A novel slip-velocity model to simulate the filtration performance of nanofiber media.

Aerosols such as PM2.5 and PM10 can have an immense impact on human health. With the outbreak of SARS-CoV-2, it is urgent to filter aerosols by media filtration technology. Electrospun nanofibers are a promising material for achieving high efficiency, low resistance, light weight, and environmentally friendly air filtration. But research on filtration theory and computer simulation of nanofiber media is still lacking. The traditional method involving computational fluid dynamics (CFD) and Maxwell's first-order slip boundary overestimates the slip velocity on the fiber surface. In this study, a new modified slip boundary was proposed, which introduced a slip velocity coefficient on the basis of the no-slip boundary to address the slip wall. Our simulation results were compared with the experimental pressure drop and particle capture efficiency of real polyacrylonitrile (PAN) nanofiber media. The computational accuracy on pressure drop of the modified slip boundary improved 24.6% and 11.2% compared with that of the no-slip boundary and Maxwell's first-order slip boundary, respectively. It was found that the particle capture efficiency near the most-penetrating particle size (MPPS) was significantly increased when slip effect occurred. This may be explained by the slip velocity on the fiber surface, which would make particles more accessible to the fiber surface and captured by interception.

Baseline physical activity and the risk of severe illness and mortality from COVID-19: a dose–response Meta-analysis

To provide a scientific basis for improved exercise-based immunity, a meta-analysis was used to explore the dose–response relationship between physical activity (PA) and the risk of severe illness and mortality related to COVID-19 (coronavirus disease 2019). To this end, we searched PubMed, Web of Science databases from January 2020 through April 2022. 14 observational studies met the criteria for inclusion in the meta-analysis, including 2840 cases of severe illness and death from COVID-19. Categorical dose–relationship analysis showed that the risks of severe illness and mortality from COVID-19 were, respectively, 46% (risk ratio (RR): 0.54;confidence intervals (CIs): 0.41-0.68) and 59% (RR = 0.41;95%CI: 0.23-0.58) lower for the highest dose of PA compared with the lowest dose of PA. The results of the continuous dose–response analysis show an inverse nonlinear relationship (Pnon-linearity < 0.05) between PA and both the risk of severe illness and mortality from COVID-19. For PA below 10 MET-h/week (MET-h/week: metabolic equivalent of task-hours/week), an increase of 4 MET-h/week (1 h of moderate-intensity or 0.5 h of high-intensity PA) was associated with 8% and 11% reductions in the risk of severe illness and mortality from COVID-19. PA above 10 MET-h/week lowered the risk of severe illness and mortality from COVID-19 by 7% and 9%, respectively, for each 4 MET-h/week increase. Doses of WHO-recommended PA levels (10 MET-h/week) may be required for more substantial reductions in the risk of severe illness and mortality from COVID-19.

Baseline physical activity and the risk of severe illness and mortality from COVID-19: A dose-response meta-analysis.

To provide a scientific basis for improved exercise-based immunity, a meta-analysis was used to explore the dose-response relationship between physical activity (PA) and the risk of severe illness and mortality related to COVID-19 (coronavirus disease 2019). To this end, we searched PubMed, Web of Science databases from January 2020 through April 2022. 14 observational studies met the criteria for inclusion in the meta-analysis, including 2840 cases of severe illness and death from COVID-19. Categorical dose-relationship analysis showed that the risks of severe illness and mortality from COVID-19 were, respectively, 46% (risk ratio (RR): 0.54; confidence intervals (CIs): 0.41-0.68) and 59% (RR = 0.41; 95%CI: 0.23-0.58) lower for the highest dose of PA compared with the lowest dose of PA. The results of the continuous dose-response analysis show an inverse nonlinear relationship (Pnon-linearity < 0.05) between PA and both the risk of severe illness and mortality from COVID-19. For PA below 10 MET-h/week (MET-h/week: metabolic equivalent of task-hours/week), an increase of 4 MET-h/week (1 h of moderate-intensity or 0.5 h of high-intensity PA) was associated with 8% and 11% reductions in the risk of severe illness and mortality from COVID-19. PA above 10 MET-h/week lowered the risk of severe illness and mortality from COVID-19 by 7% and 9%, respectively, for each 4 MET-h/week increase. Doses of WHO-recommended PA levels (10 MET-h/week) may be required for more substantial reductions in the risk of severe illness and mortality from COVID-19.

Lockdown Amid COVID-19 Ascendancy over Ambient Particulate Matter Pollution Anomaly.

