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The risks to human health posed by airborne pathogens can be mitigated by the use of ultraviolet-C (UV-C) radiation. In general, UV-C-based systems should be applied in a manner that allows effective inactivation of airborne pathogens, while controlling human exposure to below defined limits. Among the methods used to apply UV-C radiation in indoor settings to meet these objectives are UV-C-based air cleaners. These devices can be effective for the control of airborne pathogens, but methods are needed to quantify and validate their performance. To address this need, an experiment-based method and a mathematical model were developed to quantify the effects of UV-C-based air cleaners on the concentration of an aerosolized, viral challenge agent. The method and model were demonstrated to allow quantification of disinfection efficacy and to allow translation of the results from the test environment to the application environment. The primary figure-of-merit from these tests was the clean air delivery rate (CADR), which is commonly used to characterize the disinfection efficacy of these devices. The ability of a validated air cleaner to improve indoor air quality in application settings is simulated based on the measured value of CADR from laboratory tests and the mathematical model. [ABSTRACT FROM AUTHOR]

Far UV-C, informally defined as electromagnetic radiation with wavelengths between 200 and 230 nm, has characteristics that are well-suited to control of airborne pathogens. Specifically, Far UV-C has been shown to be highly effective for inactivation of airborne pathogens; yet this same radiation has minimal potential to cause damage to human skin and eye tissues. Critically, unlike UV-B, Far UV-C radiation does not substantially penetrate the dead cell layer of skin (stratum corneum) and does not reach germinative cells in the basal layer. Similarly, Far UV-C radiation does not substantially penetrate through corneal epithelium of the eye, thereby preventing exposure of germinative cells within the eye. The most common source of Far UV-C radiation is the krypton chloride excimer (KrCl*) lamp, which has a primary emission centered at 222 nm. Ozone production from KrCl* lamps is modest, such that control of indoor ozone from these systems can be accomplished easily using conventional ventilation systems. This set of characteristics offers the potential for Far UV-C devices to be used in occupied spaces, thereby allowing for improved effectiveness for inactivation of airborne pathogens, including those that are responsible for COVID-19. [ABSTRACT FROM AUTHOR]

Transmission of respiratory pathogens occurs primarily in indoor settings, interventions to reduce the risk of their transmission include increases in outdoor air introduction, filtration, and ultraviolet germicidal irradiation (UVGI). However, validating these interventions is challenging, particularly in actual applications. This study introduces an aerosol tracer system utilizing DNA as tracer molecule, aimed at quantitative characterization of the performance of indoor air cleaning systems. Two DNA tracers, designed one to be relatively UV-resistant and another relatively UV-sensitive, were employed to assess air quality changes related to filtration and ventilation and the contributions of UVGI fixtures in various built environments. We conducted controlled UV exposure experiments of DNA-tagged tracers on foil coupons, aerosolization studies in a test chamber, and in a commercial building conference room. The DNA tracer results provided insights at the point of sampling into the effects of complex airflow dynamics. Additionally, a way to scale the DNA tracer results to MS2 bacteriophage is proposed. Four distinct UV devices challenged with MS2 in a chamber test produced equivalent clean airflow rates of 13–147 CFM. Scaled equivalent clean airflow rates in a commercial building setting using the UV-sensitive tracer varied from 47 percent less to 101 percent more than the chamber results, possibly due to differences in airflow patterns, equipment configuration, and other factors. Our findings provide quantitative understanding of the interaction between UV-sensitive aerosols and the built environment, with implications for environmental monitoring, measuring UVGI fixture impact in field settings, and addressing current technologies limitations for assessing UVGI disinfection efficacy. [Display omitted] • UV surface inactivation of synthetic DNA sequences at 222, 254, and 282 nm. • Novel DNA-tagged aerosols sensitive to UV as a surrogate for viral inactivation. • New proposed method allows for UV air disinfection measurement in occupied spaces. • Equivalent clean air delivery rate estimation applying DNA-tagged aerosols. • In Situ evaluation of UV air disinfection differs from expected chamber results. [ABSTRACT FROM AUTHOR]

