Microscopy of Woven and Nonwoven Face Covering Materials: Implications for Particle Filtration.

A suite of natural, synthetic, and mixed synthetic-natural woven fabrics, along with nonwoven filtration layers from a surgical mask and an N95 respirator, was examined using visible light microscopy, scanning electron microscopy, and micro-X-ray computed tomography (µXCT) to determine the fiber diameter distribution, fabric thickness, and the volume of solid space of the fabrics. Nonwoven materials exhibit a positively skewed distribution of fiber diameters with a mean value of ≈3 μm, whereas woven fabrics exhibit a normal distribution of diameters with mean values roughly five times larger (>15 μm). The mean thickness of the N95 filtration material is 1093 μm and is greater than that of the woven fabrics that span from 420 to 650 μm.

Common Single-Use Consumer Plastic Products Release Trillions of Sub-100 nm Nanoparticles per Liter into Water during Normal Use.

This study demonstrates that commonly used consumer products such as single-use food grade nylon bags and hot beverage cups lined with low-density polyethylene release nanometer-sized plastic particles at number densities >10 L when exposed to water. The number of particles released was a function of the initial water temperature (high temperature vs ambient) for each of the tested materials. Mean particle diameters were between 30 and 80 nm with few particles >200 nm.

Disinfection of Respirators with Ultraviolet Radiation.

Data for interpreting virus inactivation on N95 face filtering respirators (FFRs) by ultraviolet (UV) radiation are important in developing UV strategies for N95 FFR disinfection and reuse for any situation, whether it be everyday practices, contingency planning for expected shortages, or crisis planning for known shortages. Data regarding the integrity, form, fit, and function of N95 FFR materials following UV radiation exposure are equally important. This article provides these data for N95 FFRs following UV-C irradiation (200 nm to 280 nm) in a commercial UV-C enclosure.

Recent developments in filtration media and respirator technology in response to COVID-19.

Abstract: The COVID-19 pandemic triggered a surge in demand for N95 or equivalent respirators that the global supply chain was unable to satisfy. This shortage in critical equipment has inspired research that addresses the immediate problems and has accelerated the development of the next-generation filtration media and respirators. This article provides a brief review of the most recent work with regard to face respirators and filtration media.

Filter Inserts Impact Cloth Mask Performance against Nano- to Micro-Sized Particles.

The United States Centers for Disease Control and Prevention and World Health Organization recognize that wearing cloth face coverings can slow the transmission of respiratory diseases via source control. Adding a partial layer of material with a high filtration efficiency (FE, ..

Hydration of Hydrophilic Cloth Face Masks Enhances the Filtration of Nanoparticles.

Under high humidity conditions that mimic respiration, the filtration efficiency (FE) of hydrophilic fabrics increases when challenged with hygroscopic nanoparticles, for example, respiratory droplets containing SARS-CoV-2. The FE and differential pressure (Δ) of natural, synthetic, and blended fabrics were measured as a function of relative humidity (RH) for particles with mobility diameters between 50 and 825 nm. Fabrics were equilibrated at 99% RH, mimicking conditions experienced when worn as a face mask.

Filtration Efficiencies of Nanoscale Aerosol by Cloth Mask Materials Used to Slow the Spread of SARS-CoV-2.

Filtration efficiency (), differential pressure (Δ), quality factor (), and construction parameters were measured for 32 cloth materials (14 cotton, 1 wool, 9 synthetic, 4 synthetic blends, and 4 synthetic/cotton blends) used in cloth masks intended for protection from the SARS-CoV-2 virus (diameter 100 ± 10 nm). Seven polypropylene-based fiber filter materials were also measured including surgical masks and N95 respirators. Additional measurements were performed on both multilayered and mixed-material samples of natural, synthetic, or natural-synthetic blends to mimic cloth mask construction methods.

Comparing Aerosol Refractive Indices Retrieved from Full Distribution and Size- and Mass-Selected Measurements.

Refractive index retrievals (also termed inverse Mie methods or optical closure) have seen considerable use as a method to extract the refractive index of aerosol particles from measured optical properties. Retrievals of an aerosol refractive index use one of two primary methods: 1) measurements of the extinction, absorption and/or scattering cross-sections or efficiencies of size- (and mass-) selected particles for mass-mobility refractive index retrievals (MM-RIR) or 2) measurements of aerosol size distributions and a combination of the extinction, absorption and/or scattering coefficients for full distribution refractive index retrievals (FD-RIR). These two methods were compared in this study using pure and mixtures of ammonium sulfate (AS) and nigrosin aerosol, which constitute a non-absorbing and absorbing material, respectively.

