C Scanning Electron Microscopy Analysis
Primary bioaerosol particles were analyzed by using a variable pressure Tescan Mira3 High-Resolution Schottky FE-SEM located in the geology department at Lund University. It should be noted that the SEM analysis was limited to three days: 9 , 12 , and 13 September, as an intensive collection of SEM images characterizing the size distributions for all the samples was not practical. During each of the three days, the size distribution and IN number were estimated for total biological aerosols and fractions obtained on each of the 5 and 1.2 m filters separately. Thus, nine pairs of measurements of active IN and size distributions were available from three intensive sampling days mentioned above and will be referred to as the nine cases hereafter.
The samples were coated with a thin layer of palladium, sputter deposited prior to the SEM analysis, to reduce charging under the electron beam. The coated samples were examined at a beam size of 15 keV with a working distance of 10 mm. The working distance was lowered for Si wafer samples to obtain clearer images of particles with a diameter D< 1.5 m.
Details of SEM analysis including sample volume, scanned area, and the number of bioaerosol images collected for filters. The values for Si wafers are given in parentheses.
After acquiring the images of bioaerosols from SEM analysis, we classified them into common PBAP groups based on size and morphology.
F Classification Of Pbaps Based On Sem Images
We innovated our own system of PBAP classification based on specimen SEM images collected from the available literature and created a list of distinct morphological features. These criteria are listed in Table 3 for the general size and morphological characteristics of different PBAP groups, based on the literature available. These characteristics form the basis for classifying PBAPs SEM images into basic groups.
Typical size ranges, concentrations in air, and general morphological characteristics of different PBAPs, based on available literature are given. Based on this information, PBAPs have been classified into different groups. Also enlisted are various studies referred to for classification of PBAPs.
Representative scanning electron microscopy images of brochosomes and leaf litter , fungal spore, bacteria, and pollen from 0911N, 0912D, and 0913D. The scale is varying for each image and is shown separately.
Citation: Journal of the Atmospheric Sciences 78, 7 10.1175/JAS-D-20-0096.1
General size and mean number concentration of various PBAP groups based on our SEM analysis.
Comparison of total bioaerosol particle number concentration measured by scanning electron microscopy with flow cytometry . Error bars for number concentrations measured by FCM were estimated based on independent runs of FCM for the same sample.
Citation: Journal of the Atmospheric Sciences 78, 7 10.1175/JAS-D-20-0096.1
Aerosol Test Chambers: Current State And Practice During The Covid
- 1MRIGlobal, Kansas City, MO, United States
- 2JRAD, Stafford, VA, United States
Respiratory infectious disease outbreaks such as those caused by coronaviruses and influenza, necessitate the use of specialized aerosol test chambers to study aspects of these causative agents including detection, efficacy of countermeasures, and aerosol survivability. The anthrax attacks from 2001 and earlier biowarfare and biodefense also influenced the study of biological aerosols to learn about how certain pathogens transmit either naturally or through artificial means. Some high containment biological laboratories, which work with Risk Group 3 and 4 agents in biosafety level -3, biosafety level-4 containment, are equipped with aerosol test chambers to enable the study of high-risk organisms in aerosolized form. Consequently, the biomedical, military and environmental sectors have specific applications when studying bioaerosols which may overlap while being different. There are countless aerosol test chambers worldwide and this number along with numerous high containment biological laboratories underscores the need for technical standards, regulatory and dual-use compliance. Here we survey common aerosol test chambers and their history, current use, and practice. Our findings reinforce the importance and need for continued collaboration among the multi-disciplinary fields studying aerobiology and biological aerosols.
Also Check: What Is The Title Of This Picture Math Worksheet
Fluorescence Applications To Surface Analysis
Luminescence from a sample can provide a tremendous amount of information about the chemistry and molecular structure of a threat. Most biological and organic materials absorb strongly in the deep UV, corresponding to their first electronic state, and will emit fluorescence and phosphorescence at longer wavelengths. One of the advantages of fluorescence and phosphorescence is that their spectra are independent of the excitation wavelength. Asher has shown that the wavelength range of fluorescence emission from organic materials is generally longer than 260 nm.4244 This advantage was further proven in subsequent publications by Nelson,45 Sparrow,46 Wu,47 and many others.
