Air Recirculation Research Articles

(503) The Impact of HEPA/Ultraviolet air recirculation system (HUAIRS) During Penile Prosthesis Surgery

Abstract Introduction Airborne bacteria are a major source of wound contamination during penile prosthesis surgery. 80% of bacteria found in the wound after surgery comes from the air. Crystalline ultraviolet C (C-UVC) filter units were designed to disinfect and recirculate the air in the operating room (OR). Objective We assess the particle-reducing capacity of C-UVC units in a highly controlled operating room setting in the office and surgery center during penile prosthesis surgery. Methods A particle counter was deployed in a positive-pressure operating room and a standard office HVAC system to measure total and viable particle counts (TPC). A HEPA/Ultraviolet air recirculation system (HUAIRS) was purchased and placed into the ORs in both locations. Weekly particle count experiments were performed for 6 months in both office OR and surgery center OR settings. A C-UVC unit was kept 4 meters from the door in both settings and the particle counter was used near the operative field. Results After 6 months of weekly office-based procedure collection of data using a particle counter an 83.4% particle reduction was seen at the 5 micron level. Initially, reads were 14,143 particles and after implementation of the HUAIRS, a total particle count was 2,299 during office penile prosthesis. In the OR at the surgery center, the same weekly data collection was employed. The initial 5 micron particle count dropped 81.74% from 6,143 particles to 1,122 once the HUAIRS system was employed. Conclusions C-UVC units have shown to be capable of significantly reducing TPC in the office and operating room setting. Reducing airborne particles using C-UVC units may reduce infection rates following penile prosthesis surgery. Disclosure Any of the authors act as a consultant, employee or shareholder of an industry for: Coloplast.

A time-varying state-space model for real-time temperature predictions in rack-based cooling data centers

Fast-growing data centers (DCs) require efficient cooling systems (such as rack-based cooling architectures) and control strategies to reduce operating costs and guarantee desired indoor conditions. Thus, this study proposed a novel real-time temperature prediction model for rack-based cooling DCs, in order to facilitate advanced control regarding cooling management and workload assignment. Specifically, a data-driven technology was introduced to estimate time-invariant model parameters, in order to avoid the time-consuming physics-based parameters extracting process. The mass conservation relationships were employed to update time-varying flow parameters in real-time to capture the nonlinear behaviors in DCs. Moreover, the proposed control-oriented thermal modeling method can model hot air recirculation and cold air bypass occurring simultaneously for the first time. The performance of the developed time-varying state-space model was validated by CFD simulation data. Additionally, the timeliness of modeling and temperature prediction was also investigated. The results show that the developed model achieves sufficient accuracy with a mean absolute error (MAE) equal to 0.28 °C, even for long prediction horizons and dynamic IT workloads. Also, the developed model has outstanding timeliness for advanced control techniques, in terms of less than 30 min for parameter identification and less than 10 s for temperature prediction.

Numerical simulation of turbulent natural convection heat transfer in an MW-class offshore wind turbine nacelle based on a multi-feature acquisition meshing technique

In order to improve the computational accuracy of numerical simulations of complex thermal environments in MW-class offshore wind turbine nacelles, this paper improves the numerical simulation method for 10 MW offshore wind turbine nacelles. Firstly, the model of the wind turbine generator system (WTGS) inside the nacelle is designed and the model is simplified. Secondly, a multi-featured acquisition meshing is performed for the turbulent thermal behavior in the nacelle, using a combination of mesh geometry parameters, mesh accuracy parameters, mesh irrelevance parameters and detection verification parameters to construct a structural mesh topology. The modified SST k-ω turbulence model is used to solve the momentum and energy equations of the nacelle model. The complex physical phenomena of air recirculation, boundary layer separation and thermal stratification in the nacelle are verified based on the calculated results and compared with the experimental data, which are in good agreement with the experimental results. This paper has certain application value and guidance significance in the field of engineering such as the design of offshore wind turbine nacelle structure and cooling system design.