Direct In Situ Mass Specific Absorption Spectra of Biomass Burning Particles Generated from Smoldering Hard and Softwoods.

Particles from smoldering biomass burning (BB) represent a major source of carbonaceous aerosol in the terrestrial atmosphere. In this study, mass specific absorption spectra of laboratory-generated smoldering wood particles (SWP) from 3 hardwood and 3 softwood species were measured in situ. Absorption data spanning from λ = 500 to 840 nm were collected using a photoacoustic spectrometer coupled to a supercontinuum laser with a tunable wavelength and bandwidth filter.

Light Source Effects on Aerosol Photoacoustic Spectroscopy Measurements.

Photoacoustic spectroscopy measurements of flame-generated soot aerosol coated with small amounts of water yielded absorption enhancements that were dependent on the laser used: quasi-continuous wave (Q-CW, ≈ 650 ps pulse duration and 78 MHz repetition rate) versus continuous wave (CW). Water coating thickness was controlled by exposing the aerosol to a set relative humidity (RH). At ≈ 85 % RH, the mass of the soot particles increased by an amount comparable to a monolayer of water being deposited and enhanced the measured absorption by 36 % and 15 % for the Q-CW and CW lasers, respectively.

Measured Wavelength-Dependent Absorption Enhancement of Internally Mixed Black Carbon with Absorbing and Nonabsorbing Materials.

Optical absorption spectra of laboratory generated aerosols consisting of black carbon (BC) internally mixed with nonabsorbing materials (ammonium sulfate, AS, and sodium chloride, NaCl) and BC with a weakly absorbing brown carbon surrogate derived from humic acid (HA) were measured across the visible to near-IR (550 to 840 nm). Spectra were measured in situ using a photoacoustic spectrometer and step-scanning a supercontinuum laser source with a tunable wavelength and bandwidth filter. BC had a mass-specific absorption cross section (MAC) of 7.

Practical Limitations of Aerosol Separation by a Tandem Differential Mobility Analyzer-Aerosol Particle Mass Analyzer.

A cavity ring-down spectrometer and condensation particle counter were used to investigate the limitations in the separation of singly and multiply charged aerosol particles by a tandem differential mobility analyzer (DMA) and aerosol particle mass analyzer (APM). The impact of particle polydispersity and morphology was investigated using three materials: nearly-monodisperse polystyrene latex nanospheres (PSL); polydisperse, nearly-spherical ammonium sulfate (AS) and polydisperse lacey fractal soot agglomerates. PSL and AS particles were easily resolved as a function of charge.

Measurement of Gas and Aerosol Phase Absorption Spectra across the Visible and Near-IR Using Supercontinuum Photoacoustic Spectroscopy.

We demonstrate a method to measure the absorption spectra of gas and aerosol species across the visible and near-IR (500 to 840 nm) using a photoacoustic (PA) spectrometer and a pulsed supercontinuum laser source. Measurements of gas phase absorption spectra were demonstrated using H2O(g) as a function of relative humidity (RH). The measured absorption intensities and peak shapes were able to be quantified and compared to spectra calculated using the 2012 High Resolution Transmission (HITRAN2012) database.

Packing density of rigid aggregates is independent of scale.

Large planetary seedlings, comets, microscale pharmaceuticals, and nanoscale soot particles are made from rigid, aggregated subunits that are compacted under low compression into larger structures spanning over 10 orders of magnitude in dimensional space. Here, we demonstrate that the packing density (θf) of compacted rigid aggregates is independent of spatial scale for systems under weak compaction. The θf of rigid aggregated structures across six orders of magnitude were measured using nanoscale spherical soot aerosol composed of aggregates with ∼ 17-nm monomeric subunits and aggregates made from uniform monomeric 6-mm spherical subunits at the macroscale.

Dependence of soot optical properties on particle morphology: measurements and model comparisons.

We report the first mass-specific absorption and extinction cross sections for size- and mass-selected laboratory-generated soot aerosol. Measurement biases associated with aerosols possessing multiple charges were eliminated using mass selection to isolate singly charged particles for a specified electrical mobility diameter. Aerosol absorption and extinction coefficients were measured using photoacoustic and cavity ring-down spectroscopy techniques, respectively, for lacey and compacted soot morphologies.

