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Introduction: Electronic cigarette users ("vapers") inhale aerosols of water, nicotine, and propylene glycol (PG) or vegetable glycerin (VG). Aerosol particle sizes should affect deposition patterns in vapers and bystanders., Methods: Aerosols were generated by a smoking machine and an electronic cigarette filled with 16mg/ml nicotine in aqueous PG or VG solution. A scanning mobility particle sizer (SMPS) counted particles of 10-1,000 nm diameters. A single puff experiment counted particles immediately and after aging 10 and 40 s. A steady-state experiment counted particles emitted from a collection chamber, untreated and after desiccation or organic vapor removal. The International Commission on Radiological Protection (ICRP) human respiratory tract model was used to estimate deposition. Results were compared to similar data from reference cigarettes., Results: Puffs generated peak particle counts at (VG) 180 nm and (PG) 120 nm. Steady-state peaks occurred around 400 nm. Organic vapor removal eliminated small particles and reduced the size and number of large particles. Desiccation reduced the total volume of particles by 70% (VG, small PG) to 88% (large PG). The ICRP model predicted 7%-18% alveolar delivery; 9%-19% venous delivery, mostly in the head; and 73%-80% losses by exhalation. Reference cigarettes generated more particles initially, but were otherwise similar; however, in vivo smoke particle deposition is higher than the model predicts., Conclusions: Nicotine delivery may depend on vaping technique, particle evolution, and cloud effects. Predicted 10% arterial and 15% venous delivery may describe bystander exposure better than vapers exposure.

The dispersion in air of nanoparticles of different sizes, materials and morphologies with controlled agglomeration involving aerosol delivery for in vivo and in vitro studies is one of the most difficult challenges in the field of nanoparticle toxicology. We describe here a nanoparticle dispersion system using an electrospray method to deliver airborne nanoparticles (approximately 10-100 nm) with spatial uniformity and controllable particle concentration for in vitro and in vivo studies. With the dispersion method, single nanoparticles (polystyrene latex particles, TiO(2), Au, Mn, quantum dots, and carbon nanotubes) can be delivered to cells and animals via the air. The degree of agglomeration can be controlled by changing the suspension feeding rate to simulate realistic conditions for exposure studies.

A new aerosol electrometer (AE), the thermal precipitation aerosol electrometer (TPAE), was designed for use with particles of sizes less than 300 nm, and its performance was experimentally evaluated. The TPAE combines the thermal precipitator with a microcurrent measurement circuit board (i.e., pre-amplifier) for measuring the current carried by collected particles. The thermal precipitator is in the disk-to-disk configuration. Heating paste and air cooling were adopted to establish the desired temperature gradient in the precipitation chamber. At a sample flow rate of 0.3 L min -1 and a temperature gradient of 264 K cm -1 , the precipitation efficiency of 70 nm particles reaches ∼100 %. The measurement range of the designed aerosol electrometer is ±5×105 fA, and the accuracy is ±2 fA (2500 to 6.25×107 cm -3 using a flow rate of 0.3 L min -1 and assuming that only singly charged particles exist in the sample). During the evaluation process, the electrical performance of the TPAE was first tested using sodium chloride (NaCl) and soot particles previously classified by a differential mobility analyzer (DMA) and compared to the reference. The precipitation performance of the TPAE was then characterized as functions of the temperature gradient, sampling flow rate and particle size. It was shown that the particle collection efficiency of the built-in thermal precipitator is inversely proportional to the sampling flow rate and proportional to the temperature gradient. The effect of particle size on the particle collection efficiency was minor for NaCl particles of sizes between 23 and 200 nm. Unlike that which was observed for the NaCl particles, a slightly positive correlation between the collection efficiency and the mobility size for soot particles (in the size range of 30–160 nm) was observed. This observation might be due to the existence of soot agglomerates. Compared to existing electrometers, the TPAE does not require the use of high-efficiency filters and includes the additional feature of the "soft" collection of particles for offline particle characterization as well as aerosol current measurement. [ABSTRACT FROM AUTHOR]