Concentrations of volatile organic compounds in vehicular cabin air – Implications to commuter exposure

In this study, 117 volatile organic compounds (VOCs) were identified and quantified inside passenger cars and buses operating city and intercity routes. The paper presents data for 90 compounds with frequency of detection equal or greater than 50% that belong to various chemical classes. Total VOC concentration (TVOCs) was dominated by alkanes followed by organic acids, alkenes, aromatic hydrocarbons, ketones, aldehydes, sulfides, amines, and phenols, mercaptans, thiophenes. VOCs concentrations were compared between different vehicle types (passenger cars - city buses - intercity buses), fuel type (gasoline - diesel - liquefied petroleum gas (LPG)), and ventilation type (air condition - air recirculation). TVOCs, alkanes, organic acids and sulfides followed the order: diesel cars > LPG cars > gasoline cars. On the contrary, for mercaptans, aromatics, aldehydes, ketones, and phenols the order was: LPG cars > diesel cars > gasoline cars. Excepting ketones that were found to be higher in LPG cars with air recirculation mode, most compounds were higher with exterior air ventilation in both, gasoline cars and diesel buses. Odor pollution, expressed by the odor activity value (OAV) of VOCs, was highest in LPG cars and minimum in gasoline cars. In all vehicle types, mercaptans and aldehydes were the major contributors to odor pollution of the cabin air with lower contributions from organic acids. The total Hazard Quotient (THQ) was less than 1 for bus and car drivers and passengers indicating that adverse health effects are not likely to occur. Cancer risk from the three VOCs following the order naphthalene > benzene > ethylbenzene. For the three VOCs the total carcinogenic risk was within the safe range. The results of this study expand our knowledge of in-vehicle air quality under real commuting conditions and give an insight into the commuters’ exposure levels during their normal travel journey.

An environmental and economic sustainability assessment of coffee production in the UK

With around two billion cups consumed daily worldwide, the coffee industry faces pressures to improve its sustainability. Focusing on the UK as the fifth largest coffee consumer in Europe, this paper presents for the first time a life cycle environmental and economic sustainability assessment of coffee production at the product and sectoral levels. Both gate-to-gate and cradle-to-gate system boundaries are considered to identify opportunities for improvements in the manufacturing process and along the supply chain. Process design and simulation are combined with life cycle assessment and life cycle costing to evaluate the sustainability of the production of ground and instant coffee roasted to different levels. Based on the functional unit of 1 tonne of coffee produced, instant coffee has higher impacts and costs than ground coffee for both system boundaries because it requires double the amount of green coffee beans and 7–11 times more energy. For gate-to-gate, roasting and packaging are the main contributors to the impacts and costs; for cradle-to-gate, cultivation of coffee beans and packaging are the hotspots. Light roasts generally have lower impacts and costs due to lower material losses and energy requirements. At the sectoral level, the coffee industry emits 863–894 kt CO2 eq. annually, contributing 1.3% to the GHG emissions from the UK food and drinks sector. Key opportunities for improvements include switching to lighter roast and pouch packaging, as well as using air recirculation roasters and silverskin as fuel. These results will be of interest to the coffee industry, policy makers and consumers.

CFD modelling of infection control in indoor environments: A focus on room-level air recirculation systems

The emergence of viral variants has driven a continuous pandemic with a higher possibility of airborne transmission and a larger scale of infective cases, posing greater demands on indoor risk control. However, the role of room-level air recirculation systems (RRSs) in infection control remains unclear due to insufficient detailed research. There are also fewer analyses of the filtering rating of recirculation filters from the perspective of multi-scale particle size. Thus, a simulation procedure to assess the performance of RRSs on infection control that accounts the transient recirculation of real virus-laden particles in multi-scale sizes was proposed, and focusing on recirculation filter strategies to balance the risk limitation and energy cost. A poorly ventilated winter classroom was selected as a typical environment equipped with RRSs to operate this procedure. Different RRS strategies (i.e., wall-mounted air conditioners (WMAC), floor-standing air conditioners (FSAC) and 4-way cassette air conditioners (WCAC)) were compared. The results show the important contribution of recirculated particles to accumulating the overall infection risk of susceptible occupants towards a high basic reproduction number (Ro > 1). Then, there is a strong correlation of the spatial distributions between high-risk zones and large vortexes at the breathing height of susceptible occupants. Considering rating suitability and filtration effectiveness, the optimization of recirculation filters on energy and cost can be suggested with comparable benefits of infection control.

