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This technical note documents the use of paper as electrospray emitters. The porous structure of the paper automatically delivers the liquid by capillary effects without the need of a mechanical pump. The liquid flow rate can be approximately quantified using Washburn equation. Despite the limited durability, paper-based electrospray emitters exhibit unique features such as ease of multiplexing, self-regulated liquid supply without need of pumps, ultra-low cost, and versatility provided through origami.

Ash formation during industrial-scale bubbling fluidized bed (BFB) and circulating fluidized-bed (CFB) combustion of bark, waste wood and paper mill sludges has been studied. The principal ash formation mechanism was the sintering of 0.2–4 μ m paper filler mineral particles into larger, porous ash agglomerates from 10 to 200 μ m in size which dominated the fly ash total mass and specific surface area. Fly ash total mass concentration at the electrostatic precipitator inlet conditions varied from 4.5 g N -1 m -3 at BFB to 8.3 g N -1 m -3 at CFB while the respective total surface area concentrations as determined with nitrogen absorption were 32 and 83 m 2 N -1 m -3 . During bark combustion in the BFB, we observed an ultrafine mode at 0.05 μ m consisting of spherical particles and their chain-type agglomerates. Ultrafine mode mass and surface area concentrations were 3 and 0.1 m 2 N -1 m -3 , respectively, as determined with the electrical low-pressure impactor and with the differential mobility analyzer. Ultrafine particles were formed via nucleation of volatilized ash species followed by particle growth via collision and coalescence and via vapor condensation. During waste wood combustion in the CFB, ultrafine particle concentration was significantly lower than during bark combustion in BFB, indicating reduced ash volatilization during CFB combustion. When co-firing sludge with bark in the BFB and with waste wood in the CFB ultrafine particle concentration was further reduced. Results from continuous aerosol measurements by the electrical low-pressure impactor (ELPI), by the scanning differential mobility analyzer (SMPS) and by the tapered element oscillating microbalance (TEOM) as the function of BFB process conditions suggest that co-combustion of sludge reduces significantly the ultrafine particle formation rate. No significant enrichment of alkali and trace metals in the ultrafine particles was observed.

In this paper several statements of Kandlikar and Ramachandran concerning the one-to-one correspondence between the spectrometric channels and aerosol size classes, overlaps of the kernels of integral equation, errors of the algebraic systems’ solutions and some inversion algorithms are discussed. It is shown that expression A −1 e ( A -linear algebraic system matrix, e -vector of the experimental errors) cannot be interpreted as the standard deviation of random errors and its adequate interpretation is given. The expressions for standard deviation of the system's solution are derived using the error propagation formula. It is indicated that known inequality for the errors of linear systems’ solutions including condition number of matrix cond is not applicable to the random errors, and the new inequality is given. The approach of smooth continuous size distribution function concept is shown to meet with difficulties since its actual realization is discrete, stochastic and has only two values: 0 and 1.

A simple equation for the inertial deposition of particles in a bent tube, derived from an analytical solution to the equation of motion for a particle and based on slug flow, is compared with the more complicated theory of Cheng and Wang (1975), with other theories and with experimental data. Its merits are discussed.

A statistical investigation is performed into the effectiveness of two disinfectants (gaseous ClO2 and weak acid hypochlorous water) in improving the indoor air quality in the reading room and study carrels of a university library in Taiwan. For each disinfectant, three different treatment modes are considered, namely a single-daily disinfection mode (SM), a twice-daily disinfection mode (TM), and a regular disinfection mode (RM). The results show that both disinfectants reduce the bacteria and fungi concentrations within the experimental areas. For the study carrel, with a relatively small and confined area, the weak acid hypochlorous water twice-daily disinfection mode (WTM) outperforms the ClO2 twice-daily disinfection mode (CTM). In the reading room, no significant difference is observed in the disinfection performance of the two disinfectants due to the large and semi-closed nature of the room. An extreme negative correlation is found among the airflow velocity, the residual bacteria and fungi concentrations. Hence, it is inferred that a higher air velocity is beneficial in spreading the disinfectant within the indoor space and improving the disinfection efficiency as a result.