Particle charging via the mixing of aerosols with unipolar ions typically results in multiple charges on particles. Particle classification and sizing, based on the electrical mobility, ideally requires all the particles being singly charged to the performance enhancement. In this study, we explored the feasibility of maximizing the singly charged fraction of particles via the control of the Nit product in a unipolar charger. The feasibility was first investigated by modeling unipolar diffusion charging. It was found that the singly charged fraction of monodisperse particles could be maximized by the control of the Nit product. A corona-based unipolar charger was also constructed to study the maximization of the singly charged fraction of monodisperse particles. It was found that a wider range of ion concentration in the charging zone could be obtained by the variation of ion-driving voltage compared to that by changing the corona-discharge current. The maximum singly charged fraction of monodisperse particles in various sizes was characterized when the charger was operated at the flow rates of 1.5 and 3.0 lpm. It was evidenced that the current charger could be conditioned to achieve a higher singly charged fraction of particles than that by bipolar chargers in the particle size range of 20–200 nm, particularly in the ultrafine particle size range. The control of Nit product in the charging zone of a unipolar charger offers a simple and effective means to enhance the singly charged fraction of particles in a given size range. Copyright © 2019 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Effective particle sizing is one of the limitations in measuring sub-3 nm aerosol. In this study we developed a miniature cylindrical differential mobility analyzer (mini- cyDMA) for sub-3 nm particle sizing. The construction of the miniature cylindrical DMA, stemmed from the cost-effective DMA (cDMA) developed by Mei et al. (2011), enables it to be operated at higher sheath flowrate than the cDMA. To keep the sheath flow laminar in the DMA classification region for the flowrate up to 30 l per minute (lpm) for better matching the flowrate required by the aerosol detector while having a good sizing resolution, the DMA components such as the inlet for sheath flow, nylon screen for flow laminarization, and the chambers for polydisperse aerosol flow inlet and excess flow exit were re-designed in the mini- cyDMA. Transfer function of the mini- cyDMA was evaluated using tetra-alkyl ammonium cations with electrical mobility diameters of 1.16 nm, 1.47 nm and 1.78 nm, respectively. A data inversion routine based on an empirical diffusive transfer function was used to obtain the transfer function of the mini- cyDMA. When classifying 1.47 nm particles at the aerosol-to-sheath flow ratio of 2.5/25 lpm, the penetration efficiency and the sizing resolution of the mini- cyDMA are 0.21 and 5.7, respectively. The mini- cyDMA was deployed to characterize newly-formed atmospheric particles and flame-generated nascent soot particles. [ABSTRACT FROM AUTHOR]

Oil-coated particles are often encountered in the ambient and industrial working environments. However, experimental investigations have rarely been carried out on the loading behavior of filters loaded with oil-coated particles. In this study, the effects of the overall particle size, oil volume percentage, filter material, and surface tension and viscosity of the coating oils on the filter loading characteristics were examined. It was found that the general oil-coated particle loading behavior of filters transitions from that of solid-only particles to that of oil-only particles as the liquid volume percentage in the test particles increases. The typical transition trend of oil-coated particle loading curves is believed to be due to an increase in the fluidity of deposited oil-coated particles as the liquid percentage increases. It is further observed that, when the liquid volume percentage in coated particles is less than 50%, the filter loading behavior is dominated by the effect of the liquid surface tension and the filter pressure drop is largely due to the solid core of coated particles. Both the surface tension and viscosity of coating liquid influence the filter loading behavior when the liquid percentage in coated particles is higher than 50%. [ABSTRACT FROM AUTHOR]

Differential mobility analyzers (DMAs) with more than one monodisperse-particle outlet can offer a number of advantages compared to conventional single monodisperse-particle outlet de-signs. A generalized theoretical model and experimental measure-ments describing the performance of a DMA with 3 monodisperse-particle outlets have been independently reported in the literature. The objective of this article is to compare the theoretical predic-tions with the measurements. Resolutions determined by the theo-retically predicted transfer functions for the three monodisperse-particle outlets are compared with measurements when the DMA was operated under different operating conditions. Predictions and measurements show good agreement when the DMA is operated at low sheath flow rates and for aerosol outlets relatively far from the aerosol inlet. For aerosol outlets relatively near the inlet there is evidence that the discrepancy between theoretical predictions and measurements may disappear at higher sheath flow rates, but the chances of flow disturbances in the classifier increase as well. The theory for multiple monodisperse-outlet DMAs is thus seen as suc-cessful in predicting the performance of this instrument, provided that disturbances in the flow field are avoided. [ABSTRACT FROM AUTHOR]