The air exchange rate measuring method by the concentration of carbon dioxide in the vehicle cabin air

BACKGROUND: Vehicle passengers may be exposed to high concentrations of hazardous substances, especially in heavy traffic and traffic jams. The air exchange rate is an important factor in assessment of the level of pollutant substances exposure on the people inside the vehicle.
 AIMS: Development of the air exchange rate measuring method, based on carbon dioxide concentration build-up in the vehicle cabin air.
 MATERIALS AND METHODS: The presented method makes possible to determine the air exchange rate in a stationary vehicle or vehicle, moving with constant velocity. The set of experiments was carried out, in which the air exchange rate was determined in a stationary vehicle and in a moving vehicle at velocities of 30, 60 and 90 km/h. For each velocity, the air exchange rate was determined for three air conditioning system modes, such as intake air supply, recirculation mode and air conditioning system off.
 RESULTS: According to the results of measurements, the air exchange rate varied from 0.42 h-1 to 76.17 h-1.
 CONCLUSIONS: The study results corresponds to the results, obtained earlier by other authors, using alternative methods, and may be used for development of regulatory requirements to control the pollutant substances exposure on the people inside vehicle cabins and for the people healthcare strategy formation.

The Concept of Non-Residential Premises: Public Law Aspect

The paper deals with the concept of premises used by public branches of law from the point of view of urban planning law. The study is original in that that in literature premises are studied primarily considering the possibility to act as the subject of civil law transactions. This paper reveals the meaning invested by the legislator in the concept of premises from the point of view of administrative, urban planning, criminal legislation, norms on safety of buildings and structures, sanitary norms and rules. Can there be premises as part of non-permanent structures? How does this relate to the real estate regime? Can there be one-room premises? It depends, for example, whether a trade pavilion needs to be equipped with a fire alarm, whether it is possible to smoke on the summer veranda of a public catering facility, whether it is necessary to equip the pavilion with air recirculation systems, and much more. How to understand what is in front of us: a separate premises or part of other premises? The possibility of cadastral registration and the technical equipment of the premises depend on this. Can the premises be non-isolated, but passable? This issue has long been faced by the practice of law enforcement in terms of cadastral registration of non-residential premises. The author considers what role the purpose of the premises has: firstly, the possibility of independent use, and secondly, the presence of a functional purpose. So, as an illustration, the question is being investigated, what will happen if you place a nightclub in a warehouse, and a medical facility in a former shop? The paper also compares the legal regime of premises as an object of civil law with the legal regime of premises as an object of public law. The general legal features of non-residential premises, characteristic of many branches of public law, are revealed.

Optimized cabinet parameters for drying lithium-ion batteries based on coupled fluid–thermal field analysis

Hot-airflow desiccation is a commonly applied technique for drying lithium-ion batteries. However, most drying cabinet designs currently suffer from poor efficiency because they evacuate steam by ejecting the hot air in the cabinet to the open air continuously. This can be addressed by closing and opening the cabinet periodically, where the temperature of the heating zone is increased as quickly as possible through internal air recirculation in the closed position, and the steam is ejected with the hot air only during the open period. Nonetheless, drying cabinet designs of this nature have been rarely subjected to numerical analysis based on computational fluid dynamics and heat transfer, and the design factors enhancing the rate of temperature increase during the closed period remain poorly understood. The present work addresses these issues by outlining a detailed numerical approach for simulating the airflow temperature of a drying cabinet during internal air recirculation in its closed position, and the characteristics of the airflow and the temperature distribution in the dryer are evaluated via transient fluid–thermal coupling analysis. The results of the numerical investigation indicate that the heating efficiency is substantially influenced by the inlet airflow velocity, the distance between the trays holding the batteries, and the size of the free space between the front door and the trays. The results demonstrate that the developed model provides a useful means of evaluating and optimizing the heating efficiency of these types of drying cabinets.

