Expiratory aerosol particle escape from surgical masks due to imperfect sealing

AbstractWearing surgical masks or other similar face coverings can reduce the emission of expiratory particles produced via breathing, talking, coughing, or sneezing. Although it is well established that some fraction of the expiratory airflow leaks around the edges of the mask, it is unclear how these leakage airflows affect the overall efficiency with which masks block emission of expiratory aerosol particles. Here, we show experimentally that the aerosol particle concentrations in the leakage airflows around a surgical mask are reduced compared to no mask wearing, with the magnitude of reduction dependent on the direction of escape (out the top, the sides, or the bottom). Because the actual leakage flowrate in each direction is difficult to measure, we use a Monte Carlo approach to estimate flow-corrected particle emission rates for particles having diameters in the range 0.5–20 μm. in all orientations. From these, we derive a flow-weighted overall number-based particle removal efficiency for the mask. The overall mask efficiency, accounting both for air that passes through the mask and for leakage flows, is reduced compared to the through-mask filtration efficiency, from 93 to 70% for talking, but from only 94–90% for coughing. These results demonstrate that leakage flows due to imperfect sealing do decrease mask efficiencies for reducing emission of expiratory particles, but even with such leakage surgical masks provide substantial control.

Download Full-text

Expiratory aerosol particle escape from surgical masks due to imperfect sealing

10.21203/rs.3.rs-142138/v1 ◽

2021 ◽

Author(s):

Christopher Cappa ◽

Sima Asadi ◽

Santiago Barreda ◽

Anthony Wexler ◽

Nicole Bouvier ◽

...

Keyword(s):

Monte Carlo ◽

Aerosol Particle ◽

Aerosol Particles ◽

Particle Emission ◽

Emission Rates ◽

Leakage Flows ◽

Surgical Masks ◽

Overall Efficiency ◽

Substantial Control ◽

Estimate Flow

Abstract Wearing surgical masks or other similar face coverings can reduce the emission of expiratory particles produced via breathing, talking, coughing, or sneezing. Although it is well established that some fraction of the expiratory airflow leaks around the edges of the mask, it is unclear how these leakage airflows affect the overall mask efficiency at blocking emission of expiratory aerosol particles. Here, we show experimentally that the aerosol particle concentrations in the leakage airflows around a surgical mask are reduced compared to no mask wearing, with the magnitude of reduction dependent on the direction of escape (out the top, the sides, or the bottom). Because the actual leakage flowrate in each direction is difficult to measure, we use a Monte Carlo approach to estimate flow-corrected particle emission rates in all orientations, from which a flow-weighted overall efficiency is derived. The overall mask efficiency, accounting both for air that passes through the mask and for leakage flows, is reduced compared to the through-mask efficiency, from 93% to 70% for talking, but from only 94% to 90% for coughing. These results demonstrate that leakage flows due to imperfect sealing do decrease mask efficiencies for reducing emission of expiratory particles, but even with such leakage surgical masks provide substantial control.

Download Full-text

Assessment of Fabric Masks as Alternatives to Standard Surgical Masks in Terms of Particle Filtration Efficiency

10.1101/2020.04.17.20069567 ◽

2020 ◽

Cited By ~ 8

Author(s):

Amy Mueller ◽

Loretta Fernandez

Keyword(s):

