Effects of table based air curtains on respiratory aerosol exposure risk mitigation at face-to-face meeting setups.

Face-to-face meetings on a conference table are a frequent form of communication. The short-range exposure risk of aerosol disease transmission is high in the scenario of susceptible facing the infectious person over the table. We propose a mitigation methodology using the air curtain to reduce direct exposure to virus-laden aerosols. A numerical model was validated with experimental data to simulate the dispersion of aerosols. A dynamic mesh was adopted to consider the head movement of a 3D thermal manikin model. Results show that nodding head increase the potential risk by 74 % compared to motionless. Subsequently, for a single air curtain, placing it in the middle of the table is more effective in preventing risks than on the sides. For double air curtains, increasing the distance between them has a greater risk reduction effect than a shorter distance. Increasing the air velocity or width is more effective than increasing the number of air curtains. A moderate velocity (1 m s-1) works well to reduce the risk of nasal breathing. A higher velocity (2 m s-1) is needed for the coughing scenario. For similar indoor environments, the air curtains on the table can offer active precautions without changing the current ventilation system.

Feasibility of respirable crystalline silica exposure reduction in small-scale tanzanite mining in Tanzania.

INTRODUCTION: Respirable crystalline silica (RCS) exposures in tanzanite gem mining have been linked to tuberculosis and silicosis among miners. We conducted a plot study to assess RCS exposures and to introduce safer mining practices in one small-scale underground tanzanite mine. MATERIALS AND METHODS: Personal and area air samples for RCS were collected during tanzanite mining operations before and after improved work practices employed to reduce exposures and analyzed using X-ray diffraction. Area samples were collected at the rest area, located approximately 300 m underground and 100 m from other work activities. Improved practices included the use of wet drilling methods and drilling with new bits. RESULTS: A total of 33 personal and 4 area air samples were collected. Pre-intervention, mean exposures for all operations, drilling operations, non-drilling activities, and area samples were 122 mg/m3, 247 mg/m3, 34.3 mg/m3, and 1.95 mg/m3, respectively which exceeded the U.S. OSHA Permissible Exposure Limit (PEL) by 2,440 times for all operations, by 4,946 times for drilling operations, by 686 times for non-drilling activities and 39 times for area samples collected at an underground rest area. The post-intervention results showed a 99% reduction of RCS exposures for wet drilling operations, 98.5% reduction for non-drilling activities, and 36% reduction for area samples. Despite improvements, post-intervention RCS exposures during drilling had a mean of 2.08 mg/m3 or more than 41 times the OSHA PEL. CONCLUSIONS: We successfully piloted a program to work with small-scale tanzanite miners to reduce RCS exposures and raise awareness about the occupational health risks of RCS, though additional measures are recommended to further reduce RCS exposures. Similar programs should be taken to scale throughout underground mining sites in Tanzania and other countries.

Reported exposures to respirable crystalline silica during construction tasks and guidance for harmonizing future research.

Airborne respirable crystalline silica (RCS) has been a widely recognized hazard in the United States for nearly 100 years, yet it continues to pose a risk to construction tradespersons, among others. RCS exposures vary widely depending on site conditions and tools and materials used. The proper use of engineering, administrative, and personal protective equipment (PPE) controls can effectively reduce exposure to RCS. Historically, others have reviewed available RCS exposure data among construction trades and reported that there were considerable data gaps and variability that needed to be addressed. This current assessment aimed to synthesize available peer-reviewed exposure studies to determine potential RCS exposures during the use of common construction materials and evaluate to what extent data gaps and variability persist. Twenty-eight studies were identified that reported RCS exposure during construction tasks. After conversion to the unit of µg/m3, reported measurements from samples collected for varying durations ranged from 6.0 to 75,500 µg/m3 for work with concrete, 80 to 4,240 µg/m3 for work with brick, <59 to 10,900 µg/m3 for work with mortar, 90 to 44,370 µg/m3 for work with engineered stone, and 70 to 380 µg/m3 for work with roof tile. To better facilitate pooling data across studies, future researchers should report their sample duration, clarify how time-weighted average (TWA) exposure data are calculated, report the silica content of the material being manipulated, and specify whether samples were collected while the task was performed in isolation or on a worksite where other silica-containing materials were also actively handled. When reporting results as respirable quartz, it is important to note whether any other polymorphic forms of silica were detected. It is ultimately the employer's responsibility to train employees and monitor and control RCS exposures on construction worksites. To do this effectively, it is important to have a clear understanding of the tasks, materials, and site conditions where intervention is most urgently needed.

