Aerosol Particle Size Research Articles

Activity size distribution and residence time of 7Be aerosols in the Arctic atmosphere

The activity size distributions of the natural radionuclide tracer 7Be in different size range fractions (<0.39 μm, 0.39–0.69 μm, 0.69–1.3 μm, 1.3–2.1 μm, 2.1–4.2 μm, 4.2–10.2 μm and >10.2 μm) were determined in the boreal atmosphere in the Arctic Research Centre of the Finnish Meteorological Institute (FMI) at Sodankylä, Finland (67°22′ N, 26°38′ E, 180 m asl). The activity median aerodynamic diameter (AMAD) ranged from 0.54 μm to 1.05 μm (average 0.83 μm). A residence time of about 8 days applies to aerosols of 0.83 μm diameter, representing the residence of aerosol particles in arctic environment. The observed positive correlation between AMAD values and RH% can be explained by the fact that condensation during high relative humidity conditions becomes more intense, resulting in increased particle sizes of atmospheric aerosols. However, greater aerosol particle sizes means higher wet scavenging rate of aerosols and as a result lower activity concentration of 7Be in the atmosphere, explaining the anti-correlation between the AMAD values and activity concentrations of 7Be. But this associated with possibly higher scavenging rates of aerosols does not necessarily alone explain the anti-correlation between the AMAD and the 7Be activities. The air mass origin associated with synoptic scale weather phenomena may contribute to that too. The Flextra model was used to assess the transport pattern and to explain the deviation in radionuclide activity concentrations and AMAD values observed in the site of investigation.

Variations in aerosol microphysical parameters of the surface air layer in the “ocean-continent” transitional zone

This article provides the study results of variations in microphysical parameters of atmospheric aerosol in the surface layer of the “ocean-continent” transitional zone. The analyzed data were obtained during the period from August 1, 2010, to December 31, 2012, at the lidar station of the Institute of Automation and Control Processes, Far Eastern Branch, Russian Academy of Sciences (IACP FEB RAS), Vladivostok. Mass concentrations of fine aerosol and black carbon and particle size distribution functions typical for the region under study were obtained. In winter, with strong north winds and low relative humidity (50 ± 20)%, dry continental aerosol predominates, and values of the aerosol number density Na are increased, with maxima in the range from 100 and 120 cm−3. In summer, when south winds prevail and the relative humidity attains 98%, sea aerosol predominates and Na took values from (5 ± 5) cm−3 in June, 2011, to (44 ± 20) cm−3 in July, 2011. Periodicity of diurnal variations in the mass and number density of atmospheric aerosol and black carbon are pronounced the best in winter. The modal radius of fine aerosol particles is from 0.275 μm in summer to 0.375 μm in winter, and of coarse aerosol particles, from 1.05 to 2.5 μm, respectively. Seasonal and diurnal variations in the mass concentration of black carbon MBC are the most stable; its values vary from (0.5 ± 0.5) μg/m3 in the early summer to (3.0 ± 2.0) μg/m3 in January–February. It has been ascertained that diurnal variations in MBC in Siberia (Tomsk) and in the “ocean-continent” transitional zone (Vladivostok) are similar in shape, but the amplitude of variations is higher in the latter case and is maximal in winter.

Reallocation in modal aerosol models: impacts on predicting aerosol radiative effects

Abstract. Atmospheric models often represent the aerosol particle size distribution with a modal approach, in which particles are described with log-normal modes within predetermined size ranges. This approach reallocates particles numerically from one mode to another for example during particle growth, potentially leading to artificial changes in the aerosol size distribution. In this study we analysed how the modal reallocation affects climate-relevant variables: cloud droplet number concentration (CDNC), aerosol–cloud interaction parameter (ACI) and light extinction coefficient (qext). The ACI parameter gives the response of CDNC to a change in total aerosol number concentration. We compared these variables between a modal model (with and without reallocation routines) and a high resolution sectional model, which was considered a reference model. We analysed the relative differences in the chosen variables in four experiments designed to assess the influence of atmospheric aerosol processes. We find that limiting the allowed size ranges of the modes, and subsequent remapping of the distribution, leads almost always to an underestimation of cloud droplet number concentrations (by up to 100%) and an overestimation of light extinction (by up to 20%). On the other hand, the aerosol–cloud interaction parameter can be either over- or underestimated by the reallocating model, depending on the conditions. For example, in the case of atmospheric new particle formation events followed by rapid particle growth, the reallocation can cause on average a 10% overestimation of the ACI parameter. Thus it is shown that the reallocation affects the ability of a model to estimate aerosol climate effects accurately, and this should be taken into account when using and developing aerosol models.