Air is a diverse mixture of gaseous and suspended solid particles. Several new substances are being added to the air daily, polluting it and causing human health effects. Particulate matter (PM) is the primary health concern among these air toxins. The World Health Organization (WHO) addressed the fact that particulate pollution affects human health more severely than other air pollutants. The spread of air pollution and viruses, two of our millennium's most serious concerns, have been linked closely. Coronavirus disease 2019 (COVID-19) can spread through the air, and PM could act as a host to spread the virus beyond those in close contact. Studies on COVID-19 cover diverse environmental segments and become complicated with time. As PM pollution is related to everyday life, an essential awareness regarding PM-impacted COVID-19 among the masses is required, which can help researchers understand the various features of ambient particulate pollution, particularly in the era of COVID-19. Given this, the present work provides an overview of the recent developments in COVID-19 research linked to ambient particulate studies. This review summarizes the effect of the lockdown on the characteristics of ambient particulate matter pollution, the transmission mechanism of COVID-19, and the combined health repercussions of PM pollution. In addition to a comprehensive evaluation of the implementation of the lockdown, its rationales-based on topographic and socioeconomic dynamics-are also discussed in detail. The current review is expected to encourage and motivate academics to concentrate on improving air quality management and COVID-19 control.

Impacts of COVID-19 Restrictions on Young Children's Outdoor Activity: A Systematic Review.

We sought to identify and synthesise available evidence to aid the understanding of the impact that COVID-19 restrictions had on the outdoor activity of children aged from birth to 12 years. Seven databases (Education Research Complete, ERIC, MEDLINE, PsycINFO, SPORTDiscus, Psychology and Behavioural Sciences Collection, WHO COVID-19 Database) were searched for relevant journal articles in English published from 2020 on. Four qualitative and eleven quantitative studies were included after screening. JBI's Critical Appraisal Tools were used for quality assessment. All qualitative studies showed an increase in outdoor activity. Less than half of the quantitative studies indicated an increase. Family demography, home characteristics, access to outdoor spaces, and parental support/encouragement/co-play were influential factors. The evidence also supports the recommendation for educators to increase children's outdoor play time to adhere to the physical distancing guidance and sanitisation requirements. Limited evidence suggests that when COVID-19 restrictions led to decreased outdoor activity, it was associated with less peer socialisation. We identified significant gaps in understanding of the impact of COVID-19 restrictions on young children's outdoor activity.

HEPA filters for airliner cabins: State of the art and future development.

The airliner cabin environment is very important to the health of passengers and crew members, and the use of high-efficiency particulate air (HEPA) filters for recirculated air in the environmental control systems (ECS) is essential for the removal of airborne particles such as SARS CoV-2 aerosols. A HEPA filter should be high efficiency, low-pressure drop, high dust-holding capacity (DHC), lightweight, and strong for use in aircraft. We conducted an experimental study on 23 HEPA filters with glass fiber media that are used in different commercial airliner models. The tested filters had a median filtration efficiency of >99.97% for particles with a diameter of 0.3-0.5 µm, a pressure drop of 134-412 Pa at rated airflow rate, and a DHC of 32.2-37.0 g/m2 . The use of nanofiber media instead of glass fiber media can reduce the pressure drop by 66.4%-94.3% and significantly increase the quality factor by analysis of literature data. The disadvantages of poor fire resistance and small DHC can be overcome by the use of flame-retardant polymers and fiber structural design. As a new lightweight and environmentally friendly filter material, nanofiber media could be used as air filters in ECS in the future.

Dual functionalisation of polyurethane foam for unprecedented flame retardancy and antibacterial properties using layer-by-layer assembly of MXene chitosan with antibacterial metal particles

Antibacterial surfaces in healthcare settings are an important tool for combating the increasing threat of antibacterial drug resistance, which the global Covid-19 pandemic has further exacerbated. Herein, we report a new method to achieve dual antibacterial and flame retardant functionalities in flexible polyurethane foam (PUF) by synthesising a multifunctional coating using a layer-by-layer assembly technique. The coating consists of Ti3C2 nanosheets and chitosan as the flame retardant and metal particles (copper or silver) for the antibacterial property. Results show that the multilayer Ti3C2/CH/Ag coating possesses excellent antibacterial performance with reductions of 99.97% in gram-negative bacteria (P. aeruginosa) and 88.9% in gram-positive bacteria (S. aureus) compared with the unmodified counterpart. Compared with the pristine PUF, the multifunctional coating yielded 66.3% reductions in the PHRR, and demonstrated outstanding smoke suppression performance with a PSPR reduction of 51.6% and a TSR decline of 65.5%. Moreover, Raman spectroscopy revealed an increased graphitisation level in the residual char of the coated foam, indicating the coating's remarkable charring performance. This exceptional multifunctional performance endows the coating technology with a great potential for eradicating the fire risks of antibacterial surfaces in healthcare settings and providing furniture, interior walls and building panels with antibacterial properties.

Corrigendum to "Evaluation of different air distribution systems in a commercial airliner cabin in terms of comfort and COVID-19 infection risk" Build. Environ., Volume 208, January 2022, 108590.

