Aerosol Generation Methods Research Articles

Explosive properties of selected aerosols determined in a spherical 5-L test chamber

Combustible liquids in the form of aerosols are important for many industrial processes. Therefore the problem of explosion hazards posed by the aerosols becomes increasingly more prominent. To correctly assess the explosion risk and fulfil the requirements of the ATEX directive, it is necessary to obtain information regarding the flammable and explosive properties of the aerosols. Unlike in the case of gases and dusts, no standard procedures aimed at obtaining quantitative information of this type exist. Factors that influence the explosion dynamics of aerosols include: concentration, droplet size, temperature etc. Some of these factors are strongly dependent on the aerosol generation methods. A prototype apparatus was designed and constructed to address that dependence. The apparatus was used in an attempt to determine the basic explosion parameters of liquid flammable aerosols. The device consisted of a 5-L spherical vessel equipped with a pump-injection system that generated aerosols as well as a spark ignition source. A wide variety of injection settings were tested to select the most suitable conditions over a broad range of concentrations and fluid properties. A measurement procedure was developed for operating the device. Prototype tests were carried out with fluids commonly used in industry: isopropanol and kerosene. The tests demonstrated the significant influence of the vessel wall temperature on the result accuracy. Correct temperature control made it possible to obtain relationships between the aerosol concentration and the following explosion parameters: maximum explosion pressure and maximum rate of pressure rise.

Generation, characterization, and comparison of human exhaled and technical aerosols for the evaluation of different air-purifying technologies against infectious aerosols

In light of the COVID-19 pandemic, the importance of protective measures against infectious aerosols has drastically increased, as the transmission of diseases via airborne particles is impacting many aspects of everyday life. The protective measures against such infections are determinant in the operation of schools and kindergartens, hygiene in hospitals and medical facilities, in offices, administrative and production facilities, hotels, and the event industry, among others. To test these protective measures, suitable test aerosols and processes are needed. These aerosols ought to be similar to aerosols exhaled by humans as those carry the pathogens and thus need to be removed from the air or inactivated. The exhaled aerosols of several healthy test subjects were characterized by their particle concentration and size distribution. In previous studies, it was found that exhaled particle concentration varies significantly from subject to subject and most of the particles can be found in the submicron size range. Aerosols technically generated through nebulization were emitted by the generators in particle concentrations several orders of magnitude higher than those exhaled by humans, independent of the aerosol generation method and nebulized fluid. The particle size distribution generated by the two nebulizers used, however, was quite similar to the measured size distributions of the human aerosols, with most of the particles below 1 µm in size. Consequently, the used aerosol generators are not suitable to mimic single individuals as active aerosol sources, but rather to provide a sufficient amount of aerosol similar to human aerosols in size distribution, which can be used in the testing of air purification technologies.

Mini-laser based submicron aerosol generator for the simple and stable simulation of combustion particulate matter

Air pollution causes millions of deaths every year. The aerosols, especially airborne nanoparticles generated by combustion, have detrimental effect on health. To protect public health against harmful aerosols, efforts to develop effective air cleaning technology have continued over the past several decades. However, the aerosol generation method used in air cleaning performance tests still rely largely on the traditional methods such as burning cigarettes, paper, and incense. Since the traditional method is inaccurate and unsteady, a more precisely controlled aerosol generation method should be developed. Here, we present a simple and inexpensive aerosol generation method that can easily and consistently produce submicron aerosols through laser ablation. This device constitutes an integrated system with a high-quality mini laser for rapid aerosol generation and a two-axis moving stage for continuous aerosol generation. We demonstrate that the concentration of generated aerosols could be easily controlled by selecting the laser irradiation time and power, resulting in the generation of ~104 particles/cm3 within a few seconds. In addition, the shape and size of generated aerosols can be controlled by changing the target material. This submicron aerosol generation process can be stably maintained for up to 1 h using small-sized (3 cm × 8 cm) affordable and accessible materials, such as wood and leather, highlighting the advantages of this inexpensive and easy-to-use combustion airborne submicron particle generation method.

