Μm Diameter Size Range Research Articles

Characterization of hollow glass microspheres with potential for regional climate intervention to preserve snow and ice surfaces

Cold regions including the Arctic are warming fast, resulting in increased losses of snow and ice cover. A climate intervention approach, where hollow glass microspheres (HGMs) are applied on snow and ice surfaces such as Artic sea ice has been suggested for ice preservation. HGMs are commercial materials, typically in the 10–200 μm diameter size range. They are very lightweight, highly reflective materials with a high crush strength. It is suggested that through that reflectivity, their application onto snow and ice surfaces can increase the albedo, and thus stabilize snow and ice covers, for example aid the formation of multiyear sea ice. In this study we tested the stability and behaviour of different HGMs under stress conditions to gain knowledge on their potential environmental fate. Stability tests, measured as maintenance of positive buoyancy, during sediment interaction, repeated freezing and thawing and prolonged exposure in seawater showed differences in environmental stability of the tested materials with stability depending on wall thickness and surface integrity. None of the tested materials seemed to be very susceptible to biofouling under the conditions tested. However, leaching of elements, especially Si was observed for some materials, potentially indicating dissolution of the HGMs in seawater over time. Further studies are needed to determine the element dissolution from HGMs and other potential environmental implications such as impacts on organisms. Although this paper is directed towards using HGMs in a local climate intervention application the findings may be of general interest for other uses of HGM materials.

A clinical observational analysis of aerosol emissions from dental procedures.

Aerosol generating procedures (AGPs) are defined as any procedure releasing airborne particles <5 μm in size from the respiratory tract. There remains uncertainty about which dental procedures constitute AGPs. We quantified the aerosol number concentration generated during a range of periodontal, oral surgery and orthodontic procedures using an aerodynamic particle sizer, which measures aerosol number concentrations and size distribution across the 0.5–20 μm diameter size range. Measurements were conducted in an environment with a sufficiently low background to detect a patient’s cough, enabling confident identification of aerosol. Phantom head control experiments for each procedure were performed under the same conditions as a comparison. Where aerosol was detected during a patient procedure, we assessed whether the size distribution could be explained by the non-salivary contaminated instrument source in the respective phantom head control procedure using a two-sided unpaired t-test (comparing the mode widths (log(σ)) and peak positions (DP,C)). The aerosol size distribution provided a robust fingerprint of aerosol emission from a source. 41 patients underwent fifteen different dental procedures. For nine procedures, no aerosol was detected above background. Where aerosol was detected, the percentage of procedure time that aerosol was observed above background ranged from 12.7% for ultrasonic scaling, to 42.9% for 3-in-1 air + water syringe. For ultrasonic scaling, 3-in-1 syringe use and surgical drilling, the aerosol size distribution matched the non-salivary contaminated instrument source, with no unexplained aerosol. High and slow speed drilling produced aerosol from patient procedures with different size distributions to those measured from the phantom head controls (mode widths log(σ)) and peaks (DP,C, p< 0.002) and, therefore, may pose a greater risk of salivary contamination. This study provides evidence for sources of aerosol generation during common dental procedures, enabling more informed evaluation of risk and appropriate mitigation strategies.

Aerosol and droplet generation from performing with woodwind and brass instruments

The performing arts have been significantly restricted due to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. We report measurements of aerosol and droplet concentrations generated when playing woodwind and brass instruments and comparisons with breathing, speaking, and singing. These measurements were conducted in a room with zero number concentration aerosol background in the 0.5-20 µm diameter size range, allowing clear attribution of detected particles to specific activities. A total of 13 instruments were examined across 9 participants. Respirable particle number concentrations and size distributions for playing instruments are consistent with those from the participant when breathing, based on measurements with multiple participants playing the flute and piccolo as well as measurements across the entire cohort. Due to substantial interparticipant variability, we do not provide a comparative assessment of the aerosol generated by playing different instruments, instead considering only the variation in aerosol yield across all instruments studied. Both particle number and mass concentrations from playing instruments are lower than those from speaking and singing at high volume, and no large droplets >20 µm diameter are detected. Combined, these observations suggest that playing instruments generates less aerosol than speaking or singing at high volumes. Moreover, there is no difference between the aerosol concentrations generated by professional and amateur performers while breathing, speaking, or singing, suggesting conclusions for professional singers may also apply to amateurs.

