Photolysis-driven indoor air chemistry following cleaning of hospital wards

Emissions from Hydrogen Peroxide Disinfection and Their Interaction with Mask Surfaces

A rise in the disinfection of spaces occurred as a result of the COVID-19 pandemic as well as an increase in people wearing facial coverings. Hydrogen peroxide was among the recommended disinfectants for use against the virus. Previous studies have investigated the emissions of hydrogen peroxide associated with the disinfection of spaces and masks; however, those studies did not focus on the emitted byproducts from these processes. Here, we simulate the disinfection of an indoor space with H2O2 while a person wearing a face mask is present in the space by using an environmental chamber with a thermal manikin wearing a face mask over its breathing zone. We injected hydrogen peroxide to disinfect the space and utilized a chemical ionization mass spectrometer (CIMS) to measure the primary disinfectant (H2O2) and a Vocus proton transfer reaction time-of-flight mass spectrometer (Vocus PTR-ToF-MS) to measure the byproducts from disinfection, comparing concentrations inside the chamber and behind the mask. Concentrations of the primary disinfectant and the byproducts inside the chamber and behind the mask remained elevated above background levels for 2-4 h after disinfection, indicating the possibility of extended exposure, especially when continuing to wear the mask. Overall, our results point toward the time-dependent impact of masks on concentrations of disinfectants and their byproducts and a need for regular mask change following exposure to high concentrations of chemical compounds.

Gas-phase microactuation using kinetically controlled surface states of ultrathin catalytic sheets

Biological systems convert chemical energy into mechanical work by using protein catalysts that assume kinetically controlled conformational states. Synthetic chemomechanical systems using chemical catalysis have been reported, but they are slow, require high temperatures to operate, or indirectly perform work by harnessing reaction products in liquids (e.g., heat or protons). Here, we introduce a bioinspired chemical strategy for gas-phase chemomechanical transduction that sequences the elementary steps of catalytic reactions on ultrathin (<10 nm) platinum sheets to generate surface stresses that directly drive microactuation (bending radii of 700 nm) at ambient conditions (T = 20 °C; Ptotal = 1 atm). When fueled by hydrogen gas and either oxygen or ozone gas, we show how kinetically controlled surface states of the catalyst can be exploited to achieve fast actuation (600 ms/cycle) at 20 °C. We also show that the approach can integrate photochemically controlled reactions and can be used to drive the reconfiguration of microhinges and complex origami- and kirigami-based microstructures.

Hydrogen peroxide emissions from surface cleaning in a single-family residence

High levels of reactive chemicals may be emitted to the indoor air during household surface cleaning, leading to poorer air quality and potential health hazards. Hydrogen peroxide (H₂O₂)-based cleaners have gained popularity in recent years, especially in times of COVID-19. Still, little is known regarding the effects of H₂O₂ cleaning on indoor air composition. In this work we monitored time-resolved H₂O₂ concentrations during a cleaning campaign in an occupied single-family residence using a cavity ring-down spectroscopy (CRDS) H₂O₂ analyzer. During the cleaning experiments, we investigated how unconstrained (i.e., "real-life") surface cleaning with a hydrogen peroxide solution influenced the indoor air quality of the house, and performed controlled experiments to investigate factors that could influence H₂O₂ levels including surface area and surface material, ventilation, and dwell time of the cleaning solution. Mean peak H₂O₂ concentrations observed following all surface cleaning events were 135 ppbv. The factors with the greatest effect on H₂O₂ levels were distance of the cleaned surface from the detector inlet, type of surface cleaned, and solution dwell time.

Measurements of Hydroxyl Radical Concentrations during Indoor Cooking Events: Evidence of an Unmeasured Photolytic Source of Radicals

The hydroxyl radical (OH) is the dominant oxidant in the outdoor environment, controlling the lifetimes of volatile organic compounds (VOCs) and contributing to the growth of secondary organic aerosols. Despite its importance outdoors, there have been relatively few measurements of the OH radical in indoor environments. During the House Observations of Microbial and Environmental Chemistry (HOMEChem) campaign, elevated concentrations of OH were observed near a window during cooking events, in addition to elevated mixing ratios of nitrous acid (HONO), VOCs, and nitrogen oxides (NO_X). Particularly high concentrations were measured during the preparation of a traditional American Thanksgiving dinner, which required the use of a gas stove and oven almost continually for 6 h. A zero-dimensional chemical model underpredicted the measured OH concentrations even during periods when direct sunlight illuminated the area near the window, which increases the rate of OH production by photolysis of HONO. Interferences with measurements of nitrogen dioxide (NO₂) and ozone (O₃) suggest that unmeasured photolytic VOCs were emitted during cooking events. The addition of a VOC that photolyzes to produce peroxy radicals (RO₂), similar to pyruvic acid, into the model results in better agreement with the OH measurements. These results highlight our incomplete understanding of the nature of oxidation in indoor environments.

