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2 Outdoor Sources of Indoor Particulate Matter
Pages 5-24

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From page 5...
... INDOOR PARTICULATE MATTER OF OUTDOOR ORIGIN AND DISPARITIES IN SOURCES AND EXPOSURES ACROSS COMMUNITIES PM2.5 arises from multiple sources including transportation, industrial, and agricultural activities; wildfire smoke, and (in coastal locations) marine vessels (Figure 2-1)
From page 6...
... 6 FIGURE 2-1  The diverse origins of ambient PM2.5. SOURCE: Ivey Slide 4 (original source: EPA, https://www.epa.gov/cmaq/overview-science-processes-cmaq)
From page 7...
... However, the top five sources of PM2.5 emissions identified in that community are paved road dust, mineral processes,5 and off-road equipment -- three source categories that reflect the community's concerns -- as well as 1  "Secondary" particles are those formed from chemical reactions in the atmosphere. 2  The South Coast Air Basin includes the western portions of Riverside and San Bernardino Counties, the southern two-thirds of Los Angeles County, and all of Orange County.
From page 8...
... The major finding from this study was that the San Bernardino residents were more at risk from exposures in their homes compared to residents of the Riverside 6  Theinfiltration factor is the ratio of indoor to outdoor PM, considering outdoor sources only. The measure is discussed in detail later in this chapter.
From page 9...
... 60 56 54 2017 2024 2029 51 50 47 45 46 40 36 34 30 30 26 26 26 Tons/year 20 12 12 12 10 9 6 5 0 Paved Road Dust Mineral Processes Cooking Residential Fuel Light Duty Passenger Off-Road Equipment Combustion Auto (LDA) FIGURE 2-2  Top five sources of PM2.5 emissions in the San Bernardino and Muscoy, California, community, actual and projected.
From page 10...
... We will probably have to consider these approaches through a historical lens where we consider the inequities that may confound our approaches, and we can do this by classifying these exposure disparities as either intentional or unintentional." By unintentional exposure disparity, she meant exposure that is not affected directly by humans, such as the wildfires that are emerging as an important source of air pollution as the climate changes. In this case, mitigation could involve increasing the air tightness of the building envelope and installing portable air cleaners, a subject discussed in the third session of the workshop.
From page 11...
... . As Stephens explained, nearly all outdoor air pollution epidemiologic studies fail to account for these facts, leading to what he called exposure misclassification, "where we are not quite sure if a central site or even a highly localized outdoor concentration of particulate matter is a reasonable surrogate for exposure." Sampling indoor and outdoor particulate matter simultaneously yields an indoor/outdoor ratio, where the indoor concentration is influenced by both what is emitted or generated indoors and what infiltrates and persists from outdoors.
From page 12...
... The metrics researchers have used to measure particulate matter infiltration factors fall into two main categories, said Stephens. The most common method uses a chemical surrogate of the samples collected on a filter and weighed.
From page 13...
... The key drivers of variability in infiltration factors include pollutant characteristics such as size, class, and chemical components of the particulate matter; the source of ventilation air; human behaviors such as
From page 14...
... Reprinted from Atmospheric Environment 45(2) , Chen C, Zhao B, Review of relationship between indoor and outdoor particles: I/O ratio, infiltration factor and penetration factor, pp.
From page 15...
... Together, the studies confirm that ultrafine and large particles do not penetrate and persist for long time periods in buildings. New Directions in Assessing Infiltration and Penetration Factors An exciting piece of research Stephens has seen recently used a low-cost sensor network to estimate infiltration factors at the scale of the building stock (Bi et al., 2021)
From page 16...
... • Improve the direct measurement of penetration factors by increas ing sample sizes and incorporating PM2.5 chemical composition, standardizing approaches, and exploring influencing factors. OUTDOOR PARTICULATE MATTER SOURCES AND THE CHEMICAL TRANSFORMATIONS THAT TAKE PLACE WHEN THEY INTERACT WITH THE INDOOR ENVIRONMENT Building on the foundations laid by Ivey and Stephens, Delphine Farmer focused on sources of particulate matter in the outdoor environment and what happens to those particles after they infiltrate the indoor environment.
From page 17...
... . Research demonstrates that particulate matter levels have been decreasing across the United States thanks to the Clean Air Act and regulatory activities that have reduced not only primary emissions but also the atmospheric chemical reactions that produce particulate matter (Jaffe et al., 2020; McClure and Jaffe, 2018)
From page 18...
... These sources are not evenly distributed across the planet -- there is more sea spray aerosol along the coasts than in the Rocky Mountains, to cite an obvious example -- so there is spatial heterogeneity in the composition of outdoor particulate matter. One recent study found that particle concentration is driven by crustal material, secondary inorganic aerosols, and biogenic secondary organic aerosol, and that anthropogenic aerosol from sources such as wood burning and vehicle wear drives the oxidative potential in that aerosol (Daellenbach et al., 2020)
From page 19...
... Oxidant levels are low indoors, but they are not zero and the oxidants that are present can react with the organic load to produce an array of oxidized organic and inorganic products that can then condense to form secondary organic aerosol (Avery et al., 2019a)
From page 20...
... Her conclusions on the basis of the studies discussed were that there is broad scientific consensus that outdoor PM2.5 influences indoor PM2.5, so reducing outdoor sources improves indoor air quality; and that once indoors, aerosols have many chemical fates -- albeit on far shorter timescales than outdoor air -- and that the resulting chemical composition of the air may influence human health. DISCUSSION Kimberly Prather, the moderator, invited questions from planning committee members and then from the webinar viewers.
From page 21...
... "They are not individualized causes, and to fix a systemic issue, you need systemic solutions." Farmer added that the nation needs to think about the different sources of outdoor particulate matter, which are out of an individual's control, and understand what those sources are and what they contribute to the health burden in disadvantaged communities. In terms of the many opportunities that exist to decrease particulate matter exposure and improve indoor air quality, she noted that while this is a socioeconomic issue, there is a need for the scientific community to do a better job explaining to all communities which approaches are the best for producing the desired results in a cost-effective manner.
From page 22...
... In the same vein, Farmer said that there is a great opportunity to apply the technologies developed to study and understand the association between what happens in the outdoor environment and the indoor environment and do so in the most vulnerable and disadvantaged communities. An online participant wanted to know what criteria the research community is focused on to quantify the intersection between particle infiltration and health, particularly regarding time-integrated exposure versus instantaneous maximum exposure.
From page 23...
... The data show that reducing particulate matter exposure by even small amounts has very substantial beneficial health effects, which is why the Clean Air Act is viewed as one of the strongest pieces of legislation in terms of extending life years of people in this country.


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