A critique of Occupational Safety and Health Administration's halfmask respirator assigned protection factor.

Halfmask air-purifying respirators are used by millions of workers to reduce inhaling air contaminants, both chemical (e.g., asbestos, styrene) and biological (e.g., SARS-CoV-2, Mycobacterium tuberculosis). In 2006, the federal Occupational Safety and Health Administration (OSHA) promulgated a standard that gave halfmask respirators an assigned protection factor (APF) of 10. This signified that OSHA assumes a fit-tested and trained wearer will experience a 10% maximum total inward leakage of contaminated air into the facepiece. To derive APF = 10, OSHA analyzed data from 16 workplace studies of the efficacy of halfmask respirators worn against particulate contaminants. In this commentary, I contend that, in considering the data, OSHA made several errors that overstated halfmask respirator efficacy. The errors were (i) failing to properly account for within-wearer and between-wearer variability in respirator efficacy; (ii) ignoring the effect of particle deposition in the respiratory tract; (iii) aggregating unbalanced data within and between studies, and effectively double-counting the data in some studies; and (iv) ignoring the effect that particle size exerts in penetrating respirator facepiece leak paths. The net result is that OSHA's APF = 10 can lead to excessive toxicant exposure for many workers.

Evaluating silicosis risk: Assessing dust constitution and influence of water as a primary prevention measure in cutting and polishing of silica agglomerates, granite and marble.

An increasing number of silicosis cases have been reported related to the use of silica agglomerates. Many studies agree on the severity of this disease, which often presents with severe clinical forms in young workers and after a short latency period. Are there differences in the composition of dust generated by cutting and polishing with silica agglomerates versus granite and marble? Does the use of water injection reduce the risk associated with the use of these materials? We carried out a comparative observational-analytical study, measuring the concentration of dust generated during different machining operations on three different materials: granite, marble, and silica agglomerates. The effect of water injection on dust generation was evaluated. Personal sampling pumps were used, connected to a cyclone with polyvinyl chloride filters. The flow rate of the pumps was adjusted using a piston flowmeter. Measurements with a cascade impactor were made to assess the size distribution of respirable crystalline silica particles within the respirable fraction. In addition, environmental measurements with a spectrometer were made. 10 tests were carried out on granite and silica agglomerates for each procedure. In the case of marble, with very low silica content, only 2 tests of each type were carried out. Duration of each measurement was between 6 and 25 min. Cleaning times were set for each of the operations. The amount of dust collected in the respirable fraction was 70.85, 32.50 and 35.78 mg/m3 for dry cutting; 6.50, 3.75 and 3.95 mg/m3 for wet cutting; and 21.35, 13.68 and 17.50 mg/m3 for dry polishing, for granite, marble, and silica agglomerates respectively. Dry procedures in marble, silica agglomerates and granite showed higher dust concentration of particles smaller than 0.5 µm. Silica agglomerates showed higher concentrations of respirable crystalline silica particles than granite and marble, mainly with dry procedures. The greater production of small particles in dry and wet procedures with silica agglomerates shows that water injection is an insufficient preventive measure.

Release and health outcomes of exposure to chalk particles in classrooms: a systematic literature review.

This systematic review explores the release and health outcomes of exposure to chalk particles in classrooms. A literature search was conducted on Scopus, Google Scholar, and the Web of Science. Chalk particles contribute significantly to poor indoor air quality in classrooms. Higher concentrations of PM2.5 chalk particles were found in the front row (14.25 µg/m3) and near the chalkboard (19.07 µg/m3). Inhalation and dermal are significant exposure routes; hence, teachers and learners are at risk of developing respiratory and skin disorders. Inhalation of chalk particles correlates with reduced lung function in teachers and learners. The release and size of chalk particles depend on the activities, type of chalk sticks, and texture of the chalkboards. Wiping the chalkboard releases more chalk particles of smaller size (3.85-9.3 µm) than writing (10.57-92.91 µm). A shift from chalk sticks and chalkboards in classrooms is necessary to mitigate the associated health risks.