Controlled, Parametric, Individualized, 2D and 3D Imaging Measurements of Aerosol Deposition in the Respiratory Tract of Healthy Human Volunteers:In VivoData Analysis

To provide a validation dataset for aerosol deposition modeling, a clinical trial was performed in which the inhalation parameters and the inhaled aerosol were controlled or characterized. Eleven, healthy, never-smokers, male participants completed the study. Each participant performed two inhalations of (99m)Tc-labeled aerosol from a vibrating mesh nebulizer, which differed by a single controlled parameter (aerosol particle size: "small" or "large"; inhalation: "deep" or "shallow"; carrier gas: air or a helium-oxygen mix). The deposition measurements were made by planar imaging, and single photon emission computed tomography-computed tomography (SPECT-CT). The difference between the mean activity measured by two-dimensional imaging and that delivered from the nebulizer was 2.7%, which was not statistically significant. The total activity deposited was significantly lower in the left lung than in the right lung (p<0.0001) with a mean ratio (left/right) of 0.87±0.1 standard deviation (SD). However, when normalized to lung air volume, the left lung deposition was significantly higher (p=0.0085) with a mean ratio of 1.08±0.12 SD. A comparison of the three-dimensional central-to-peripheral (nC/P3D) ratio showed that it was significantly higher for the left lung (p<0.0001) with a mean ratio (left/right) of 1.36±0.20 SD. The effect of particle size was statistically significant on the nC/P3D ratio (p=0.0014), extrathoracic deposition (p=0.0037), and 24-hr clearance (p<0.0001), contrary to the inhalation parameters, which showed no effect. This article presents the results of an analysis of the in vivo deposition data, obtained in a clinical study designed to provide data for model validation. This study has demonstrated the value of SPECT imaging over planar, the influence of particle size on regional distribution within the lung, and differences in deposition between the left and right lungs.

Identification and Classification of Different Aerosol Types over a Subtropical Rural Site in Mpumalanga, South Africa: Seasonal Variations as Retrieved from the AERONET Sunphotometer

This paper reports the observational results of aerosol optical characteristics, modification processes and discrimination of key aerosol types over Skukuza (24.9°S, 31.5°E, and 150 m), a subtropical rural site in South Africa (SA), using CIMEL Sunphotometer data, part of the AErosol RObotic NETwork (AERONET), from December 2005 to November 2006. The results show that a pronounced spectral and temporal variability in the optical properties of aerosols is mainly due to anthropogenic emissions. The discrimination of different aerosol types over Skukuza is also made using the daily mean values of aerosol optical depth at 500 nm (AOD500) and Angstrom exponent (α440-870) by applying the threshold values. The results of the analysis indentified three individual components (biomass burning/urban (BU), desert dust (DD) and clean maritime (CM) aerosol types) of differing origin, composition and optical characteristics, and revealed that the percentage contribution of each of type of aerosol changed significantly from season to season. We also derived the curvature of a2 in an attempt to obtain information on aerosol-particle size and type, although the results revealed that the curvature alone is not enough to achieve this. In addition,, we analyzed the seasonal changes in aerosol characteristics using the classification scheme introduced in Gobbi et al. (2007) based on the measured scattering properties (α, dα) derived from the Sunphotometer data. The results show that during spring an extremely large fraction of fine-mode aerosols (η > 70%, Rf ~0.1 µm) in the turbid atmosphere was mainly caused by local anthropogenic pollution or biomass aerosol transported from forest fires. Whereas in summer, the low AOD (< 0.2) and smaller α (< 1.0) and η < 50% suggest the influence of transported mineral dust (coarse) over the region.

