Particle Emissions from Chrome Plating

Aerosol particles formed from the bursting of small gas bubbles emitted from the anode and cathode electrodes during electrolytic chrome plating were measured with a laboratory apparatus. The measured aerosol particle emission factors were about 5.15 mg particles/amp-hour or 3.81 mg Cr^{+ 6}/amp hour. The cathode gases generated more particles on a gas volume basis with 20 mg particles/liter hydrogen gas evolved from the cathode compared to 1 mg particles/liter oxygen gas evolved from the anode. With about 35% more cathode hydrogen gas evolved than anode oxygen gas evolved and with the much greater particle emissions caused by the cathode hydrogen on a gas volumetric basis, the aerosol particle emissions from the cathode bubble bursting were about 97% of the total particle mass emissions. The particle size distributions measured from the cathode had a mass median aerodynamic diameter of about 38 μ m whereas the anode mass median particle diameter was about 8 μ m. The anode particle mass size distribution was bimodal with peaks at about 0.6 and 24 μ m diameter. The cathode particle mass size distribution was trimodal with peaks at 2.5, 9, and about 60 μ m diameter.     

Development of an Aerosol Mass Spectrometer for Size and Composition Analysis of Submicron Particles

The importance of atmospheric aerosols in regulating the Earth's climate and their potential detrimental impact on air quality and human health has stimulated the need for instrumentation which can provide real-time analysis of size resolved aerosol, mass, and chemical composition. We describe here an aerosol mass spectrometer (AMS) which has been developed in response to these aerosol sampling needs and present results which demonstrate quantitative mea surement capability for a laboratory-generated pure component NH₄ NO₃ aerosol. The instrument combines standard vacuum and mass spectrometric technologies with recently developed aerosol sampling techniques. A unique aerodynamic aerosol inlet (developed at the University of Minnesota) focuses particles into a narrow beam and efficiently transports them into vacuum where aerodynamic particle size is determined via a particle time-of-flight (TOF) measurement. Time-resolved particle mass detection is performed mass spectrometrically following particle flash vaporization on a resistively heated surface. Calibration data are presented for aerodynamic particle velocity and particle collection efficiency measurements. The capability to measure aerosol size and mass distributions is compared to simultaneous measurements using a differential mobility analyzer (DMA) and condensation particle counter (CPC). Quantitative size classification is demonstrated for pure component NH₄ NO₃ aerosols having mass concentrations 0.25_mu g m -3. Results of fluid dynamics calculations illustrating the performance of the aerodynamic lens are also presented and compared to the measured performance. The utility of this AMS as both a laboratory and field portable instrument is discussed.     

Variations in the Size and Chemical Composition of Nitrate-Containing Particles in Riverside,CA

High time resolution measurements of nitrate-containing particles were made in Riverside, CA using an automated particle nitrate monitor and an aerosol time-of-flight mass spectrometer. The automated particle nitrate monitor provides quantitative data on the concentration of total particle-bound nitrate with a temporal resolution of 10 min. The aerosol time-of-flight mass spectrometer provides continuous data on aerodynamic size and single particle chemical composition. Data sets acquired with the two instruments are compared for a two-day intensive sampling period in August 1997 as part of the 1997 Southern California Ozone Study-North American Research Strategy for Tropospheric Ozone (SCOS97-NARSTO). Temporal variations in the number of nitrate-containing particles observed by the mass spectrometry system track (R² 0.73) the nitrate mass concentrations measured by the automated particle nitrate monitor. Both systems detected four periods of elevated nitrate concentrations of several hours duration. For these periods, the nitrate mass concentrations as measured by the automated particle nitrate monitor were similar, ranging from 11 to 19 mu g m3. However, the particle size and single particle composition of nitrate-containing particles as measured by the aerosol time-of-flight mass spectrometer were distinctly different. Specifically, the nitrate maxima observed in the midmorning hours were characterized by supermicrometer nitrate particles associated with either ammonium and organic species or sodium. The afternoon maxima were characterized by submicrometer ammonium nitrate particles, most of which contained organic material.     