A new single-capillary electrospray (ES) aerosol generator has been developed for monodisperse particle production with maximal transmission efficiency. The new generator consists of both a spray chamber in a point-to-orifice-plate configuration and a charge reduction chamber that can hold up to 4 Nuclespot ionizers (Model P-2042, NRD Inc.). The 2 chambers are partitioned by an orifice plate. To optimize the particle transmission efficiency of the prototype, a systematic study was performed on the generator by varying the system setup and operation. Two key dimensions of the generator setup, the orifice diameter and the distance from the capillary tip to the orifice plate, were varied. Fluorescence analysis was applied to characterize the loss of ES-generated particles at different locations of the prototype. It was found that particle loss in the generator could be reduced by either increasing the orifice diameter or decreasing the distance between the capillary tip and the orifice plate. Increasing either the total radioactivity of the ionizers or the flowrate of the particle carrier gas also further decreased the particle loss in the system. The maximum particle transmission efficiency of 88.0% was obtained with the spray chamber fully opened to the charge reduction chamber, the capillary tip at the same level as the orifice plate, and 4 bipolar ionizers installed. [ABSTRACT FROM AUTHOR]

Abstract: A new DC-corona-based charge conditioner for particles was developed for the processes in which electrical charges on particles are critical to successful operations. The prototype conditioner consists of an outer metal case and a corona discharge tube module capped with a metal screen at one end. A pointed tungsten needle was used in the tube module to produce ions via corona discharge. Ions produced in the tube module were driven into particle charging zone via the voltage difference between the module and conditioner cases. The particle charging zone of the conditioner was designed for quick particle exit once the particles are electrically charged, thus reducing the loss of charged particles. Two unique design features were included in the prototype conditioner, i.e., the implementation of parallel directions of electrical and aerosol flow fields, and variable control of ion concentration in the charging zone. Through the experimental evaluation, we found that the conditioner achieved its highest extrinsic charging efficiency, equivalent or higher than those of existed DC-corona-based particle chargers, when operated at the condition of a 3lpm (liters per minute) aerosol flow rate, a 2μA corona current and a 600V ion-driving voltage. A tandem-DMA technique was utilized to characterize extrinsic charge distributions of particles with various sizes. Last, the birth-and-death charging model with the Fuchs limiting sphere theory for calculating the ion–particle combination coefficient was applied to obtain the charging ion concentration under the various operations of the prototype. [ABSTRACT FROM AUTHOR]

Abstract: We have developed a miniature disk electrostatic aerosol classifier (mini-disk EAC) for use in electrical mobility-based personal nanoparticle instrumentation for measurement of personal exposures to nanoaerosols. The prototype consists of two parallel disk electrodes separated by an electrically insulating spacer, to create the particle classification zone. The aerosol enters and exits the classification zone along the bottom disk electrode. An additional, particle-free sheath flow is used to improve the measurement resolution. The transmission measurement of the mini-disk EAC for DMA-classified particles shows that particle losses due to diffusion and electrical image forces were low. The particle penetration at 10nm diameter (the designed lower size limit for the classifier) was 67% when the prototype was operated at the aerosol and sheath flow rates of 0.5 and 1.0lmin−1, respectively. The performance of the mini-disk EAC was experimentally characterized using the particle cutoff curves that describe their penetration through the classifier as a function of applied voltage across the two disk electrodes. Based on the measurement of particle penetration at different aerosol and sheath flows, it was found that the aerosol and sheath flow rates of 0.5 and 1.5lmin−1 were optimal for classifier operation. Finally, a semi-empirical model was also developed to describe the transfer function of the mini-disk EAC for non-diffusive particles. [Copyright &y& Elsevier]

Abstract: The performance of an electrical aerosol detector (EAD; TSI Model 3070A) was experimentally evaluated for measuring the integral parameters of particles (i.e., total length concentration of particles, and the total surface area concentrations of particles deposited in a human lung). The EAD consists of a unipolar diffusion charger with an ion trap, and aerosol electrometer. We first evaluated the performance of the EAD charger. Both polydisperse and monodisperse particles of Ag, NaCl, and oleic acid (with the dielectric constants of infinite, 6.1 and 2.5) were then generated to evaluate the particle material effect on the EAD readout. [Copyright &y& Elsevier]