Assessment of inhalation exposure to microplastic particles when disposable masks are repeatedly used.

Wearing masks to prevent infectious diseases, especially during the COVID-19 pandemic, is common. However, concerns arise about inhalation exposure to microplastics (MPs) when disposable masks are improperly reused. In this study, we assessed whether disposable masks release inhalable MPs when reused in simulated wearing conditions. All experiments were conducted using a controlled test chamber setup with a constant inspiratory flow. Commercially available medical masks with a three-layer material, composition comprising polypropylene (PP in the outer and middle layers) and polyethylene (PE in the inner layer), were used as the test material. Brand-new masks with and without hand rubbing, as well as reused medical masks, were tested. Physical properties (number, size, and shape) and chemical composition (polymers) were identified using various analytical techniques such as fluorescence staining, fluorescence microscopy, and micro-Fourier Transform Infrared Spectroscopy (µFTIR). Scanning Electron Microscopy (SEM) was used to scrutinize the surface structure of reused masks across different layers, elucidating the mechanism behind the MP generation. The findings revealed that brand-new masks subjected to hand rubbing exhibited a higher cumulative count of MPs, averaging approximately 1.5 times more than those without hand rubbing. Fragments remained the predominant shape across all selected size classes among the released MPs from reused masks, primarily through a physical abrasion mechanism, accounting for >90 % of the total MPs. The numbers of PE particles were higher than PP particles, indicating that the inner layer of the mask contributed more inhalable MPs than the middle and outer layers combined. The released MPs from reused masks reached their peak after 8 h of wearing. This implies that regularly replacing masks serves as a preventive measure and mitigates associated health risks of inhalation exposure to MPs.

Validation of N95 respirator models for pressure drop and particle capture efficiency.

Despite efforts to apply administrative and engineering controls to minimize worker exposure to aerosols, filtering facepiece respirators (FFRs) continue to be an important form of personal protective equipment in hard-to-control settings such as healthcare, agriculture, and construction. Optimizing the performance of FFRs can be advanced with the use of mathematical models that incorporate the forces that act on particles during filtration as well as those filter characteristics that influence filter pressure drop. However, a thorough investigation of these forces and characteristics using measurements of currently available FFRs has not been undertaken. Filter characteristics such as fiber diameter and filter depth were measured from samples taken from six currently-available N95 FFRs from three manufacturers. A filtration model was developed that included diffusion, inertial and electrostatic forces to estimate the filtration of an aerosol with a Boltzmann charge distribution. The diameter of the filter fibers was modeled as either a single "effective" diameter or as a lognormal distribution of diameters. Both modeling schemes produced an efficiency curve that simulated efficiency measurements made over a range of particle diameters (0.01 - 0.3 µm) with the use of a scanning mobility particle sizer in the region where efficiency is at a minimum. However, the method using a distribution of fiber diameters produced a better fit for particles > 0.1 µm. The coefficients associated with a simple form of the diffusion equation constituting a power law incorporating the Peclet number were adjusted to enhance model accuracy. Likewise, the fiber charge of the electret fibers was also adjusted to maximize model fit but remained within levels reported by others. A filter pressure drop model was also developed. Results demonstrated the need for a pressure drop model applicable to N95s relative to existing models developed with the use of fibers with larger diameters than those used in current N95 FFRs. A set of N95 FFR characteristics are provided that can be used to develop models of typical N95 FFR filter performance and pressure drop in future studies.

Managing Quartz Exposure in Apartment Building and Infrastructure Construction Work Tasks.