Health Care Providers ◽

Ambient Air ◽

Filtration Efficiency ◽

Airborne Particles ◽

Particle Removal ◽

Breathing Zone ◽

Care Providers ◽

Particle Filtration ◽

Surgical Masks ◽

Mask Design

AbstractIn response to the critical shortage of medical masks resulting from the COVID-19 pandemic, large portions of the population are mobilizing to produce cloth masks using locally-sourced fabrics, however the efficacy of these masks as a means of protecting the wearer from airborne particles carrying virus is not well known. Further, existing protocols are designed for testing the fit and performance N95 respirators and tight-fitting facemasks rather than the relatively more loose-fitting surgical mask style most cloth masks follow. In this study tools and methods typically used to assess tight-fitting facemasks were modified to assess the efficacy of community-produced fabric and commercially-produced surgical masks in terms of protecting the wearer from airborne particles that may be carrying virus. Two TSI PortaCount (model 8028) instruments were operated concurrently to collect particle counts (particles/cm3) in size range 0.02 to >1 µm from ambient air and air just inside the breathing zone of the mask (1 measurement per second, evaluation period of 1 minute per test). Percent particle removal was determined for ten home-made, fabric masks of different designs, with and without filter layers, as well as three commercially-produced surgical-type masks. N95 masks were used to validate the method, and a 3M model 1826 surgical mask was used as a baseline for comparison of other masks of this style. Home-made masks worn as designed always had lower particle removal rates than the 3M masks, achieving between 38% and 96% of this baseline. As has been previously observed by Cooper et al. (1983), adding a layer of nylon stocking over the masks minimized the flow of air around the edges of the masks and improved particle filtration efficiency for all masks, including all commercial products tested. Use of a nylon stocking overlayer brought the particle filtration efficiency for five of the ten fabric masks above the 3M surgical mask baseline. This rapid testing method (<2 hours per mask design) provides a holistic evaluation of mask particle removal efficacy (material, design, and fit), and use of this method for testing a wider range of mask materials and designs will provide the public and health care providers with information needed to optimize health protection given resources at hand.

Download Full-text

The effectiveness of an air cleaner in controlling droplet/aerosol particle dispersion emitted from a patient's mouth in the indoor environment of dental clinics

Journal of The Royal Society Interface ◽

10.1098/rsif.2009.0516 ◽

2009 ◽

Vol 7 (48) ◽

pp. 1105-1118 ◽

Cited By ~ 34

Author(s):

Chun Chen ◽

Bin Zhao ◽

Weilin Cui ◽

Lei Dong ◽

Na An ◽

...

Keyword(s):

Aerosol Particle ◽

Aerosol Particles ◽

Ventilation System ◽

Particle Dispersion ◽

Control Measures ◽

Airflow Rate ◽

Particle Removal ◽

Dental Clinic ◽

Dental Clinics ◽

Air Cleaner

Dental healthcare workers (DHCWs) are at high risk of occupational exposure to droplets and aerosol particles emitted from patients' mouths during treatment. We evaluated the effectiveness of an air cleaner in reducing droplet and aerosol contamination by positioning the device in four different locations in an actual dental clinic. We applied computational fluid dynamics (CFD) methods to solve the governing equations of airflow, energy and dispersion of different-sized airborne droplets/aerosol particles. In a dental clinic, we measured the supply air velocity and temperature of the ventilation system, the airflow rate and the particle removal efficiency of the air cleaner to determine the boundary conditions for the CFD simulations. Our results indicate that use of an air cleaner in a dental clinic may be an effective method for reducing DHCWs' exposure to airborne droplets and aerosol particles. Further, we found that the probability of droplet/aerosol particle removal and the direction of airflow from the cleaner are both important control measures for droplet and aerosol contamination in a dental clinic. Thus, the distance between the air cleaner and droplet/aerosol particle source as well as the relative location of the air cleaner to both the source and the DHCW are important considerations for reducing DHCWs' exposure to droplets/aerosol particles emitted from the patient's mouth during treatments.

Download Full-text

Influence of particle size and operating parameters on virus ultrafiltration efficiency

Water Science & Technology Water Supply ◽

10.2166/ws.2011.005 ◽

2011 ◽

Vol 11 (1) ◽

pp. 31-38

Author(s):

Angayar K. Pavanasam ◽

Ali Abbas ◽

Vicki Chen

Keyword(s):