Abstract: A corona-based unipolar aerosol charger has been constructed, and its performance has been systematically evaluated. The prototype consists of completely separated corona ionization and charging chambers. With this configuration the electrostatic loss of charged particles is eliminated, and particle loss by diffusion and the space charge effect is minimized by the angular injection of the ionizer flow and the rapid exit of charged particles. The charger performance was optimized by varying different operational parameters, i.e., total and ionizer flowrates, and ion concentration. It was found that operation with one corona ionizer gave higher extrinsic charging efficiency than operation with two ionizers. The corona-discharge current has negligible effect on the charging performance. Operating the charger at a total flowrate of 5lpm, with 1.0lpm flow in each of the two ionizers, gave the highest extrinsic charging efficiency. Further, the performance of prototype charger was not compromised even at a total flowrate of 10lpm. The charger provides higher extrinsic charging efficiency than other corona-based unipolar chargers. Extrinsic charge distributions for particles of different sizes were at last measured by the tandem-DMA technique. [Copyright &y& Elsevier]

A new DMA column has been designed with the capability of simultaneously extracting monodisperse particles of different sizes in multiple stages. We call this design a multistage DMA, or MDMA. A prototype MDMA has been constructed and experimentally evaluated in this study. The new column enables the fast measurement of particles in a wide size range, while preserving the powerful particle classification function of a DMA. The prototype MDMA has three sampling stages, capable of classifying monodisperse particles of three different sizes simultaneously. The scanning voltage operation of a DMA can be applied to this new column. Each stage of MDMA column covers a fraction of the entire particle size range to be measured. The covered size fractions of two adjacent stages of the MDMA are designed somewhat overlapped. The arrangement leads to the reduction of scanning voltage range and thus the cycling time of the measurement. The modular sampling stage design of the MDMA allows the flexible configuration of desired particle classification lengths and variable number of stages in the MDMA. The design of our MDMA also permits operation at high sheath flow, enabling high-resolution particle size measurement and/or reduction of the lower sizing limit. Using the tandem DMA technique, the performance of the MDMA, i.e., sizing accuracy, resolution, and transmission efficiency, was evaluated at different ratios of aerosol and sheath flowrates. Two aerosol sampling schemes were investigated. One was to extract aerosol flows at an evenly partitioned flowrate at each stage, and the other was to extract aerosol at a rate the same as the polydisperse aerosol flowrate at each stage. We detail the prototype design of the MDMA and the evaluation result on the transfer functions of the MDMA at different particle sizes and operational conditions. [ABSTRACT FROM AUTHOR]

Thermophoretic deposition of aerosol particles (particle diameter ranges from 0.038 to 0.498 μm) was measured in a tube (1.18 m long, 0.43 cm inner diameter, stainless steel tube) using monodisperse NaCl test particles under laminar and turbulent flow conditions. In the previous study by Romay et al., theoretical thermophoretic deposition efficiencies in turbulent flow regime do not agree well with the experimental data. In this study, particle deposition efficiencies due to other deposition mechanisms such as electrostatic deposition for particles in Boltzmann charge equilibrium and laminar and turbulent diffusions were carefully assessed so that the deposition due to thermophoresis alone could be measured accurately. As a result, the semiempirical equation developed by Lin and Tsai in laminar flow regime and the theoretical equation of Romay et al. in turbulent flow regime are found to fit the experimental data of thermophoretic deposition efficiency very well with the differences of less than 1.0% in both flow regimes. It is also found that Talbot's formula for the thermophoretic coefficient is accurate while Waldmann's free molecular formula is only applicable when Kn is greater than about 3.0. [ABSTRACT FROM AUTHOR]

Particle inertial deposition in a tube with an abrupt contraction was studied experimentally and numerically at low pressure. Measurements were performed for particle deposition onto an orifice plate (orifice diameter: 1.16 cm) placed in a tube (inner diameter: 3.48 cm). The system pressure ranged from 27 to 37 Pa (0.2–0.28 Torr) and the flow Reynolds number, Re, in the tube was 3.0. Spatially uniform aerosols were produced in the low-pressure environment by the method developed by Sato et al. (Aerosol Sci. Technol., 2001). The observed deposition-efficiency curve as a function of the Stokes number, Stk, is different from that obtained for Re⩾100 at atmospheric pressure (J. Aerosol Sci. 21 (1990) 29; J. Aerosol Sci. 26 (1995) 563). The difference was confirmed by numerical studies. The numerical results for Re=0.1–30 revealed that the deposition curve shifts to a larger Stokes number as the Reynolds number decreases due to flow-pattern changes near the orifice plate. An empirical deposition-efficiency curve was obtained as a function of the Stokes number, the Reynolds number, and the contraction ratio (the ratio of the tube inner diameter to the orifice diameter), R. [Copyright &y& Elsevier]