The present report describes exposure to respirable silica and dust in the construction industry, as well as means to manage them. The average exposure in studied work tasks (n = 148) amounted to 64% of the Finnish OEL value of 0.05 mg/m3. While 10% of exposure estimates exceeded the OEL, the 60% percentile was well below 10% of the OEL, as was the median exposure. In other words, exposure was low in more than half of the tasks. Work tasks where exposure was low included construction cleaning, work management, installation of concrete elements, rebar laying, driving work machines equipped with cabin air intake filtration, and landscaping, in addition to some road construction tasks. Excessive exposure (>OEL) was related to not using respiratory protection at all or not using it for long enough after the dusty activity ceased. Excessive exposures were found in sandblasting, dismantling facade elements, diamond drilling, drilling hollow-core slabs, drilling with a drilling rig, priming of explosives, tiling, use of cabinless earthmoving machines, and jackhammering, regardless of whether the hammering took place in an underpressurized compartment or not. Even in these tasks, it was possible to perform the work safely, following good dust prevention measures and, when necessary, using respiratory protection suitable for the job. Furthermore, in all tasks with generally low exposure, one could be significantly exposed through the general air or by making poor choices in terms of dust control.

Effectiveness of Inexpensive Cloth Facemasks and Their Amendments to Reduce Ambient Particulate Exposures: A Case of Kathmandu, Nepal.

Inexpensive cloth masks are widely used to reduce particulate exposures, but their use became ubiquitous after the outbreak of COVID-19. A custom experimental setup (semiactive at 5.1 m/s airflow rate) was fabricated to examine the efficiency of different types of commercial facemasks collected randomly from street vendors. The sample (N = 27) including (n = 16) cloth masks (CMs), (n = 7) surgical masks (SMs), and (n = 4) N95 filtering facepiece respirators (FFRs), of which SMs and N95 FFRs taken as a standard for efficiency comparison were all tested against ambient aerosols (PM2.5 and PM10 µg/m3). The prototype cloth masks (PTCMs) (N = 5) design was tailored, and their performance was assessed and compared with that of standard commercial masks. The filtering efficiency tested against ambient coarse particulates (PM10) ranged from (5% to 34%) for CMs with an average of 16%, (37% to 46%) for SMs with an average of 42%, (59% to 72%) for PTCMs with an average of 65%, and (70% to 75%) for N95 FFRs with an average of 71%, whereas against fine particulates (PM2.5), efficacy ranged from (4% to 29%) for CMs with an average of 13%, (34% to 44%) for SMs with an average of 39%, (53% to 68%) for PTCMs with an average of 60%, and (68% to 73%) for N95 FFRs with an average of 70%, respectively. The efficiency followed the order N95 FFRs > PTCMs > SMs > CMs showing poor exposure reduction potential in CMs and high exposure reduction potential in N95 FFRs and PTCMs. Amendment in existing CMs using eco-friendly cotton fabric with better facial adherence can protect human health from exposure to fine particulates <2.5 µm and can reduce the risk of micro-plastic pollution caused by polypropylene (PP) facemasks.

The Problem with 'Suction Only' Methods to Reduce Surgical Smoke Exposure.

Surgical staff and patients are frequently exposed to surgical smoke and there is mounting evidence that this may be harmful. Borsetti et al. have devised a novel approach to minimising intraoperative exposure to surgical smoke. Here, I briefly outline my concerns with the 'suction only' approach to addressing this problem. LEVEL OF EVIDENCE V: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Evaluation of a self-cleaning portable dust collector for reducing worker exposures to silica at hydraulic-fracturing sites.