Fossil fuel emissions derived from crude oil have a significant impact on the environment, climate change, air pollution, and others. Under these circumstances, there is a great interest in alternative energy resources, especially those that are able to reduce the emission of atmospheric pollutants. The aim of this study is to evaluate the burning emissions of the following binary mixture and biofuels: commercial diesel (diesel with 5% of biodiesel, B5), pure soy biodiesel (B100), additivated biodiesel (B100 adt) stored at 40 °C for 1, 2, and 3 weeks, and additivated ethanol (Ethanol adt). The burning emissions were evaluated by the levels of benzene, toluene, ethylbenzene, and xylenes (BTEX) and total particulate matter (TPM). The quality of the biofuels was given by oxidative stability during storage. The combustion products were originated from a diesel cycle stationary engine, operating in 1800 rpm and 0% load. For a greater reliability in the results, some figures of merit were evaluated for the determination of BTEX by gas chromatography and flame ionization detection (GC-FID) and the particulate matter was determined by gravimetric analysis. Results show that operating time of the engine influences combustion efficiency. During the initial 15 min, cold engine start, there was increasing in BTEX and TPM emissions, when comparing B100 and B5. Regarding to the storage period of 1–2 weeks, B100, B100 adt, and B5 showed reduction of approximately 36%, 16%, and 4% for TPM, respectively. Evaluating each component of BTEX, the benzene emissions were greater for biofuels, which is in agreement with previous studies. As observed for TPM, the storage time of 1–2 weeks was beneficial for the mitigation of aromatic emissions. A reduction about 60% percent was measured for benzene and ethylbenzene. However, these emissions can also be influenced by the engine operating conditions (load and speed), engine type, and characteristics of biofuels. Additivated ethanol also presented low emissions for these pollutants as well as the lowest percentage of emissions of TPM. It is noteworthy that Ethanol adt present the lowest percentage of benzene emission.

Based on the characteristics of ash cake deposition, the single channel model and the packed bed model, a mathematical model of filtration process of wall-flow filter for ash deposition in cake has been proposed. The effects of the amount of ash load and the distribution of ash deposition in cake on the filtration characteristic of filter are analyzed. Results show that the filtration efficiency improves rapidly with the increase of ash load while ash layer proportion is nonzero. When ash layer proportion is zero (i.e. ash plug proportion is 100%), the filtration efficiency decreases with the increase of ash load. Otherwise, the filtration efficiency improves with the increase of ash layer proportion while the ash load is constant. Considering the effects of ash on both filtration efficiency and flow resistance, the active regeneration system is more helpful to balance the correlation between filtration efficiency and flow resistance for ash tends to build up at the end of the channels in active system. The experimental results have verified the accuracy of mathematical model.

The electrical and particle collection characteristics of a 1200-m3/h-dry electrostatic precipitator (ESP) and a 400-m3/h-wet ESP for a 0.7 MW-oxygen-pulverized coal (Oxy-PC) combustion and carbon capture and storage (CCS) pilot plant were evaluated under varying air and oxygen combustion operational parameters of the ESPs. The corona current of a dry ESP reduced by oxy-firing was compared with that for the same applied voltage with air firing, which resulted in a decreased collection performance during oxy-firing at the same applied voltage. However, the decreased collection performance could be avoided by simply increasing the applied voltage to reach the same corona power consumption as with air firing because the collection performance of the ESP was an exponential function of the power consumption divided by the gas flow rate regardless of combustion conditions. The wet ESP used here had a thin water film on the collection plates due to the patented design of the collection plates, with water supplied by gravitational force from holes on the collection plates with TiO2 nanoparticles coated on ball blasted surface. The system only consumed water at a rate of 1.7 L/min/m2. The collection efficiency of the wet ESP was higher than 90% even for fine particles and mists, which enabled an overall particle collection efficiency of 99.98% to be achieved with both the dry and wet ESPs, corresponding to total gravimetric emission of 1.8 mg/m3 at the inlet of the CCS facility. The wet ESP had the additional effect of removing SO2 and SO3 at 64.5% and 23.1% efficiency, respectively.

