Abstract: There are several characteristics of silver agglomerates that are not incorporated in existing models for agglomerate dynamics. These characteristics include particle alignment in the electric field, necking between particles, polydispersity of the primary particles, and variable primary sphere size. Estimates of these features on the agglomerate dynamics were computed as perturbations to the Chan-Dahneke agglomerate model. The variable primary sphere size effect results in the largest change from the idealized model with about a 10% increase in scaling exponents for both friction coefficient â number of primary particles (η) and mass-mobility diameter (Dfm). The second largest change is a 4% decrease in the exponent η and a 4% increase in the exponent (Dfm) from the alignment in the electric field. The effects of necking between particles and polydispersity of the primary particles are negligible for the two exponents. The combined effect, excluding the variable primary particle size, results in a 17.5% decrease in the dynamic shape factor for agglomerates with a 300 nm mobility diameter. Adjusting the model by this amount provides a significant improvement in the agreement between the model and silver agglomerate measurements for the dynamic shape factor. Experimentally the number of primary spheres is determined from the mass of the agglomerate assuming a constant primary sphere diameter. The predicted apparent exponent η based on a 10% variability in the primary sphere size is about a 5% less than the apparent exponent assuming a constant primary sphere size. This is a significant effect relative to the observed 15% decrease in η (Shin et al., 2009a) as the agglomerate size increases from the free molecular regime into the transition regime.
Abstract: This paper reports on an experimental study of the deposition of well-characterized silica agglomerates in a cast of a section of a human lung. Deposition of the agglomerates is compared with the deposition of oleic acid spheres and sodium chloride particles for a range of mobility sizes, agglomerate properties (primary particle size and mass-mobility exponent) and inspiratory flow rates. In most cases, agglomerate deposition was significantly greater than that of the oleic acid and sodium chloride particles. Deposition of agglomerates with a more open structure was greater than that of relatively more compact (but still non-spherical) agglomerates. Deposition also increased with the flow rate. Because of the large physical size of the agglomerates, as well as the crenulated flow path through the model and the flow rate dependence, it is likely that interception is responsible for the enhanced deposition of the agglomerates.
Abstract: We present laboratory studies and field observations that explore the role of aminium salt formation in atmospheric nanoparticle growth. These measurements were performed using the Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS) and Ultrafine Hygroscopicity Tandem Differential Mobility Analyzers. Laboratory measurements of alkylammonium-carboxylate salt nanoparticles show that these particles exhibit lower volatilities and only slightly lower hygroscopicities than ammonium sulfate nanoparticles. TDCIMS measurements of these aminium salts showed that the protonated amines underwent minimal decomposition during analysis, with detection sensitivities comparable to those of organic and inorganic deprotonated acids. TDCIMS observations made of a new particle formation event in an urban site in Tecamac, Mexico, clearly indicate the presence of protonated amines in 8-10 nm diameter particles accounting for about 47% of detected positive ions; 13 nm particles were hygroscopic with an average 90% RH growth factor of 1.42. Observations of a new particle formation event in a remote forested site in Hyytiälä, Finland, show the presence of aminium ions with deprotonated organic acids; 23% of the detected positive ions during this event are attributed to aminium salts while 10 nm particles had an average 90% RH growth factor of 1.27. Similar TDCIMS observations during events in Atlanta and in the vicinity of Boulder, Colorado, show that aminium salts accounted for 10-35% of detected positive ions. We conclude that aminium salts contribute significantly to nanoparticle growth and must be accounted for in models to accurately predict the impact of new particle formation on climate.
Abstract: Particle mobility size spectrometers often referred to as DMPS (Differential Mobility Particle Sizers) or SMPS (Scanning Mobility Particle Sizers) have found a wide application in atmospheric aerosol research. However, comparability of measurements conducted 5 world-wide is hampered by lack of generally accepted technical standards with respect to the instrumental set-up, measurement mode, data evaluation as well as quality control. This article results from several instrument intercomparison workshops conducted within the European infrastructure project EUSAAR (European Supersites for Atmospheric Aerosol Research). Under controlled laboratory conditions, the number size 10 distribution from 20 to 200nm determined by mobility size spectrometers of different design are within an uncertainty range of ñ10% after correcting internal particle losses, while below and above this size range the discrepancies increased. Instruments with identical design agreed within ñ3% in the peak number concentration when all settings were done carefully. Technical standards were developed for a minimum requirement 15 of mobility size spectrometry for atmospheric aerosol measurements. Technical recommendations are given for atmospheric measurements including continuous monitoring of flow rates, temperature, pressure, and relative humidity for the sheath and sample air in the differential mobility analyser. In cooperation with EMEP (European Monitoring and Evaluation Program), a new uniform data structure was introduced for 20 saving and disseminating the data within EMEP. This structure contains three levels: raw data, processed data, and final particle size distributions. Importantly, we recommend reporting raw measurements including all relevant instrument parameters as well as a complete documentation on all data transformation and correction steps. These technical and data structure standards aim to enhance the quality of long-term size 25 distribution measurements, their comparability between different networks and sites, and their transparency and traceability back to raw data.