[This corrects the article DOI: 10.1016/j.buildenv.2021.108590.].

Prevalence of and risk factors for depressive and anxiety symptoms in a large sample of Chinese adolescents in the post-COVID-19 era.

BACKGROUND: Depressive and anxiety symptoms are widespread among adolescents today, creating a large social problem. However, few previous studies have addressed depression and anxiety among adolescents in Chinese cohorts. The aim of this study was to evaluate the prevalence of and risk factors for depressive and anxiety symptoms among Chinese middle school adolescent students in the post-COVID-19 era. METHODS: A total of 22,380 middle school students from Jiangsu Province were surveyed online, and their general demographic data were collected. The Patient Health Questionnaire-9 (PHQ-9) was used to assess depressive symptoms, and the seven-item Generalized Anxiety Disorder (GAD-7) scale was used to measure anxiety symptoms. RESULTS: Of these participants (aged 12-17 years), 25.6% had depressive symptoms, 26.9% had anxiety symptoms, and 20.6% had a combination of depression and anxiety symptoms. The prevalence of depressive symptoms was higher in female adolescents (27.6%) than in male adolescents (23.7%; χ2 = 45.479, P = 0.000), and the proportion with anxiety symptoms was higher among female adolescents (28.6%) than among male adolescents (25.4%; χ2 = 29.390, P = 0.000). Furthermore, binary logistic regression analysis showed that gender, region, and parental relationship were significantly associated with depressive symptoms among adolescents, while age, gender, region, and parental relationship were significantly associated with anxiety symptoms. CONCLUSIONS: Our findings demonstrated that the prevalence of reported depressive and anxiety symptoms in Chinese adolescents are high. Female gender, urban region, and poor parental relationship may be risk factors for depressive and anxiety symptoms. Furthermore, policy makers, schools, and families need to pay more attention to the psychological health of adolescents, develop response plans and take early intervention measures to reduce the prevalence of adolescent depression and anxiety.

A Method to Generate Experimental Aerosol with Similar Particle Size Distribution to Atmospheric Aerosol

The SARS-CoV virus spreads in the atmosphere mainly in the form of aerosols. Particle air filters are widely used in indoor heating, ventilation, and air-conditioning (HVAC) systems and filtration equipment to reduce aerosol concentration and improve indoor air quality. Requirements arise to rate filters according to their mass-based filtration efficiency. The size distribution of test aerosol greatly affects the measurement results of mass-based filtration efficiency and dust loading of filters, as well as the calibration of optical instruments for fine-particle (PM2.5) mass concentration measurement. The main objective of this study was to find a new method to generate a chemically nontoxic aerosol with a similar particle size distribution to atmospheric aerosol. We measured the size distribution of aerosols generated by DEHS (di-ethyl-hexyl-sebacate), PSL (poly-styrene latex), olive oil, and 20% sucrose solution with a collision nebulizer in a wide range of 15 nm–20 μm. Individually, none of the solutions generated particles that share a similar size distribution to atmospheric aerosol. We found that the 20% sucrose solution + olive oil mixture solution (Vss:Voo = 1:2) could be used to generate a chemically nontoxic aerosol with similar particle number/volume size distribution to the atmospheric aerosol (t-test, p < 0.05). The differences in the mass-base filtration efficiency measured by the generated aerosol and the atmospheric aerosol were smaller than 2% for MERV 7, 10, 13, and 16 rated filters. The aerosol generated by the new method also performed well in the calibration of optical-principle-based PM2.5 concentration measurement instruments. The average relative difference measured by a tapered element oscillating microbalance (TEOM) and a Dusttrak Model 8530 (calibrated by aerosol generated by the new method) was smaller than 5.8% in the real-situation measurement.

Evaluation of different air distribution systems in a commercial airliner cabin in terms of comfort and COVID-19 infection risk.

The air distribution system in an airliner plays a key role in maintaining a comfortable and healthy environment in the aircraft cabin. To evaluate the performance of a novel displacement ventilation (DV) system and a traditional mixing ventilation (MV) system in an airliner cabin, this study conducted experiments and simulations in a seven-row cabin mockup. This investigation used ultrasonic anemometers and T-thermocouples to measure the air velocity, temperature and distribution of 1 µm and 5 µm particles. Simulation verifications were performed for these operating conditions, and additional scenarios with different occurrence source locations were also simulated. This study combined the Wells-Riley equation with a real case based on a COVID-19 outbreak among passengers on a long-distance bus to obtain the COVID-19 quanta value. Through an evaluation of the airflow organization, thermal comfort, and risk of COVID-19 infection, the two ventilation systems were compared. This investigation found that polydisperse particles should be used to calculate the risk of infection in airliner cabins. In addition, at the beginning of the pandemic, the infection risk with DV was lower than that with MV. In the middle and late stages of the epidemic, the infection risk with MV can be reduced when passengers wear masks, leading to an infection risk approximately equal to that of DV.

