacco smoke, volatile organic compounds, and radon. IED’s program activities include technical guidance and assistance; public information and education; partnerships with industry, nongovernmental organizations, other federal organizations, states, tribes, and communities; and the promotion and synthesis of research.

IED’s indoor air activities involve translating the consensus science on indoor environmental quality, including risk assessment and risk reduction, into non-regulatory policy and program guidance; promoting the use and adoption of that guidance through outreach and technical assistance; and collaborating with governmental and private entities to implement that guidance. It also maintains a robust research and research support portfolio.

The division’s efforts on indoor exposure to particulate matter include:

  • enhancing awareness of indoor PM mitigation technology and health effects research;
  • updating and disseminating web content on wildfire smoke and indoor air quality, air cleaners, filtration, and dust control; and
  • increasing outreach and technical assistance to promote actions that reduce exposure to PM indoors.

Links to this work are found on the division’s website (EPA, 2023). IED staff developed a comprehensive literature review on indoor PM levels that informed and provided references for the committee (Ilacqua et al., 2022).

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7https://www.epa.gov/indoor-air-quality-iaq/introduction-indoor-air-quality.

Suggested Citation:"2 Background." National Academies of Sciences, Engineering, and Medicine. 2024. Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions. Washington, DC: The National Academies Press. doi: 10.17226/27341.
×

NATIONAL ACADEMIES REPORTS ADDRESSING RELATED TOPICS

Several National Academies reports have addressed topics relevant to the evaluation of the health effects of indoor exposure to airborne agents and the mitigation of adverse effects from such exposures. Salient publications are summarized below.8

Indoor Pollutants (NRC, 1981) provided a comprehensive assessment of the then-available scientific literature regarding various pollutants found indoors. It addressed sources and characterization, health effects, and control of a wide range of adverse indoor exposures, including volatile organic compounds, radon, formaldehyde, asbestos and other fibers, tobacco smoke, excessive moisture, and biological agents like mold and bacteria. The report emphasized the importance of proper ventilation and control measures to mitigate exposure and offered recommendations for improving building design and ventilation systems to enhance indoor air quality. It highlighted significant research gaps and recommended a collaborative effort among federal agencies to assess exposures and their effect on health.

Policies & Procedures for Control of Indoor Air Quality (NRC, 1987) identified best practices for operational procedures to minimize air quality issues in nonindustrial office buildings. The report highlighted that poor indoor air quality can both cause illness in building occupants and reduce their productivity. It indicated that indoor PM concentration is among the important metrics that need to be characterized to evaluate the performance of building systems. The report concluded that there is a mismatch between the complexity of those systems and the knowledge base of the people responsible for operating, maintaining, and managing them, and it recommended that training and education be developed and those responsible for the systems be encouraged to take advantage of this training in order to promote the systems’ proper oversight.

Indoor Allergens: Assessing and Controlling Adverse Health Effects (IOM and NRC, 1993) explored the relationship between the indoor environment and human health, focusing on the population sensitive to indoor allergens and suffering with chronic or intermittent allergic disease. The report emphasized the need to develop standardized test procedures for rating the effectiveness of air cleaning devices and other methods for removal of known size classes of particles containing allergens. It suggested that further research was needed to evaluate the role of cleaning in controlling for allergic diseases caused by the dissemination of particulate matter, noting that while housekeeping is the most common means of removing allergens, the physical cleaning process itself may risk dispersing fine particles into indoor air, and a high-efficiency particulate air (HEPA) filter may be needed to offset this allergen exposure.

Clearing the Air: Asthma and Indoor Air Exposures (IOM, 2000) assessed the literature regarding the relationship between indoor air quality and asthma. The report noted that studies consistently report an association between exposure to high outdoor levels of air pollutants, including particulate matter, and adverse respiratory health effects. It explained that fine particles of outdoor origin readily penetrate indoors and that there is an association between particulate matter exposure and asthma exacerbation but not asthma development (outside of tobacco smoke). The possible mechanisms for asthma exacerbation named in the report included reflex bronchoconstriction via nonspecific irritant effects, direct toxicity to the airway epithelium and resident immune cells, and induction of an inflammatory immune response. The report

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8 In addition, several NASEM reports have addressed environmental tobacco smoke (ETS), an important source of multiple pollutants in indoor environments, including fine particulate matter. ETS exposure and health impacts were outside the scope of this study but were most recently addressed in the 2018 report Public Health Consequences of E-Cigarettes.

Suggested Citation:"2 Background." National Academies of Sciences, Engineering, and Medicine. 2024. Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions. Washington, DC: The National Academies Press. doi: 10.17226/27341.
×

concluded that limiting or eliminating sources and using HEPA filters were the most straightforward means of addressing indoor particulate matter exposures.