National Institute for Occupational Safety and Health (NIOSH) researchers continue to study worker exposure to respirable crystalline silica (RCS) and develop interventions to reduce these exposures. Occupational overexposures to RCS continue to cause illness and deaths in many industries and RCS has been identified as a serious exposure risk associated with hydraulic- fracturing operations during oil and gas extraction. In 2016 the Occupational Safety and Health Administration (OSHA) reduced the permissible exposure limit (PEL) to 0.05 milligrams of silica per cubic meter of air, averaged over an 8-hour day. This mandate requires hydraulic-fracturing operations to implement dust controls and safer work methods to protect workers from silica exposures above this PEL by June 23, 2021. At hydraulic-fracturing sites utilizing sand movers, pneumatic transfer of fracking sand is the primary source of aerosolized RCS. Currently, there are limited commercially available engineering controls for the collection of dust emitted from thief hatches on sand movers. The goal of this research is to develop a robust, cost-effective, weather resistant, portable, self-cleaning dust collection system that can be retrofitted onto sand mover thief hatches. A prototype was designed, built, and tested, and it was determined that the system could handle flows in the range of 600 to 1300 cfm with loading/cleaning cycle times of 40 and 5 minutes respectively and demonstrated operating efficiencies of 97-99%. Further development of this NIOSH prototype is being done in collaboration with an industry partner with the goal of developing a commercially viable, cost-effective solution to reduce RCS at hydraulic-fracturing sites around the world.Implications: This research has verified that airborne dust created by pneumatic transfer of fracking sand can be effectively collected using a passive cartridge filter system, and that the filters can be cleaned using blasts of air. Mounting these units to the thief hatches of sand movers will significantly reduce dust emissions from sand movers on hydraulic fracturing sites. Thus, this system offers the Oil and Gas Industry a method to reduce worker exposure to RCS on hydraulic fracturing sites that utilize sand movers. The success of this prototype has led researchers to devise a modified version for collecting dust at conveyor transfer points.

Benefits and limitations of field-based monitoring approaches for respirable dust and crystalline silica applied in a sandstone quarry.

With the advent of new sensing technologies and robust field-deployable analyzers, monitoring approaches can now generate valuable hazard information directly in the workplace. This is the case for monitoring respirable dust and respirable crystalline silica concentration levels. Estimating the quartz amount of a respirable dust sample by nondestructive analysis can be carried out using portable Fourier transform infrared spectroscopy (FTIR) units. Real-time respirable dust monitors, combined with small video cameras, allow advanced assessments using the Helmet-CAM methodology. These two field-based monitoring approaches, developed by the National Institute for Occupational Safety and Health (NIOSH), have been trialed in a sandstone quarry. Twenty-six Helmet-CAM sessions were conducted, and forty-one dust samples were collected around the quarry and analyzed on-site during two events. The generated data generated were used to characterize concentration levels for the monitored areas and workers, to identify good practices, and to illustrate activities that could be improved with additional engineered control technologies. Laboratory analysis of the collected samples complemented the field finding and provided an assessment of the performance of the field-based techniques. Only a fraction of the real-time respirable dust monitoring sessions data could be corrected with laboratory analysis. The average correction factor ratio was 5.0. Nevertheless, Helmet-CAM results provided valuable information for each session. The field-based quartz monitoring approach overestimated the concentration by a factor of 1.8, but it successfully assessed the quartz concentration trends in the quarry. The data collected could be used for the determination of a quarry calibration factor for future events. The quartz content in the dust was found to vary from 14% to 100%, and this indicates the need for multiple techniques in the characterization of respirable dust and quartz concentration and exposure. Overall, this study reports the importance of the adoption of field-based monitoring techniques when combined with a proper understanding and knowledge of the capabilities and limitations of each technique.

Elevated exposures to respirable crystalline silica among engineered stone fabrication workers in California, January 2019-February 2020.

BACKGROUND: Workers fabricating engineered stone face high risk for exposure to respirable crystalline silica (RCS) and subsequent development of silicosis. In response, the California Division of Occupational Safety and Health (Cal/OSHA) performed targeted enforcement inspections at engineered stone fabrication worksites. We investigated RCS exposures and employer adherence to Cal/OSHA's RCS and respiratory protection standards from these inspections to assess ongoing risk to stone fabrication workers. METHODS: We extracted employee personal air sampling results from Cal/OSHA inspection files and calculated RCS exposures. Standards require that employers continue monitoring employee RCS exposures and perform medical surveillance when exposures are at or above the action level (AL; 25 µg/m3 ); exposures above the permissible exposure limit (PEL; 50 µg/m3 ) are prohibited. We obtained RCS and respiratory protection standard violation citations from a federal database. RESULTS: We analyzed RCS exposures for 152 employees at 47 workplaces. Thirty-eight (25%) employees had exposures above the PEL (median = 89.7 µg/m3 ; range = 50.7-670.7 µg/m3 ); 17 (11%) had exposures between the AL and PEL. Twenty-four (51%) workplaces had ≥1 exposure above the PEL; 7 (15%) had ≥1 exposure between the AL and PEL. Thirty-four (72%) workplaces were cited for ≥1 RCS standard violation. Twenty-seven (57%) workplaces were cited for ≥1 respiratory protection standard violation. CONCLUSIONS: Our investigation demonstrates widespread RCS overexposure among workers and numerous employer Cal/OSHA standard violation citations. More enforcement and educational efforts could improve employer compliance with Cal/OSHA standards and inform employers and employees of the risks for RCS exposure and strategies for reducing exposure.

