Aerosol Particle Size Research Articles

Characterization of a head-only aerosol exposure system for nonhuman primates

A well-characterized exposure chamber is necessary to generate reproducible atmospheres for inhalation toxicology studies. The aim of the present study was to characterize a head-only exposure chamber for non-human primates. Aerosols containing bovine serum albumin (BSA) were used to characterize a 16-L dynamic airflow head-only exposure chamber. A 250-ml plastic bottle with a respirator attached located inside the chamber was used to simulate a breathing head. Chamber leak rate, mixing, and aerosol spatial distributions were quantified. The chamber concentration profile was measured at the chamber exhaust using an aerodynamic particle sizer. Aerosol spatial distribution was determined by collecting filter samples at several chamber locations. The particle size distribution was determined by collecting cascade impactor samples at several chamber locations. The estimated chamber leak rate was within standards suggested in the literature. The measured average aerosol residence time was similar to theoretical aerosol residence time, suggesting that the chamber was mixing well. Additionally, the average concentration measured at each of the sampling locations within the chamber was similar, and the within-run coefficients of variation (CV) across all sampling locations was similar to those reported in previously published studies, again suggesting that the aerosol concentration throughout the chamber was uniform. The particle size distribution was similar throughout the exposure chamber. Additionally, the BSA concentration and particle size distributions measured in the breathing zone of the simulated head were not significantly different from measurements made elsewhere in the chamber, suggesting that respiration does not affect the average aerosol concentration or particle size distribution at the mouth.

Measurements of the Equilibrium Size of Supersaturated Aqueous Sodium Chloride Droplets at Low Relative Humidity Using Aerosol Optical Tweezers and an Electrodynamic Balance

An approach for examining the hygroscopicity of single aerosol particles over a broad range in relative humidity (RH) using aerosol optical tweezers is presented and compared with measurements made using an electrodynamic balance. In particular, benchmark measurements on aqueous sodium chloride aerosol are presented over the RH range 45-75% (293 K), a RH range that had not previously been explored with aerosol optical tweezers. Measurements of the variation in equilibrium wet droplet size with RH are made using cavity-enhanced Raman scattering, with an accuracy of 1 nm in the determination of the wet particle radius. The full range of optical tweezers experimental measurements (including previous dual trapping comparative studies approaching a saturation relative humidity of 100%) are compared with determinations using other experimental techniques and with a range of model treatments. An assessment of the models and all experimental data for estimating the equilibrium size of a sodium chloride droplet suggests that the size can be predicted with an accuracy of better than 0.1% over the RH range 48-100%. Discrepancies between different measurements lead to an increase in uncertainty above 1% below an RH of 48% as efflorescence is approached. The optical tweezers' measurements of equilibrium size consistently agree with model predictions to within an error of 1% (<50 nm for the size range explored here) and mostly with an error of less than +/-0.1%. These data demonstrate the highly accurate nature of measurements of thermodynamic equilibrium size by aerosol optical tweezers and suggest that this approach may be used to investigate the competition between thermodynamic and kinetic factors in governing aerosol particle size over the full RH range.

Aerosol Remote Sensing From Space: Determination of Atmospheric Aerosol Properties Using Satellite Measurements; Bad Honnef, Germany, 16–19 August 2009

Aerosol optical depth (AOD), a measure of how much light is attenuated by aerosol particles, provides scientists information about the amount and type of aerosols in the atmosphere. Recent developments in aerosol remote sensing was the theme of a workshop held in Germany. The workshop was sponsored by the Wilhelm and Else Heraeus Foundation and attracted 67 participants from 12 countries.The workshop focused on the determination (retrieval) of AOD and its spectral dependence using measurements of changes to the solar radiation backscattered to space. The midvisible AOD is usually applied to define aerosol amount, while the size of aerosol particles is indicated by the AOD spectral dependence and is commonly expressed by the Angstrom parameter. Identical properties retrieved by different sensors, however, display significant diversity, especially over continents. A major reason for this is that the derivation of AOD requires more accurate determination of nonaerosol contributions to the sensed satellite signal than is usually available. In particular, surface reflectance data as a function of the viewing geometry and robust cloud‐clearing methods are essential retrieval elements. In addition, the often needed assumptions about aerosol properties in terms of absorption and size are more reasons for the discrepancy between different AOD measurements.