Airborne biological agents, albeit intentionally released or naturally occurring, pose one of the biggest threats to public health and security. In this study, a microwave assisted nanofibrous air filtration system was developed to disinfect air containing airborne pathogens. Aerosolized E. coli vegetative cells and B. subtilis endospores, as benign surrogates of pathogens, were collected on nanofibrous filters and treated by microwave irradiation. Both static on-filter and dynamic in-flight tests were carried out. Results showed that E. coli cells were efficiently disinfected in both static and in-flight tests, whereas B. subtilis endospores were more resistant to this treatment. Microwave power level was found to be the major factor determining the effectiveness of disinfection. Both thermal and non-thermal effects of microwave irradiation contributed to the disinfection. Reducing flow velocity to decrease heat loss yielded higher disinfection efficiency.

Experiments were conducted on a 4-cylinder direct-injection diesel engine which has a compressing ratio of 19, using ultra low sulfur diesel blended with ethanol using 1–1.5% by volume of 1-dodecanol as the solvent to investigate the particulate emissions of the engine under five engine loads and at engine speeds of 1800 and 2400 rev/min. Blended fuels containing 6.1%, 12.2%, 18.2% and 24.2% by volume of ethanol, corresponding to 2%, 4%, 6% and 8% by mass of oxygen in the blended fuel, were used. At both engine speeds, with an increase in ethanol in the fuel, the smoke opacity, the particulate mass concentration and the total number of nano-size particles are all reduced. A diesel oxidation catalyst (Finnkat) was used and found to further reduce particulate emission. The smoke opacity, the particulate mass concentration and the total number concentration at 2400 rev/min are higher than those at 1800 rev/min.

Recently, the protection of health care workers from tuberculosis-containing aerosols has been the subject of considerable debate. An experimental apparatus and test protocol were developed to measure the collection efficiency of surgical mask and respirator filter media using a microbial aerosol challenge. Mycobacterium chelonae (M. chelonae) , used as a surrogate for Mycobacterium tuberculosis , was generated from liquid suspension using a Collison nebulizer. Upstream and downstream concentrations of viable aerosol particles were measured using Andersen cascade impactors, while total particle concentrations were measured with an aerodynamic particle sizer (APS). A monodisperse polystyrene latex (PSL) sphere aerosol (0.804 μm) was used in separate experiments to measure filter efficiency; concentrations were determined with the APS. The mycobacterial aerosol ranged in size from 0.65 to 2.2 μm when measured with the cascade impactor. A similar size range was found with the APS, yielding a count median diameter of about 0.8 μm. Samples of the mycobacterial aerosol were collected on glass slides, stained M. chelonae , as determined by environmental scanning electron microscope, were found to be rod shaped with an average length of 2 μm and average width of 0.3 μm. To evaluate the apparatus over a range of filter efficiencies (10–100%), different layers of fiberglass filter paper were tested for penetration using a 0.12 μm dioctyl phthalate (DOP) aerosol measured with a light scattering photometer, in addition to the mycobacterial and PSL aerosols. For the range of efficiencies tested it was shown that filter collection of DOP was linearly related to that of both mycobacterial and PSL sphere aerosols ( r 2 = 0.99), demonstrating that an inert aerosol may be used to predict the collection of biological aerosols by such filter media.

The resuspension of radioactive particulate material has been recognised as being of importance in dose assessments following releases to the environment. This short paper summarises the results of a wind tunnel study of small particle resuspension from vegetation surfaces.