Y. Picó, V. Andreu, in, 2014
Aerosols Droplets And Airborne Spread: Everything You Could Possibly Want To Know
This post was based on the best available evidence at the beginning of the pandemic . The information contained is still very relevant, but there is also now an updated/companion review specifically looking at the transmission of COVID-19 , that can be found here.
The rapid emergence of COVID-19 has created tremendous uncertainty in medicine. We dont know where this pandemic is headed. We dont know the ideal management strategy. Every day brings conflicting information. Emergency medicine is a field that embraces uncertainty, but knowledge is an important pillar of our sense of control in medicine, and COVID-19 is doing a good job highlighting massive gaps in our knowledge. One of those gaps is the precise mechanisms through which infectious diseases spread and how best to protect ourselves. We hear terms like aerosol generating and droplets, but their precise meaning can be unclear, and so it is hard to know how to adjust our practice. In this post, I will review everything I have been able to learn about aerosols and droplets, how they spread, and how they should impact our practice.
Recommended Reading: What Does Iso Mean In Biology
What Is Aerosol And Example
An aerosol is a collection of solid particles or liquid droplets dispersed in air. Examples include smoke, fog, sea spray and pollution particles from vehicles.
What does aerosol mean in medical terms?
Aerosol: A fine spray or mist. Medications in aerosol form can be administered via a nebulizer and inhaled.
Small Particles With Large Impacts
Atmospheric aerosols consist of small particles of solids, like dust, and liquids, like water, suspended in the atmosphere. Atmospheric aerosols can be either emitted directly into the atmosphere as a particle, like ash, or form when emitted gases undergo complex chemical reactions and condense as particles. Aerosols also have a wide range of sources and can be further classified as natural or anthropogenic, which originate from human-related activities. There are many different types of natural aerosols, including dust, sea-salt, smoke, and those from living sources, referred to as biogenic aerosols.
Atmospheric aerosols range in size from a few nanometersthe size of a DNA moleculeto tens of micronsthe width of a human hairin diameter. The size of a particle alters its behavior, including how long it remains suspended in the air. Aerosol systems are complex, undergoing chemical reactions that can cause the aerosols to evaporate and recondense. This complexity makes it challenging to predict and model aerosol properties.
Don’t Miss: What Does M M Mean In Chemistry
Remote Detection Of Harmful Atmospheric Compounds
The early detection and identification of potentially harmful airborne pathogens and ozone-depleting molecules in the atmosphere have become a major issue for both defense and public security and for public health reasons. This requires fast detection of the source location, three-dimensional mapping of the plume as it propagates, and unambiguous identification of the molecules and agents among the broad variety of atmospheric background aerosols. Several methods, including the use of nonlinear light detection and ranging , ultraviolet resonance fluorescence, and air laser sensor, have been demonstrated that meet these broad objectives.
Most harmful bioaerosols, like the Bacillus anthracis , are bacteria typically 0.51 m in size . Depending on the spreading conditions, they can agglomerate in clusters of sizes up to 10 m. The bioagents contain natural fluorophores, like amino acids, nicotine amides, and flavins, which can be used as characteristic tracers of their biological nature. LIDAR is an attractive technique for the detection and identification of these particles in nearly real-time, indicated by the backscattered fluorescence signal that carries characteristic spectral information from the bioaerosol. The detection limit of a LIDAR system using the best commercially available 266-nm Nd:YAG laser would be on the order of only a few hundred meters in a high-ozone urban environment due to Rayleigh scattering and ozone absorption .
H.S. Lee, … R.M. Serino, in, 2014
Identification Of Programmatic Gaps
The significant findings of the gap analysis were that, in general:
Of special critical interest is replacement of key, experienced NIOSH aerosol experts who have left or will soon leave the Institute. Formal planning, funding, recruitment, and staffing of mentorship programs should be provided to bridge this gap. A full and detailed analysis of specific gap issues will be a priority for any continuing activity of this, or related, team.
