Indoor Exposure to Fine Particulate Matter and Practical Mitigation Approaches Proceedings of a Workshop (2022) / Chapter Skim
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Pages 65-84
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From page 65... ...
. Levels in the breathing zone were considerably higher than the room average levels when the occupants were seated, but when they walked around the room the personal particulate matter cloud dissipated because the room floor was clean and the room air became relatively well mixed by their movement.
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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... ...
Inside the body, a contaminant can lead to a dose, and ultimately to altered structure and function, and adverse health outcomes. Koehler clarified that for particulate matter, "dose" may not be the best measure of exposure because the relationship between exposure and dose is a strong function of particle size.
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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... ...
Licina noted that repeatability and reproducibility could be influenced by the particulate matter concentration, range, source type, and drift. For example, the reproducibility for cigarette smoke is higher compared to Arizona test dust,1 and most sensors detect higher concentrations of organic than inorganic particulate matter at identical concentrations because of differences in the absorption and scattering properties of these two types of particulate matter.
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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... ...
Other needs include developing low-cost sensors for ultrafine particulate matter, a challenge given that particles smaller than 0.3 microns do not scatter enough light and cannot be detected reliably using inexpensive optical methods. Licina noted that, depending on the source of particulate matter, low-cost PM2.5 sensors may in fact detect agglomerated ultrafine particles.
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From page 76... ...
He would like to see research to identify the type of information that low-cost sensor networks can provide to help manage particulate matter levels in schools. "I do not think we are at the point yet where we can say we understand what these monitors can do such that we are ready to recommend to school districts that they buy a bunch of monitors and use them to help manage their indoor environmental air quality," said Nazaroff.
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From page 77... ...
In response to a question about particulate matter exposure on weekdays versus weekends, Koehler acknowledged that there probably are differences. She also addressed an inquiry about whether the high concentration of small particles in rural areas could be soluble organic aerosols from trees or forests instead of resuspended particulate matter from roads, agreeing that this could be the case but adding that "these measures are mass based and there is very little ability to distinguish between the different sources." A workshop observer asked the panelists to list approaches for identifying sources of particulate matter that have the most potent health effects, as a step to targeting those sources for control.
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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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From page 79... ...
It also informs and validates control efforts. As Bhangar noted, knowledge about the health effects of particulate matter exposure is only as good as the metrics and measurements used to create that knowledge.
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From page 80... ...
80 INDOOR EXPOSURE TO FINE PARTICULATE MATTER Fourth, the speakers identified a number of challenges to measuring exposure and dose and the possibility of mischaracterizing both. They also noted the challenges of developing and selecting metrics and measurement methods for different applications and environments.
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From page 81... ...
3. To what extent can filters and mechanical systems or standalone air cleaners reduce exposure to PM2.5 and its health effects indoors?
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From page 82... ...
systems, which means they do not add outside air but only recirculate air already inside the building. Measured recirculation rates -- the number of house volumes that go through the system when it is operating -- span a wide range (Figure 8-1)
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From page 83... ...
note that "[r] untime is influenced by climate and season but also by building characteristics, equipment sizing, occupant preferences, and operations and maintenance" (p.
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From page 84... ...
. In residential settings, it is common for HVAC systems to have a filter slot 2 Electret filters are those whose filter media has been modified by the manufacturer to initially have an electrostatic charge on the fibers.
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