We use a non-dimensional framework to examine the applicability of photocatalytic oxidation (PCO) to reduce bioaerosol concentration in heating, ventilation, and air conditioning (HVAC) systems. Two non-dimensional parameters: collection efficiency and dimensionless photon flux were used to evaluate the performance of two PCO reactor geometries: 1) honeycomb (HC) and 2) parallel plate (PP) since bioaerosol deposition and photon utilization are prerequisites for effective inactivation in collection based PCO systems. Collection efficiencies of the HC for bioaerosols (0.01–10 μm) were modeled by varying aspect ratios from 25 to 100, air velocities from 0.5 to 2 m/s, and charge numbers from 10 to 10000. The collection efficiencies and the photon fluxes of HC and PP were compared using prior literature studies. The modeling results show that larger bioaerosols (5–10 μm) have a higher collection efficiency than other aerosols for low velocities and longer channels. Larger aspect ratios (channels that are longer for a given diameter) are needed than those found in most commercial HC products, since the effects of gravitational settling and diffusion are inadequate for bioaerosol collection. Furthermore, using ionizers to increase the collection efficiency of PCO systems proved ineffective. The efficiency only increased 2 to 5 times for 0.01–1 μm bioaerosols for charge numbers on the order of 1000. These charge numbers may be impractical to obtain for this size range. PP requires longer channel lengths than HC to achieve the same collection efficiencies. However, the PP configuration has better photon utilization characteristics than HC. [Display omitted] • The potential of photocatalytic oxidation (PCO) in HVAC systems is analyzed. • A framework is proposed to assess honeycomb (HC) & parallel plate (PP) geometries. • Bioaerosol collection & photon utilization are compared for HC & PP geometries. • Removing bioaerosols requires longer channels than commonly used. • PP is better suited for bioaerosol inactivation using PCO in HVAC systems. [ABSTRACT FROM AUTHOR]

A multi-pronged approach to health policy and programs related to open defecation (OD) is proposed via a qualitative study conducted in rural India. A dialogic and dialectic perspective is employed to interpret the key findings from nine focus groups, highlighting the dialectical views toward OD and latrines. Findings indicate that current policy may be too narrow as it does not fully deal with the multiple reasons, including social communication as well as gender, cultural, health and work identity issues, for OD. The results suggest that OD is more complicated than it appears and a multi-pronged, poly-vocal approach to health communication campaigns and policy should be considered. [ABSTRACT FROM AUTHOR]

The presence of gas-phase trichloramine (NCl 3) in indoor swimming pool facilities is associated with adverse health outcomes among swimmers and other pool users, as well as degradation of pool infrastructure. Given their similarities in terms of volatility (i.e., Henry's law constant), the dynamic behaviors of NCl 3 and carbon dioxide (CO 2) in the air above indoor pools were postulated to be similar. Experiments were conducted to characterize and quantify the dynamic behavior of gas-phase NCl 3 and CO 2 in a mechanically ventilated swimming pool facility. The results of these time-course measurements allowed for examination of the effects of background water circulation and swimmer-induced mixing on the dynamics of both compounds in the air space above an indoor swimming pool. Measured gas-phase NCl 3 concentrations exceeded the suggested guideline values of 300 μg/m3 or 500 μg/m3 during periods of heavy use. Measured gas-phase CO 2 concentration followed a similar dynamic pattern as gas-phase NCl 3 ; gas-phase CO 2 concentrations often exceeded 1000 ppm v during swimming meets. Mass balance models for gas-phase NCl 3 and CO 2 were developed to relate the characteristics of the indoor pool environment to their dynamics. The results of these modeling efforts indicated that the similarity of CO 2 transfer behavior to NCl 3 may allow the use of CO 2 , which can be measured with low-cost infrared gas sensors, as a control parameter for NCl 3. Moreover, the models that were developed to describe the dynamic behaviors of these volatile compounds may serve as tools for pool design, optimization of pool operations, and control of their mechanical ventilation systems. [Display omitted] • Swimming promotes the transfer of volatile compounds from water to air. • Gas-phase NCl 3 concentrations in indoor pool facilities often exceed WHO guidance. • CO 2 control measures are likely to yield effective control of NCl 3 in pool facilities. • Models were developed to simulate gas-phase NCl 3 and CO 2 dynamics in indoor pools. • The NCl 3 model can inform control strategies to improve IAQ in indoor pools. [ABSTRACT FROM AUTHOR]

