Large-scale evaluation of microorganism inactivation by bipolar ionization and photocatalytic devices.

The COVID-19 pandemic has raised awareness in the spread of disease via airborne transmission. As a result, there has been increasing interest in technologies that claim to reduce concentrations of airborne pathogens in indoor environments. The efficacy of many of these emerging technologies is not fully understood, and the testing that has been done is often conducted at a small scale and not representative of applied settings. There is currently no standard test method for evaluating air treatment technologies, making it difficult to compare results across studies or technology types. Here, a consistent testing approach in an operational-scale test chamber with a mock recirculating heating, ventilation, and air conditioning (HVAC) system was used to evaluate the efficacy of bipolar ionization and photocatalytic devices against the non-enveloped bacteriophage MS2 in the air and on surfaces. Statistically significant differences between replicate sets of technology tests and control tests (without technologies active) are apparent after 1 h, ranging to a maximum of 0.88 log10 reduction for the bipolar ionization tests and 1.8 log10 reduction for the photocatalytic device tests. It should be noted that ozone concentrations were elevated above background concentrations in the test chamber during the photocatalytic device testing. No significant differences were observed between control and technology tests in terms of the amount of MS2 deposited or inactivated on surfaces during testing. A standardized, large-scale testing approach, with replicate testing and time-matched control conditions, is necessary for contextualizing laboratory efficacy results, translating them to real-world conditions, and for facilitating technology comparisons.

Relative contributions of selected multigeneration products to chamber SOA formed from photooxidation of a range (C10-C17) of n-alkanes under high NO x conditions.

A series of chamber experiments was conducted to investigate the composition of secondary organic aerosol (SOA) following oxidation of a range of parent n-alkanes (C10-C17) in the presence of NO x . The relative contribution of selected species representing first, second, and higher generation products to SOA mass was measured using a high-resolution aerosol mass spectrometer. Gas chromatography was also used for a limited set of amenable species. Relative contributions varied substantially across the range of investigated alkanes reflecting slight changes in SOA composition. The contribution of first-generation cyclic hemiacetal is minimal toward the small end of the investigated range and gradually increase with n-alkane size. The relative contribution of second generation and higher nitrate-containing species, in contrast, decrease with an increased alkane size. A similar trend is observed for relative contribution of organonitrates to SOA. Finally, SOA yield and composition are sensitive to water vapor concentrations. This sensitivity is limited to a narrow range (dry to ~15% RH) with little, if any, impact above 15% suggesting that this impact may be negligible under ambient conditions. The impact of water vapor also appears to decrease with increasing alkane carbon number.

Ultra-Fast Degradation of Chemical Warfare Agents Using MOF-Nanofiber Kebabs.

The threat associated with chemical warfare agents (CWAs) motivates the development of new materials to provide enhanced protection with a reduced burden. Metal-organic frame-works (MOFs) have recently been shown as highly effective catalysts for detoxifying CWAs, but challenges still remain for integrating MOFs into functional filter media and/or protective garments. Herein, we report a series of MOF-nanofiber kebab structures for fast degradation of CWAs. We found TiO2 coatings deposited via atomic layer deposition (ALD) onto polyamide-6 nanofibers enable the formation of conformal Zr-based MOF thin films including UiO-66, UiO-66-NH2 , and UiO-67. Cross-sectional TEM images show that these MOF crystals nucleate and grow directly on and around the nanofibers, with strong attachment to the substrates. These MOF-functionalized nanofibers exhibit excellent reactivity for detoxifying CWAs. The half-lives of a CWA simulant compound and nerve agent soman (GD) are as short as 7.3 min and 2.3 min, respectively. These results therefore provide the earliest report of MOF-nanofiber textile composites capable of ultra-fast degradation of CWAs.

Impact of test methodology on the efficacy of triethylene glycol (Grignard Pure) against bacteriophage MS2.

The COVID-19 pandemic has raised interest in using chemical air treatments as part of a strategy to reduce the risk of disease transmission, but more information is needed to characterize their efficacy at scales translatable to applied settings and to develop standardized test methods for characterizing the performance of these products. Grignard Pure, a triethylene glycol (TEG) active ingredient air treatment, was evaluated using two different test protocols in a large bioaerosol test chamber and observed to inactivate bacteriophage MS2 in air (up to 99.9% at 90 min) and on surfaces (up to 99% at 90 min) at a concentration of approximately 1.2 - 1.5 mg/m3. Introducing bioaerosol into a TEG-charged chamber led to overall greater reductions compared to when TEG was introduced into a bioaerosol-charged chamber, although the differences in efficacy against airborne MS2 were only significant in the first 15 min. Time-matched control conditions (no TEG present) and replicate tests for each condition were essential for characterizing treatment efficacy. These findings suggest that chemical air treatments could be effective in reducing the air and surface concentrations of infectious pathogens in occupied spaces, although standard methods are needed for evaluating their efficacy and comparing results across studies. The potential health impacts of chronic exposure to chemicals should also be considered, but those were not evaluated here.