Bioaerosol exposure assessment and the protection of civil/governmental/military establishments from bioterrorism require the development of low-power bioaerosol collectors that are able not only to efficiently collect airborne microorganisms, but also to preserve their biological integrity. In search for such a method, a new bioaerosol sampler was evaluated. In this device, the airborne microorganisms are imparted electrical charges and are then deposited in an electrical field onto a growth medium (agar). Experiments were conducted with Pseudomonas fluorescens vegetative cells, Bacillus subtilis var. niger (BG) endospores (used to simulate the spores of anthrax-causing Bacillus anthracis when testing bioaerosol sensors) and Penicillium brevicompactum fungal spores. It was found that 80–90% of initially “charge-neutralized” biological particles were removed from the air, when a small amount of ionization was generated in the electrostatic precipitator's (ESP) inlet and a precipitation voltage of ±4000 V was applied across the agar plates. Over 70% of viable BG and P. brevicompactum spores entering the ESP were enumerated as colony forming units. The bioefficiency of the new sampler was about the same as that of the Biosampler, which was tested in parallel. In experiments with sensitive P. fluorescens vegetative cells, the ESP enumerated twice as many cells as the Biosampler. The latter result indicates that the electrostatic collection method may be especially useful for the collection and enumeration of sensitive airborne microorganisms. Experiments investigating the effect of aging time on the amount of electrical charge carried by the airborne microorganisms showed that the level of electrical charge gradually decreases with increasing aging time. However, even after the P. fluorescens cells had remained airborne for an hour, they retained enough electrical charge to be collected with efficiency higher than 70%.

A method and test system have been developed for the laboratory evaluation of the performance of bioaerosol samplers. The method differentiates between the overall physical sampling efficiency (which reflects the inlet and collection efficiencies) and the biological sampling efficiency (which reflects the survival of the test microorganisms during the sampling process). The number concentrations of laboratory-generated bioaerosol particles are measured with an aerosol size spectrometer up- and downstream of the bioaerosol sampler being tested. In a bioaerosol impactor, which was specially designed for testing microbiological aspects of bioaerosol sampling, the inlet and collection efficiencies are differentiated by measuring downstream of the collection surface location with and without the collection surface in place. The number of recovered particles is counted as microcolonies with a microscope after sampling the bioaerosol particles into agar and culturing them. The total recovery of these bioaerosol particles is determined as a ratio of the number of viable microorganisms recovered to the number of bioaerosol particles present in the air sampling volume upstream from the sampler. This total recovery is a measure of the ratio of culturable to non-culturable bacteria present in the air. By measuring physical and microbiological aspects simultaneously, information is gained on aspects of bioaerosol sampling that cannot be determined by either of these branches of science alone. This is exemplified by tests on the influence of relative humidity and desiccation time on colony count. The newly-developed system can be used to test any bioaerosol sampler. A special single-stage impactor was designed, built and used to study how different sampling and analysis variables affect the total recovery of bioaerosol particles. The designed impactor was calibrated using PSL particles. Its inlet sampling efficiency was found to be within the range of 96–99.5%, depending on the sampling conditions and particle size, if the latter is less than 8 μm (this range represents single bacteria, bacterial agglomerates, and fungi). The collection efficiency was found to be about 100% when collecting PSL particles larger than 0.7 μm in diameter at 201 min−1 or higher air flows. The total recovery of microorganisms measured under these conditions is characterized only by the “survivability” of microorganisms during their sampling. It was found that relative humidity had a pronounced effect on total Pseudomonas fluorescens recovery. Experimental data also showed that the sampling time may be limited due to bacterial desiccation and subsequent loss in viability of collected microorganisms.

An alternative microthread to spider's web, used in airborne survival studies of microorganisms outdoors, was developed using a modified commercial hot glue gun and ethylene vinyl acetate resin. This produced consistent, fine, strong and inert fibres, with far greater ease and speed than spiders. Survival of two bacteria suspended on glue fibres was found to be comparable to that on spider's web both indoors and outdoors.

Woods of a variety of types have been subjected to a standardized simulation of sanding as a test of dustiness. The harder woods give rise to finer dust, and at a lower rate, but the mass of dust produced for unit mass of wood removed is relatively constant. Coarse sandpaper, however, removes significantly more wood than fine, but with the same rate of production of airborne dust.

In asphalt mass production, limestone filler is used to improve the properties of asphalt. SO2emission can be reduced by 90 % when limestone filler is injected directly to drying drum, where lime reacts with flue gas.