Simultaneous Elemental Composition and Size Distributions of Submicron Particles in Real Time Using Laser Atomization Ionization Mass Spectrometry

Composition and size of individual submicron particles have been measured using a laser atomization ionization mass spectrometry technique, the Particle Blaster. Individual particles are quantitatively converted to atomic cations, providing information on both their complete elemental composition and particle size. Measured average atomic ratios for 100 nm particles of sodium chloride is 1.12 +- 0.36 (Cl:Na), for 50 nm particles of silica is 1.93 +- 0.52 (O:Si), and for 64 nm polystyrene latex spheres (PSL) is 1.13 +- 0.19 (H:C), in excellent agreement with the empirical formulae. Calculated particle sizes agree well with electrostatic classifier or TEM measurements in the size range of 17-900 nm diameter for particles of sodium chloride, silicon, and PSL. Size distributions are also obtain able, giving narrower distributions than are measured with an electrostatic classifier, for particles of alumina, silica, sodium chloride, and PSL spheres. Comparison with TEM data shows comparable primary particle sizes, but numerous particle aggregates are detected by the Particle Blaster which are unreported by the TEM measurements.     

Exhaust Particle Size Distribution Measurements at the Tuscarora Mountain Tunnel

On-road particle size distributions were measured at the Tuscarora Mountain tunnel on the Pennsylvania Turnpike in May 1999. The data were obtained using a scanning mobility particle sizer. The nucleation modes of the size distributions contained most of the particles on a number concentration basis and exhibited peak diameters ranging from 11 to 17 nm. This observation is consistent with previous calculations and measurements, indicating that significant numbers of ultrafine aerosol particles can be expected in close proximity to busy motorways. The experiment provided 4 case studies for which the tunnel inlet data could be used to correct data obtained at the outlet, allowing for estimates of particle production within the tunnel. Exhaust particle production rates per vehicle kilometer were estimated; the results are presented with the caveat that the measurements were affected by ambient dilution. The 4 case study nucleation mode sizes varied inversely with ambient temperature. The light-duty vehicle contributions to the ultrafine particle distributions were apparently dominated by the heavy-duty vehicle contributions.     

A New Time-of-Flight Aerosol Mass Spectrometer (TOF-AMS)—Instrument Description and First Field Deployment

We report the development and first field deployment of a new version of the Aerosol Mass Spectrometer (AMS), which is capable of measuring non-refractory aerosol mass concentrations, chemically speciated mass distributions and single particle information. The instrument was constructed by interfacing the well-characterized Aerodyne AMS vacuum system, particle focusing, sizing, and evaporation/ionization components, with a compact TOFWERK orthogonal acceleration reflectron time-of-flight mass spectrometer. In this time-of-flight aerosol mass spectrometer (TOF-AMS) aerosol particles are focused by an aerodynamic lens assembly as a narrow beam into the vacuum chamber. Non-refractory particle components flash-vaporize after impaction onto the vaporizer and are ionized by electron impact. The ions are continuously guided into the source region of the time-of-flight mass spectrometer, where ions are extracted into the TOF section at a repetition rate of 83.3 kHz. Each extraction generates a complete mass spectrum, which is processed by a fast (sampling rate 1 Gs/s) data acquisition board and a PC. Particle size information is obtained by chopping the particle beam followed by time-resolved detection of the particle evaporation events. Due to the capability of the time-of-flight mass spectrometer of measuring complete mass spectra for every extraction, complete single particle mass spectra can be collected. This mode provides quantitative information on single particle composition. The TOF-AMS allows a direct measurement of internal and external mixture of non-refractory particle components as well as sensitive ensemble average particle composition and chemically resolved size distribution measurements. Here we describe for the first time the TOF-AMS and its operation as well as results from its first field deployment during the PM _2.5 Technology Assessment and Characterization Study—New York (PMTACS-NY) Winter Intensive in January 2004 in Queens, New York. These results show the capability of the TOF-AMS to measure quantitative aerosol composition and chemically resolved size distributions of the ambient aerosol. In addition it is shown that the single particle information collected with the instrument gives direct information about internal and external mixture of particle components.     