A Laboratory Dust Generator Applying Vibration to Soil Sample: Mineralogical Study and Compositional Analyses

AbstractA laboratory study was carried out using a vibrating system (SyGAVib) to produce aerosols from four soils collected in the central Tunisian region around Sfax. The aim of this device is to mimic dust emission by natural wind erosion. Using compositional analysis, the dust produced was compared to (i) dust generated in a wind tunnel by the same soils, (ii) fine sieved and (iii) original bulk soils, and (iv) naturally occurring aerosol samples collected in the same area. The relative quartz content strongly decreases from bulk to fine soils, and again from fine soils to both wind tunnel and vibration‐generated aerosols. Compositional data analysis (CoDA) clearly shows (i) a silica dilution effect in bulk soils, and (ii) that if silica is removed from the composition, the elemental compositions of fine soils and generated aerosols are similar but differ from bulk soils. Both aerosol generation methods produce material with chemical compositions that are also close to those measured in field‐sampled aerosols, and the fine soil composition is much closer to that of field and laboratory aerosols than to the parent soil. Aerosols generated from soils in the laboratory, either using a vibrating system or a wind tunnel, can be used as surrogates of the particles collected directly in the field.

Assessment of the Acute Inhalation Toxicity of Airborne Particles by Exposing Cultivated Human Lung Cells at the Air-Liquid Interface.

Here, we present a specially designed modular in vitro exposure system that enables the homogenous exposure of cultivated human lung cells at the ALI to gases, particles or complex atmospheres (e.g., cigarette smoke), thus providing realistic physiological exposure of the apical surface of the human alveolar region to air. In contrast to sequential exposure models with linear aerosol guidance, the modular design of the radial flow system meets all requirements for the continuous generation and transport of the test atmosphere to the cells, a homogenous distribution and deposition of the particles and the continuous removal of the atmosphere. This exposure method is primarily designed for the exposure of cells to airborne particles, but can be adapted to the exposure of liquid aerosols and highly toxic and aggressive gases depending on the aerosol generation method and the material of the exposure modules. Within the framework of a recently completed validation study, this exposure system was proven as a transferable, reproducible and predictive screening method for the qualitative assessment of the acute pulmonary cytotoxicity of airborne particles, thereby potentially reducing or replacing animal experiments that would normally provide this toxicological assessment.

Natural sources and experimental generation of bioaerosols: Challenges and perspectives

Experimental aerosol generation methods aim to represent natural processes; however, the complexity is not always captured and unforeseen variability may be introduced into the data. The current pr...

3D aerosol printing as method to obtain low-temperature ceramic layers of printed circuit boards

A method for the synthesis of the polyaluminosilicates (PAS) with the macromolecules of dendrimer morphology has been developed. A quantum-chemical assessment of thermodynamically possible mechanisms to develop the populations of short-chain aluminosilicates (nuclei of dendrimer macromolecules) has been carried out followed by the domains generation from the dendrimer assemblies capable to contain up to 80 % wt of the dispersed filler particles into their interdomain spaces by means of the GAUSSIAN B3LYP/6-31G (d) software package. A quantitative calculation of the parameters determining the composition of PAS macromolecules and the size of the dendrimer assemblies has been carried out. A method for the synthesis of monomeric precursor-powder has been developed. A new low-temperature ceramic composite material for 3D aerosol printing has been developed on the basis of the PAS and highly dispersed precursor-powder. The processes of 3D aerosol printing of the PAS filled with monomeric precursor-powder have been researched. An optimal method for aerosol generation has been chosen that does not affect the PAS supramolecular structure. The ceramic dielectric layers with high consumer properties have been obtained by means of 3D aerosol printing.

3D aerosol printing of new low-temperature ceramic layers and coatings based on polyaluminosilicates filled with highly dispersed fillers used in microelectronics and medicine

A new low temperature ceramic material for 3D printing based on polyaluminosilicate has been synthesized. Some of the synthesis stages are controlled by the parameters set for 3D aerosol printing. The processes of 3D aerosol printing of polyaluminosilicates filled with a highly dispersed filler have been studied. An optimal method for aerosol generation has been chosen that does not affect the supramolecular structure of a polyaluminosilicate binder. Ceramic dielectric topologies with high thermal conductivity and layer thickness in the nanometer range have been obtained by means of 3D aerosol printing of the synthesized material for the first time.

Polycondensation processes occurring during 3D aerosol printing with new ceramic materials based on nanostructured highly dispersed fillers of polyaluminosilicates used in nano- and microelectronics and medicine

A new low temperature ceramic material for 3D printing based on polyaluminosilicate has been synthesized. Some of the synthesis stages are controlled by the parameters set for 3D aerosol printing. The processes of 3D aerosol printing of polyaluminosilicates filled with a highly dispersed filler have been studied. An optimal method for aerosol generation has been chosen that does not affect the supramolecular structure of a polyaluminosilicate binder. Ceramic dielectric topologies with high thermal conductivity and layer thickness in the nanometer range have been obtained by means of 3D aerosol printing of the synthesized material for the first time.