Facility- and ward-level factors associated with SARS-CoV-2 outbreaks among residents in long-term care facilities: A retrospective cohort study

Long-term care facilities (LTCFs) have been disproportionately impacted by COVID-19. Yet, the reasons why certain LTCFs are affected more by outbreaks are poorly understood. This study aimed to identify the facility- and ward-level factors associated with SARS-CoV-2 outbreaks among LTCF residents. We conducted a retrospective cohort study of multiple Dutch LTCFs (N=60; with 298 wards providing care for ∼5600 residents) from September 2020 to June 2021. A dataset was constructed linking SARS-CoV-2 cases among LTCF residents to facility- and ward-level factors. Multilevel logistic regression analyses examined the associations between these factors and the likelihood of a SARS-CoV-2 outbreak among residents. During periods of the Classic variant, the mechanical recirculation of air was associated with significantly increased odds of a SARS-CoV-2 outbreak. During periods of the Alpha variant, the factors associated with significantly increased odds included large ward size (≥21 beds), wards providing psychogeriatric care, fewer restrictions on staff movement between wards and facilities, and a greater number of cases among staff (>10 cases). Policy and protocols on reducing resident density, staff movement, and mechanical recirculation of air in buildings are recommended to enhance outbreak preparedness in LTCFs. The implementation of low-threshold preventive measures among psychogeriatric residents is important because they appear as a particularly vulnerable group.

Mitigation of breathing contaminants: Exhaust location optimization for indoor space with impinging jet ventilation supply

Densely occupied spaces (e.g., classrooms) are generally over-crowded and pose a high risk of cross-infection during the pandemic of COVID-19. Among various ventilation systems, impinging jet ventilation (IJV) system might be promising for such spaces. However, the exhaust location of the IJV system used for densely occupied classrooms is unclear. This study aims to investigate the effects of exhaust location on the removal of exhaled contaminants in a classroom (15 × 7 × 5 m3) occupied by 50 students. Exhaled contaminants are modeled by a tracer gas released at the top of each manikin. The reference case has three exhausts evenly distributed in the ceiling. The results indicate that: a) a recirculation airflow entraining exhaled contaminants exists above the occupied zone; b) this recirculation air flow entrains contaminants and accumulates them at the upper part of the room near the diffuser; c) locating merely one exhaust on the same side of the supply diffuser leads to the best indoor air quality, i.e., it reduces the mean age of air from 278 s to 243 s, the mass fraction of CO2 from 753 ppm to 726 ppm, and the concentration of tracer gas from 305 ppm to 266 ppm; d) this layout still performs the best when the supply velocity drops to 0.5 m/s. It is worth noting that the proposed layout has fewer exhausts than the reference case but performs better. These results conclude that the exhaust for large spaces is not evenly distributed but depends on the indoor airflow pattern: the key is locating the exhaust near the region with high contaminant concentration. Factors determining the recirculation airflow are suggested to be further studied.