Exosomes in colorectal carcinoma formation: ALIX under the magnifying glass

AbstractExosomes are small membrane vesicles that have important roles in transporting a great variety of bioactive molecules between epithelial compartment and their microenvironment during tumor formation including colorectal adenoma–carcinoma sequence. We tested the mRNA expression of the top 25 exosome-related markers based on ExoCharta database in healthy (n=49), adenoma (n=49) and colorectal carcinoma (n=49) patients using Affymetrix HGU133 Plus2.0 microarrays. Most related genes showed significantly elevated expression including PGK1, PKM, ANXA5, ENO1, HSP90AB1 and MSN during adenoma–carcinoma sequence. Surprisingly, the expression of ALIX (ALG 2-interacting protein X), involved in multivesicular body (MVB) and exosome formation, was significantly reduced in normal vs adenoma (P=5.02 × 10−13) and in normal vs colorectal carcinoma comparisons (P=1.51 × 10−10). ALIX also showed significant reduction (P<0.05) at the in situ protein level in the epithelial compartment of adenoma (n=35) and colorectal carcinoma (n=37) patients compared with 27 healthy individuals. Furthermore, significantly reduced ALIX protein levels were accompanied by their gradual transition from diffuse cytoplasmic expression to granular signals, which fell into the 0.6–2 μm diameter size range of MVBs. These ALIX-positive particles were seen in the tumor nests, including tumor–stroma border, which suggest their exosome function. MVB-like structures were also detected in tumor microenvironment including α-smooth muscle actin-positive stromal cells, budding off cancer cells in the tumor front as well as in cancer cells entrapped within lymphoid vessels. In conclusion, we determined the top aberrantly expressed exosome-associated markers and revealed the transition of diffuse ALIX protein signals into a MVB-like pattern during adenoma–carcinoma sequence. These tumor-associated particles seen both in the carcinoma and the surrounding microenvironment can potentially mediate epithelial–stromal interactions involved in the regulation of tumor growth, metastatic invasion and therapy response.

Measurements of aerosol size-resolved hygroscopicity at sub and supermicron sizes

[1] Airborne measurements of size-resolved aerosol hygroscopicity are presented using an optical particle counting and sizing technique. The measurement range of 0.25 to 3.5 μm is significantly greater, and extends to larger sizes, than previous in situ techniques. Preliminary results reveal a peak in aerosol hygroscopicity in the 0.5 –1.5 μm diameter size range in both marine and polluted aerosols. Geometric growth factors range from 1.3 to 1.5 and 1.1 to 1.3 for the sub and super-micron particles, respectively.

Fluorescence spectra of atmospheric aerosol at Adelphi, Maryland, USA: measurement and classification of single particles containing organic carbon

Abstract We measured laser-induced fluorescence spectra from individual supermicron-sized atmospheric particles drawn into our laboratory at Adelphi, MD, an urban site in the Washington, DC metroplex. A virtural impactor concentrator is used along with an aerodynamic-focusing-nozzle which forms, within an optical chamber, a focused aerosol jet where single aerosol particles can be interrogated on-the-fly with a pulsed 266-nm-wavelength laser. Sample rates are a few liter per minute, and are size dependent. Crossed-diode laser beams indicate when a particle is traversing the sample region and are used to trigger the UV laser to fire and the gated intensified CCD to record the fluorescence spectrum. Our breadboard fluorescence particle spectrometer measures particles in the 3–10 μm diameter size range. Typical trigger rates are a few per second. The usable spectral range is from about 295 to 605 nm. The majority of the particles have very weak fluorescence (on average 8 percent of particles have fluorescence signals above noise). The spectra were grouped using a heirarchical cluster analysis, with parameters chosen so that spectra typically cluster into 4–12 main categories. From the set of all cluster spectra we chose 8 template spectra for reanalyzing all the data. On average, 92 percent (81–94 percent) of the spectra were similar to these templates (using the same thresholds used for the cluster analysis). The major emission bands of the most commonly occurring spectra have peaks: near 460 nm (28 percent of fluorescent particles on average), a very broad hump, and may be humic acids or humic like substances; near 317 nm (on average 24 percent of fluorescent particles); near 321 and 460 nm (a double hump, 12 percent of fluorescent particles); and near 341 nm (8 percent of fluorescent particles). Some of the fluorescence in spectra peaking in the 317–341 nm range is probably from dicyclic aromatics and heterocyclics, including the amino acid tryptophan in biological particles such as bacteria and spores.