Particle Size ◽

Filtration Efficiency ◽

Transmembrane Pressure ◽

Operating Parameters ◽

Particle Removal ◽

Major Step ◽

Virus Removal ◽

Virus Particles ◽

Key Factor ◽

Effect Of Particle Size

In water treatment, virus removal using ultrafiltration is a major step towards better water quality. In this paper, we study virus filtration efficiency using surrogate virus particles and via statistical surface-response approach. We focus on the effect of particle size (20–100 nm range) as a key factor along with the effects of transmembrane pressure (20–60 kPa range) and feed flowrate (0.3–1.0 L/F;min range) on the filtration virus removal efficiency (LRV). The particle size is shown to impart a great deal of influence on surrogate particle removal. The effect of particle-to-pore-size ratio is reported for comparison of membrane molecular weight cut off (MWCO) performance. It was shown experimentally and through the developed empirical regression model that transmembrane pressure plays a major role in controlling the filtration efficiency along with flowrate. In the studied experimental range, higher LRV values are obtained at lower transmembrane pressure (20 kPa) and at higher feed flowrate (1 L/F;min). Further the effect on LRV of the interaction between transmembrane pressure and particle size seems to be more significant than that of the interaction of flowrate with particle size.

Download Full-text

Laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF): performance, reference spectra and classification of atmospheric samples

Atmospheric Measurement Techniques ◽

10.5194/amt-11-2325-2018 ◽

2018 ◽

Vol 11 (4) ◽

pp. 2325-2343 ◽

Cited By ~ 11

Author(s):

Xiaoli Shen ◽

Ramakrishna Ramisetty ◽

Claudia Mohr ◽

Wei Huang ◽

Thomas Leisner ◽

...

Keyword(s):

Laser Ablation ◽

Aerosol Particle ◽

Mass Spectrometer ◽

Size Range ◽

Aerosol Particles ◽

Time Of Flight ◽

Polystyrene Latex ◽

Dust Particles ◽

Data Set ◽

Flight Mass Spectrometer

Abstract. The laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF, AeroMegt GmbH) is able to identify the chemical composition and mixing state of individual aerosol particles, and thus is a tool for elucidating their impacts on human health, visibility, ecosystem, and climate. The overall detection efficiency (ODE) of the instrument we use was determined to range from ∼  (0.01 ± 0.01) to ∼  (4.23 ± 2.36) % for polystyrene latex (PSL) in the size range of 200 to 2000 nm, ∼  (0.44 ± 0.19) to ∼  (6.57 ± 2.38) % for ammonium nitrate (NH4NO3), and ∼  (0.14 ± 0.02) to ∼  (1.46 ± 0.08) % for sodium chloride (NaCl) particles in the size range of 300 to 1000 nm. Reference mass spectra of 32 different particle types relevant for atmospheric aerosol (e.g. pure compounds NH4NO3, K2SO4, NaCl, oxalic acid, pinic acid, and pinonic acid; internal mixtures of e.g. salts, secondary organic aerosol, and metallic core–organic shell particles; more complex particles such as soot and dust particles) were determined. Our results show that internally mixed aerosol particles can result in spectra with new clusters of ions, rather than simply a combination of the spectra from the single components. An exemplary 1-day ambient data set was analysed by both classical fuzzy clustering and a reference-spectra-based classification method. Resulting identified particle types were generally well correlated. We show how a combination of both methods can greatly improve the interpretation of single-particle data in field measurements.

Download Full-text

Filtration performance of novel microfibrous media embedded with nanofiber flocs for aerosol particle removal

Nanotechnology ◽

10.1088/1361-6528/aaf3d4 ◽

2018 ◽

Vol 30 (7) ◽

pp. 075603 ◽

Cited By ~ 1

Author(s):

Pengfei Zhao ◽

Amulya Poudyal ◽

Wenhua H Zhu ◽

Bruce J Tatarchuk

Keyword(s):

Aerosol Particle ◽

Particle Removal ◽

Filtration Performance

Download Full-text

Inward and outward effectiveness of cloth masks, a surgical mask, and a face shield

10.1101/2020.11.18.20233353 ◽

2020 ◽

Author(s):

Jin Pan ◽

Charbel Harb ◽

Weinan Leng ◽

Linsey C. Marr

Keyword(s):