Size, composition, and mixing state of individual aerosol particles in a South China coastal city

Aerosol samples were collected in summer in Macao, a coastal city of the Pearl River Delta Region in China. Morphology, size, elemental composition, and mixing state of individual aerosol particles were determined by scanning electron microscopy coupled energy dispersive X-ray (SEM/EDX) and transmission electron microscopy (TEM). Based on the morphologies of 5711 aerosol particles, they consist of soot (32%), mineral (17%), secondary (22%), and unknown fine particles (29%). The sizes of these particles were mostly distributed between 0.1 and 0.4 μm. Compositions of 202 mineral particles were obtained by SEM/EDX. Mineral particles were mainly classified into three types: Si-rich, Ca-rich, and Na-rich. The compositions of typical mineral particles can indicate their sources in sampling location. For example, mineral particles, collected along the main street, were associated with trace amounts of heavy metals, such as Zn, Ti, Mn, Ba, Pb, and As. TEM observations indicate that most Na-rich particles were aged sea salt particles (e.g., Na 2SO 4 and NaNO 3) which formed through heterogeneous chemical reactions between sea salt and acidic gases. Additionally, aging time of soot was short in Macao due to high humidity, high temperature, and high levels of sunlight in Macao. Most of soot and fine mineral dust particles were internally mixed with secondary particles.

北京奥运期间大气细粒子谱与能见度、PM10质量浓度对比分析

北京奥运期间大气细粒子谱与能见度、PM10质量浓度对比分析

Aerosol behavior during SIC control rod failure in QUENCH-13 test

Abstract In a nuclear reactor severe accident, radioactive fission products as well as structural materials are released from the core by evaporation, and the released gases form particles by nucleation and condensation. In addition, aerosol particles may be generated by droplet formation and fragmentation of the core. In pressurized water reactors (PWR), a commonly used control rod material is silver–indium–cadmium (SIC) covered with stainless steel cladding. The control rod elements, Cd, In and Ag, have relatively low melting temperatures, and especially Cd has also a very low boiling point. Control rods are likely to fail early on in the accident due to melting of the stainless steel cladding which can be accelerated by eutectic interaction between stainless steel and the surrounding Zircaloy guide tube. The release of the control rod materials would follow the cladding failure thus affecting aerosol source term as well as fuel rod degradation. The QUENCH experimental program at Forschungszentrum Karlsruhe investigates phenomena associated with reflood of a degrading core under postulated severe accident conditions. QUENCH-13 test was the first in this program to include a silver–indium–cadmium control rod of prototypic PWR design. To characterize the extent of aerosol release during the control rod failure, aerosol particle size distribution and concentration measurements in the off-gas pipe of the QUENCH facility were carried out. For the first time, it was possible to determine on-line the aerosol concentration and size distribution released from the core. These results are of prime importance for model development for the proper calculation of the source term resulting from control rod failure. The on-line measurement showed that the main aerosol release started at the bundle temperature maximum of T ∼ 1570 K at hottest bundle elevation. A very large burst of aerosols was detected 660 s later at the bundle temperature maximum of T ∼ 1650 K, followed by a relatively steady aerosol release until core cooling by quench when the on-line measurements were stopped. Cd was released first from the control rod, followed by In, and finally, by Ag. The particle size distributions were bimodal indicating two aerosol formation mechanisms, evaporation followed by nucleation and condensation, as well as droplet and fragment generation. Generally, release is modelled as evaporation from molten regions of control rod materials. Clearly, results of this investigation give evidence of contribution by entrainment of droplets and fragmented material.