Aerosols flowing in a tube under vacuum conditions, e.g., in semiconductor processing equipment, are often found to have a nonuniform profile due to low Reynolds number flow (Bae et al. 1998). A novel method to produce spatially uniform aerosols in a flow tube at low pressure has been developed. The method employs a counter-flow injection configuration. Two identical critical orifices of 200 μm in diameter are installed opposite each other in an aerosol mixing chamber. The opposing aerosol jets from the two orifices result in turbulent and uniform mixing of the two aerosol streams. Aerosols 0.3 μm or less in diameter, at a pressure as low as 1 Torr, are shown to be distributed uniformly over a cross section of a tube with an inner diameter of 3.48 cm. This method has been further improved to provide spatially uniform aerosols at lower pressures by using a pressure reducer downstream of the aerosol mixing chamber. The arrangement provides spatially uniform aerosols at a pressure as low as 0.2 Torr. [ABSTRACT FROM AUTHOR]

While surface area is one of the most important atmospheric aerosol properties in health effects, methods for online measurement of surface area are not widely available and/or require complex operations. In this paper, we describe an integrated measurement method that can continuously monitor the total surface area, as well as the total number and volume, of atmospheric aerosols. Three integral aerosol sensors - (i) a condensation particle counter (CPC) for number concentration measurement, (ii) a mass concentration monitor (MCM) for mass concentration measurement, and (iii) an electrical aerosol detector (EAD) for current measurement of charged aerosol - are used in this study. Signals from the three sensors are converted into a lognormal size distribution by minimizing the difference between the measured signals and the theoretical values based upon a size distribution model, the instrument calibration, and its theoretical responses. Results from a 20 day continuous sampling period show that the calculated total surface area from integrated measurement correlates well with that of particle sizing measurement. The calculated lognormal size distribution parameters between the two methods have similar values. These results suggest that the integrated measurement method is feasible to continuously measure total number, surface area, and volume concentrations. As the integrated measurement method can yield results in near real time, it can be used for online measurement of atmospheric aerosols. [ABSTRACT FROM AUTHOR]

Micro-Cantilever (MCL) is a thin film structure that is applied for aerosol particle mass sensing. Several modifications to the rectangular MCL (length-to-width ratio, slots at the anchor, serrations at its side edges) are made to deduce the role and influence of the shape of rectangular MCL-based aerosol mass sensors and reduce gas damping. A finite element fluid-structure interaction model was used to investigate the performance of MCL. It is found that (I) the mass sensitivity and quality factor decline with the increasing of length-to-width ratio which alters the resonant frequency of the MCL. The optimum conditions, including the length-to-width ratio (σlw = 5) and resonant frequency (f0 = 540.7 kHz) of the MCL, are obtained with the constant surface area (S = 45,000 μm2) in the frequency domain ranging from 0 to 600 kHz. (II) The slots can enhance the read-out signal and bring a small Q factor drop. (III) The edge serrations on MCL significantly reduce the gas damping. The results provide a reference for the design of aerosol mass sensor, which makes it possible to develop aerosol mass sensor with high frequency, sensitivity, and quality. [ABSTRACT FROM AUTHOR]

Abstract: A twin-head electrospray (THES) aerosol generation system with one spray head producing positively charged particles and the other producing negatively charged ones has been constructed and its performance has been experimentally evaluated in this study. The charge-enhanced coagulation between oppositely charged droplets generated by the THES was verified by the measuring the resultant particle size distributions via a scanning mobility particle sizer (SMPS), the imaging of dye-labeled coagulated particles via a fluorescence microscope and the chemical composition characterization of generated particles via high-efficiency liquid chromatography (HPLC). The characterization time of charge-enhanced coagulation in our study''s generator was estimated to be in the order of 10−5 s under the tested operational conditions. The size evolution due to charge-enhanced coagulation was studied for particles with initial sizes ranging from 10 to 710nm. Compared with those prior to the coagulation, the size distributions of particles upon coagulation became broader. Further, regardless the initial charge levels, the peaks of resultant particle size distributions were about 1.3 times larger than the corresponding ones before coagulation, indicating the collision of two oppositely charged particles. As expected, the number of charges on the resultant particles was significantly reduced in the THES generation system. However, only a small fraction of resultant particles carried zero electrical charge. Our study also evidenced that a maximal 70% transmission efficiency can be achieved for the THES system. It is therefore concluded that the twin-head ES technique makes it feasible to take unique advantage of electrosprayed particles without any charge reduction scheme. [Copyright &y& Elsevier]