The influence of photochemistry on outdoor to indoor NO2 in some European museums

This paper reports 1 year of monthly average NO₂ indoor to outdoor (I/O) concentrations measured in 10 European museums, and a simple steady-state box model that explains the annual variation. The measurements were performed in the EU FP5 project Master (EVK-CT-2002-00093). The work provides extensive documentation of the annual variation of NO₂ I/O concentration ratios, with ratios above unity in the summer, in situations with no indoor emissions of NO₂ . The modelling included the most relevant production and removal processes of NO₂ and showed that the outdoor photolysis was the probable main explanation of the annual trends in the NO₂ I/O concentration ratios.

Indoor Air Quality in Healthcare Units—A Systematic Literature Review Focusing Recent Research

The adequate assessment and management of indoor air quality in healthcare facilities is of utmost importance for patient safety and occupational health purposes. This study aims to identify the recent trends of research on the topic through a systematic literature review following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) methodology. A total of 171 articles published in the period 2015–2020 were selected and analyzed. Results show that there is a worldwide growing research interest in this subject, dispersed in a wide variety of scientific journals. A textometric analysis using the IRaMuTeQ software revealed four clusters of topics in the sampled articles: physicochemical pollutants, design and management of infrastructures, environmental control measures, and microbiological contamination. The studies focus mainly on hospital facilities, but there is also research interest in primary care centers and dental clinics. The majority of the analyzed articles (85%) report experimental data, with the most frequently measured parameters being related to environmental quality (temperature and relative humidity), microbiological load, CO2 and particulate matter. Non-compliance with the WHO guidelines for indoor air quality is frequently reported. This study provides an overview of the recent literature on this topic, identifying promising lines of research to improve indoor air quality in healthcare facilities.

Spatiotemporal characterization of irradiance and photolysis rate constants of indoor gas-phase species in the UTest house during HOMEChem

We made intensive measurements of wavelength-resolved spectral irradiance in a test house during the HOMEChem campaign and report diurnal profiles and two-dimensional spatial distribution of photolysis rate constants (J) of several important indoor photolabile gases. Results show that sunlight entering through windows, which was the dominant source of ultraviolet (UV) light in this house, led to clear diurnal cycles, and large time- and location-dependent variations in local gas-phase photochemical activity. Local J values of several key indoor gases under direct solar illumination were 1.8-7.4 times larger-and more strongly dependent on time, solar zenith angle, and incident angle of sunlight relative to the window-than under diffuse sunlight. Photolysis rate constants were highly spatially heterogeneous and fast photochemical reactions in the gas phase were generally confined to within tens of cm of the region that were directly sunlit. Opening windows increased UV photon fluxes by 3 times and increased predicted local hydroxyl radical (OH) concentrations in the sunlit region by 4.5 times to 3.2 × 10⁷  molec cm^-3 due to higher J values and increased contribution from O₃ photolysis. These results can be used to improve the treatment of photochemistry in indoor chemistry models and are a valuable resource for future studies that use the publicly available HOMEChem measurements.