Aerosol Optical Properties Retrieved from a Prede Sky Radiometer over an Urban Site of Beijing, China

SKYNET is an international research network of ground-based Prede sky radiometers for the observation and monitoring of aerosol–cloud–radiation interactions in the atmosphere. The algorithm developed by SKYNET is SKYRAD.pack, which can be used to process the measurement data of Prede instruments. In this study, the latest SKYRAD.pack software (Version 5.0) has been used to retrieve the aerosol optical properties measured by a SKYNET Prede sky radiometer over an urban site of Beijing, China. Continuous data have been processed over a two-year period, and inversion products, including aerosol optical depth (AOD), Angstrom exponent (α), volumes of different aerosol particle size distributions, and single-scattering albedos (SSA), have been analyzed.

Detections and analyses of aerosol optical properties under different weather conditions using multi-wavelength Mie lidar

A multi-wavelength Mie-scattering lidar is designed and established for detecting the aerosol profiles under different weather conditions. And inversion algorithm about multi-wavelength lidar signal is studied. The atmosphere observations are carried out in Xi'an city in the winter of 2013 by using the multi - wavelength lidar. The mixed-layer depth, aerosol particle size characteristics, and atmosphere extinction are studied and analyzed on haze, cloudy and sunny days. The mixed layer depth is lower on haze day and is just about 0.4 km, while it can reach 0.5-0.8 km on sunny day. The aerosol particle characteristics are discussed under different weather conditions by using two Ångström exponents, one for the short - wavelength range (355 nm/532 nm) and other for long-wavelength range (532 nm/1064 nm). The long-wavelength Ångström exponent is less than the short-wavelength Ångström exponent on haze day, and it is contrary on sunny day. The results show that there are more coase particles on pollution day. The Ångström exponents significantly decrease, and even become negative in the clouds, showing that cloud particles are relatively large.

Impacts of Aerosol Particle Size Distribution and Land Cover Land Use on Precipitation in a Coastal Urban Environment Using a Cloud-Resolving Mesoscale Model

Urban environments influence precipitation formation via response to dynamic effects, while aerosols are intrinsically necessary for rainfall formation; however, the partial contributions of each on urban coastal precipitation are not yet known. Here, the authors use aerosol particle size distributions derived from the NASA aerosol robotic network (AERONET) to estimate submicron cloud condensation nuclei (CCN) and supermicron CCN (GCCN) for ingestion in the regional atmospheric modeling system (RAMS). High resolution land data from the National Land Cover Database (NLCD) were assimilated into RAMS to provide modern land cover and land use (LCLU). The first two of eight total simulations were month long runs for July 2007, one with constant PSD values and the second with AERONET PSDs updated at times consistent with observations. The third and fourth runs mirrored the first two simulations for “No City” LCLU. Four more runs addressed a one-day precipitation event under City and No City LCLU, and two different PSD conditions. Results suggest that LCLU provides the dominant forcing for urban precipitation, affecting precipitation rates, rainfall amounts, and spatial precipitation patterns. PSD then acts to modify cloud physics. Also, precipitation forecasting was significantly improved under observed PSD and current LCLU conditions.

Dust Particle Size Distribution Inversion Based on the Multi Population Genetic Algorithm

The aerosol number size distribution is the main parameter for characterizing aerosol optical properties and physical properties, it has a major influence on radiation forcing. With regard to some disadvantages in the traditional methods, a method based on the multi population genetic algorithm (MPGA) is proposed and employed to retrieve the aerosol size distribution of dust particles. The MPGA principles and design are presented in detail. The MPGA has better performance compared with conventional methods. In order to verify the feasibility of the inversion method, the measured aerosol optical thickness (AOT) data of dust particles taken by a sun photometer are used and a series of comparisons between the simple genetic algorithm (SGA) and MPGA are carried out. The results show that the MPGA presents better properties when compared with the SGA with smaller inversion errors, smaller population size and fewer generation numbers to retrieve the aerosol size distribution. The MPGA inversion method is analyzed using the background day, dust storm event and seasonal size distribution. The method proposed in this study has important applications and reference value for aerosol particle size distribution inversion.