Indoor ozone/terpene reactions as a source of indoor particles

This paper reports effects of reactions between ozone and selected terpenes on the concentrations and size distributions of airborne particles in a typical indoor setting. The studies were conducted in adjacent, identical offices. In the first set of experiments, known concentrations of ozone and a selected terpene (either d-limonene, α-terpinene, or a terpene-based cleaner whose major constituent is α-pinene) were deliberately introduced into one of the offices while the other office served as a control. Subsequent particle formation and redistribution were monitored with an eight-channel optical particle counter. Particle formation was observed in each terpene system, but was greatest in the case of d-limonene. The number of particles in the 0.1–0.2 μm diameter size range was as much as 20 times larger in the office with deliberately supplemented ozone and d-limonene than in the office serving as the control. The concentration differences in the larger size ranges developed with time, indicating the importance of coagulation and condensation processes in this indoor environment. In the second set of experiments, d-limonene was deliberately introduced into one of the offices, but ozone was not supplemented in either office; instead, the indoor ozone concentrations were those that happened to be present (primarily as a consequence of outdoor-to-indoor transport). In the office that contained supplemental d-limonene, the concentrations of the 0.1–0.2 μm particles tracked those of indoor ozone (the limiting reagent) and were as much as 10 times greater than levels measured in the comparable office that did not contain supplemental d-limonene. The results demonstrate that ozone/ terpene reactions can be a significant source of sub-micron particles in indoor settings, and further illustrate the potential for reactions among commonly occurring indoor pollutants to markedly influence indoor environments.

In situ measurement of the aerosol size distribution in stratospheric solid rocket motor exhaust plumes

The concentration and size distribution of aerosol in the stratospheric exhaust plumes of two Space Shuttle rockets and one Titan IV rocket were measured using a two component aerosol sampling system carried aboard a WB‐57F aircraft. Aerosol size distribution in the 0.01 µm to 4 µm diameter size range was measured using a two component sampling system. The measured distributions display a trimodal form with modes near 0.005 µm, 0.09 µm, and 2.03 µm and are used to infer the relative mass fractionation among the three modes. While the smallest mode has been estimated to contain as much as 10% of the total mass of SRM exhaust alumina, we find show that the smallest mode contains less than 0.05% of the alumina mass. This fraction is so small so as to significantly reduce the likelihood that heterogeneous reactions on the SRM alumina surfaces could produce a significant global impact on stratospheric chemistry.

Secondary Formation and the Smoky Mountain Organic Aerosol: An Examination of Aerosol Polarity and Functional Group Composition During SEAVS

Size-resolved particle samples were collected in the Smoky Mountains at Look Rock, TN, during the Southeastern Aerosol and Visibility Study (SEAVS) July−August 1995 and analyzed directly by Fourier transform infrared (FTIR) spectroscopy for functional group and chemical bond information. Twenty-eight samples were also gently rinsed in hexane, acetone, and water and reanalyzed after each rinse. Direct FTIR analyses of substrates rinsed with solvents enabled separation by polarity and identification of sulfur-containing organics even though samples were too small for traditional extraction and analysis (approximately 10−15 μg). The submicron organic aerosol was predominantly polar. Most of the nonpolar material, including aliphatic carbon and various minerals, was concentrated in particles greater than 1.0 μm and is most likely from primary biogenic and geogenic emissions, such as plant waxes and windblown soil dust. Unlike Los Angeles, carbonyl size distributions were unimodal and usually peaked in the 0.5−1.0 μm diameter size range. The predominance of sulfate, carbonyl, and organosulfur absorbances, the polarity of the aerosol, and the carbonyl size distributions indicate that secondary formation processes have a large influence on the concentrations, composition, and size distributions of the Smoky Mountain aerosol.