Direct measurements of mass-specific optical cross sections of single-component aerosol mixtures.

The optical properties of atmospheric aerosols vary widely, being dependent upon particle composition, morphology, and mixing state. This diversity and complexity of aerosols motivates measurement techniques that can discriminate and quantify a variety of single- and multicomponent aerosols that are both internally and externally mixed. Here, we present a new combination of techniques to directly measure the mass-specific extinction and absorption cross sections of laboratory-generated aerosols that are relevant to atmospheric studies.

Different mechanisms govern the two-phase Brust-Schiffrin dialkylditelluride syntheses of Ag and Au nanoparticles.

Here we report the first unambiguous identification of the chemical structures of the precursor species involving metal (Au and Ag) ions and Te-containing ligands in the Brust-Schiffrin syntheses of the respective metal nanoparticles, through which the different reaction pathways involved are delineated.

Crumpled nanopaper from graphene oxide.

Graphene oxide (GO) in aqueous solution was aerosolized and rapidly dried to produce crumpled nanopaper-like sheets. Online size selection and aerosol mass analysis was used to determine the fractal dimension (D) of crumpled GO nanosheets as 2.54 ± 0.

Mechanistic insights on one-phase vs. two-phase Brust-Schiffrin method synthesis of Au nanoparticles with dioctyl-diselenides.

Metal precursors in the one-phase (1p) and two-phase (2p) Brust-Schiffrin method (BSM) synthesis of Au nanoparticles (NPs) using dioctyl-diselenides were identified. A single dominant type of metal precursor was found in the 1p synthesis as compared to multiple ones in the 2p synthesis, which was proposed as the key reason why the former is better than the latter.

A volcano curve: optimizing methanol electro-oxidation on Pt-decorated Ru nanoparticles.

Controlled Pt adlayers were deposited on commercial Ru nanoparticles (NPs) using an industrially scalable one-pot ethylene glycol (EG) reduction based method and were characterized by X-ray diffraction (XRD), electrochemical (EC) CO stripping voltammetry, inductively-coupled plasma optical emission spectrometry (ICP-OES), X-ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM). Compared with the previously used "spontaneous deposition", the wet chemistry-based EG method is less technically demanding, i.e.

Molecule-induced interface states dominate charge transport in Si-alkyl-metal junctions.

Semiconductor-molecule-metal junctions consisting of alkanethiol monolayers self-assembled on both p(+) and n(-) type highly doped Si(111) wires contacted with a 10 µm Au wire in a crossed-wire geometry are examined. Low temperature transport measurements reveal that molecule-induced semiconductor interface states control charge transport across these systems. Inelastic electron tunneling spectroscopy also highlights the strong contribution of the induced interface states to the observed charge transport.

Demonstration of molecular assembly on Si (100) for CMOS-compatible molecule-based electronic devices.

In this work, we establish the potential of a UV-promoted direct attachment of alkanes with alcohol and thiol linkers to the silicon (100) surfaces for use in molecular electronic devices with increased potential for integration with existing CMOS technologies. Characterization of the self-assembled monolayers via Fourier transform infrared spectroscopy, spectroscopic ellipsometry, and X-ray photoemission spectroscopy shows that the films assembled on the Si (100) are comparable in quality, aliphatic monolayer coverage, and extent of substrate oxidation to those assembled on the more extensively studied Si (111) crystal face. Simple Si (100)-based electronic devices fabricated with the monolayers exhibited molecule-dependent electrical characteristics.

Origin of discrepancies in inelastic electron tunneling spectra of molecular junctions.

We report inelastic electron tunneling spectroscopy (IETS) of multilayer molecular junctions with and without incorporated metal nanoparticles. The incorporation of metal nanoparticles into our devices leads to enhanced IET intensity and a modified line shape for some vibrational modes. The enhancement and line-shape modification are both the result of a low lying hybrid metal nanoparticle-molecule electronic level.

Directed electroless growth of metal nanostructures on patterned self-assembled monolayers.

The directed placement of Cu nanostructures on surfaces has been studied using a combination of scanning probe lithography and electroless metal deposition onto nanopatterned SAMs of 16-mercaptohexadecanoic acid (16-MHA) on Au. In situ studies using nanoscale molecular gradients reveal how controlling the areal density of the 16-MHA molecules dictates the nucleation and growth of the metal nanostructures. The influence of controlling pattern line spacing and tip path on pattern feature fidelity is also discussed.