Chemical and statistical interpretation of sized aerosol particles collected at an urban site in Thessaloniki, Greece

The size distribution of aerosol particles (PM0.015-PM18) in relation to their soluble inorganic species and total water soluble organic compounds (WSOC) was investigated at an urban site of Thessaloniki, Northern Greece. The sampling period was from February to July 2007. The determined compounds were compared with mass concentrations of the PM fractions for nano (N: 0.015 < Dp < 0.06), ultrafine (UFP: 0.015 < Dp < 0.125), fine (FP: 0.015 < Dp < 2.0) and coarse particles (CP: 2.0 < Dp < 8.0) in order to perform mass closure of the water soluble content for the respective fractions. Electrolytes were the dominant species in all fractions (24–27%), followed by WSOC (16–23%). The water soluble inorganic and organic content was found to account for 53% of the nanoparticle, 48% of the ultrafine particle, 45% of the fine particle and 44% of the coarse particle mass. Correlations between the analyzed species were performed and the effect of local and long-range transported emissions was examined by wind direction and backward air mass trajectories. Multivariate statistical analysis (cluster analysis and principal components analysis) of the collected data was performed in order to reveal the specific data structure. Possible sources of air pollution were identified and an attempt is made to find patterns of similarity between the different sized aerosols and the seasons of monitoring. It was proven that several major latent factors are responsible for the data structure despite the size of the aerosols – mineral (soil) dust, sea sprays, secondary emissions, combustion sources and industrial impact. The seasonal separation proved to be not very specific.

The solid-state and morphological characteristics of particles generated from solution-based metered dose inhalers: Influence of ethanol concentration and intrinsic drug properties

The aerosol performance, physical properties and formation process of two corticosteroids (beclomethasone dipropionate and fluticasone propionate) and caffeine (active pharmaceutical ingredients: APIs) from ethanol-based pressurized metered dose inhaler solution formulations, containing various ethanol fractions, were evaluated using cascade impaction, thermal analysis and scanning electron microscopy. In general, the final aerosol particle size distribution (post USP induction port) was unaffected by ethanol concentration (mass median aerodynamic diameter and geometric standard deviation values for each formulation were independent of ethanol concentration (%, w/w) in the initial formulation). However, ethanol concentration directly affected the percentage of particles that passed the USP induction, resulting in a significant decrease in fine particle fraction, across all formulations, as ethanol was increased. Thus it can be concluded that particle size is governed by initial droplet diameter and API concentration, while performance is governed by drying time. The physico-chemical properties and morphology of the dried API particles, collected from cascade impactor stages, showed that the solid state was related to the glass transition temperature (Tg) and, to some extent, the saturated hydrofluoroalkane propellant (HFA)/ethanol solubility of the APIs. The low Tg API caffeine, with high HFA solubility resulted in crystalline particles, while the high Tg corticosteroids were amorphous. Furthermore, the final structure of the particles was dependent on the ethanol concentration and drying kinetics after initial droplet formation. This study has shown that the solid-state physico-chemical properties and morphology of particles is intrinsically linked to the API properties and drying kinetics of the propellant/co-solvent. These variations in aerosol efficiency, particle morphology and solid-state characteristics may have direct effects on drug efficacy and bioavailability after deposition in the lung.

Boosting the aerodynamic properties of vibrating-mesh nebulized polymeric nanosuspensions

Pulmonary application of drug-loaded polymeric nanosuspensions is achieved by vibrating-mesh nebulizers, which allow for an output of intact nanocarriers from the nebulizer reservoir. However, adequate aerosol droplet sizes are a prerequisite for an efficient pulmonary deposition. The current study discloses experimental findings useful to optimize the aerodynamic characteristics of formulations atomized by the vibrating-mesh nebulizers Aeroneb(®) Pro and eFlow(®)rapid. Parameters with significant influence on the aerosol droplet diameter were identified by a statistical design analysis rating size results from laser diffraction. Subsequently, the effect of selected biocompatible solutes on the aerodynamic performance of nebulized formulations was studied and correlated with their physicochemical properties. Vibrating-mesh generated aerosols were significantly affected by the dynamic viscosity and conductivity of the applied formulation. Consequently, an increase in viscosity enhancer (sucrose and poly(ethylene glycol)) or electrolyte (NaCl and CaCl2) content caused the droplet diameter to decrease. Similarly, purified nanosuspensions revealed a considerable decline in aerosol particle size upon excipient addition. However, coating of polymeric nanoparticles with poloxamer and poly(vinyl alcohol) was necessary to avoid electrolyte-induced nanoparticle aggregation. Overall, the current study emphasizes that supplementation of nanosuspensions with biocompatible solutes is an excellent means to tailor the characteristics of aerosols generated by vibrating-mesh technology.