The use of a wet filtration process for the removal of submicron sticky particles has been successfully trialed at a commercially operating strip galvanising facility and achieve a removal rate of 98.6% and 98% for total particles and chloride components respectively. These removal rates were achieved at a facility with a long history of producing semi-wet sticky particles, over a wide particle size distribution between 0.01 and 300 μm. The use of a wet filtration system can be seen as a very effective tool to allow existing commercial facilities to augment their existing wet scrubber technology without large capital expense.

The rate of deposition of particles to smooth extended surfaces and horizontal filter paper has been measured in a large wind tunnel. The particles used covered the size range from 0·08 to 30 μm and the effect of wind speed was also investigated. The results provide some confirmation of theoretical predictions for deposition rates to smooth surfaces and they have also been used to evaluate the performance of a dry deposition sampler, made from filter paper, which has been used to sample the natural aerosol.

A phenomenological description is presented of the relation between pressure drop, gas velocity and other gas and filter variables for a fibrous filter medium. Experimental and theoretical consideration extends to viscous and inertial flow, compressible and incompressible flow, and to conditions of slip and slip-free flow. Pressure drop Δp (N/m2) is shown to be given closely by the relation Δp = p i C i − (p i C i ) 2 − 2p i Lv i k 1μ a + k 2ρiVi β 1 2 where pi (N/m2) is the inlet pressure, C4 (dimensionless) is the inlet Cunningham correction (fiber diameter replacing the usual sphere diameter), L (m) is the filter mat thickness, vt (m/sec) is the inlet face velocity, p (daP) is the gas viscosity, pi (kg/m3) is the gas density, and β/k2 (m) and a/k2 (m2) are filter constants, the last being the specific permeability of Darcy's law. Experimental data obtained with Institute of Paper Chemistry 1478 filter paper over the ambient pressure range 0·0013 to 0·86 atm (corresponding to the range of Knudsen numbers 6 to 0·01) are in good agreement with the theory, which is presumably valid to much higher pressures. Methods are described for correlating experimental data in terms of dimensionless groups and, on the basis of relatively few measurements near atmospheric conditions, for estimating pressure drop over a broad range of ambient pressures and gas velocities.

This paper jointly addresses numerical and physical challenges related to the modeling of coalescence filtration through vertical filter cartridges, put forth in the following papers by Starnoni, M. and C. Manes: • Starnoni, M., & Manes, C. (2021). A multiphase multicomponent flow and transport model for liquid aerosol filtration in coalescence fibrous filters. Separation and Purification Technology, 266, 118574. • Starnoni, M., & Manes, C. (2022). On the interplay between pressure and gravitational forces in coalescence filters. Journal of Aerosol Science, 105953. In particular, it provides the multidimensional extension of the one-dimensional model presented in Starnoni and Manes (2021) to the general case where internal gravity-induced flows play an effective role. Key to the implementation is the decomposition of the moving oil volumes along the different directions proportionally to the dimensionless number SM, a new quantity introduced in Starnoni and Manes (2022) describing the interplay between the forces dictating the oil dynamics. To validate the implementation, an experimental setup available in the literature is replicated, showing very good agreement in terms of all relevant quantities, namely saturation, pressure drop and drainage volumes. A generalized ‘Network, Channel and Film’ model is also formulated, which extends the scope of application of the original Jump and Channel model by Kampa et al. (2014) to filters with coarser fibrous microstructure. In particular, the existence of an additional flow mechanism termed ‘network’ is postulated, which is characterized by a complex multidimensional oil patterns configuration spanning the entire filter’s height and evolving, in a macroscopic sense, along the direction identified by SM.