CFD Simulation of Temperature and Air Flow in a Natural Convection Solar Tunnel Dryer with a Bare Flat-Plate Chimney

Computational Fluid Dynamics simulation of a natural convection solar tunnel dryer with a bare flat-plate chimney is presented. The chimney’s function is to create airflow in the dryer through the buoyancy effect by re-heating the air coming from the drying unit and is therefore a major factor in the drying rate. CFD simulation was therefore employed to study the temperature and airflow in the dryer and determine the areas that could be improved upon. The design of the solar tunnel dryer geometry used in this simulation was done in SOLIDWORKS 2016 whereas the simulation of temperature distribution of airflow inside the dryer was performed using SOLIDWORKS 2016 flow simulation program in a steady-state regime. The boundary conditions were set using the obtained experimental data. The simulation results showed that the chimney losses heat, that there is air recirculation in the collector, that the airflow experiences some pressure loss as it moves from the drying chamber to the chimney, and that there is some reduction of the velocity in some parts of the dryer. The simulated and experimental collector efficiencies were found to be 33.09 and 37.63%, respectively, giving a mean relative deviation of collector temperature of 5.1%. To improve the performance of the dryer, insulating and glazing of the chimney is suggested as well as using a curved joint between the chimney and the drying chamber.

Global performance analysis of a solar-driven indoor CO2/H2O capture system for air quality enhancement and cooling energy saving

A human-eco-friendly building requires high indoor air quality (IAQ) and low carbon emissions. Existing natural/mechanical ventilation methods rely on frequent exchange with fresh ambient air to remove excess respiratory CO2 for high IAQ. However, in tropical or subtropical regions, the introduced ambient air features higher humidity and temperature over indoor air, which inevitably increases the energy burden of air conditioning (AC) accompanied with severe CO2 emission. To circumvent this paradox, this study developed a dynamic solar-driven indoor CO2/H2O capture system with selective air recirculation. Rather than simply introducing ambient air to reduce indoor CO2 concentration, this scheme actively captures CO2/H2O and selectively returns post-captured air with sub-ambient temperature, relative humidity and CO2 concentration, thus sustaining high IAQ with reduced AC load and CO2 emission. The system’s feasibility and stability are demonstrated through a 20-city global study and a 10-variable sensitivity analysis. Compared to traditional methods, this new system could save up to 64 % of cooling energy while maintaining the indoor CO2 concentration below 1000 ppm and relative humidity within 25 %-55 %. The energy-saving potential of the proposed system increases in regions with larger AC demands, as evidenced by Dakar achieving the highest energy-saving potential and thus decreasing CO2 emission. This system could further reduce CO2 emission by direct capture and storage, whose amount is positively correlated to the amount of solar irradiance in cities. Furthermore, the system demonstrates robustness under off-design conditions and is flexible to be scaled up/down. Overall, this study provides effective-green ventilation strategies and paves the way for developing human-eco-friendly buildings.

Numerical investigation on particle removal and energy consumption of supplied and recirculated ventilation for industrial workshop

In the weld back-cleaning process, many high-concentration pollutants are produced, which can lead to health problems after prolonged exposure. In this study, a novel recirculating stratified ventilation system is proposed that combines supply and recirculating ventilation. It reduces indoor particulate concentration and exhausts air volume based on the air gouging process in a casting workshop. The influences of the supplied and recirculated air velocities on the particle removal efficiency and energy consumption were investigated and compared with those of a traditional exhaust system. The computational fluid dynamics-discrete phase model coupling method was adopted. First, the feasibility of the model was verified using previously published experimental data. The concentration of the unsteady particles was then simulated with different supplied and recirculated air velocities in the ventilation system. The particles were dispersed owing to the influence of the heat-source temperature. With an increasing supplied air velocity and constant recirculated air velocity, the average particle concentration was decreased. The results show that the particle removal efficiency can be improved by approximately 100%, and 90% of the energy can be saved to achieve the same removal efficiency as a traditional ceiling exhaust system.