Optimizing the primary particle size distributions of pressurized metered dose inhalers by using inkjet spray drying for targeting desired regions of the lungs

Conventional suspension pressurized metered dose inhalers (pMDIs) suffer not only from delivering small amounts of a drug to the lungs, but also the inhaled dose scatters all over the lung regions. This results in much less of the desired dose being delivered to regions of the lungs. This study aimed to improve the aerosol performance of suspension pMDIs by producing primary particles with narrow size distributions. Inkjet spray drying was used to produce respirable particles of salbutamol sulfate. The Next Generation Impactor (NGI) was used to determine the aerosol particle size distribution and fine particle fraction (FPF). Furthermore, oropharyngeal models were used with the NGI to compare the aerosol performances of a pMDI with monodisperse primary particles and a conventional pMDI. Monodisperse primary particles in pMDIs showed significantly narrower aerosol particle size distributions than pMDIs containing polydisperse primary particles. Monodisperse pMDIs showed aerosol deposition on a single stage of the NGI as high as 41.75 ± 5.76%, while this was 29.37 ± 6.79% for a polydisperse pMDI. Narrow size distribution was crucial to achieve a high FPF (49.31 ± 8.16%) for primary particles greater than 2 µm. Only small polydisperse primary particles with sizes such as 0.65 ± 0.28 µm achieved a high FPF with (68.94 ± 6.22%) or without (53.95 ± 4.59%) a spacer. Oropharyngeal models also indicated a narrower aerosol particle size distribution for a pMDI containing monodisperse primary particles compared to a conventional pMDI. It is concluded that, pMDIs formulated with monodisperse primary particles show higher FPFs that may target desired regions of the lungs more effectively than polydisperse pMDIs.

HST hot-Jupiter transmission spectral survey: evidence for aerosols and lack of TiO in the atmosphere of WASP-12b

We present Hubble Space Telescope (HST) optical transmission spectra of the transiting hot-Jupiter WASP-12b, taken with the Space Telescope Imaging Spectrograph instrument. The resulting spectra cover the range 2900–10 300 Å which we combined with archival Wide Field Camera 3 spectra and Spitzer photometry to cover the full optical to infrared wavelength regions. With high spatial resolution, we are able to resolve WASP-12A's stellar companion in both our images and spectra, revealing that the companion is in fact a close binary M0V pair, with the three stars forming a triple-star configuration. We derive refined physical parameters of the WASP-12 system, including the orbital ephemeris, finding the exoplanet's density is ∼20 per cent lower than previously estimated. From the transmission spectra, we are able to decisively rule out prominent absorption by TiO in the exoplanet's atmosphere, as there are no signs of the molecule's characteristic broad features nor individual bandheads. Strong pressure-broadened Na and K absorption signatures are also excluded, as are significant metal-hydride features. We compare our combined broad-band spectrum to a wide variety of existing aerosol-free atmospheric models, though none are satisfactory fits. However, we do find that the full transmission spectrum can be described by models which include significant opacity from aerosols: including Rayleigh scattering, Mie scattering, tholin haze and settling dust profiles. The transmission spectrum follows an effective extinction cross-section with a power law of index α, with the slope of the transmission spectrum constraining the quantity αT = −3528 ± 660 K, where T is the atmospheric temperature. Rayleigh scattering (α = −4) is among the best-fitting models, though requires low terminator temperatures near 900 K. Sub-micron size aerosol particles can provide equally good fits to the entire transmission spectrum for a wide range of temperatures, and we explore corundum as a plausible dust aerosol. The presence of atmospheric aerosols also helps to explain the modestly bright albedo implied by Spitzer observations, as well as the near blackbody nature of the emission spectrum. Ti-bearing condensates on the cooler night-side is the most natural explanation for the overall lack of TiO signatures in WASP-12b, indicating the day/night cold trap is an important effect for very hot Jupiters. These findings indicate that aerosols can play a significant atmospheric role for the entire wide range of hot-Jupiter atmospheres, potentially affecting their overall spectrum and energy balance.