Absolute Mass and Size Measurement of Monodisperse Particles Using a Modified Millikan's Method: Part I—Theoretical Framework of the Electro-Gravitational Aerosol Balance

A new method for accurate mass and size measurement of monodisperse particles is proposed. In this method, charged aerosol particles are introduced into parallel plate electrodes similar to the Millikan cell, and the number of particles left suspended after a certainty holding time has elapsed is measured. The particle survival rate as a function of the voltage applied to the electrodes is used to determine the particle mass. The particle size is deduced by using the particle density which is determined in a separate experiment. The expression of the particle survival function, which is defined as the survival rate as a function of the mass, for particles with and without Brownian diffusion is derived. The sensitivity of this method to the number average diameter, as well as other size distribution parameters, is analyzed on the basis of the survival function.     

Calibration of a particle mass spectrometer using polydispersed aerosol particles

Routine calibrations of online aerosol chemical composition analyzers are important for assessing data quality during field measurements. The combination of a differential mobility analyzer (DMA) and condensation particle counter (CPC) is a reliable, conventional method for calibrations. However, some logistical issues arise, including the use of radioactive material, quality control, and deployment costs. Herein, we propose a new, simple calibration method for a particle mass spectrometer using polydispersed aerosol particles combined with an optical particle sizer. We used a laser-induced incandescence–mass spectrometric analyzer (LII-MS) to test the new method. Polydispersed aerosol particles of selected chemical compounds (ammonium sulfate and potassium nitrate) were generated by an aerosol atomizer. The LII section was used as an optical particle sizer for measuring number/volume size distributions of polydispersed aerosol particles. The calibration of the MS section was performed based on the mass concentrations of polydispersed aerosol particles estimated from the integration of the volume size distributions. The accuracy of the particle sizing for each compound is a key issue and was evaluated by measuring optical pulse height distributions for monodispersed ammonium sulfate and potassium nitrate particles as well as polystyrene latex particles. A comparison of the proposed method with the conventional DMA-CPC method and its potential uncertainties are discussed.

Copyright © 2018 American Association for Aerosol Research     

An Evaluation of Mass-Weighted Size Distribution Measurements with the Model 3320 Aerodynamic Particle Sizer

The ability of the Model 3320 aerodynamic particle sizer (APS) to make accurate mass-weighted size distribution measurements was investigated. Significant errors were observed in APS size distribution measurements with measured mass median aerodynamic diameters (MMADs) as much as 17 times higher than from cascade impactor measurements. Analysis of APS correlated time-of-flight and light scattering data indicated that the MMAD distortions were due to a few anomalous large particle measurements (～0.1% of the total measurements) with surprisingly low scattered light. Computational fluid dynamics modeling indicated that these anomalous measurements were due to particles that deviated from the intended aerosol pathway and recirculated through the APS measurement volume at low velocities leading to erroneous large particle measurements. A technique for removing erroneous measurements based on correlated aerodynamic diameter and light scattering values is presented. When this technique was used, APS and cascade impactor size distribution measurements agreed well.     

Size Distribution Change of Titania Nano-Particle Agglomerates Generated by Gas Phase Reaction,Agglomeration, and Sintering

In the manufacturing of nanometer-sized material particlulates by aerosol gas-to-particle conversion processes, it is important to analyze how the gas-phase chemical reaction, nucleation, agglomeration, and sintering rates control the size distribution and morphology of particles. In this study, titania particles were produced experimentally by the thermal decomposition of titanium tetraisopropoxide (TTIP) and oxidation of titanium tetrachloride (TiCl 4 ) using a laminar flow aerosol reactor. The effect of reaction temperature on the size and morphology of the generated particles was investigated under various conditions. The size distributions of agglomerates were measured using a DMA/CNC system. The size distributions of primary particles were measured using TEM pictures of the agglomerates sampled by a thermophoretic aerosol sampler. In order to model the growth of both agglomerates and primary particles simultaneously, a two-dimensional discrete-sectional representation of the size distribution was employed, solving the aerosol general dynamic equation for chemical reaction, agglomeration, and sintering. Qualitative agreement between the experimentally observed results and the simulation are satisfactory for the large variations in reactor temperature explored.     