Case Report: Exposure to Respirable Crystalline Silica and Respiratory Health Among Australian Mine Workers.

Occupational exposure to respirable crystalline silica (RCS) is common in a range of industries, including mining, and has been associated with adverse health effects such as silicosis, lung cancer, and non-malignant respiratory diseases. This study used a large population database of 6,563 mine workers from Western Australia who were examined for personal exposure to RCS between 2001 and 2012. A standardized respiratory questionnaire was also administered to collect information related to their respiratory health. Logistic regression analyses were performed to ascertain the association between RCS concentrations and the prevalence of respiratory symptoms among mine workers. The estimated exposure levels of RCS (geometric mean 0.008mg/m3, GSD 4.151) declined over the study period (p < 0.001) and were below the exposure standard of 0.05 mg/m3. Miners exposed to RCS had a significantly higher prevalence of phlegm (p = 0.017) and any respiratory symptom (p = 0.013), even at concentrations within the exposure limit. Miners are susceptible to adverse respiratory health effects at low levels of RCS exposure. More stringent prevention strategies are therefore recommended to protect mine workers from RCS exposures.

Understanding Filtering Facepiece Respirators.

How to ensure adequate protection.

Efficacy of Ventilation, HEPA Air Cleaners, Universal Masking, and Physical Distancing for Reducing Exposure to Simulated Exhaled Aerosols in a Meeting Room.

There is strong evidence associating the indoor environment with transmission of SARS-CoV-2, the virus that causes COVID-19. SARS-CoV-2 can spread by exposure to droplets and very fine aerosol particles from respiratory fluids that are released by infected persons. Layered mitigation strategies, including but not limited to maintaining physical distancing, adequate ventilation, universal masking, avoiding overcrowding, and vaccination, have shown to be effective in reducing the spread of SARS-CoV-2 within the indoor environment. Here, we examine the effect of mitigation strategies on reducing the risk of exposure to simulated respiratory aerosol particles within a classroom-style meeting room. To quantify exposure of uninfected individuals (Recipients), surrogate respiratory aerosol particles were generated by a breathing simulator with a headform (Source) that mimicked breath exhalations. Recipients, represented by three breathing simulators with manikin headforms, were placed in a meeting room and affixed with optical particle counters to measure 0.3-3 µm aerosol particles. Universal masking of all breathing simulators with a 3-ply cotton mask reduced aerosol exposure by 50% or more compared to scenarios with simulators unmasked. While evaluating the effect of Source placement, Recipients had the highest exposure at 0.9 m in a face-to-face orientation. Ventilation reduced exposure by approximately 5% per unit increase in air change per hour (ACH), irrespective of whether increases in ACH were by the HVAC system or portable HEPA air cleaners. The results demonstrate that mitigation strategies, such as universal masking and increasing ventilation, reduce personal exposure to respiratory aerosols within a meeting room. While universal masking remains a key component of a layered mitigation strategy of exposure reduction, increasing ventilation via system HVAC or portable HEPA air cleaners further reduces exposure.

Health benefits of decreases in on-road transportation emissions in the United States from 2008 to 2017.