Societal shifts due to COVID-19 reveal large-scale complexities and feedbacks between atmospheric chemistry and climate change.

The COVID-19 global pandemic and associated government lockdowns dramatically altered human activity, providing a window into how changes in individual behavior, enacted en masse, impact atmospheric composition. The resulting reductions in anthropogenic activity represent an unprecedented event that yields a glimpse into a future where emissions to the atmosphere are reduced. Furthermore, the abrupt reduction in emissions during the lockdown periods led to clearly observable changes in atmospheric composition, which provide direct insight into feedbacks between the Earth system and human activity. While air pollutants and greenhouse gases share many common anthropogenic sources, there is a sharp difference in the response of their atmospheric concentrations to COVID-19 emissions changes, due in large part to their different lifetimes. Here, we discuss several key takeaways from modeling and observational studies. First, despite dramatic declines in mobility and associated vehicular emissions, the atmospheric growth rates of greenhouse gases were not slowed, in part due to decreased ocean uptake of CO2 and a likely increase in CH4 lifetime from reduced NO x emissions. Second, the response of O3 to decreased NO x emissions showed significant spatial and temporal variability, due to differing chemical regimes around the world. Finally, the overall response of atmospheric composition to emissions changes is heavily modulated by factors including carbon-cycle feedbacks to CH4 and CO2, background pollutant levels, the timing and location of emissions changes, and climate feedbacks on air quality, such as wildfires and the ozone climate penalty.

Simulation Study of a Novel Cylindrical Micro-Electrostatic Particulate Air Filter with High Filtration Efficiency and Low Resistance

The purification of indoor pathogenic microorganisms has become a topic of concern. The use of nonwoven media air filters causes high resistance, and the problem of noise limited their application under high air volume. Thus, we propose a micro-electrostatic filter, which has improved performance compared to an electrostatic filter, with a new type of cylindrical structure to tackle indoor pathogenic microbial aerosol pollution. Through simulation, it is found that the filtration performance of a cylindrical structure is better than that of a plate structure under all simulation conditions. For particles larger than 1 μm, the shortest theoretical length of the dust collecting plate required for the cylindrical structure is 34% shorter than that for the plate structure. For 0.1 μm particles, the filtration efficiency of the cylindrical structure is nearly 20~30% (the maximum value is 29.76%) higher than that of the plate structure, while the air velocity is 1.5 m/s~2.5 m/s. The resistance of the cylindrical micro-electrostatic filter is only half of that of the combined plate type micro-electrostatic filter, indicating that the cartridge structure has enormous energy-saving potential. The introduction of the quality factor further proves that the integrated filtration performance of the cartridge micro-electrostatic filter is better. The application of cylindrical micro-electrostatic filters in HVAC systems can help improve indoor air quality and reduce health risks.

Experimental evaluation of particle exposure at different seats in a single-aisle aircraft cabin.

During the COVID-19 pandemic, exposure to particles exhaled by infected passengers in commercial aircraft cabins has been a great concern. Currently, aircraft cabins adopt mixing ventilation. However, complete mixing may not be achieved, and thus the particle concentration in the respiratory zone may vary from seat to seat in a cabin. To evaluate the particle exposure in a typical single-aisle aircraft cabin, this investigation constructed an aircraft cabin mockup for experimental tests. Particles were released from a single source or dual sources at different seats to represent particles exhaled by infected passengers. The particle concentrations in the respiratory zones at various seats were measured and compared. The particle exposure was evaluated in both a cross section and a longitudinal section. Leaving the middle seat vacant to reduce particle exposure was also addressed. In addition, the velocity fields and air temperatures were measured to provide a better understanding of particle transport. It was found that the particle exposure at the window seat is always the lowest, regardless of the particle release locations. If the passenger seated in the middle does not release particles, his/her presence enhances the particle dispersion and thereby reduces the particle exposure for adjacent passengers. In the cabin mockup, the released particles can be transported across at least four rows of seats in the longitudinal direction.

Optimization of multi-V filter design for airliner environmental control system using an empirical model

With the wide use of multi-V filters in aircraft cabins, it is necessary to establish a pressure drop prediction and optimization model for multi-V HEPA cabin filters. Based on approximate solution of the Navier-Stokes equation and with the aid of CFD simulations, we developed an empirical equation for the overall pressure drop across a multi-V HEPA cabin filter. The measured pressure drop across the filter was used to verify the accuracy of the empirical equation. The equation was then used to develop two optimized design procedures for multi-V HEPA cabin filters with low pressure drop and high filtration efficiency. The structural parameters of the filters obtained by the two design procedures were consistent and very close to the actual parameters. Compared with CFD, this empirical equation is easier to use and involves only a short calculation time. The empirical equation and optimized design procedures are useful for filter design.