Fractional Aerosol Filtration Efficiency of In-Duct Ventilation Air Cleaners

The filtration efficiency of ventilation air cleaners is highly particle-size dependent over the 0.01 to 3 μm diameter size range. Current standardized test methods, which determine only overall efficiencies for ambient aerosol or other test aerosols, provide data of limited utility. Because particles in this range are respirable and can remain airborne for prolonged time periods, measurement of air cleaner fractional efficiency is required for application to indoor air quality issues. The objectives of this work have been to 1) develop a test apparatus and procedure to quantify the fractional filtration efficiency of air cleaners over the 0.01 to 3 μm diameter size range and 2) quantify the fractional efficiency of several induct air cleaners typical of those used in residential and office ventilation systems. Results show that efficiency is highly dependent on particle size, flow rate, and dust load present on the air cleaner. A minimum in efficiency was often observed in the 0.1 to 0.5 μm diameter size range. The presence of a dust load frequently increased an air cleaner's efficiency; however, some air cleaners showed little change or a decrease in efficiency with dust loading. The common furnace filter had fractional efficiency values of less than 10% over much of the measurement size range.

Secondary organic aerosol formation and transport — II. Predicting the ambient secondary organic aerosol size distribution

The size distribution of atmospheric secondary organic aerosol is simulated by a Lagrangian trajectory model that includes descriptions of gas-phase chemistry, inorganic and organic aerosol thermodynamics, condensation/evaporation of aerosol species, dry deposition and emission of primary gaseous and particulate pollutants. The model is applied to simulate the dynamics of aerosol size and composition along trajectories on 27–28 August 1987 during the Southern California Air Quality Study (SCAQS). The secondary organic aerosol material is predicted to condense almost exclusively on the submicron aerosol in agreement with the available measurements, and its size distribution for Claremont, CA, is predicted to be unimodal with a mass mean diameter of roughly 0.2 μm. The distributions of the various secondary organic aerosol species are predicted to be essentially the same. The secondary organic aerosol (SOA) size distribution is found to depend crucially on the mass and size distribution of primary aerosol on which the secondary species condense and on the surface accomodation coefficient of the condensable species. The SOA size distribution is predicted not to be significantly affected by diffusional dry deposition, sources and sinks of ammonia, emissions of VOC, and secondary aerosol yields from precursor hydrocarbons. A bimodal secondary organic aerosol size distribution is predicted only if the submicron primary dust particles reside mainly in the 0.5–1.0 μm diameter size range, or if the condensable species have a strong preference (an accomodation coefficient difference of two orders of magnitude) for the 0.5–1.0 μm diameter particles. The secondary organic aerosol distribution in Claremont is predicted to shift slightly towards the larger aerosol particles during the nighttime hours with it mass mean diameter peaking around midnight at 0.21 μm and having its minimum in early afternoon at 0.18 μm. In coastal locations of the Los Angeles basin, secondary organic material exists in relatively smaller particles (mass mean diameter 0.16 μm) but in far inland locations it condenses on the available larger particles (mass mean diameter 0.23 μm).

Surface aerosol measurements at Barrow during AGASP-II

Measurements at Barrow during the second Arctic Gas and Aerosol Sampling Program (AGASP-II), conducted in April 1986, showed no rapid long-range transport from lower-latitude source regions to Barrow, and only limited vertical transport from above the boundary layer to the surface. New aerosol size distribution measurements in the 0.005–0.1 μm diameter size range using a Nuclepore-filter diffusion battery apparatus showed a median diameter of about 0.01 μm during times of high condensation nucleus (CN) concentrations. Aerosol black carbon concentrations exceeding 400 ng m−3 were detected at the surface and were more strongly correlated with CN concentrations than with aerosol scattering extinction (σsp), suggesting that aerosol carbon was generally associated with small particles rather than large particles. Measurements at Barrow during AGASP-I, conducted in March–April 1983, showed a series of aerosol events detected at the ground that were caused by rapid long-range transport paths to the vicinity of Barrow from Eurasia. These events were strongly correlated with aerosol loading in the vertical column (optical depth).