Particle Size ◽

Respiratory Tract ◽

Filtration Efficiency ◽

The Other ◽

Woven Fabric ◽

Protection Efficiency ◽

Overall Efficiency

AbstractWe evaluated the effectiveness of 11 face coverings for material filtration efficiency, inward protection efficiency on a manikin, and outward protection efficiency on a manikin. At the most penetrating particle size, the vacuum bag, microfiber cloth, and surgical mask had material filtration efficiencies >50%, while the other materials had much lower filtration efficiencies. However, these efficiencies increased rapidly with particle size, and many materials had efficiencies >50% at 2 μm and >75% at 5 μm. The vacuum bag performed best, with efficiencies of 54-96% for all three metrics, depending on particle size. The thin acrylic and face shield performed worst. Inward protection efficiency and outward protection efficiency were similar for many masks; the two efficiencies diverged for stiffer materials and those worn more loosely (e.g., bandana) or more tightly (e.g., wrapped around the head) compared to a standard earloop mask. Discrepancies between material filtration efficiency and inward/outward protection efficiency indicated that the fit of the mask was important. We calculated that the particle size most likely to deposit in the respiratory tract when wearing a mask is ∼2 μm. Based on these findings, we recommend a three-layer mask consisting of outer layers of a flexible, tightly woven fabric and an inner layer consisting of a material designed to filter out particles. This combination should produce an overall efficiency of >70% at the most penetrating particle size and >90% for particles 1 μm and larger if the mask fits well.

Download Full-text

Aerosol particle characteristics measured in the United Arab Emirates and their response to mixing in the boundary layer

10.5194/acp-2021-243 ◽

2021 ◽

Author(s):

Jutta Kesti ◽

John Backman ◽

Ewan James O'Connor ◽

Anne Hirsikko ◽

Eija Asmi ◽

...

Keyword(s):

Boundary Layer ◽

Aerosol Particle ◽

United Arab Emirates ◽

Wind Direction ◽

Aerosol Particles ◽

Surface Wind ◽

Number Concentration ◽

Particle Properties ◽

Boundary Layer Height

Abstract. Aerosol particles play an important in role in the microphysics of clouds and hence on their likelihood to precipitate. In the changing climate already dry areas such as the United Arab Emirates (UAE) are predicted to become even drier. Comprehensive observations of the daily and seasonal variation in aerosol particle properties in such locations are required reducing the uncertainty in such predictions. We analyse observations from a one-year measurement campaign at a background location in the United Arab Emirates to investigate the properties of aerosol particles in this region, study the impact of boundary layer mixing on background aerosol particle properties measured at the surface and study the temporal evolution of the aerosol particle cloud formation potential in the region. We used in-situ aerosol particle measurements to characterise the aerosol particle composition, size, number and cloud condensation nuclei (CCN) properties, in-situ SO2 measurements as an anthropogenic signature and a long-range scanning Doppler lidar to provide vertical profiles of the horizontal wind and turbulent properties to monitor the evolution of the boundary layer. Anthropogenic sulphate dominated the aerosol particle mass composition in this location. There was a clear diurnal cycle in the surface wind direction, which had a strong impact on aerosol particle total number concentration, SO2 concentration and black carbon mass concentration. Local sources were the predominant source of black carbon, as concentrations clearly depended on the presence of turbulent mixing, with much higher values during calm nights. The measured concentrations of SO2, instead, were highly dependent on the surface wind direction as well as on the depth of the boundary layer when entrainment from the advected elevated layers occurred. The wind direction at the surface or of the elevated layer suggests that the cities of Dubai, Abu Dhabi and other coastal conurbations were the remote sources of SO2. We observed new aerosol particle formation events almost every day (on four days out of five on average). Calm nights had the highest CCN number concentrations and lowest κ values and activation fractions. We did not observe any clear dependence of CCN number concentration and κ parameter on the height of the daytime boundary layer, whereas the activation fraction did show a slight increase with increasing boundary layer height, due to the change in the shape of the aerosol particle size distribution where the relative portion of larger aerosol particles increased with increasing boundary layer height. We believe that this indicates that size is more important than chemistry for aerosol particle CCN activation at this site. The combination of instrumentation used in this campaign enabled us to identify periods when anthropogenic pollution from remote sources that had been transported in elevated layers was present, and had been mixed down to the surface in the growing boundary layer.