The Generation And Properties Of Solid Monodisperse Aerosols Of Stearic Acid And Carnauba Wax

A monodisperse aerosol generator (MAGE) was used to generate calibration or monodisperse aerosols containing stearic acid and carnauba wax. Some of the factors affecting the size of aerosol particles generated with the MAGE were determined. The factors include: temperature of operation of the MAGE, type and purity of coating material used. The reproducibility of aerosol particles and stability of the aerosol generated were evaluated. The performance characteristics of the MAGE over an extended period of time of operation were also established. The calibration aerosols generated with the MAGE can be used in situ for studies of aerosol deposition measurement equipment. Keywords: Generation, Calibration aerosols, Monodisperse aerosol generator, Performance characteristics

Influence of physical properties and chemical composition of sample on formation of aerosol particles generated by nanosecond laser ablation at 213 nm

The influence of sample properties and composition on the size and concentration of aerosol particles generated by nanosecond Nd:YAG laser ablation at 213 nm was investigated for three sets of different materials, each containing five specimens with a similar matrix (Co-cemented carbides with a variable content of W and Co, steel samples with minor differences in elemental content and silica glasses with various colors). The concentration of ablated particles (particle number concentration, PNC) was measured in two size ranges (10–250 nm and 0.25–17 µm) using an optical aerosol spectrometer. The shapes and volumes of the ablation craters were obtained by Scanning Electron Microscopy (SEM) and by an optical profilometer, respectively. Additionally, the structure of the laser-generated particles was studied after their collection on a filter using SEM. The results of particle concentration measurements showed a significant dominance of particles smaller than 250 nm in comparison with larger particles, irrespective of the kind of material. Even if the number of particles larger than 0.25 µm is negligible (up to 0.1%), the volume of large particles that left the ablation cell can reach 50% of the whole particle volume depending on the material. Study of the ablation craters and the laser-generated particles showed a various number of particles produced by different ablation mechanisms (particle splashing or condensation), but the similar character of released particles for all materials was observed by SEM after particle collection on the membrane filter. The created aerosol always consisted of two main structures — spherical particles with diameters from tenths to units of micrometers originally ejected from the molten surface layer and µm-sized “fibres” composed of primary agglomerates with diameters in the range between tens and hundreds of nanometers. The shape and structure of ablation craters were in good agreement with particle concentration measurements. Samples with a high crater rim and melted bottom produced the highest number of large spherical particles. The mass values of all produced aerosols were calculated from the measured ablation crater volumes and sample densities.

Impactor designed to increase mass output rate of nanoparticles from a pneumatic nebulizer

A modular impactor was designed to remove large droplets from aerosols generated by a pneumatic nebulizer, the Six-Jet Atomizer from TSI Inc. (Shoreview, MN), with the aim of generating dry nanoparticles. Three interchangeable nozzle heads were designed to provide droplet cutoff diameters of 0.5, 1, and 2 μm at an air flow rate of 8.3×10 −4 m 3 s −1 (50 L min −1), which corresponds to all six jets of the nebulizer operated at 25 °C and an air pressure of 241 kPa (35 psi). The collection and output characteristics of the 0.5 μm impactor were evaluated from dry particle size distributions produced by nebulizing an aqueous solution with a NaCl mass fraction of 1% both with and without the impactor present. The impactor characteristic cutoff curve was sharp (impactor geometric standard deviation, GSD imp=1.15–1.19) with a 50% cutoff diameter d 50 that ranged from 0.48 μm at 3.0×10 −4 m 3 s −1 to 0.74 μm at 11.7×10 −4 m 3 s −1. The rate of dry NaCl particle generation ranged from 0.5 to 5 g s −1 (0.04 to 0.4 g day −1) with mass median diameters MMD p =80–123 nm and geometric standard deviations GSD p =1.6–1.8 (depending on flow rate). Anomalous negative impactor efficiencies were observed at flow rates >8.3×10 −4 m 3 s −1 for 100 to 400 nm droplets and at all flow rates for droplets smaller than 100 nm. This phenomenon will be investigated further as a way to increase the generation rate of nanoparticles. A step-by-step procedure is presented for the selection of an appropriate impactor design and operating flow rate for a desired maximum aerosol particle size.