Microlubrication Effects During End Milling AISI 1018 Steel

Flood cooling is primarily used to cool and lubricate the cutting tool and workpiece interface during a machining process. But the adverse health effects caused by the use of flood coolants are drawing manufacturers' attention to develop methods for controlling occupational exposure to cutting fluids. Microlubrication serves as an alternative to flood cooling by reducing the volume of cutting fluid used in the machining process. In this study the effects of microlubrication during end milling of AISI 1018 steel was investigated using vegetable based cutting fluid aerosol. A solid carbide cutting tool was used with varying cutting speeds and feed rates having a constant depth of cut. A full factorial experiment was conducted and regression models were generated along with parameter optimization for the aerosol mass concentration and the aerosol particle size. The study shows that with a proper selection of the cutting parameters it is possible to reduce the aerosol mass concentration in end milling under microlubrication. But more scientific assessments are needed to lower the mass concentration of the aerosol particles, below the recommended value of 5 mg/m3 by Occupational Safety and Health Administration (OSHA). Limited studies have been reported to investigate the effectiveness and quality of mist produced under microlubrication. No study has been reported to date on end milling 1018 steel under microlubrication.

Investigation of aerosol based emission of MEA due to sulphuric acid aerosol and soot in a Post Combustion CO2 Capture process

The prevention of emissions of amine species is of high importance for the overall sustainability and performance of Post Combustion CO2 Capture facilities. There is a clear understanding of amine emissions based on volatility in the treated flue gas. Emission via aerosols from Post Combustion CO2 Capture facilities has only been pointed out recently. Thus, there is little knowledge about emission via aerosols in contrast to emission based on volatility. It has been found that flue gas quality plays an important role for emissions caused by aerosols formation. In this work, we study the experimental assessment of the impact of flue gas quality on the level of monoethanolamine (MEA) emission via aerosols. In a dedicated test rig, effects of the flue gas components such as sulphuric acid aerosols and extremely fine particles like soot has been studied. An aerosol generator capable of producing controlled amounts of soot and dosing sulphuric acid aerosol to a mobile CO2 capture mini-plant was used as a test equipment for this study. Soot particle number concentration were in the range of 104–106 per cm3. The particle number concentration for different amount of H2SO4 aerosols were in the order of 108 per cm3. Amine emissions up to 4.3ppmv (12mg/Nm3 for MEA) is considered to be as an upper limit for the design of a Post Combustion CO2 Capture plant. MEA emissions in the presence of soot particles were in the range of 100–200mg/Nm3 which is 2–4 times higher than baseline vapour based emissions of about 45mg/Nm3. The expected particle size of H2SO4 aerosols is well below 100nm, while the corresponding mass concentration range is between 1 and 5mg/m3. The MEA emissions observed due to H2SO4 aerosols were in the range of 600–1100mg/Nm3. Moreover, parametric tests have shown that besides flue gas quality, the absorber temperature profile and the presence of CO2 in the flue gas are pre-requisite for aerosol emissions. It is evident that the observed level of emissions in this study are unacceptable. Therefore, it is imperative that fundamental know-how about aerosol formation and reduction is generated in order to design appropriate counter measures.

Aerosol extinction-to-backscatter ratio derived from passive satellite measurements

Abstract. Spaceborne reflectance measurements from the POLDER instrument are used to study the specific directional signature close to the backscatter direction. The data analysis makes it possible to derive the extinction-to-backscatter ratio (EBR), which is related to the inverse of the scattering phase function for an angle of 180° and is needed for a quantitative interpretation of lidar observations (active measurements). In addition, the multidirectional measurements are used to quantify the scattering phase function variations close to backscatter, which also provide some indication of the aerosol particle size and shape. The spatial distributions of both parameters show consistent patterns that are consistent with the aerosol type distributions. Pollution aerosols have an EBR close to 70, desert dust values are on the order of 50 and EBR of marine aerosols is close to 25. The scattering phase function shows an increase with the scattering angle close to backscatter. The relative increase ∂lnP/∂γ is close to 0.01 for dust and pollution type aerosols and 0.06 for marine type aerosols. These values are consistent with those retrieved from Mie simulations.

