Indoor Exposure to Fine Particulate Matter and Practical Mitigation Approaches Proceedings of a Workshop (2022) / Chapter Skim
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6 Indoor Exposure to Particulate Matter: Metrics and Assessment
6 Indoor Exposure to Particulate Matter: Metrics and Assessment
Pages 61-78
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From page 61... ...
Dusan Licina (Swiss Federal Institute of Technology, Lausanne) spoke about low-cost indoor particulate matter sensors and how they can be used and misused.
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From page 62... ...
For the bulk of the PM2.5 mass, particles range in size from 0.01 to 2.5 microns, a 250-fold span in diameter and a 16 millionfold span in mass between the largest and smallest particles, which Nazaroff pointed out is the same mass ratio between an Etruscan shrew and a gray whale. Chemically, the composition of fine particles incudes elemental and organic carbon, with vastly diverse chemical composition, as well as crustal materials, inorganic salts, metals, microbes, and other constituents.
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From page 63... ...
Size and spatial complexity exist, too, in the distribution of different size particles in the three major regions of the respiratory tract (Figure 6-2)
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From page 64... ...
clearly showed the variations in indoor particulate matter concentrations throughout the day as different activities occur inside the home. He explained that what this highlights about temporal variability is that relying on time-averaged indoor concentration measurements without accounting for the correlation with occupancy can mischaracterize indoor exposure.
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From page 65... ...
For size complexity, he suggested using PM2.5 mass concentration or some suitable proxy as the source of best information if the aim is practicality. For ultrafine particles (PM0.1)
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From page 66... ...
Among the alternative measurement methods are • light scattering, which is good for particle sizes ranging from 0.3 to 10 microns • electrical mobility to produce size-resolved data for ultrafine particles • condensation particle counters for measuring ultrafine particle number concentrations • filter-based sampling, a standard method for time-integrated mass concentration and some chemical composition data. He noted that practical constraints are different for personal monitoring compared to indoor air sampling.
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From page 67... ...
He also noted three possible performance metrics for indoor particulate matter filtration: efficiency, clean air delivery rate, and effectiveness. Efficiency is the fractional removal of particles, the clean air delivery rate combines efficiency with the flow rate through the device, and effectiveness refers to the extent to which the controlled condition is better than the uncontrolled condition.
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From page 68... ...
In closing, Nazaroff cited a quote attributed to Albert Einstein: "Everything should be made as simple as possible, but not simpler." The intervention opportunities with the biggest potential to improve human health include a combination of resident and school environment improvements. THE CHALLENGE OF MOVING FROM THE MEASUREMENT OF INDOOR PM2.5 TO EVALUATING OCCUPANT EXPOSURE Kirsten Koehler began by presenting an environmental health paradigm developed some 30 years ago (Figure 6-5)
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From page 69... ...
Personal Exposure Monitoring Even a dense network of low-cost sensors would not yield information on all the important sources of indoor particulate matter or the various discrete exposures an individual experiences during the day. This is where personal monitoring comes into play.
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From page 70... ...
When she and her colleagues conducted a similar study, in which 50 asthmatic children in Baltimore carried a backpack with air sampling equipment for 4 consecutive days, they found that home exposures were higher than ambient exposures for some of the children. FIGURE 6-6 Variability of PM2.5 exposures by person, day, and microenvironment.
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From page 71... ...
In closing, Koehler reiterated the complexity of extrapolating from particulate matter measurements to exposure, and the fact that exposure has different meanings according to where it is monitored and over what time frame. "For particulate matter, we might want to think carefully about the metric of exposure that we use…not just PM10 and PM2.5, but thinking more about lung deposit or ultrafine particles that deposit at higher fractions."
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From page 72... ...
What this means, he said, is that what is relevant today might be outdated in just a few years. The second caveat is that more research is available on low-cost sensors used for outdoor particulate matter monitoring, and the result is that the type of monitoring networks established for outdoor air are not available for indoor particulate monitoring with low-cost sensors.
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From page 73... ...
When comparing the use of these sensors in the laboratory versus a field setting, it is difficult to maintain a low particulate matter concentration over a long time in the laboratory, and the composition and concentration of a test aerosol in the lab may not be representative of aerosols in the study area. On the other hand, in the field it is necessary to account for variable particle composition, size, and changing environmental factors.
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From page 74... ...
Currently, no local building, health, or safety code requires continuous monitoring of indoor particulate matter. The US Green Building Council's WELL Building Standard, a performance-based system for measuring, certifying, and monitoring features of the built environment that impact human health and wellbeing, does not require indoor monitoring of particulate matter, but it does offer an option to earn additional points on their rating system if one PM10 or PM2.5 sensor is in place for every 325 square meters of space, a figure that Licina characterized as arbitrary.
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From page 75... ...
"Advancing knowledge in low-cost measurement techniques for indoor particulate matter increases the likelihood that future control interventions can be used both to prevent undesired health consequences and to promote beneficial health outcomes," said Licina. DISCUSSION Moderator Elizabeth Matsui summarized her impression from the perspective of someone interested in the health effects of indoor particulate matter.
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From page 76... ...
A workshop participant asked if there is value in using lung-deposited surface area as a metric for measuring ultrafine particles and comparing that with the foam sampler Koehler developed. Koehler thought that would be a useful comparison, but had not seen evidence that lung-deposited surface area is the "right" metric to use when trying to relate ultrafine particle exposures to health consequences.
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From page 77... ...
Koehler replied that this is a difficult problem given the variety of potential sources and the data that Nazaroff showed regarding the short timescales over which particle concentration can significantly change. Nazaroff observed, though, that real-time monitoring, coupled with some combination of occupant diaries and realtime metadata measurement, does provide an opportunity to disentangle the contributors of indoor sources to indoor exposures without having to rely on chemical speciation of sources; this has been done to a limited extent and could be expanded to larger populations.
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From page 78... ...
Nazaroff pointed out that the building envelope does a good job of stopping ultrafine particles from infiltrating to the indoor environment and that indoor sources seem to dominate, which should make their assessment more feasible. Given the ways in which these particles can affect humans, he concluded that "ultrafine particles are another big world that is on the horizon in terms of public health concern."
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