Plasma-Activated Aerosolized Hydrogen Peroxide (aHP) in Surface Inactivation Procedures.

Hydrogen peroxide is a strong oxidant that possesses an antimicrobial activity. It has been successfully used in surface/room decontamination processes either under the form of hydrogen peroxide vapor (HPV) or of vaporized hydrogen peroxide (VHP). Aerosolized hydrogen peroxide (aHP) offers a third alternative. The technology relies on the dispersion of aerosols of a hydrogen peroxide solution often complemented with silver cations. aHP provides an inexpensive and safe approach to treat contaminated rooms but sometimes fails to achieve the 6-log10 reduction limit in the number of viable microorganisms. Here, we used a venturi-based aHP generator that generates 4 mm in size aerosols from a 12% plasma-activated hydrogen peroxide solution free of silver cations. We could successfully and constantly inactivate bacterial growth from biological indicators containing at least 106 spores of Geobacillus stearothermophilus placed on stainless steel discs wrapped in Tyvek pouches. We could also show that the biological indicators placed at various locations in a class II biosafety cabinet were equally inactivated, showing that hydrogen peroxide aerosols migrate through HEPA filters. Considering that our method for aerosol generation is simple, reproducible, and highly effective at inactivating spores, our approach is expected to serve as a relatively cost effective alternative method for disinfecting potentially contaminated rooms or surfaces.

Aerosol size distribution measurement of electronic cigarette emissions using combined differential mobility and inertial impaction methods: Smoking machine and puff topography influence.

A combination of a real-time high resolution aerosol differential mobility spectrometer (DMS500) and an electrical low pressure impactor (used as a traditional impactor) was applied to simultaneously collect real-time data and analyze particle size by weighing the mass of the aerosol collected on the impactor stages. Nonrefillable fixed-power as well as refillable and power adjustable e-cigarettes (e-cigs) were tested at various puffing flow rates. Two types of smoking machines were used: a smoke cycle simulator that provides instantaneous straight sample delivery to the analyzer and a Human Profile Pump that utilizes two synchronized pistons and operates by sample pull-push mode. Chemical analysis of the major components of e-liquid (propylene glycol, vegetable glycerol, water, and nicotine) was made using a proton nuclear magnetic resonance method. Limited amounts of samples collected on impactor stages were analyzed by liquid chromatography time-of-flight mass-spectrometry to find newly formed semi- or low-volatile organic compounds in e-cig aerosol and by transmission electron microscopy to check for the presence of nanoparticles in e-cig emissions. Differential mobility and inertial impaction methods showed comparable particle size results. Method of aerosol generation (type of the smoking machine) as well as puffing topography affected the e-cig particle size. Newly formed semi- or low-volatile organic compounds as well as metal nanoparticles were found in e-cig aerosol.

A Cost-Effective Method of Aerosolizing Dry Powdered Nanoparticles

The ability to produce nanoscale aerosols from dry powdered material is needed for studies of the toxicity and environmental transformation and fate of manufactured nanoparticles. Wet aerosol generation methods can alter particle chemistry, while dry methods often cannot produce truly nanoscale aerosols. We have developed a cost-effective dry dispersion technique for manufactured nanoparticles and have demonstrated its use with C60 fullerene, TiO2, and CeO2. The system disperses dry powders to create aerosols with mode diameters below 100 nm. Average mode and median diameters for each of the tested manufactured nanoparticles are 91 and 107 nm for C60, 65 and 77 nm for TiO2, and 40 and 43 nm for CeO2. All aerosols exhibit right-skewed unimodal distributions and irregular morphology. Aerosol mass concentrations produced by the dispersion system vary linearly with the mass of nanomaterial loaded into it and are of a magnitude appropriate for inhalation nanotoxicology studies. This work demonstrates the abili...