Decades of air pollution regulation have yielded enormous benefits in the United States, but vehicle emissions remain a climate and public health issue. Studies have quantified the vehicle-related fine particulate matter (PM2.5)-attributable mortality but lack the combination of proper counterfactual scenarios, latest epidemiological evidence, and detailed spatial resolution; all needed to assess the benefits of recent emission reductions. We use this combination to assess PM2.5-attributable health benefits and also assess the climate benefits of on-road emission reductions between 2008 and 2017. We estimate total benefits of $270 (190 to 480) billion in 2017. Vehicle-related PM2.5-attributable deaths decreased from 27,700 in 2008 to 19,800 in 2017; however, had per-mile emission factors remained at 2008 levels, 48,200 deaths would have occurred in 2017. The 74% increase from 27,700 to 48,200 PM2.5-attributable deaths with the same emission factors is due to lower baseline PM2.5 concentrations (+26%), more vehicle miles and fleet composition changes (+22%), higher baseline mortality (+13%), and interactions among these (+12%). Climate benefits were small (3 to 19% of the total). The percent reductions in emissions and PM2.5-attributable deaths were similar despite an opportunity to achieve disproportionately large health benefits by reducing high-impact emissions of passenger light-duty vehicles in urban areas. Increasingly large vehicles and an aging population, increasing mortality, suggest large health benefits in urban areas require more stringent policies. Local policies can be effective because high-impact primary PM2.5 and NH3 emissions disperse little outside metropolitan areas. Complementary national-level policies for NOx are merited because of its substantial impacts-with little spatial variability-and dispersion across states and metropolitan areas.

The protective performance of reusable cloth face masks, disposable procedure masks, KN95 masks and N95 respirators: Filtration and total inward leakage.

Face coverings are a key component of preventive health measure strategies to mitigate the spread of respiratory illnesses. In this study five groups of masks were investigated that are of particular relevance to the SARS-CoV-2 pandemic: re-usable, fabric two-layer and multi-layer masks, disposable procedure/surgical masks, KN95 and N95 filtering facepiece respirators. Experimental work focussed on the particle penetration through mask materials as a function of particle diameter, and the total inward leakage protection performance of the mask system. Geometric mean fabric protection factors varied from 1.78 to 144.5 for the fabric two-layer and KN95 materials, corresponding to overall filtration efficiencies of 43.8% and 99.3% using a flow rate of 17 L/min, equivalent to a breathing expiration rate for a person in a sedentary or standing position conversing with another individual. Geometric mean total inward leakage protection factors for the 2-layer, multi-layer and procedure masks were <2.3, while 6.2 was achieved for the KN95 masks. The highest values were measured for the N95 group at 165.7. Mask performance is dominated by face seal leakage. Despite the additional filtering layers added to cloth masks, and the higher filtration efficiency of the materials used in disposable procedure and KN95 masks, the total inward leakage protection factor was only marginally improved. N95 FFRs were the only mask group investigated that provided not only high filtration efficiency but high total inward leakage protection, and remain the best option to protect individuals from exposure to aerosol in high risk settings. The Mask Quality Factor and total inward leakage performance are very useful to determine the best options for masking. However, it is highly recommended that testing is undertaken on prospective products, or guidance is sought from impartial authorities, to confirm they meet any implied standards.

A smart mask for active defense against airborne pathogens.

Face masks are a primary preventive measure against airborne pathogens. Thus, they have become one of the keys to controlling the spread of the COVID-19 virus. Common examples, including N95 masks, surgical masks, and face coverings, are passive devices that minimize the spread of suspended pathogens by inserting an aerosol-filtering barrier between the user's nasal and oral cavities and the environment. However, the filtering process does not adapt to changing pathogen levels or other environmental factors, which reduces its effectiveness in real-world scenarios. This paper addresses the limitations of passive masks by proposing ADAPT, a smart IoT-enabled "active mask". This wearable device contains a real-time closed-loop control system that senses airborne particles of different sizes near the mask by using an on-board particulate matter (PM) sensor. It then intelligently mitigates the threat by using mist spray, generated by a piezoelectric actuator, to load nearby aerosol particles such that they rapidly fall to the ground. The system is controlled by an on-board micro-controller unit that collects sensor data, analyzes it, and activates the mist generator as necessary. A custom smartphone application enables the user to remotely control the device and also receive real-time alerts related to recharging, refilling, and/or decontamination of the mask before reuse. Experimental results on a working prototype confirm that aerosol clouds rapidly fall to the ground when the mask is activated, thus significantly reducing PM counts near the user. Also, usage of the mask significantly increases local relative humidity levels.