Barrow surface aerosol: 1976–1986

Measurements at Barrow during the first Arctic Gas and Aerosol Sampling Program (AGASP-I), conducted in March–April 1983, showed a series of aerosol events detected at the ground that coincided with rapid long-range transport paths from Eurasia to the vicinity of Barrow. These events were strongly correlated with aerosol loading in the vertical column (optical depth). Aerosol and meteorological measurements at Barrow during the second AGASP (AGASP-II), conducted in April 1986, indicate no rapid long-range transport from lower-latitude source regions to the vicinity of Barrow, and only limited vertical transport from above the boundary layer to the surface. Aerosol size distribution measurements in the 0.005–0.1 μm diameter size range using a Nuclepore-filter diffusion battery apparatus showed a median diameter of about 0.01 μm during times of high condensation nucleus (CN) concentrations and 0.05 μm during low concentrations. Aerosol black carbon concentrations exceeding 200 ng m −3 were detected at the surface and were more strongly correlated with CN concentrations than with aerosol scattering extinction ( σ sp ), suggesting that aerosol carbon was generally associated with small particles rather than large particles. A continuous record of CN and σ sp measurements is available from 1976 to the present. The σ sp data show a strong annual cycle, having a maximum exceeding 10 −5 m −1 in the winter and spring (the Arctic haze), and a minimum of about 10 −6m −1 in the summer and fall. The CN data show a semiannual cycle, having a maximum of several hundred per cubic centimeter coinciding with the maximum in σ sp in early spring, and a secondary maximum in August. Minima in CN concentration of about 100 cm −3 occur in summer and late fall. No significant diurnal cycle appears in either the CN or σ sp long-term records.

Ice-forming nuclei in air masses over the Gulf of Mexico

Aerosol particles collected over the Gulf of Mexico during the period from 20 July to 30 August 1986 were examined for their ability to nucleate ice by condensation-followed-by-freezing. Ice-forming nuclei (IFN) in the 0.1–0.4 μm-diameter size range nucleated ice at a temperature of −4°C; their concentrations were between 2 and 10 m −3. Fractions of aerosol particles in that size range nucleating ice at the initial (the highest) temperatures were between 10 −8 and 10 −7. Peaks in the concentration of dimethyl sulfide (DMS) (0800 h) preceded peaks in ice-nucleating temperatures (1300 h) by 5 h; this is sufficient time for DMS molecules to be oxidized to sulfates and to produce mixed aerosol particles through coagulation of different-sized aerosol particles and absorption of sulfur-bearing gas molecules. Fractions of aerosol particles larger than 0.2 μm in diameter containing SO 2− 4 ions were larger than 0.90; most of the time they were 0.99–1.00. All IFN displayed characteristic features of mixed IFN, that is of marine origin (part of IFN concentration independent of temperature) and of continental origin (part of IFN concentration dependent on temperature).