Size distribution of sulfur species in fine and ultrafine aerosol particles using sulfur K-edge XANES

The sulfur species existing in different size aerosol particles were determined based on the ‘white line’ energy shift and the features of post edge structure of sulfur K-edge XANES (X-ray Absorption Near Edge Structure). The results indicated that sulfates were dominant sulfur species in aerosol particles. However, small amount of reductive sulfur species were also found in the ultrafine aerosol particles(<0.1 μm). Sulfates in aerosols mostly exhibited as (NH4)2SO4 and gypsum. Most (NH4)2SO4 distributed in aerosol particles finer than 0.952 μm, while gypsum was the dominant sulfate in coarse aerosols.

Limited temperature response to the very large AD 1258 volcanic eruption

The large AD 1258 eruption had a stratospheric sulfate load approximately ten times greater than the 1991 Pinatubo eruption. Yet surface cooling was not substantially larger than for Pinatubo (∼0.4 K). We apply a comprehensive Earth System Model to demonstrate that the size of the aerosol particles needs to be included in simulations, especially to explain the climate response to large eruptions. The temperature response weakens because increased density of particles increases collision rate and therefore aerosol growth. Only aerosol particle sizes substantially larger than observed after the Pinatubo eruption yield temperature changes consistent with terrestrial Northern Hemisphere summer temperature reconstructions. These results challenge an oft‐held assumption of volcanic impacts not only with respect to the immediate or longer‐term temperature response, but also any ecosystem response, including extinctions.

Characterization of Florida red tide aerosol and the temporal profile of aerosol concentration

Red tide aerosols containing aerosolized brevetoxins are produced during the red tide bloom and transported by wind to coastal areas of Florida. This study reports the characterization of Florida red tide aerosols in human volunteer studies, in which an asthma cohort spent 1 h on Siesta Beach (Sarasota, Florida) during aerosolized red tide events and non-exposure periods. Aerosol concentrations, brevetoxin levels, and particle size distribution were measured. Hourly filter samples were taken and analyzed for brevetoxin and NaCl concentrations. In addition, the aerosol mass concentration was monitored in real time. The results indicated that during a non-exposure period in October 2004, no brevetoxin was detected in the water, resulting in non-detectable levels of brevetoxin in the aerosol. In March 2005, the time-averaged concentrations of brevetoxins in water samples were moderate, in the range of 5–10 μg/L, and the corresponding brevetoxin level of Florida red tide aerosol ranged between 21 and 39 ng/m 3. The temporal profiles of red tide aerosol concentration in terms of mass, NaCl, and brevetoxin were in good agreement, indicating that NaCl and brevetoxins are components of the red tide aerosol. By continuously monitoring the marine aerosol and wind direction at Siesta Beach, we observed that the marine aerosol concentration varied as the wind direction changed. The temporal profile of the Florida red tide aerosol during a sampling period could be explained generally with the variation of wind direction.

Cloud condensation nuclei in pristine tropical rainforest air of Amazonia: size-resolved measurements and modeling of atmospheric aerosol composition and CCN activity