Damp Indoor Spaces and Health (IOM, 2004) reported on a comprehensive review of the research regarding the relationship between damp or moldy indoor environments and the manifestation of adverse health effects, particularly respiratory and allergic symptoms. The report highlighted the fact that particulate allergen exposure often occurs episodically because of the inadvertent disturbance and resuspension of reservoirs of biologic agents by human activities. This means of exposure is likely not to be accurately captured by environmental area samplers, and it is nearly impossible to measure all relevant microenvironments when trying to measure particulate exposure, making personal sampling of particulate matter a preferred method for evaluating biologic agents.

Green Schools: Attributes for Health and Learning (NRC, 2007) reviewed the results of the then-available studies on green schools9 to determine their effects on student learning and teacher productivity. The report stated that particulate matter pollutants in schools are of both indoor and outdoor origin and are associated with asthma and other respiratory symptoms and with a set of building-related symptoms including eye, nose, and throat irritation. It observed that indoor and outdoor particles and certain volatile organic compounds (VOCs) are effectively removed by filtration, but most filters used in schools are designed to collect particles larger than 10 μm and are thus relatively inefficient at removing submicron-sized particles. The report proposed strategies to mitigate particulate matter pollutants such as anti-idling measures for vehicles outside the building, the elimination of gas-fired pilot lights, and discouraging fossil fuel burning equipment indoors.

Climate Change, the Indoor Environment, and Health (IOM, 2011) summarized the state of scientific understanding with respect to the effects of climate change on indoor air and public health. The report found that climate change mitigation strategies could improve or worsen fine-particle exposure associated with cooking and that increased wildfire incidence would increase community exposure to fine particles, leaving low-income households at a higher risk. It suggested that attention should be directed toward improving understanding of the effectiveness of indoor environments as a shelter against pollutants of outdoor origin that may be altered due to climate change.

Health Risks of Indoor Exposure to Particulate Matter: Workshop Summary (NASEM, 2016) summarized a series of public workshops on the state of the science regarding the health risks of indoor exposure to particulate matter. The workshops explored the primary sources of particulate matter, the chemistry and dynamics of particulate matter, and issues related to particulate matter exposure. In addition, it discussed the health risks associated with exposure to particulate matter and how to engage the public on these issues.

Microbiomes of the Built Environment: A Research Agenda for Indoor Microbiology, Human Health, and Buildings (NASEM, 2017) reviewed both what was known about the intersection of microbial biology, chemistry, building science, and human physiology and how new tools may facilitate advances in understanding the ecosystem of built environments and effects on human health and well-being. The report discussed particle filtration and balancing ventilation and outdoor air quality for the management of fine particles. It pointed out that an emphasis on the benefits of reducing indoor fine particle concentrations for occupant health have

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9 The report defined “green schools” as those whose goals were “(1) to support the health and development (physical, social, intellectual) of students, teachers, and staff by providing a healthy, safe, comfortable, and functional physical environment; and (2) to have positive environmental and community attributes” (p. 2).

Suggested Citation:"2 Background." National Academies of Sciences, Engineering, and Medicine. 2024. Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions. Washington, DC: The National Academies Press. doi: 10.17226/27341.
×

led to requirements for and use of higher levels of filter efficiency in buildings. It observed that reducing fine particles from outdoor air via filtration required the use of filters with higher MERV10 ratings and can be expensive but that technologies were being developed to reduce these costs.

Indoor Exposure to Fine Particulate Matter and Practical Mitigation Approaches: Proceedings of a Workshop (NASEM and NAE, 2022) summarized presentations and discussions that took place during three workshops held virtually in 2021 that addressed the state of the science on exposure to fine particulate matter indoors, its health impacts, and engineering approaches and interventions to reduce exposure risks, including practical mitigation solutions in residential settings. The workshop presentations examined sources of fine particulate matter, health effects of exposure to indoor fine particulate matter, metrics and assessment of indoor exposure to fine particulate matter, mitigation strategies, and occupant responses to indoor fine particulate matter. Speakers observed that both technological and behavioral interventions were needed to mitigate fine particulate matter exposure.

Why Indoor Chemistry Matters (NASEM, 2022) explored indoor chemistry from different perspectives, including the sources and reservoirs of indoor chemicals and the ability of these chemicals to undergo transformations and partitioning in the indoor environment. The report described the mass and number concentrations of particulate matter in various size fractions and the elemental composition of fine particulate matter with respect to typical sources. It also discussed the variety of fine particle monitors available and their ability to identify episodic events and relative changes in the same indoor setting. The committee responsible for the report highlighted the need to develop testing approaches that consider both efficacy and byproduct formation in a representative range of real-world environments with respect to fine particles.