Bench-scale experiments were conducted with municipal wastewater effluent samples to examine the feasibility of combined application of ozone and ultraviolet (UV) radiation for disinfection. Effluent samples displayed rapid initial ozone demand, which promotes ozone transfer but diminishes disinfection efficacy. Ozone doses up to 10 mg/L yielded only trace quantities of residual ozone; despite the fact that initial ozone demand was never exceeded, quantifiable (though variable) inactivation of E. coli was observed, along with modest improvements of UV transmittance. Results from collimated beam experiments demonstrated that compliance with effluent discharge permit limitations could be achieved consistently with a UV254 dose of 12.4 mj/cm² at a pre-ozonation dose of 2 to 3 mg/L. In the absence of pre-ozonation, consistent compliance was observed at a UV dose of 16.5 mj/cm². No evidence of synergism between ozone and UV254 radiation was found in the measured inactivation responses of E. coli. Water Environ. Res., 84, 2017 (2012). [ABSTRACT FROM AUTHOR]

Laboratory experiments were performed to demonstrate an experimental method for measuring the UV dose-response behavior among air-exposed microorganisms, and to quantify the effect of relative humidity on this behavior. These experiments included two nonpathogenic microorganisms as surrogates for airborne microbial pathogens: Bacillus subtilis spores and coliphage MS2. UV dose-response behavior of these microorganisms was measured as a function of relative humidity (RH). Microorganisms were transferred to membrane filters at less than monolayer coverage and were subjected to exposure to UV radiation delivered from a collimated beam to a planar surface in a humidity-controlled environment at two germicidally active wavelengths: 254 nm and 282 nm. Dose-response data for Bacillus subtilis spores and coliphage MS2 exposed to UV radiation were fit to the Phenotypic Persistence and External Shielding (PPES) model. B. subtilis spores showed a modest effect of RH on the UV dose-response behavior, whereas essentially no effect of RH was evident for air-exposed MS2 for their UV dose-response behavior at 254 nm or 282 nm. [ABSTRACT FROM AUTHOR]

Experiments were conducted to elucidate the mechanism of the reaction between free chlorine and urea. In combination with findings of previous investigations, the results of these experiments indicate a process by which urea undergoes multiple N-chlorination steps. The first of these steps results in the formation of N-chlorourea; this step appears to require Cl2 to proceed and is the overall rate-limiting step in the reaction for conditions that correspond to most swimming pools. N-Chlorourea then appears to undergo further chlorine substitution; the fully N-chlorinated urea molecule is hypothesized to undergo hydrolysis and additional chlorination to yield NCl3 as an intermediate. NCl3 is hydrolyzed to yield NH2Cl and NHCl2, with subsequent decay to stable end products, including N2 and NO3-. Conversion of urea-N to nitrate is pH-dependent. The pattern of nitrate yield is believed to be attributable to the fact that when urea serves as the source of reduced-N, entry into the reactions that describe chlorination of ammoniacal nitrogen is through NCl3, whereas when NH3 is the source of reduced-N, entry to these reactions is through NH2Cl. [ABSTRACT FROM AUTHOR]

OBJECTIVES: Recent studies have explored the potential for swimming pool disinfection by-products (DBPs), which are respiratory irritants, to cause asthma in young children. Here we describe the state of the science on methods for understanding children's exposure to DBPs and biologics at swimming pools and associations with new-onset childhood asthma and recommend a research agenda to improve our understanding of this issue. DATA SOURCES: A workshop was held in Leuven, Belgium, 21--23 August 2007, to evaluate the literature and to develop a research agenda to better understand children's exposures in the swimming pool environment and their potential associations with new-onset asthma. Participants, including clinicians, epidemiologists, exposure scientists, pool operations experts, and chemists, reviewed the literature, prepared background summaries, and held extensive discussions on the relevant published studies, knowledge of asthma characterization and exposures at swimming pools, and epidemiologic study designs. SYNTHESIS: Childhood swimming and new-onset childhood asthma have clear implications for public health. If attendance at indoor pools increases risk of childhood asthma, then concerns are warranted and action is necessary. If there is no such relationship, these concerns could unnecessarily deter children from indoor swimming and/or compromise water disinfection. CONCLUSIONS: Current evidence of an association between childhood swimming and new-onset asthma is suggestive but not conclusive. Important data gaps need to be filled, particularly in exposure assessment and characterization of asthma in the very young. Participants recommended that additional evaluations using a multidisciplinary approach are needed to determine whether a clear association exists. [ABSTRACT FROM AUTHOR]