Instrument Busy Time and Mass Measurement using Aerosol Time-of-Flight Mass Spectrometry

Aerosol Time-of-Flight Mass Spectrometry (ATOFMS) instruments have been used widely to measure the size and composition of single ambient aerosol particles. ATOFMS data do not directly and quantitatively represent aerosol composition because the instruments exhibit non-linear response to particle concentration, size, and composition. Our approach is to analyze separately the components of non-linear ATOFMS response using field sampling data in order to understand ATOFMS response to ambient aerosols so that ATOFMS data can be scaled to more closely represent ambient aerosols. In this work we examine the effect of instrument busy time, mainly the time to process and save data, on ATOFMS response to ambient aerosols sampled during the 1999 Bakersfield Instrument Intercomparison Study (BIIS). During this study an ATOFMS instrument was operated alternately in normal and fast scatter data acquisition modes. In fast scatter mode, the instrument does not record mass spectra, minimizing instrument busy time; these data were used to determine particle arrival rates. Busy time in normal mode was found by a comparison of the number of particles detected to that expected for a Poisson process modified to include busy time. During the BIIS experiment, the ATOFMS instrument was busy between 5 and 95% of the nominal sampling time; thus busy time cannot be ignored for accurate quantitative analysis of ATOFMS data. ATOFMS data were scaled for on-line time and transmission efficiency, found by comparison with reference aerosol measurements, in order to estimate fine particle mass concentrations. Fine aerosol mass concentrations from scaled ATOFMS data demonstate semi-quantitative agreement with independent measurements using Beta Attenuation Monitors. We recommend that ATOFMS instruments be modified to measure busy time directly.     

Comparison of Two Aerodynamic Lenses as an Inlet for a Single Particle Laser Ablation Mass Spectrometer

By means of a newly designed portable aerosol mass spectrometer SPLAT (Single Particle Laser Ablation Time-of-flight mass spectrometer) for the analysis of single atmospheric aerosol particles we investigated the system performance in dependency on two different aerodynamic lenses (Liu and Schreiner type) capable of focusing particles with diameters ranging from 80 nm to 800 nm and 300 nm to 3000 nm, respectively. By using the pressure regulated Schreiner lens, the instrument is independent of variations in atmospheric pressure which would lead to changing dynamical properties of the aerosol particles. Active pressure control inside the inlet system facilitates airborne measurements without complicated corrections. With the Liu setup no pressure regulation was used. Here the overall efficiency of our instrument was 7% while with the Schreiner setup 2% was achieved. The Liu lens setup is optimal for measuring submicron particles at low particle concentrations. To detect supermicron particles the Schreiner lens setup is favored. Together with these experiments we present key details of the SPLAT setup and its characterization. Our instrument is able to measure simultaneously the size and the chemical composition of individual aerosol particles larger than 300 nm in diameter. It uses forward scattered light of single aerosol particles at two positions to determine their vacuum aerodynamic diameter from the flight time between the two lasers. Chemical analysis of the particles is done by laser ablation mass spectrometry utilizing a bipolar time-of-flight mass spectrometer.     

Distinguishing between Two Aerosol Size Distributions

A technique is presented to quantitatively determine the similarity or dissimilarity between aerosol size distributions measured with cascade impactors. The method is useful regardless of the mass loading as long as an accurate size distribution can be obtained from the data. The technique uses lognormal best fits of the data and an augmented Student's t-test to quantitatively determine the difference between the two particle size distributions.     