Download Full-text

CCN measurements at the Princess Elisabeth Antarctica Research Station during three austral summers

10.5194/acp-2018-245 ◽

2018 ◽

Cited By ~ 1

Author(s):

Paul Herenz ◽

Heike Wex ◽

Alexander Mangold ◽

Quentin Laffineur ◽

Irina V. Gorodestkaya ◽

...

Keyword(s):

Southern Ocean ◽

Aerosol Particle ◽

Aerosol Particles ◽

Source Region ◽

Austral Summer ◽

Research Station ◽

Air Masses ◽

Potential Source ◽

The Antarctic ◽

Aitken Mode

Abstract. For three austral summer seasons (2013–2016, each from December to February) aerosol particles arriving at the Belgian Antarctic research station Princess Elisabeth (PE), in Dronning Maud Land in East Antarctica were characterized in terms of number concentrations of total aerosol particles (NCN) and cloud condensation nuclei (NCCN), the particle number size distribution (PNSD), the aerosol particle hygroscopicity and the influence of the air mass origin on NCN and NCCN. In general NCN was found to range from 40 to 6700 cm−3 with a median of 333 cm−3, while NCCN was found to cover a range between less than 10 and 1300 cm−3 for supersaturations (SS) between 0.1 and 0.7 %. It is shown that the aerosol is Aitken mode dominated and is characterized by a significant amount of freshly, secondarily formed aerosol particles, with 94 % and 36 % of the aerosol particles are smaller than 90 nm and &approx; 35 nm, respectively. Measurements of the basic meteorological parameters as well as the history of the air masses arriving at the measurement station indicate that the station is influenced by both, continental air masses originating from the Antarctic inland ice sheet (continental events – CE) and marine air masses originating from the Southern Ocean (marine events – ME). CEs came along with rather constant NCN and NCCN values, which we denote to be Antarctic continental background concentrations. MEs however cause large fluctuations in NCN and NCCN caused by scavenging due to precipitation or new particle formation based on marine precursors. The application of Hysplit back trajectories in form of the potential source contribution function (PSCF) analysis indicate, that the region of the Southern Ocean is a potential source of Aitken mode particles. For particles larger than &approx; 110 nm (CCN measured at SS of 0.1 %) the Antarctic ice shelf regions were found to be a potential source region, most likely due to the emission of sea salt aerosol particles, released from snow particles from surface snow layers by sublimation, e.g., during periods of high wind speed, leading to drifting or blowing snow. On the basis of the PNSDs and NCCN, the critical diameter for cloud droplet activation and the aerosol particle hygroscopicity parameter κ were determined to be 110 nm and 1, respectively, for a SS of 0.1 %. The region of the Antarctic inland plateau however was not found to feature a significant source region for CN and CCN measured at the PE station in austral summer.

Download Full-text

Depth Filtration Assisted by Electrical Fields

Water Science & Technology ◽

10.2166/wst.1993.0212 ◽

1993 ◽

Vol 27 (10) ◽

pp. 95-99 ◽

Cited By ~ 2

Author(s):

G. S. Solt

Keyword(s):

Electrical Properties ◽

Physical Properties ◽

Filtration Efficiency ◽

Particle Removal ◽

Electrical Field ◽

Electrical Fields ◽

Main Drawback ◽

Depth Filtration ◽

Conductivity Water ◽

The Relationship

Depth filtration of liquids is a well established process. Its main drawback is that it does not effectively remove particles smaller than about 2-3 µm diameter, because they do not normally approach near enough to the surface of the medium to become attached to it. A static electrical field overcomes this by promoting electrophoretic movement of the particles. The work has studied particle removal from low conductivity water through fibrous depth filters and has covered a variety of fibres with different physical properties. The results yield a fibre efficiency series, which suggest the relationship between filtration efficiency and the electrical properties of the fibre.

Download Full-text