REFERENCES

EPA (U.S. Environmental Protection Agency). 2023. Indoor air quality. https://www.epa.gov/indoor-air-quality-iaq (accessed July 28, 2023).

Ilacqua, V., Scharko, N., Zambrana, J., and Malashock, D. 2022. Survey of residential indoor particulate matter measurements, 1990–2019. Indoor Air 32(7):e13057.

IOM (Institute of Medicine). 2000. Clearing the air: Asthma and indoor air exposures. Washington, DC: National Academy Press.

IOM. 2004. Damp indoor spaces and health. Washington, DC: National Academy Press.

IOM. 2011. Climate change, the indoor environment, and health. Washington, DC: The National Academies Press.

IOM and NRC (Institute of Medicine and National Research Council). 1993. Indoor allergens: Assessing and controlling adverse health effects. Washington, DC: National Academy Press.

NASEM (National Academies of Sciences, Engineering, and Medicine). 2016. Health risks of indoor exposure to particulate matter: Workshop summary. Washington, DC: The National Academies Press.

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10 Minimum Efficiency Reporting Value (MERV) documents a filter’s ability to capture 0.3–10 micron (µm) particles. The MERV rating scale runs from 1 to 16, with MERV 16 filters being capable of capturing ≥95% of particles in that size range.

Suggested Citation:"2 Background." National Academies of Sciences, Engineering, and Medicine. 2024. Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions. Washington, DC: The National Academies Press. doi: 10.17226/27341.
×

NASEM. 2017. Microbiomes of the built environment: A research agenda for indoor microbiology, human health, and buildings. Washington, DC: The National Academies Press.

NASEM. 2018. Public health consequences of e-cigarettes. Washington, DC: The National Academies Press.

NASEM. 2022. Why indoor chemistry matters. Washington, DC: The National Academies Press.

NASEM and NAE (National Academies of Sciences, Engineering, and Medicine and National Academy of Engineering). 2022. Indoor exposure to fine particulate matter and practical mitigation approaches: Proceedings of a workshop. Washington, DC: The National Academies Press.

NRC (National Research Council). 1981. Indoor pollutants. Washington, DC: National Academy Press.

NRC. 1987. Policies & procedures for control of indoor air quality. Washington, DC: National Academy Press.

NRC. 2007. Green schools: Attributes for health and learning. Washington, DC: The National Academies Press.

Suggested Citation:"2 Background." National Academies of Sciences, Engineering, and Medicine. 2024. Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions. Washington, DC: The National Academies Press. doi: 10.17226/27341.
×
Page 18
Suggested Citation:"2 Background." National Academies of Sciences, Engineering, and Medicine. 2024. Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions. Washington, DC: The National Academies Press. doi: 10.17226/27341.
×
Page 19
Suggested Citation:"2 Background." National Academies of Sciences, Engineering, and Medicine. 2024. Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions. Washington, DC: The National Academies Press. doi: 10.17226/27341.
×
Page 20
Suggested Citation:"2 Background." National Academies of Sciences, Engineering, and Medicine. 2024. Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions. Washington, DC: The National Academies Press. doi: 10.17226/27341.
×
Page 21
Suggested Citation:"2 Background." National Academies of Sciences, Engineering, and Medicine. 2024. Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions. Washington, DC: The National Academies Press. doi: 10.17226/27341.
×
Page 22
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Schools, workplaces, businesses, and even homes are places where someone could be subjected to particulate matter (PM) – a mixture of solid particles and liquid droplets found in the air. PM is a ubiquitous pollutant comprising a complex and ever-changing combination of chemicals, dust, and biologic materials such as allergens. Of special concern is fine particulate matter (PM2.5), PM with a diameter of 2.5 microns (<0.0001 inch) or smaller. Fine PM is small enough to penetrate deep into the respiratory system, and the smallest fraction of it, ultrafine particles (UFPs), or particles with diameters less than 0.1 micron, can exert neurotoxic effects on the brain. Overwhelming evidence exists that exposure to PM2.5 of outdoor origin is associated with a range of adverse health effects, including cardiovascular, pulmonary, neurological and psychiatric, and endocrine disorders as well as poor birth outcomes, with the burden of these effects falling more heavily on underserved and marginalized communities.

Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Solutions explores the state-of the-science on the health risks of exposure to fine particulate matter indoors along with engineering solutions and interventions to reduce risks of exposure to it, including practical mitigation strategies. This report offers recommendations to reduce population exposure to PM2.5, to reduce health impacts on susceptible populations including the elderly, young children, and those with pre-existing conditions, and to address important knowledge gaps.

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