Health Risks of Indoor Exposure to Particulate Matter Workshop Summary (2016) / Chapter Skim
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4 Characterizing Indoor Exposure Levels
4 Characterizing Indoor Exposure Levels
Pages 41-58
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From page 41... ...
PM2.5 EXPOSURE CHARACTERIZATION PROVIDES INSIGHTS INTO SOURCES AND TRANSFORMATIONS1 As had been discussed in earlier workshop sessions, Barbara Turpin said, indoor PM2.5 concentrations represent a balance between sources and sinks, and the sources include indoor emissions of particles and outdoorto-indoor transport of particles. The sinks include the deposition of particles on indoor surfaces, filtration by HVAC systems, and exfiltration of 1 Thissection is based on the presentation by Barbara Turpin, a professor of environmental sciences and engineering at the University of North Carolina Gillings School of Global Public Health, and the statements are not endorsed or verified by the National Academies of Sciences, Engineering, and Medicine.
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From page 42... ...
She and her colleagues measured the amount of particulate organic matter indoors versus outdoors and calculated that, on average, 71 to 76 percent of the organic carbon in indoor PM2.5 comes from indoor sources, with a lower bound estimate of 41 percent (Polidori et al., 2006)
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From page 43... ...
Calculations using data collected in southern California show that at a typical indoor air exchange rate, only approximately 12 percent of the outdoor particulate nitrate is found indoors. The degree to which the components of outdoor PM2.5 penetrate and persist indoors vary broadly, from 4 percent for soil components to 78 percent for sulfate (Lunden et al., 2008; Meng et al., 2007; Polidori et al., 2006)
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From page 44... ...
. That latter result was not surprising, she said, given that there is so much organic carbon generated indoors and that these modeled values exclude indoor sources.
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From page 45... ...
The infiltration factors reported here were calculated from a model that considers the particle size-dependence of the infiltration factor, the various particle size distributions of different chemical components of outdoor PM2.5 and the air exchange rate for a typical [AER = 0.45 h–1] and low-income [AER = 0.90 h–1]
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From page 46... ...
. Subsequent modeling studies for a more complex mixture of organic compounds yielded similar results which correlated geographic differences in temperature gradients, air conditioning and heating use, and indoor organic matter emissions to indoor organic PM composition (Hodas and Turpin, 2014)
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From page 47... ...
In another study, Harrison and his colleagues measured particle size distributions both in an unoccupied, sealed walkway with little ventilation above a busy highway and from the nearby roadside. When they plotted the ratio of indoor to outdoor numbers by particle size, the results, as Harrison recounted, were surprising in that there was a rapid decline in indoor-tooutdoor ratio at larger diameters (see Figure 4-6)
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From page 48... ...
Evaporation of UFPs is a possible third mechanism, one Harrison believes to be important because the walls of the unoccupied room were likely to serve as a sink for the SVOCs that dominate the composition of traffic-generated UFPs. Another study, also conducted in Bologna, measured indoor and outdoor PM at the front and back of two buildings -- one on a heavily trafficked street and a second on a low-traffic residential street -- during hot and cold seasons (Zauli Sajani et al., 2016)
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From page 49... ...
Harrison then addressed the subject of exposure and, in particular, the difference between measurements of personal exposure to PM versus the results from static indoor monitoring. Data from one study showed that personal exposure to carbon monoxide and nitrogen dioxide was well reflected by a static room monitor, but the personal measurement for PM10 was always higher than that determined from the static measurement (Kim et al., 2002)
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From page 50... ...
SOURCES: Harrison slide 13, from Zauli Sajani et al.
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From page 51... ...
He wondered if particles from indoor origins such as cooking and resuspended house dust are as toxic as the outdoor pollutant mixtures measured in most epidemiological studies and if the elemental carbon component of diesel particles is comparable in toxicity to the organic component, which is largely from lubricating oil. He also wondered if the fact that buildings are very protective for UFPs, SVOCs, and nitrates matters in terms of health risk and what the determinants and significance of the personal cloud of particles is for health.
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From page 52... ...
There are many instances, too, where stoves are used not only for cooking but also as a source of supplemental heat in low-income households, which would potentially increase exposures to nitrogen oxides and PM beyond what might be included in typical models of indoor exposure. Adamkiewicz presented data for some of these housing-related variables (see Table 4-2)
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From page 53... ...
The most important finding, he said, was that there were many more indoor factors than the outdoor pollution level that affected indoor PM levels. "Even at very high outdoor air pollution levels and high air exchange rates, the biggest impacts were from indoor factors," he said.
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From page 54... ...
As an example of the type of analysis he would like to see more of, Adamkiewicz cited an effort that used American Housing Survey and census data, combined with data on activities and smoking prevalence, to model indoor PM2.5 concentrations (Chahine et al., 2011)
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From page 55... ...
While there are many caveats concerning the use of this model, Adamkiewicz said that it does provide the ability to try various what-if scenarios and start to develop an understanding of how exposures may vary at a population level. As a final example of research on the role that smoking plays in determining indoor PM levels, Adamkiewicz described a study he and his colleagues have been conducting using real-time data from in-unit public housing sites (Russo et al., 2015)
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From page 56... ...
As a concluding thought, Adamkiewicz said he would like to see more work aimed at understanding how household activities affect indoor PM levels and how exposure disparities are related to conditions or activities
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From page 57... ...
FIGURE 4-10 Real-time PM2.5 levels in a smoker's housing unit and adjacent unoccupied unit. SOURCES: Adamkiewicz slide 18, from Russo et al.
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From page 58... ...
DISCUSSION Richard Corsi asked Adamkiewicz if any comparisons are being made between new conventional housing and new green housing because, he said, in his mind it is not a fair comparison to pit new green housing against existing housing. Adamkiewicz acknowledged Corsi's point and said that the only counter to that question is whether all new public housing should be green.
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