First Advisor
Elliott Gall
Term of Graduation
January 2026
Date of Publication
6-1-2026
Document Type
Thesis
Language
English
Subjects
Clean Air Delivery Rate, Gas Phase Surface Interactions, Indoor Air Quality
Physical Description
1 online resource ( pages)
Abstract
Portable air cleaners are playing an increasingly important role in managing indoor air quality in response to pressing issues like wildfire smoke events. Smoke is a complex mixture of gases and particulate matter; while established test methods exist for particulate matter, the dynamic behavior of gaseous pollutants is not well accounted for in current test methods. This is because prevailing air cleaner testing methods typically treat background losses as irreversible, whereas gases can engage in partitioning to and from test chamber surfaces. Ignoring these sorption interactions causes inaccurate estimation of an air cleaner’s impact.
A new approach has been developed to determine the gas-phase clean air delivery rate (CADR) that accounts for surface interactions and can be conducted simultaneously with particle CADR tests. This novel method uses real-time measurement of target gas-phase compounds across the following periods: 1) steady state, 2) adsorption, 3) air cleaning, and 4) desorption. From these periods, it is proposed that environment-specific sorption coefficients and dynamic surface mass concentration can be determined alongside CADR in a test of ∼4 hours in duration. The proposed method is developed using naphthalene, a semi-volatile organic compound, and a test chamber with sorptive surfaces introduced (stainless steel, cotton fabric on the floor, cotton fabric on the floor and walls, painted surfaces, and a high-pile rug) to conduct experiments across five levels of anticipated sorptive strength. Considering these surface interactions will lead to a more accurate determination of gas-phase air cleaner CADR values.
These data periods allow for an estimation of the accumulated mass of said target compounds on the internal test chamber surfaces, informing understanding of the relationship between air cleaning and surface contamination. This approach can be used to inform understanding of the state of a test chamber (e.g., chamber surface mass loading) as well as surface-mediated exposure pathways in realistic environments.
This novel approach of gas phase air cleaner testing was repeatable and consistent with the range of CADR values found for other similar compounds, though to our knowledge, this work represents the first estimate of naphthalene CADR under room-scale chamber test conditions. The method had a 5% average error between replicates (range: 0.8%–13.2%). This method was also independent of the elapsed time of the air cleaning analysis period, unlike the industry standard pulldown method. The average percent difference between the 20-60 minute analysis across all trials was 4.3% where the pulldown method had an average percent difference of 34.2% across all trials. The CADR values decreased over the extent of the experimental matrix, but this is attributed to the molecular filter becoming loaded.
Additional experiments were ran using this novel method to understand the effect the gas phase air cleaning strength during injection has on surface mass loading by analyzing the air concentration rebound during the desorption period. These experiments were held for three different levels of air cleaning and two surfaces, stainless steel and a high-pile rug. When the air cleaner was operated on its highest strength, both the adsorption surface uptake and desorption re-emissions were at their lowest across the experiments conducted here. This occurred because less naphthalene was initially adsorbed onto the surfaces, leaving less available for release during the desorption period. These findings highlight important implications for remediation strategies during atmospheric pollution events, such as wildfires.
Exposure modeling was performed over a 1 h period using experimentally determined effective emission rates from the desorption period for the second set of experiments. Operating an air cleaner at 115 cmh during the injection of naphthalene led to a substantial reduction in modeled exposure during the 1 h period for both stainless steel and high-pile rug experiments. Specifically, this level of air cleaning resulted in a 61% reduction in exposure for stainless steel and a 73% reduction for the high-pile rug, compared to conditions without air cleaning. Operating an air cleaner at 40 cmh reduced the modeled exposure for the stainless steel experiments by 26% although this reduction in exposure did not occur for the high-pile rug experiments due to variance in the effective emission rates for the high-pile rug 40 cmh experiments. For indoor environments with soft furnishings, such as residential settings, these results indicate that higher-capacity air cleaners are necessary to achieve meaningful reductions in exposure post-pollution events.
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Recommended Citation
Coffland, Casey Douglas, "Improved Method of Evaluating Gas-Phase Air Cleaners Considering Adsorption and Desorption Mechanisms to and from Internal Test Chamber Surfaces" (2026). Dissertations and Theses. Paper 7120.