The transition from spark to arc discharge and its implications with respect to nanoparticle production

The synthesis of nanoparticles by means of electrical discharges between two electrodes in an inert gas at atmospheric pressure, as driven by a constant current ranging from a few milliamps to tens of amps, is investigated in this work. An extensive series of experiments are conducted with copper as a consumable electrode and pure nitrogen as the inert gas. Three different DC power supplies are used to drive electrical discharges for the entire operating current range. Then, three electrical discharge regimes (spark, glow, and arc) with distinct voltage–current characteristics and plasma emission spectra are recognized. For the first time, nanoparticles are synthesized by evaporation of an electrode by atmospheric pressure inert gas DC glow discharge of a few millimeters in size. The discharge regimes are characterized in terms of the mass output rate and the particle size distribution of the copper aerosols by means of online (tapered element oscillating microbalance, TEOM; and scanning mobility particle sizer, SPMS) and offline (gravimetric analysis; small and wide angle X-ray scattering, SWAXS; and transmission electron microscopy, TEM) techniques. The electrical power delivered to the electrode gap and the gas flow rate are two major parameters determining the aerosol mass output rate and the aerosol particle size distribution. The mass output rate of copper aerosols raises from 2 mg h−1 to 2 g h−1 when increasing the electrical power from 9 to 900 W. The particle mean size (SMPS dg) varies between 20 and 100 nm depending upon the electrical power and the gas flow rate, whereas the particle size dispersion (SMPS σg) ranges from 1.4 to 1.7 and is only weakly dependent on the gas flow rate.

Improvement of MODIS aerosol retrievals near clouds

AbstractThe retrieval of aerosol properties near clouds from reflected sunlight is challenging. Sunlight reflected from clouds can effectively enhance the reflectance in nearby clear regions. Ignoring cloud 3‐D radiative effects can lead to large biases in aerosol retrievals, risking an incorrect interpretation of satellite observations on aerosol‐cloud interaction. Earlier, we developed a simple model to compute the cloud‐induced clear‐sky radiance enhancement that is due to radiative interaction between boundary layer clouds and the molecular layer above. This paper focuses on the application and implementation of the correction algorithm. This is the first time that this method is being applied to a full Moderate Resolution Imaging Spectroradiometer (MODIS) granule. The process of the correction includes converting Clouds and the Earth's Radiant Energy System broadband flux to visible narrowband flux, computing the clear‐sky radiance enhancement, and retrieving aerosol properties. We find that the correction leads to smaller values in aerosol optical depth (AOD), Ångström exponent, and the small mode aerosol fraction of the total AOD. It also makes the average aerosol particle size larger near clouds than far away from clouds, which is more realistic than the opposite behavior observed in operational retrievals. We discuss issues in the current correction method as well as our plans to validate the algorithm.

Effect of Particle Size on the Performance of an N95 Filtering Facepiece Respirator and a Surgical Mask at Various Breathing Conditions.

The effect of aerosol particle size on the performance of an N95 filtering facepiece respirator (FFR) and a surgical mask (SM) was evaluated under different breathing conditions, including breathing frequency and mean inspiratory flow (MIF) rate. The FFR and SM were sealed on a manikin headform and challenged with charge-equilibrated NaCl aerosol. Filter penetration (Pfilter) was determined as the ratio of aerosol concentrations inside and outside the FFR/SM size-selectively (28 channels) within a range of 20 to 500 nm. In addition, the same models of the FFR and SM were donned, but not sealed, on an advanced manikin headform covered with skin-like material. Total inward leakage (TIL), which represents the total particle penetration, was measured under conditions identical to the filter penetration experiment. Testing was conducted at four mean MIFs (15, 30, 55 and 85 L/min) combined with five breathing frequencies (10, 15, 20, 25 and 30 breaths/min). The results show that SM produced much higher Pfilter and TIL values, and thus provide little protection against aerosols in the size range tested. Pfilter was significantly affected by particle size and breathing flow rate (p <0.05) for the tested FFR and SM. Surprisingly, for both devices, Pfilter as a function of the particle size exhibited more than one peak under all tested breathing conditions. The effect of breathing frequency on Pfilter was generally less pronounced, especially for lower MIFs. For the FFR and SM, TIL increased with increasing particle size up to about 50 nm; for particles above 50 nm, the total penetration was not significantly affected by particle size and breathing frequency; however, the effect of MIF remained significant.