Evaluating the Sensitivity of the Mass-Based Particle Removal Calculations for HVAC Filters in ISO 16890 to Assumptions for Aerosol Distributions
Abstract
:1. Introduction
2. Methods
3. Results
3.1. Origin of the Historical Ambient Aerosol Distributions Used in ISO 16890
3.2. How Relevant Are the Historical Ambient Aerosol Distributions Used in ISO 16890 Today?
3.3. How Does the Outdoor-to-Indoor Transport of Ambient Aerosol Distributions Affect Estimates of ePM for Particles of Outdoor Origin?
3.4. How Does the Use of Indoor Aerosol Distributions Affect Estimates of ePM?
4. Discussion
- The urban and rural ambient aerosol distributions used in ISO 16890 date back to the 1970s, and have number concentrations that greatly exceed most recent ambient aerosol distributions. However, the shape of the number distributions are somewhat similar to more recent ambient distributions, albeit with some deviations in the ~0.05–0.5 µm size range.
- Differences in estimates of ePM for filtration of 100% outdoor air made using the historical ambient aerosol distributions in ISO 16890 and more modern ambient distributions can be substantial (particularly for ePM2.5).
- Failing to account for size-resolved transformations that typically occur during outdoor-to-indoor transport, particularly in residential buildings, yields estimates of ePM for indoor particles of outdoor origin that are overestimated by as much as ~15% (on a relative basis) for the four HVAC filters investigated herein.
- The use of indoor aerosol distributions to represent indoor particulate matter that is a mixture of indoor and outdoor sources rather than assuming filtration of 100% outdoor air yields relatively large differences in estimates of ePM10, but estimates of ePM1 and ePM2.5 were actually quite similar.
- The historical and static ambient aerosol distributions should be updated to reflect more modern ambient environments.
- The standard should reconsider its use of the somewhat artificial distinction that filters that were designed to filter primarily PM1 and PM2.5 size fractions be characterized using only the urban aerosol distribution, and that filters designed to filter primarily PM10 be characterized using only on the rural volume distribution. Given that HVAC filters are currently marketed and sold to consumers without the distinction of whether the filter should be used in an urban or rural environment, and that suburban and other environments are not explicitly addressed, this practice will likely lead to more confusion than clarity.
- The standard should be modified in order to allow for estimations of ePM based on other commonly used HVAC system configurations in addition to 100% outdoor, including 100% recirculation systems, and mixed outdoor/recirculation systems with variable outdoor air fractions in which indoor PM is a mixture of aerosols that are generated indoors and transported from outdoors (often through building envelopes, particularly in residences, but not always).
- To support item #3 above, further research should be conducted in order to more robustly characterize indoor aerosol distributions in a wide variety of building types and under a variety of conditions (e.g., varying emission sources, ventilation rates, etc.).
- Although not explicitly address herein, the vast majority of particles in both indoor and outdoor environments (on a number basis) are typically smaller than 0.3 µm (and typically ultrafine particles, or UFPs, smaller than 0.1 µm) [36,54,55]. Therefore, ISO 16890 and other standards should consider adopting measures of removal efficiency for size-resolved and/or total UFPs to better characterize the impact that filters can have on IAQ.
5. Conclusions
Acknowledgments
Conflicts of Interest
References
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Distribution | Mode 1 | Mode 2 | Mode 3 | ||||||
---|---|---|---|---|---|---|---|---|---|
N (#/cm3) | Dg (µm) | logσg | N (#/cm3) | Dg (µm) | logσg | N (#/cm3) | Dg (µm) | logσg | |
Urban | 9.93 × 104 | 0.013 | 0.245 | 1.1 × 103 | 0.014 | 0.666 | 3.64 × 104 | 0.050 | 0.337 |
Rural | 6650 | 0.015 | 0.225 | 147 | 0.054 | 0.557 | 1990 | 0.084 | 0.266 |
Distribution | Mode 1 | Mode 2 | Mode 3 | ||||||
---|---|---|---|---|---|---|---|---|---|
N (#/cm3) | Dg (µm) | logσg | N (#/cm3) | Dg (µm) | logσg | N (#/cm3) | Dg (µm) | logσg | |
Abt et al. (2000) | 10,700 | 0.065 | 0.280 | 3.5 | 0.8 | 0.180 | 0.4 | 1.5 | 0.280 |
Long et al. (2001) | 6660 | 0.055 | 0.300 | 1 | 1 | 0.150 | 0.15 | 3.0 | 0.180 |
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Stephens, B. Evaluating the Sensitivity of the Mass-Based Particle Removal Calculations for HVAC Filters in ISO 16890 to Assumptions for Aerosol Distributions. Atmosphere 2018, 9, 85. https://doi.org/10.3390/atmos9030085
Stephens B. Evaluating the Sensitivity of the Mass-Based Particle Removal Calculations for HVAC Filters in ISO 16890 to Assumptions for Aerosol Distributions. Atmosphere. 2018; 9(3):85. https://doi.org/10.3390/atmos9030085
Chicago/Turabian StyleStephens, Brent. 2018. "Evaluating the Sensitivity of the Mass-Based Particle Removal Calculations for HVAC Filters in ISO 16890 to Assumptions for Aerosol Distributions" Atmosphere 9, no. 3: 85. https://doi.org/10.3390/atmos9030085
APA StyleStephens, B. (2018). Evaluating the Sensitivity of the Mass-Based Particle Removal Calculations for HVAC Filters in ISO 16890 to Assumptions for Aerosol Distributions. Atmosphere, 9(3), 85. https://doi.org/10.3390/atmos9030085