Pharmaceutical aerosols for the treatment and prevention of Tuberculosis

Historically, pharmaceutical aerosols have been employed for the treatment of obstructive airway diseases, such as asthma and chronic obstructive pulmonary disease, but in the past decades their use has been expanded to treat lung infections associated with cystic fibrosis and other respiratory diseases. Tuberculosis (TB) is acquired after inhalation of aerosol droplets containing the bacilli from the cough of infected individuals. Even though TB affects other organs, the lungs are the primary site of infection, which makes the pulmonary route an ideal alternative route to administer vaccines or drug treatments. Optimization of formulations and delivery systems for anti-TB vaccines and drugs, as well as the proper selection of the animal model to evaluate those is of paramount importance if novel vaccines or drug treatments are to be successful. Pharmaceutical aerosols for patient use are generated from metered dose inhalers, nebulizers, and dry powder inhalers (DPIs). In addition to the advantages of providing more efficient delivery of the drug, low cost, and portability, pharmaceutical dry powder aerosols are more stable than inhalable liquid dosage forms and do not require refrigeration. Methods to manufacture dry powders in respirable sizes include micronization, spray drying, and other proprietary technologies. Inhalable dry powders are characterized in terms of their drug content, particle size, and dispersibility to ensure deposition in the appropriate lung region and effective aerosolization from the device. These methods will be illustrated as they were applied for the manufacture and characterization of powders containing anti-tubercular agents and vaccines for pulmonary administration. The influence of formulation, selection of animal model, method of aerosol generation, and administration on the efficacy demonstrated in a given study will be illustrated by the evaluation of pharmaceutical aerosols of anti-TB drugs and vaccines in guinea pigs by our group.

Synthesis of Cobalt Nanoparticle and Fabrication of Magnetoresistance Devices by Ion-Assisted Aerosol Generation Method

The ionization chemical vapor deposition (ionization CVD) method, which is one of the ion-assisted aerosol generation methods, was used to synthesize Co nanoparticles and fabricate a magnetoresistance device using them. A cobalt tricarbonyl nitrosyl vapor is ionized by a high-pressure ionizer before being fed into the reactor. It reacts and forms nanoparticles by a thermal decomposition reaction in the furnace reactor. Particles deposit electrostatically on an insulator substrate that has two Au electrodes and fill the gap between the electrodes. This Co-nanoparticle device is then annealed under hydrogen gas to deoxidize the deposited particles. After annealing, two copper wires are attached to the two Au electrodes to connect with a DC voltage supplier and an ammeter. The magnetoresistance of the device was evaluated by measuring its electrical resistance using a superconducting quantum interference device (SQUID) magnetometer. The X-ray diffraction patterns of the nanoparticles before and after anneali...

The Cell Membrane as a Major Site of Damage during Aerosolization of Escherichia coli

This study aimed to provide data on the survival and site of damage of Escherichia coli cells following aerosolization using two different techniques, nebulization and flow focusing. Four metabolic stains were assessed for their ability to detect respiratory activities and membrane homeostasis in aerosolized E. coli cells. The degree of sublethal injury increased significantly over the 10-min period of aerosolization in E. coli cells aerosolized by using the Collison nebulizer, reaching up to 99.9% of the population. In contrast, a significantly lower proportion of the population was sublethally damaged during aerosolization using the flow-focusing aerosol generator (FFAG). Concomitantly, loss of membrane homeostasis increased at a higher rate in nebulized cells (68 to 71%) than in those aerosolized by using the FFAG (32 to 34%). The activities of respiratory enzymes decreased at increased rates in nebulized cells (27 to 37%) compared to the rates of decrease in cells aerosolized by using the FFAG (59 to 61%). The results indicate that the physiology of an aerosolized bacterium is linked to the method of aerosol generation and may affect the interpretation of a range of aerobiological phenomenon.

Characterization of a method for aerosol generation from heavy fuel oil (HFO) as an alternative to emissions from ship diesel engines

This work describes a laboratory method to synthesize aerosols with properties similar to those emitted by ocean going ships. In this method, an oxy-hydrogen flame burner nebulizes and combusts heavy fuel oil (HFO). The oil was fed to the burner via a syringe pump at a maximum rate of 15 ml/h. Adjusting the feed temperature of the oil and the use of a quenching ring in the burner, it is possible to obtain an aerosol with a mode diameter of about 11 nm. This is close to the reported 5–8 nm for the nano-mode of ship emissions. Filter samples were also analyzed for elemental carbon, organic carbon and anion composition. No elemental carbon mass was detected and only a few sulfur containing compounds were present. A chemical equilibrium model was applied for both oxy-hydrogen flame and 2-stroke ship diesel engine combustion conditions to predict equilibrium concentrations, chemical formula and phase of vanadium and nickel containing compounds. The model confirmed that the real-world ship diesel engine and the oxy-hydrogen flame burner combustion processes produced the same vanadium, nickel and sulfur particulate matter (PM) products in terms of chemical formula and phase. Both the 5–8 nm particles from real-world ship emissions and the laboratory synthesized particles contain transition metals. Transmission electron microscope (TEM) images of laboratory synthesized particles show similar morphology to those sampled from a ship. Cloud condensation nuclei (CCN) measurement indicates that neither laboratory generated nor ship emitted aerosol is hygroscopic. To our knowledge, this is the first time the 5–8 nm particles emitted from ships have been aptly synthesized on a laboratory scale.