Emission Rates Due to Indoor Activities: Indoor Aerosol Model Development,Evaluation, and Applications

This study presents an indoor aerosol model based on size-resolved and multi-compartment approach. The current indoor aerosol model is also developed with a semi-empirical technique to estimate the emission rates due to indoor sources of aerosol particles. We present in this study a methodology to predict and estimate the best-fit input parameters for the current indoor aerosol model. The performance of the current indoor aerosol model in its single-compartment form was evaluated against previously measured indoor-outdoor aerosol data sets from an office room with mechanical ventilation and a family house with natural ventilation. The indoor aerosol model simulations show that the current methodology used to predict the best-fit input parameters to the indoor aerosol model is efficient. As expected, the penetration factor, aerosol particle deposition, and ventilation rate are the most important parameters in the indoor-outdoor relationship of aerosol particles transport. The emission rate analysis showed that fine aerosol particles production was as high as 26 particle/cm ³ s during wood burning in a fireplace. The emission rate was about eight times this value during grilling in a fireplace and sauna heating. Indoor activities take place in another room may significantly increase the aerosol particle concentrations in other rooms in the building. Therefore, it is recommended to use extra air cleaners in houses to reduce the number concentrations of emitted aerosol particles. The quantitative and qualitative results obtained by the current indoor aerosol model in this study are building and condition specific. Applying the current model to a broad range of conditions and previously measured indoor-outdoor aerosol data sets provides better understanding of aerosol particle characteristics indoors, especially regarding the aerosol particles produced during different indoor activities.     

A diethylene glycol condensation particle counter for rapid sizing of sub-3 nm atmospheric clusters

Abstract

This article describes the modification of a laminar flow, thermally diffusive universal-fluid condensation particle counter (standard operation: 50% detection efficiency at 5?nm) to rapidly measure the size distribution of sub 3?nm aerosol. Sub 3?nm detection was achieved by using diethylene glycol as the working fluid, which enabled high instrument super-saturations while minimizing homogenous nucleation of the working fluid; a detection efficiency of 50% was achieved at 1.6?nm with laboratory-generated ammonium sulfate (AS) aerosol. Rapid aerosol sizing beneath 3?nm was achieved by inverting the measured grown droplet size distribution (1?s sampling) to recover the sampled aerosol size distribution. The developed inversion algorithm utilizes analytical kernel functions determined from the instrument response to pseudo-monodisperse AS aerosol from 1.5?nm to 20?nm, generated by a high-resolution DMA and a nano DMA. The inversion algorithm was tested numerically with assumed, idealized aerosol size distributions consistent with observed new particle formation events, yielding a reasonable agreement between inverted and assumed aerosol size distributions below 3?nm. This technique provides a measure of the aerosol size assuming an aerosol composition identical to that of the aerosol used to generate the experimentally determined kernel function.

Copyright © 2018 American Association for Aerosol Research     

Absorption and Scattering Properties of Dust Clouds at 10.5-μm

Mass-density-normalized absorption and extinction coefficients for arid region soil-based dust were measured at a wavelength of 10.5 μm using photoacoustical techniques, short-path transmissometry, and aerosol dosimetry. An environmental chamber incorporating strong circulation, as well as the various aerosol sampling systems, was specifically designed for aerosol size distributions with particles as large as 40 μm in radius.

The mass extinction coefficient was found to be 0.22 m²/g, while the single scattering albedo, determined from the absorption and extinction coefficients, was 0.5. Calculations of these properties were based on two approaches: analyses of size distributions from photomicrographs of filter samples and analyses of the results obtained using a mixed-medium settling theory. In both cases, Mie theory was applied despite the clearly irregular particle forms. Agreement was close to the measured value for both approaches. The expected overestimation of the optical properties for the former model did not occur. Larger particles in this range are included because of their relevance to arid region dust clouds.     