High‐Speed and Low‐Energy Actuation for Pneumatic Soft Robots with Internal Exhaust Air Recirculation

Multichamber soft pneumatic actuators (m‐SPAs) are widely used in soft robotic systems to achieve versatile grasping and locomotion. However, existing m‐SPAs have slow actuation speed and are either limited by a finite air supply or require energy‐consuming hardware to continuously supply compressed air. Herein, these shortcomings by introducing an internal exhaust air recirculation (IEAR) mechanism for high‐speed and low‐energy actuation of m‐SPAs are addressed. This mechanism recirculates the exhaust compressed air and recovers the energy by harnessing the rhythmic actuation of multiple chambers. A theoretical model to guide the analysis of the IEAR mechanism, which agrees well with the experimental results, is developed. Comparative experimental results of several sets of m‐SPAs show that the IEAR mechanism significantly improves the actuation speed by more than 82.4% and reduces the energy consumption per cycle by more than 47.7% under typical conditions. The promising applications of the IEAR mechanism in various pneumatic soft machines and robots such as a robotic fin, fabric‐based finger, and quadruped robot are further demonstrated. An interactive preprint version of the article can be found at: https://doi.org/10.22541/au.166428178.80668101/v1.

Experimental study on the solar drying of Rhubarb (Rheum ribes L.) with parabolic trough collector assisted with air recycling system, nanofluid and energy storage system

In the present work the thermo-economical calculation of dried Rhubarb slices in a dryer integrated parabolic trough solar collector assisted with air recycling mechanism and Al2O3 3.75 % as working fluid was investigated. Using air recycling system at the inlet section of the dryer and phase change material increases the thermal performance of the dryer and reduces the drying time of Rhubarb slices. Two adjustable valves at inlet and outlet part of the dryer and the amount of return flow was considered to control the airflow. In this study, the effect of air recycling flow at the inlet part of indirect chamber at four levels of 0–25–50–70 % was considered and the amount of specific energy consumption, total drying efficiency and solar collector efficiency was analyzed. To determine the performance of the system, Rhubarb slices in 5 mm as thin layer were used. In addition, CFD modeling was applied to predict temperature changes inside the dryer. The drying time decreased with increasing the recirculation of air, considerably. The overall drying efficiency increased about 2.32–8.21 %, and specific energy consumption decreased at least 1.91 % by applying air recycling mechanism, nanofluid and PCM in dryer related to the system without them. The exergy efficiency for drying of Rhubarb slices varies between 35.4 and 61.3 %. The optimization of the system was carried out based on the conditions and the result revealed this leads to decrease the payback time.

Vehicle cabin air quality: influence of air recirculation on energy use, particles, and CO2

In this study, simulations were performed to investigate the influence of different vehicle climate ventilation strategies, mainly the air recirculation (REC) degree, on the cabin air quality and climate system power. The focus of air quality is on the cabin particle concentrations including PM2.5 (particles of aerodynamic diameter less than 2.5 μm), UFP (ultrafine particles of aerodynamic diameter less than 100 nm), and cabin CO2 concentration. Three outside climates (cold, intermediate, and warm) and three outside particle concentrations are studied. The studied vehicle originally shows possibilities to meet WHO PM2.5 guideline of 15 μg/m3 with a new filter. The aged filter have reduced performance, especially when outside concentration is high. Increased REC shows advantages in all the three climates in reducing particles and climate power for the studied vehicle. Application of 70% REC (70% of ventilation air is recirculated air) on average lowers PM2.5 by 55% and 39% for a new and aged filter, respectively. 70% REC with a new filter reduces cabin PM2.5 below guideline of 15 μg/m3 in all conditions. The reduction of UFP counts results are generally similar to that of PM2.5. Increased REC also lessens the average climate system power by up to 27% on average. When REC is increased, the cabin CO2 concentration arises accordingly, and the magnitude is relevant to the passengers. In all studied conditions with 1 passenger, 70% REC does not increase CO2 above the common guideline of 1000 ppm. 70% REC is not recommended with more than 1 passengers in cold and intermediate climate and 2 passengers in warm climate. Besides, to avoid the potential windscreen fog risk in cold climate, REC should be avoided when passengers are more than 3. Except for constant REC values, a sample study investigates a dynamic control of the REC. It shows the possibility of continuously optimizing REC to reduce the climate power and particles, while maintaining the CO2 concentration below 1000 ppm. In warm climate with 1 passenger boarded, the average optimized REC is 90%, which in comparison with base case lead to 44% PM2.5 reduction and 12% climate power reduction.