Abstract. Atmospheric aerosol particles serving as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. We have measured and characterized CCN at water vapor supersaturations in the range of S=0.10–0.82% in pristine tropical rainforest air during the AMAZE-08 campaign in central Amazonia. The effective hygroscopicity parameters describing the influence of chemical composition on the CCN activity of aerosol particles varied in the range of κ≈0.1–0.4 (0.16±0.06 arithmetic mean and standard deviation). The overall median value of κ≈0.15 was by a factor of two lower than the values typically observed for continental aerosols in other regions of the world. Aitken mode particles were less hygroscopic than accumulation mode particles (κ≈0.1 at D≈50 nm; κ≈0.2 at D≈200 nm), which is in agreement with earlier hygroscopicity tandem differential mobility analyzer (H-TDMA) studies. The CCN measurement results are consistent with aerosol mass spectrometry (AMS) data, showing that the organic mass fraction (forg) was on average as high as ~90% in the Aitken mode (D≤100 nm) and decreased with increasing particle diameter in the accumulation mode (~80% at D≈200 nm). The κ values exhibited a negative linear correlation with forg (R2=0.81), and extrapolation yielded the following effective hygroscopicity parameters for organic and inorganic particle components: κorg≈0.1 which can be regarded as the effective hygroscopicity of biogenic secondary organic aerosol (SOA) and κinorg≈0.6 which is characteristic for ammonium sulfate and related salts. Both the size dependence and the temporal variability of effective particle hygroscopicity could be parameterized as a function of AMS-based organic and inorganic mass fractions (κp=κorg×forg +κinorg×finorg). The CCN number concentrations predicted with κp were in fair agreement with the measurement results (~20% average deviation). The median CCN number concentrations at S=0.1–0.82% ranged from NCCN,0.10≈35 cm−3 to NCCN,0.82≈160 cm−3, the median concentration of aerosol particles larger than 30 nm was NCN,30≈200 cm−3, and the corresponding integral CCN efficiencies were in the range of NCCN,0.10/NCN,30≈0.1 to NCCN,0.82/NCN,30≈0.8. Although the number concentrations and hygroscopicity parameters were much lower in pristine rainforest air, the integral CCN efficiencies observed were similar to those in highly polluted megacity air. Moreover, model calculations of NCCN,S assuming an approximate global average value of κ≈0.3 for continental aerosols led to systematic overpredictions, but the average deviations exceeded ~50% only at low water vapor supersaturation (0.1%) and low particle number concentrations (≤100 cm−3). Model calculations assuming a constant aerosol size distribution led to higher average deviations at all investigated levels of supersaturation: ~60% for the campaign average distribution and ~1600% for a generic remote continental size distribution. These findings confirm earlier studies suggesting that aerosol particle number and size are the major predictors for the variability of the CCN concentration in continental boundary layer air, followed by particle composition and hygroscopicity as relatively minor modulators. Depending on the required and applicable level of detail, the information and parameterizations presented in this paper should enable efficient description of the CCN properties of pristine tropical rainforest aerosols of Amazonia in detailed process models as well as in large-scale atmospheric and climate models.

The Research Possibility of Definition Mass Biological Nanoobjects Using Terahertz Laser Ablation Method

Possibility of mass definition using terahertz laser ablation method for biological nanoobjects is researched. Diffusion spectrometer of aerosols was applied for measuring the size of dispersed products of terahertz laser ablation. Dependence of molecular mass from the aerosol particle size was obtained for fragments of DNA λ-hind. This work was carried out using THz radiation of free electron laser of Siberian center of photochemical researches.

Release of VOCs and Particles During Use of Nanofilm Spray Products

Here, we present emission data on VOCs and particles emitted during simulated use of four commercial nanofilm spray products (NFPs) used for making easy-to-clean or self-cleaning surfaces on floors, ceramic tiles, and windows. The aim was to characterize the emitted VOCs and to provide specific source strength data for VOCs and particles released to the airduring use of the products. Containers with NFP were mounted on a spray-stand inside a closed stainless steel chamber with no air exchange. NFPs were sprayed in amounts corresponding to 1 m2 surface toward a target plate at a distance of 35 cm. Released VOCs were measured by a combination of air sampling on Tenax TA adsorbent followed by thermal desorption GC/MS and GC/FID analysis and real time measurements using a miniature membrane inlet mass spectrometer. Particles were measured using a fast mobility particle sizer and an aerosol particle sizer. A number of VOCs were identified, including small alcohols, ketones and ethers, chlorinated acetones, a perfluorinated silane, limonene, and cyclic siloxanes. The number of generated particles was on the order of 3 x 10(8) to 2 x 10(10) particles/m3 per g sprayed NFP and were dominated by nanosize particles.