Nature of ice-forming nuclei in marine air masses

Aerosol particles collected over the Pacific Ocean between 7°N and 5°S latitude and 110° to 142°W longitude during the period from 23 May to 19 June 1985 were examined for their ability to nucleate ice by sorption, freezing, and condensation-followed-by-freezing. Ice-forming nuclei (IFN) active by sorption in the temperature range between − 4° and − 17°C were not found in the air masses of pure marine origin. The highest temperatures of freezing of water drops placed on aerosol particles larger than 0.3 μm and below 0.3 μm in diameter were − 12° and − 4°C, respectively. Maximum concentrations of IFN active by condensation-followed-by-freezing at initial ice nucleation temperatures of − 4°, − 6°, and − 7°C were found over some areas to be 40 ± 5, 10, and 401 −1, respectively; these concentrations were of a patchy character over the Pacific Ocean where upwelling regions were present, and they were found to be independent of temperature for the temperature range from the initial ice nucleation temperatures down to − 17°C. Aerosol particles active as IFN were in the 0.1–0.3 μm diameter size range; they were hydrophobic particles and consisted of a chemical compound or compounds that completely vaporized in 10 −6 mm Hg vacuum, indicating that they were neither bacteria nor proteins. It was found that the IFN always existed in the presence of sulfate-bearing aerosol particles smaller than 0.3 μm in diameter and that the sulfate ion is an integral part of the ice nucleating particle. A relation was also found between SO 4 2− ion concentration, the temperature of ice nucleation (the temperature-concentration curve has a maximum), and the nature of the hydrophobic surface. The result of this relationship is that some of the cloud droplets growing in an updraft can be immune to freezing when the concentration of the SO 4 2− ion in solution is too low. Upon evaporation of droplets, the increasing concentration of SO 4 2− ions reaches the critical concentration at the ice nucleation (freezing) curve and causes evaporating droplets to freeze; this supports the Hobbs-Rangno observations. The freezing of condensing and evaporating droplets is time-dependent and therefore depends on the dynamics of clouds.

The interplanetary dust environment beyond 1 AU and in the vicinity of the ringed planets (tutorial talk)

The dust population at 1 AU is known for all sizes between μm and cm to an accuracy better than one order of magnitude. It was observed by Helios that the fine grained dust (μm to 100 μm) decreases with increasing sun distance ∞ r −1.3, at least between 0.3 and 1 AU /1/. Two Pioneer 10 11 dust experiments observed the dust distribution beyond 1 AU in the 10 to 100 μm diameter size range for the first time directly with contradicting results. The penetration experiment saw a constant flux out to 20 AU while the optical experiment observed a decrease of the dust number densities until 3.3 AU, but no scattered light was recorded further out. An attempt is made to explain these observations on the basis of the socalled ‘Greenberg’-particles: cometary core/mantle grains with organic mantle material. The observed enhancement of the dust flux by 1 or 2 orders of magnitudes near Jupiter and Saturn are interpreted as being caused by gravitational focussing, ejecta from jovian/saturnian satellites and electrostatic fragmentation products.

2.3.6 Specific Sources of Extraterrestrial Particles

Sampling of magnetic particles in the 5 to 20 µm diameter size range on the earth’s surface at different latitudes was used to detect meteor streams composed of particles of masses too small to be detected by other means. Magnetic spheroid concentration peaks appeared simultaneously at different latitudes in the Northern and Southern Hemispheres, proving that the majority of spheroids is of extraterrestrial origin. Extraterrestrial particles consist of two major classes: (1) magnetic particles containing a high concentration of iron oxide in the form of magnetite; and (2) glassy particles containing a low concentration of iron and a large concentration of Si and Al; they contain Ni, Mn, Cr and Ti; the concentration of Ti is approximately one hundred times larger in glassy particles than in magnetic spheroids. Comparison of chemical composition of particles collected from different meteor streams must be very carefully evaluated; chemical composition of surfaces and interiors of magnetic particles is different due to selective fractionation of different chemical compounds between molten and solid phases and due to evaporation during entry of meteoritic particles into the atmosphere. The presence of H2O, CO2 and CnH2n+2 in internal cavities of a few spheroids was found to be difficult to explain; those gases were associated with meteoritic particles and consequently they existed in space. The yearly earth flux of extraterrestrial particles can only be determined by the summation of daily fluxes obtained at different latitudes; the daily flux changes from year to year. Fluxes of particles present in January and October were calculated. Particles collected in January seem to originate from sources present between November 6 and January 15; during this period of time S. and N. Taurid, Geminid, Ursid and Quadrantid meteor streams are active. Particles collected in October seem to originate from the unknown meteor stream or from the Giacobini-Zinner meteor stream providing it is preceded by micrometeoritic particles approximately two weeks prior to the visual display.