Measuring the Mass Extinction Efficiency of Elemental Carbon in Rural Aerosol

Previous measurements of the mass absorption efficiency of ambient elemental carbon (EC) indicate that EC optical properties vary with location and imply that the variations may be due to different particle size distributions and composition at different locations (Liousse et al. 1993). For this reason, optical properties appropriate to regional characteristics of EC, determined over the wavelengths of light significant for aerosol extinction, are needed to adequately model the radiative impact of this species. Here we present a method for measuring one of these properties, the mass extinction efficiency (m 2 g -1 ) of EC, as a function of particle size and wavelength of light. In this method, size segregated atmospheric aerosol particles are collected on Nucleopore filters. The filter samples are extracted in a mixture of 30% isopropanol and 70% deionized distilled water to form a suspension of insoluble EC particles. Transmission of light through the extraction liquid is measured over wavelengths from 300 to 800 nm using a spectrophotometer. The transmission measurements taken through the liquid extract are mathematically converted to EC extinction coefficients in air. Although the conversion is a function of a parameter determined from Mie theory, which assumes monodisperse, spherical particles with a known density and refractive index relative to the medium, the method is shown to be reasonably insensitive to these assumptions. Using EC mass concentration obtained from a parallel sample, the EC mass extinction efficiency (in air) is calculated from the extinction coefficient (in air). This method is applied to a rural Midwestern, midcontinental aerosol. In general, the EC mass extinction efficiency in air is highest at lower wavelengths and for smaller particles. For particles with diameters between 0.09 and 2.7 w m and an assumed density of 1.9 g cm -3 , the measured EC mass extinction efficiency at 550 nm ranges from 7.3 to 1.7 m 2 g -1 .     

Ultrafine Particle Sampling with the UNC Passive Aerosol Sampler

A model is presented to describe the collection of ultrafine particles by the UNC passive aerosol sampler. In this model, particle deposition velocity is calculated as a function of particle size, shape and other properties, as well as a function of sampler geometry. To validate the model, deposition velocities were measured for ultrafine particles between 15 and 90 nm in diameter. Passive aerosol samplers were placed in a 1 m ³ test chamber and exposed to an ultrafine aerosol of ammonium fluorescein. SEM images of particles collected by the samplers were taken at 125 kX magnification. Experimental values of deposition velocity were then determined using data from these images and from concurrent measurements of particle concentration and size distribution taken with an SMPS. Deposition velocities from the model and from the experiments were compared and found to agree well. These results suggest that the deposition velocity model presented here can be used to extend the use of the UNC passive aerosol sampler into the ultrafine particle size region.     

Size Distribution Measurement of Carbonaceous Particulate Matter Using a Low Pressure Impactor with Quartz Fiber Substrates

The collection characteristics of a small deposit area low pressure impactor (SDI) were studied in order to employ the impactor for size distribution measurements of carbonaceous matter. In this work, the SDI was calibrated for soft and porous quartz substrate material in a series of laboratory experiments. The collection efficiency curves were measured by using monodisperse dioctyl sebacate particles and by applying two different detection methods. One method was based on the detection of current carried by charged test particles, and the other measured number concentrations of particles in bipolar charge equilibrium by two condensation particle counters. Concerning the particle size corresponding to a 50% collection efficiency (D ₅₀ ), significant shifts toward smaller particle sizes were found for the quartz fiber substrates compared with the flat plates. Also the shapes of the collection efficiency curves differed considerably: quartz substrate gave less steep curves than plain impaction plates. The new calibration was applied to field data from urban and rural sites. Compared with the original calibration of the SDI, the new calibration changed the measured size distributions of organic and elemental carbon. In addition, a reasonable size-segregated mass closure was achieved by combining data from thermal-optical analysis and ion-chromatography.     

In-situ characterization of ultrafine particles by laser-induced incandescence: sizing and particle structure determination

The laser-induced incandescence (LII) method is applied to the in situ size analysis of aerosol particles of different origin at room temperature. A detailed theoretical model of the particle heating and cooling for the different size fractions incorporating a solution of a Fredholm integral equation of the first kind is used to retrieve the particle size distribution from the time-dependent aerosol thermal emission detected after a ns laser pulse. The results are compared with TEM data of deposited aerosol particles along with online measurements employing a differential mobility analyzer (DMA). Besides the size distribution, the LII signal contains information on the internal structure of particle agglomerates, which can be obtained by analyzing the changes in the measured size distribution with the laser pulse energy. The objective of the paper is an evaluation of LII for its capability to measure the size distributions of various types of aerosols in the size range about 5–200 nm and to determine the primary particle sizes in the case of agglomerated particles.