이어도 해양종합과학기지에서의 에어로솔 수 농도 변동

To examine the fluctuations of aerosol number concentration with different size in the boundary layer of marine area during summer season, aerosol particles were assayed in the Ieodo Ocean Research Station, which is located 419 km southwest of Marado, the southernmost island of Korea, from 24 June to 4 July, 2008. The Laser Particle Counter (LPC) was used to measure the size of aerosol particles and NCEP/NCAR reanalysis data and sounding data were used to analyze the synoptic condition. The distribution of aerosol number concentration had a large variation from bigger particles more than 3 in diameter to smaller particles more than 1 in diameter with wind direction during precipitation. The aerosol number concentration decreased with increasing temperature. An increase (decrease) of small size of aerosol (0.30.5 in diameter) number concentration was induced by convergence (divergence) of the wind fields. The aerosol number concentration of bigger size more than 3 in diameter after precipitation was removed as much as 8994% compared with aerosol number concentration before precipitation. It is considered that the larger aerosol particles would be more efficient for scavenging at marine boundary layer. In addition, the aerosol number concentration with divergence and convergence could be related with the occurrence and mechanism of aerosol in marine boundary layer.

Design and performance of an automatic regenerating adsorption aerosol dryer for continuous operation at monitoring sites

Abstract. Sizes of aerosol particles depend on the relative humidity of their carrier gas. Most monitoring networks require therefore that the aerosol is dried to a relative humidity below 50% r.H. to ensure comparability of measurements at different sites. Commercially available aerosol dryers are often not suitable for this purpose at remote monitoring sites. Adsorption dryers need to be regenerated frequently and maintenance-free single column Nafion dryers are not designed for high aerosol flow rates. We therefore developed an automatic regenerating adsorption aerosol dryer with a design flow rate of 1 m3/h. Particle transmission efficiency of this dryer has been determined during a 3 week experiment. The lower 50% cut-off was found to be smaller than 3 nm at the design flow rate of the instrument. Measured transmission efficiencies are in good agreement with theoretical calculations. One dryer has been successfully deployed in the Amazon river basin. We present data from this monitoring site for the first 6 months of measurements (February 2008–August 2008). Apart from one unscheduled service, this dryer did not require any maintenance during this time period. The average relative humidity of the dried aerosol was 27.1+/−7.5% r.H. compared to an average ambient relative humidity of nearly 80% and temperatures around 30°C. This initial deployment demonstrated that these dryers are well suitable for continuous operation at remote monitoring sites under adverse ambient conditions.

Oxidation of polystyrene aerosols by VUV-photolysis and/or ozone

Aerosols of submicron polystyrene particles were oxidized by either vacuum-ultraviolet (VUV) irradiation in the presence of molecular oxygen (O(2)) and/or by ozone (O(3)). Different degrees of oxidation and oxidative degradation were reached by VUV-photolysis depending on radiant energy, O(2) and H(2)O concentrations in the bulk gas mixture as well as on particle diameter. The same functionalization was obtained by exposing the aerosol to O(3), however, oxidation, in particular oxidative degradation, was less efficient. The evolution of hydroxyl and carbonyl functions introduced was quantified by ATR-FTIR spectroscopy of filtered particles, and oxidative degradation of the polymer particles was confirmed by determining size and number of aerosol particles before and after oxidation. Efficiency analyses are based on the results of an O(3) actinometry and on an evaluation of the rate of absorbed photons by the aerosol particles in function of their size.

Critical size of aerosol particles in physical and chemical deposition

Problems related to the critical size of aerosol particles, when the vapor condensation coefficient depends on the particle size, the influence of electromagnetic fields, as well as on the presence of adsorbable foreign gases in the system, are studied theoretically. The problem of the critical size of particles in chemical deposition is discussed.

Phase Functions of Relatively Large Particle Size of Non-Spherical Aerosols Containing Bubbles

Phase Functions of Relatively Large Particle Size of Non-Spherical Aerosols Containing Bubbles