Factors affecting wavelength-resolved ultraviolet irradiance indoors and their impacts on indoor photochemistry

We measured wavelength-resolved ultraviolet (UV) irradiance in multiple indoor environments and quantified the effects of variables such as light source, solar angles, cloud cover, window type, and electric light color temperature on indoor photon fluxes. The majority of the 77 windows and window samples investigated completely attenuated sunlight at wavelengths shorter than 320 nm; despite variations among individual windows leading to differences in indoor HONO photolysis rate constants (J_HONO ) and local hydroxyl radical (OH) concentrations of up to a factor of 50, wavelength-resolved transmittance was similar between windows in residential and non-residential buildings. We report mathematical relationships that predict indoor solar UV irradiance as a function of solar zenith angle, incident angle of sunlight on windows, and distance from windows and surfaces for direct and diffuse sunlight. Using these relationships, we predict elevated indoor steady-state OH concentrations (0.80-7.4 × 10⁶ molec cm^-3 ) under illumination by direct and diffuse sunlight and fluorescent tubes near windows or light sources. However, elevated OH concentrations at 1 m from the source are only predicted under direct sunlight. We predict that reflections from indoor surfaces will have minor contributions to room-averaged indoor UV irradiance. These results may improve parameterization of indoor chemistry models.

Systematic review on use, cost and clinical efficacy of automated decontamination devices

BACKGROUND

More evidence is emerging on the role of surface decontamination for reducing hospital-acquired infection (HAI). Timely and adequate removal of environmental pathogens leads to measurable clinical benefit in both routine and outbreak situations.

OBJECTIVES

This systematic review aimed to evaluate published studies describing the effect of automated technologies delivering hydrogen peroxide (H202) or ultra-violet (UV) light on HAI rates.

METHODS

A systematic review was performed using relevant search terms. Databases were scanned from January 2005 to March 2020 for studies reporting clinical outcome after use of automated devices on healthcare surfaces. Information collected included device type, overall findings; hospital and ward data; study location, length and size; antimicrobial consumption; domestic monitoring; and infection control interventions. Study sponsorship and duplicate publications were also noted.

RESULTS

While there are clear benefits from non-touch devices in vitro, we found insufficient objective assessment of patient outcome due to the before-and-after nature of 36 of 43 (84%) studies. Of 43 studies, 20 (47%) used hydrogen peroxide (14 for outbreaks) and 23 (53%) used UV technology (none for outbreaks). The most popular pathogen targeted, either alone or in combination with others, was Clostridium difficile (27 of 43 studies: 63%), followed by methicillin-resistant Staphylococcus aureus (MRSA) (16 of 43: 37%). Many owed funding and/or personnel to industry sponsorship (28 of 43: 65%) and most were confounded by concurrent infection control, antimicrobial stewardship and/or cleaning audit initiatives. Few contained data on device costs and rarely on comparable costs (1 of 43: 2%). There were expected relationships between the country hosting the study and location of device companies. None mentioned the potential for environmental damage, including effects on microbial survivors.

CONCLUSION

There were mixed results for patient benefit from this review of automated devices using H202 or UV for surface decontamination. Most non-outbreak studies lacked an appropriate control group and were potentially compromised by industry sponsorship. Concern over HAI encourages delivery of powerful disinfectants for eliminating pathogens without appreciating toxicity or cost benefit. Routine use of these devices requires justification from standardized and controlled studies to understand how best to manage contaminated healthcare environments.

Hydrogen Peroxide Emission and Fate Indoors during Non-bleach Cleaning: A Chamber and Modeling Study

Activities such as household cleaning can greatly alter the composition of air in indoor environments. We continuously monitored hydrogen peroxide (H₂O₂) from household non-bleach surface cleaning in a chamber designed to simulate a residential room. Mixing ratios of up to 610 ppbv gaseous H₂O₂ were observed following cleaning, orders of magnitude higher than background levels (sub-ppbv). Gaseous H₂O₂ levels decreased rapidly and irreversibly, with removal rate constants (k_H2O2) 17-73 times larger than air change rate (ACR). Increasing the surface-area-to-volume ratio within the room caused peak H₂O₂ mixing ratios to decrease and k_H2O2 to increase, suggesting that surface uptake dominated H₂O₂ loss. Volatile organic compound (VOC) levels increased rapidly after cleaning and then decreased with removal rate constants 1.2-7.2 times larger than ACR, indicating loss due to surface partitioning and/or chemical reactions. We predicted photochemical radical production rates and steady-state concentrations in the simulated room using a detailed chemical model for indoor air (the INDCM). Model results suggest that, following cleaning, H₂O₂ photolysis increased OH concentrations by 10-40% to 9.7 × 10⁵ molec cm^-3 and hydroperoxy radical (HO₂) concentrations by 50-70% to 2.3 × 10⁷ molec cm^-3 depending on the cleaning method and lighting conditions.