Effect of Aerosol Generation Method on Measured Saturation Pressure and Enthalpy of Vaporization for Dicarboxylic Acid Aerosols

To date, most studies of the thermodynamic properties of organic aerosols have utilized test aerosols generated by spray atomization followed by a diffusion drying step. Some evidence points to possible biases in measured thermodynamic properties stemming from the presence of residual solvent (water or alcohol) in the dried aerosol. In the current study we compared measurements of thermodynamic properties of organic aerosols generated by atomization of aqueous solutions to those generated by homogeneous condensation using a modified Sinclair-La Mer generator. In particular, using the Integrated Volume Method (Saleh et al. 2008), we measured and compared the saturation pressure (P sat ) at 298 K and enthalpy of vaporization (ΔH) of C-6 (adipic) and C-9 (azelaic) dicarboxylic acid aerosol generated using these techniques. We found that P sat and ΔH exhibited no statistically significant difference across the tested aerosol generation methods, indicating that any residual solvent carried by the particles had no impact on the measurements. For adipic acid, we obtained P sat of 3.3 × 10−5 (±0.9 × 10−5) Pa and ΔH of 132 (±8) kJ/mol with atomization, and P sat of 4.2 × 10− 5 (±2.2 × 10−5) Pa and ΔH of 126 (±21) kJ/mol with homogeneous condensation; for azelaic acid, we obtained P sat of 1.4 × 10−5 (±0.5 × 10−5) Pa and ΔH of 145 (±15) kJ/mol with atomization, and P sat of 0.9 × 10− 5 (±0.3 × 10− 5) Pa and ΔH of 158 (±17) kJ/mol with homogeneous condensation. In addition, SEM images of the acids generated by the two methods showed no obvious difference in surface morphology.

A Methodology to Study Impactor Particle Reentrainment and a Proposed Stage Coating for the NGI

Mass-weighted aerodynamic particle-size distribution (APSD) is a key attribute for pharmaceutical products developed to deliver drugs to or through the lungs. In development and quality control, APSD is primarily determined using multistage cascade impactors. For impactor techniques, particle reentrainment is critical because it may lead to an overestimation of the respirable fraction. To avoid reentrainment, the collection surfaces need to be coated with a suitable material. In this study a method was developed to test flow dependence of particle reentrainment in the Next Generation Pharmaceutical Impactor (NGI) at flow rates ranging from 20 to 80 L/min, and was used to test three coating materials: glycerol coating, aqueous coating with, and without soaked filter paper. Uncoated cups were also tested. In the experimental setup a Vilnius Aerosol Generator generated a flow-independent dry powder aerosol, consisting of micronized insulin. The glycerol coating was not well suited to reduce particle reentrainment at flows >or=40 L/min. The soaked filter paper coating was found to give nearly the same particle size distributions regardless of flow and was therefore judged to be the best of those tested. Using liquid only, without the filter paper, gave the same particle size distributions as soaked filter paper for flows <or=40 L/min, while at >or=60 L/min particle reentrainment increased with flow. However, for most applications liquid coating reduced particle reentrainment to an extent at which further reduction was irrelevant. Particle reentrainment was prevalent for uncoated cups at all flow rates tested. This study shows the advantage of using a stable and flow-independent aerosol generation method to examine particle reentrainment at various flows through the NGI. For insulin dry powder, the use of an aqueous solution as cup coating, preferably with a filter, reduced particle reentrainment to a minimum. The results were confirmed in a study with a DPI.

Nanoparticle aerosol generation methods from bulk powders for inhalation exposure studies

Inhalation toxicity studies of nanoparticles require production of test aerosols with a number of acceptable characteristics. Five different generation methods for producing a nanoparticle aerosol from the bulk powder were evaluated with the goal of producing an acceptable aerosol that is homogenous, has a consistent concentration over time in which the magnitude may be intentionally varied, and has a size distribution that is both unimodal and has a small geometric mean diameter relative to the primary particle size of the nanoparticle bulk powder. Four types of bulk powders were evaluated including titanium dioxide, silicon dioxide, polymer-coated silver, and single walled carbon nanotubes. A nebulizer was the only tested method able to produce a consistent aerosol of sufficient magnitude. However, the resulting aerosol contains particles derived from the carrier water. Prior sonication of the nanoparticle suspension alone was found to be not useful for deagglomerating nanoparticles.

Nanoparticle aerosol generation methods from bulk powders for inhalation exposure studies

Nanoparticle aerosol generation methods from bulk powders for inhalation exposure studies