Abstract: Transport and physical/chemical properties of nanoparticle agglomerates depend on primary particle size and agglomerate structure (size, fractal dimension, and dynamic shape factor). This research reports on in situ techniques for measuring such properties. Nanoparticle agglomerates of silica were generated by oxidizing hexamethyldisiloxane in a methane/oxygen diffusion flame. Upon leaving the flame, agglomerates of known electrical mobility size were selected with a differential mobility analyzer (DMA), and their mass was measured with an aerosol particle mass analyzer (APM), resulting in their mass fractal dimension, D(f), and dynamic shape factor, chi. Scanning and transmission electron microscopy (SEM/TEM) images were used to determine primary particle diameter and to qualitatively investigate agglomerate morphology. The DMA-APM measurements were reproducible within 5%, as determined by multiple measurements on different days under the same flame conditions. The effects of flame process variables (oxygen flow rate and mass production rate) on particle characteristics (D(f), and chi) were determined. All generated particles were fractal-like agglomerates with average primary particle diameters of 12-93 nm and D(f) = 1.7-2.4. Increasing the oxygen flow rate decreased primary particle size and D(f), while it increased chi. Increasing the production rate increased the agglomerate and primary particle sizes, and decreased chi without affecting D(f). The effects of oxygen flow rate and particle production rate on primary particle size reported here are in agreement with ex situ measurements in the literature, while the effect of process variables on agglomerate shape (chi) is demonstrated for the first time to our knowledge.
Abstract: Nanoparticles in colloidal suspensions are analyzed in various laboratory and manufacturing processes such as PSL manufacturing and generation, characterization of polishing slurries, liquid filter characterization, water quality testing, and drug manufacturing. Size information can be obtained using Dynamic Light Scattering (DLS), laser diffraction, or Optical Particle Counters (OPCs), but size resolution of these instruments is relatively poor and size accuracy is affected by the optical properties of the suspension. A conventional nebulizer can be used in series with an SMPS to obtain size information, however this is difficult for particles smaller than 100 nm as dissolved residue from the liquid interferes with the particle size distribution.
In this paper we present a device and method for counting and sizing nanoparticles in liquids down to 10 nm with good accuracy and resolution. The TSI Model 3985 Liquid Nanoparticle Sizer (LNS) combines an ultrafine nebulizer with an SMPS. The nebulizer of the LNS employs online dilution control using ultrapure water (UPW) and a peristaltic pump for metering of the liquid sample. The generated aerosol has a mean droplet size of 300 nm, which is heated and dried before being sampled by the SMPS at a flow rate of about 1 L/min. In addition to sizing capabilities, the number concentration of the liquid sample is determined within 10 percent.
The LNS has been used to characterize suspensions of gold, alumina, PSL, colloidal silica, and macromolecules such as dextran. Real-time measurement of the coefficient of variation (CV) of PSL and gold size distributions is in excellent agreement with the CV published by manufacturers. The LNS has also been used to characterize polishing slurries and measure removal efficiency of liquid filters as a function of particle size, filter pore size, and filter loading. Particle sizing data from these studies are presented.
Abstract: Atmospheric nucleation leads to the formation of new particles that influence concentrations of cloud condensation nuclei, thereby affecting humanâs impact on climate. Size-resolved measurements extending down to molecular dimensions can provide information on chemical and physical processes that lead to nucleation. We report the first atmospheric measurements of cluster and nanoparticle number distribution functions over the complete range of sizes, extending down to single sulfuric acid molecules. Two new instrument systems were deployed during the 2009 Nucleation and Cloud Condensation Nuclei campaign (NCCN) in Atlanta, Georgia. The Cluster CIMS, a mass spectrometer, detected sulfuric acid vapor and neutral molecular clusters that contained three and four sulfuric acid molecules. The DEG SMPS, an aerosol mobility spectrometer equipped with a diethylene glycol condensation particle counter, extended measurements of nano condensation nuclei (nano CN) down to sizes close to 1 nm. A pair of conventional aerosol mobility spectrometers was used to measure the number distribution functions of particles larger than 3 nm. The smallest nano CN that were detected by the DEG SMPS are comparable in size to the size 3 and 4 clusters detected by the Cluster CIMS, and the distribution functions measured by the Cluster CIMS and DEG typically agree to within the estimated measurement uncertainty. The DEG SMPS and the conventional nano SMPS typically agree to within a factor of two in the overlapping 3 to 10 nm range.
Abstract: Although much work has been done to determine the factors which influence the deposition of spherical particles in the human lung, the deposition of agglomerates remains relatively under-studied. Because of common human exposure, combined with concerns about nanoparticle toxicity, it is important to fully understand the transport and deposition of agglomerates in the human lung.
In this study, mobility classified, flame generated silica agglomerates$^1, oleic acid spheres and sodium chloride crystals were used to measure penetration through a cast of lung generations 3-8. Agglomerate morphology was quantified by the mass-mobility exponent, E$_m , given by:
m=k*d$_(me)$^(Em)
Number concentrations were measured upstream and downstream of the model using identical condensation particle counters. This was repeated for a range of mobility sizes (25-300nm), E$_m (1.9-2.4), primary particle sizes (10-100nm), and constant flow rates (simulating inspiratory flows of 8-96 l/min). Depending on properties, these agglomerates can have maximum projected lengths several times larger than their mobility size, but aerodynamic sizes several times smaller.
Deposition efficiency increases as E$_m decreases and also as primary particle size decreases. Increasing the flow rate through the lung model increases deposition efficiency. At a given size and flow rate, deposition of âopenâ agglomerates with small primary particles is 2-3 times higher than that of spheres. This discrepancy between spheres and agglomerates exists when deposition is expressed both in terms of mobility size (diffusional deposition depends on mobility size) as well as aerodynamic size (impaction depends on aerodynamic size), suggesting that an additional mechanism must be important. Because of the large physical size of the agglomerates, as well as frequent streamline bends in the model and the flow rate dependence, it is likely that interception is responsible for the enhanced deposition of the agglomerates.
(1) Scheckman, J.; Mcmurry, P.; Pratsinis, S., Langmuir 2009, 25(14), 8248.