Abstract: In aerosol research and applications, a differential mobility analyzer (DMA) is now considered the standard tool for sizing and classifying monodisperse particles in the sub-micrometer and nanometer size ranges. However, DMA application at the pilot or industrial production scale remains infeasible because of the low mass throughput. A simple way to scale up DMA operation is to use multiple DMA columns. The manufacture and maintenance costs of existing DMAs, however, limit such a scale-up. A cost-effective DMA column (named cDMA) has thus been developed in this work to address the above issue. To reduce its manufacturing cost, the prototype was constructed using parts requiring little machining. The cDMA column was also designed for easy maintenance and easy variation of the classification length for any application-specified size range. In this study, prototypes with two particle classification lengths, 1.75 and 4.50cm, were constructed and their performance was experimentally evaluated at sheath-to-aerosol flowrate ratios of 5:1, 10:1, and 15:1 via the tandem DMA (TDMA) technique. It was concluded that both prototype cDMAs, operated at a sheath/aerosol flowrate ratio less than 15:1 and with a polydisperse aerosol flowrate of 1.0lpm, achieved sizing resolution comparable to that offered by Nano-DMA. The longer cDMA had comparable transmission efficiency to that of Nano-DMA, and the shorter cDMA exceeded the performance of Nano-DMA. Hence, the cDMA with the shorter (1.75cm) classification length is better suited for the characterization of macromolecular samples. [Copyright &y& Elsevier]

Abstract: A Bayesian inversion routine is described in which data from tandem differential mobility analysis (TDMA) can be used to determine fundamental parameters for charging models as a function of particle size. The measurement and inversion techniques were verified using simulated data for particles in the 50–500nm range undergoing unipolar diffusion charging as described by Fuchs’ limiting sphere theory, for which the fundamental charging parameter is the product of the unipolar ion concentration and residence time within the charger, the so-called nt product. Under conditions where the average particle charge is greater than one unit charge, the inversion routine is precisely and accurately able to determine the nt value. The inversion routine breaks down, however, when the average number of charges per particle is well below unity, i.e. for low nt values or for small particle sizes. Incorporation of charging efficiency data in addition to TDMA data can allow for use of the inversion routine when the average number of charges per particle is low. With its limitations known, the inversion routine was applied to determine the nt value for the unipolar charger used in the TSI electrical aerosol detector (EAD), model 3070A, for particles in the 50–200nm size range. The effective nt value within the EAD charger decreased with decreasing particle size, implying that charged particle losses occur within the EAD charger. The described inversion routine is unique in its ability to determine size dependent charge model parameters, and can be utilized with any given charging model. It is expected that this technique will be of use in advancing the understanding of aerosol particle charging models and in future design of unipolar chargers. [Copyright &y& Elsevier]

Two circular electrical aerosol classifiers (CirEACs), i.e., one in large diameters (large version, LV) and the other in small diameters (small version, SV), were designed and their performance was evaluated in this study. The design of CirEACs stems from the demand to have an extended particle size classification range for a miniature electrical mobility classifier while keeping it compact in the package. A CirEAC is constructed by two coaxially aligned cylinders. The particle classification channel is established in the annular spacing defined by two cylinders. Aerosol stream flows into the classification channel via a one-end-closed tube with a series of side holes for reducing the particle loss and keeping particles away from both channel sidewalls. Clean sheath flow is distributed to the entire width of CirEAC channel via a tube similar in design to the aerosol inlet one. The total flow exits the CirEAC from a tube in the same type as the aerosol inlet one. The effects of total flow rate, aerosol-to-sheath flow rate ratio, and particle size on the penetration curves of CirEACs were studied. It is found that the optimal performance of CirEACs was observed when operated at the total flow rate of 1.8 lpm and the aerosol-to-sheath flow rate ratio of 0.2. A 2-D model is also presented to derive the transfer function of CirEACs. The experimental transfer function of CirEAC LV agrees well with that estimated theoretically using the working sheath flow rate (defined as the portion of total sheath flow rate underneath the aerosol slit opening). In comparison, the CirEAC LV possesses a steeper penetration curve, wider total flow rate range (1.2 – 3.6 lpm), and broader particle size range (5 – 300 nm) than the CirEAC SV. The CirEAC SV however has a higher transmission efficiency than the CirEAC LV because of its shorter particle classification length. [ABSTRACT FROM AUTHOR]