A Fast Integrated Mobility Spectrometer (FIMS) with a wide dynamic size range has been developed for rapid aerosol size distribution measurements. The design and model evaluation of the FIMS are presented in the preceding paper (Paper I, Wang et al., 2017 ), and this paper focuses on the experimental characterization of the FIMS. Monodisperse aerosol with diameter ranging from 8 to 600 nm was generated using a Differential Mobility Analyzer (DMA), and was measured by the FIMS in parallel with a Condensation Particle Counter (CPC). The mean particle diameter measured by the FIMS is in good agreement with the DMA centroid diameter. Comparison of the particle concentrations measured by the FIMS and CPC indicates the FIMS detection efficiency is essentially 100% for particles with diameters of 8 nm or larger. For particles smaller than 20 nm or larger than 200 nm, FIMS transfer function and mobility resolution can be well represented by the calculated ones based on simulated particle trajectories in the FIMS. For particles between 20 and 200 nm, the FIMS transfer function is boarder than the calculated, likely due to non-ideality of the electric field, including edge effects near the end of the electrode, which are not represented by the 2-D electric field used to simulate particle trajectories.

Inhaled aerosols whether beneficial or harmful express their effects depending on the amount initially deposited in the body (i.e. the deposition dose), with clearance mechanisms including dissolution, mucociliary transport and translocation then determining retained dose in the respiratory tract. The many regions of the respiratory tract differ in their shapes, cellular makeups, defenses, and pathologies. As a result, predicting, measuring, and simulating initial deposition doses and subsequent events for deposited particles, vapors and gases presents formidable challenges. Interest in supplementing and in some cases replacing laboratory animals in inhalation studies with in vitro cellular exposures, challenges researchers with both designing exposure systems and defining the internal doses to exposed cells. Addressing these challenges requires the cooperation and collaboration of many specialists that do not normally meet at discipline-specific conferences. To address that historical limitation, research related to the dosimetry of inhaled aerosols has been addressed at a series of three issue oriented international conferences. This paper addresses the research-related needs and recommendations from the third, October 2019 conference held in Irvine, CA, USA. Conference participants were invited to submit suggestions related to research. This paper includes those suggestions plus some offered by e-mail after the conference. Over 40 submitted suggestions are organized into several categories. Sample suggestions include; 1. research-related activities should address an identified health related problem; 2. in vitro aerosol systems require development in order to have better-defined doses to cells and to represent actual in vivo exposures; 3. additional knowledge on respiratory tract anatomy is needed for several species and for the variations within humans and other species; 4. dosimetric models should be expanded in scope, and should improve their usability by non-modelers; and 5. there is value in introducing newcomers to the field of inhaled aerosols. Collaborations among several disciplines are emphasized in order to advance inhaled dosimetry models and their applications to laboratory and real-life inhalation exposures. The suggestions reported here are a snapshot in time from experts from a variety of disciplines. The categories represent the major topic areas discussed at the meeting, but within each area the recommendations are not prioritized. As such, they do not carry the approval of any research institutions, research funding agencies, private entities, or regulatory agencies. The authors are solely responsible for the contents of this paper.

A fast integrated mobility spectrometer (FIMS) was previously developed to characterize submicron aerosol size distributions at a frequency of 1 Hz and with high size resolution and counting statistics ( Kulkarni & Wang (2006a) , Kulkarni & Wang (2006b) ; Olfert, Kulkarni, & Wang, 2008 ). However, the dynamic size range of the FIMS was limited to one decade in particle electrical mobility. It was proposed that the FIMS dynamic size range can be greatly increased by using a spatially varying electric field ( Wang, 2009 ). This electric field creates regions with drastically different field strengths in the separator, such that particles of a wide diameter range can be simultaneously classified and subsequently measured. A FIMS incorporating this spatially varying electric field is developed. This paper describes the theoretical frame work and numerical simulations of the FIMS with extended dynamic size range, including the spatially varying electric field, particle trajectories, activation of separated particles in the condenser, and the transfer function, transmission efficiency, and mobility resolution. The influences of the particle Brownian motion on FIMS transfer function and mobility resolution are examined. The simulation results indicate that the FIMS incorporating the spatially varying electric field is capable of measuring aerosol size distribution from 8 to 600 nm with high time resolution. The experimental characterization of the FIMS is presented in an accompanying paper.