Don’t Miss: Introduction To 3 Dimensional Geometry
What Is An Example Of An Aerosol
An aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. Aerosols can be natural or anthropogenic. Examples of natural aerosols are fog, dust, forest exudates and geyser steam.
What are aerosols used for?
aerosol therapy use of an aerosol for respiratory care in the treatment of bronchopulmonary disease. The major purpose of this is the delivery of medications or humidity or both to the mucosa of the respiratory tract and pulmonary alveoli.
Stability Of Generated Aerosol Particles
Stability of nanoparticle agglomerates is critical for estimating size distribution of aerosolized particles from nano-powders or other sources. At nanotechnology workplaces, workers can be exposed via inhalation to potentially toxic substances during handling and processing of nanomaterials. Nanoparticles in the air often form agglomerates due to attractive inter-particle forces, such as van der Waals force or electrostatic force if the particles are charged. As a result, aerosol particles are usually observed as agglomerates rather than individual particles. For exposure and risk assessments of airborne nanoparticles, it is important to know about the size distribution of aerosols. When inhaled by humans, particles with different diameters are deposited in varied locations of the central and periphery respiratory system. Particles in nanoscale have been shown to penetrate the air-blood barrier in lungs and be translocated into secondary organs in the human body, such as the brain, heart and liver. Therefore, the knowledge on stability of nanoparticle agglomerates is important for predicting the size of aerosol particles, which helps assess the potential risk of them to human bodies.
Influenza: Droplet Or Airborne
We need to think about the practical implications of all this basic science. Nobody is all that worried about influenza right now, but it is important to know a little bit about the transmission of influenza, because almost all of our PPE recommendations are based on extrapolations from this more common disease. Although the science is not definitive, it appears that influenza is transmitted by both large and small droplets . However, although airborne transmission is possible, large droplet or contact transmission is probably responsible for the vast majority of disease transmission.
Although some experts seem to doubt that influenza can be spread through small droplets or airborne droplet nuclei, there are multiple lines of evidence that support this hypothesis. Studies in ferrets showed that influenza spread even when the animals were separated by S and U shaped ducts that would not allow for the passage of larger droplets, indicating that infection was conveyed either by droplet-nuclei or very fine dust particles. Likewise, in studies of mice, lower ventilation rates led to higher transmission rates, leading the authors to conclude spread must be by airborne droplet nuclei. There are numerous other animal studies demonstrating the spread of influenza uphill over distances longer than droplets are supposed to travel, strongly supporting the conclusion of airborne spread.
B Aerosol Measurements And Sample Collection
1) Aerosol size distribution measurements
The aerosol size distribution and number concentration at the ATTO site were measured by a Scanning Mobility Particle Sizer and an Aerodynamic Particle Sizer . The SMPS measures the electrical mobility diameter , while the APS gives aerodynamic diameters of the particles. There were frequent interruptions in aerosol measurements during our observational period due to lightning strikes and associated damage to the power supply and installation. Therefore, simultaneous measurements of the aerosol size distribution from both the SMPS and APS were available only for a few days.
2) Aerosol collection by filter method
Daily sampling plan along with sampling type, time duration, flow rate, volume sampled, sampling purpose, and the instrument used for sample analysis.
Cascade filter samples were collected with an average volumetric sample flow rate of 4 L min1 for approximately 4 h each day. In addition, a set of cascade filters with a sample flow rate of 1.5 L min1 was collected for about 16 h. A set of aerosol samples with a sample volume of about 200 L was collected using only a 0.2 m filter to estimate IN concentrations activated by the immersion-freezing mode in Frankfurt Ice Nuclei Deposition Experiment chamber.