The variation of ambient relative humidity (RH) affects the water uptake of aerosols in the atmosphere, thereby altering the aerosol size distribution and mass concentration. In this study, aerosol size distributions under both dry and ambient RH conditions are measured using an active RH-controlled dry-ambient aerosol size spectrometer (DAASS) at an urban site in Beijing during the springtime of 2021, and the aerosol liquid water content (ALWC) is derived accordingly. During the measurement period, a sharp increase of the ALWC was commonly observed when ambient RHs reached above 50%, demonstrating a potential phase change of the aerosol which further increases the rate of water uptake. Considerably high ALWC events were observed during the nighttime, with further elevated ambient RH above 60%. The liquid water accounts for up to 42.5% of the total aerosol volume, corresponding to a maximum ALWC of 8.79 μg m−3. The evolution of geometric mean diameter of accumulation mode particles agrees well with the enhancement of the ALWC (R2 of 0.73), revealing a significant growth of accumulation mode particles resulting from water uptake. Besides, by investigating the RH-dependent ambient aerosol surface area concentration, it is found that the aerosol surface area concentration can be underestimated by ∼20% under dry conditions when the ambient RH elevates to above 70%. • Sharp increases of the ALWC were observed under ambient RHs above 50% during the nighttime. • The aerosol water uptakes are represented by a significant growth of accumulation mode particles. • The aerosol surface area concentration can be underestimated under dry conditions when the ambient RH elevates to above 70%. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the performance of a thermal precipitator of the disk-to-disk type was investigated experimentally and numerically. The prototype precipitator was basically two disks separated via a circular Teflon® spacer. The temperatures of the two disks (one at elevated temperature and the other at room temperature) were individually controlled by a silicone heating element and running water at room temperature. Monodisperse particles of sodium chloride and fluorescein sodium were used to investigate the particle collection efficiency of the precipitator when operated under various aerosol flowrates and temperature gradients. Our experimental data showed that the particle collection efficiency of the precipitator remained approximately constant for test particles with diameters smaller than 300nm and noticeably decreased as the particle diameter increased beyond 300nm. A numerical model was developed and showed that the calculated particle collection efficiency was in reasonable agreement with experiment observations. Finally, a simple model was developed to estimate the particle collection efficiency of a typical disk-to-disk thermal precipitator. The model indicated that the particle collection efficiency of a disk-to-disk precipitator is a function of cold-disk deposition area, the average thermophoretic velocity, and the aerosol flowrate. This model may be useful in the future design of a thermal precipitator with the similar configurations. [Copyright &y& Elsevier]

A dry-ambient aerosol size spectrometer (DAASS) was previously developed to conduct measurements of aerosol water content at ambient relative humidity (RH) conditions. However, the RH difference of ambient RH and DAASS conditioning humidity (i.e., 10–20%, particularly when the DAASS operated at a high ambient RH) may introduce uncertainties in estimation of aerosol water content. In this study, we present a prototype of an RH-controlled DAASS. By employing an active RH controlling method, we resolve the discrepancy between the ambient RH and the DAASS conditioning RH, therefore extending the accurate measurement of aerosol water content to a wide RH range. The performance of this RH-controlled DAASS was characterized by both the laboratory evaluation and a 10-day field deployment. Results showed that the DAASS conditioning RH agreed well with the ambient RH (R2 of 0.993 when ambient RH up to 90%), with an average RH offset of less than 1.5%. The fraction of aerosol-bound water in the total ambient aerosol volume was ~10% under RHs below 50% and increased to ~50% when the ambient RH reached above 85%. • Improved DAASS system for aerosol liquid water content measurement. • High accuracy of RH control for measuring aerosol size distribution under ambient RH. • Field deployment of liquid water content measurement of atmospheric particles. [ABSTRACT FROM AUTHOR]