Performance of a thermoelectric heat pump with recirculation and regenerative heat recovery

In this paper, the thermoelectric heat pump performance is enhanced by air recirculation and regenerative energy recovery. Compared to conventional vapor-compressed heat pumps, TEHP is more stable, safer, and flexible in arrangement, but is relatively less efficient. Therefore, the use of air recirculation combined with regenerative heat recovery is dedicated to increasing the efficiency of the heat pump and recovering some of the energy, thus reducing energy consumption. Experimental results show that the COP of the air recirculation TEHP is as high as about 3.7. At 1 m/s air velocity, the COP with recirculation is 51–73% higher than without recirculation. In the system experiments for heat exchanger test applications, the percentage of regenerative heat recovery was up to 12%. The combination of regenerative heat recovery and air recirculation further improved the energy efficiency of the heat exchanger test system to a maximum energy efficiency ratio of 2.85. The energy-saving measures of TEHP with recirculation and regenerative heat recovery resulted in better energy savings than the conventional heat exchanger test device with resistance heating. It is of great reference significance in fields of thermoelectric technology applications.

Innovative photoelectrocatalytic water remediation system for ammonia abatement

Ammonia, produced by human and animal activities, contributes to water and soil pollution because it is toxic for aquatic flora and fauna, and responsible for eutrophication. In this work, the photoelectrocatalytic (PEC) oxidation of ammonia is investigated employing a stainless-steel PEC reactor, consisting of a central UV Hg-vapor lamp surrounded by a metallic Ti mesh coated with a photoactive TiO2 film, directly grown by Plasma Electrolytic Oxidation (PEO). The so prepared TiO2 film is characterized by XRD, SEM, UV–vis DRS and IPCE. The PEC reactor operates at 4 V potential drop between the TiO2 coated mesh (photoanode) and the body of the reactor (cathode). The effect of the operating parameters (recirculation flowrate and air bubbling) and type of electrolyte solution (KCl or K2SO4) on the PEC performance are investigated in terms of ammonia conversion and selectivity to nitrite, nitrate and molecular nitrogen. Full ammonia conversion (XNH3) with a selectivity to molecular nitrogen up to 67 % are attained after 12 h in 5 mM KCl electrolyte solution. Nitrite is produced within the first 6 h irradiation and then fully converted into nitrate. By contrast, only a slight XNH3 (ca. 10 %) is observed in K2SO4 electrolyte solution. These results suggest that chlorine has a crucial role in the ammonia PEC oxidation process: photo-generated holes on the photoanode surface can oxidize Cl− to Cl• (electro-induced process), which is a reactive radical able to oxidase ammonia.

Studying the efficiency of air cleaners at removing various indoor air impurities in classrooms and the relation to pupils’ symptoms

The existing knowledge on the effect of air cleaners in reducing different indoor impurities and health symptoms in real-life applications is still insufficient. PUHHO study aimed to fill this knowledge gap with a blinded intervention study in 18 primary school classrooms. The study was conducted during 8 weeks with 2 weeks without air cleaner, 3 weeks with air cleaner in full operation (filtration) with moderate airflow (200 - 400 m3/h) and 3 weeks sham operation (air cleaner blowing air without filtration). The latter two interventions were conducted in a blinded and mixed setup. Small, but statistically non-significant reductions in particulate matter levels (PM2.5; particulate matter with diameter less than 2.5 µm and PM10; diameter of particles less than 10 µm) were observed when comparing air cleaner filtration to air recirculation alone (sham operation). The use of air cleaners had no significant effect on the level of total volatile organic compounds (TVOC). Air cleaners did not have significant effect on the microbial levels or on the microbiome of the classrooms. Filtration by air cleaners was found to statistically significantly reduce upper (4.0%) and lower airway (2.5%) and other (4.0%) symptoms, but a nearly equivalent effect was observed with air recirculation alone.