3) Aerosol collection by PEAC7
Read Also: What Is Precipitation In Geography
Comparing N95 And Surgical Masks
We actually use masks for 2 different purposes and it results in a common misunderstanding among the lay public. We can use masks to keep droplets out of the respiratory tract , but we can also use masks to keep droplets in . The surgical mask is significantly less effective than the N95 at keeping particles out, but it is very good at keeping particles in. . With coughing and sneezing patients in the hospital, one of the most important infection control strategies is placing surgical masks on the patients to limit the number of droplets then make it to the environment. Similarly, when hospitals are asking employees to wear surgical masks at all times right now, it is not a strategy designed primarily to protect employees, but to limit unintentional spread from asymptomatic or minimally symptomatic individuals.
Charity Home For Handicapped Children
Four prototypes were built and tested during the months of September and October 2003. The new prototypes were tested and the performances for VOC and bioaerosol removal and remediation were within 90 % of the benchmark unit . Permission was obtained to field test two of the Prototype Units at the Home of the Loving Faithfulness at Castle Peak Road, Sheung Shui. The Home is situated between two busy highways and next to a Tofu factory. Therefore, the particulate and bioaerosol levels at the site were high, and this was believed to be the main contributing factor in the high incidence of respiratory illnesses in the children. The two Prototype Units were placed at one of the children’s room shown in Fig. 12.9-13 and were operated 10 h/day for 7 days a week from May until September of 2004. The room houses ten children and only has one window-mounted, air conditioner that was turned on occasionally during summer nights, but more often windows were left opened and the fan was turned on. This means that the room temperature and humidity fluctuates depending on the weather. The temperature ranges between 22 to 33 °C and the relative humidity was between 60 to 92 % during the three months measurement. Also, the particulate and bioaerosol levels can change dramatically from day to day.
Table 12.9-4. An example of a single day prototype Unit field test results at HKUST University canteen.
Rajiv Kohli, in, 2012
Read Also: How To Type Math Symbols In Word
B Observations Of Total In
The observations of total IN including deposition and condensation-freezing IN and immersion freezing IN are shown in Fig. 5. Figures 5ac show the concentration of IN activated by deposition and condensation-freezing modes determined as a function of temperature and relative humidity over ice obtained by the FRIDGE-STD measurements. No active IN at temperatures warmer than 20°C was detected with this instrument, suggesting that their concentrations may have been lower than the detection threshold of 0.01 L1. For a given temperature and RHice, large day-to-day variability in IN concentration was observed. The results indicate that higher IN concentrations were associated with higher RHice at any given temperature. The mean IN concentration at 25°C ranged from 0.03 to 0.43 L1 for RHice between 120% and 130%, in agreement with recent measurements by Schrod et al. at the ATTO site. During the field campaign, the highest concentration of deposition and condensation freezing IN measured by FRIDGE-STD was 4.5 L1 at 30°C.
The concentration of IN activated by deposition and condensation freezing mode in the FRIDGE-STD chamber at 20°, 25°, and 30°C. The dotted vertical lines in indicate saturation with respect to water. Cumulative IN concentrations activated by immersion freezing mode from separate experiments in FRIDGE-IMM are shown. The cumulative immersion freezing IN concentrations for 0911N, 0912D, and 0913D from the analysis in LINDA are also shown.
Model Prediction Of Biological Particles For 5 And 12 M Filters
Prediction of biological ice nuclei concentrations by new empirical parameterization based on the size distribution of PBAPs on 5 and 1.2 m filter is shown in Fig. D1.
Prediction of biological ice nuclei concentrations by new empirical parameterization based on the size distribution of PBAPs in 0911N, 0912D, and 0913D shown as a function of temperature for various bioaerosol species. The total biological ice nuclei concentrations from the empirical parameterization are compared with the observed values from the drop freezing experiments with LINDA. For each case, the predictions based on PBAP size distribution from 5 and 1.2 m are shown separately. Black dotted lines in the plot of 1.2 m filter represent the upper and lower bounds in predicting ice nuclei concentrations due to uncertainties in collection efficiency.
Citation: Journal of the Atmospheric Sciences 78, 7 10.1175/JAS-D-20-0096.1
Recommended Reading: How To Find Speed In Physics