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Single particle characterization using a light scattering module coupled to a time-of-flight aerosol mass spectrometer

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E. S. Cross
E. S. Cross
E. S. Cross
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T. B. Onasch
T. B. Onasch
T. B. Onasch
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Canagaratna M
Canagaratna M
Canagaratna M
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J. T. Jayne
J. T. Jayne
J. T. Jayne
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Abstract and Figures

We present the first single particle results obtained with an Aerodyne time-of-flight aerosol mass spectrometer coupled with a light scattering module (LS-ToF-AMS). The instrument was deployed at the T1 ground site approximately 40 km northeast of the Mexico City Metropolitan Area as part of the MILAGRO field study in March of 2006. The LS-ToF-AMS acquires both ensemble average and single particle data. Over a 75-h sampling period from 27–30 March 2006, 12 853 single particle mass spectra were optically-triggered and saved. The single particles were classified based on observed vaporization histories and measured chemical compositions. The single particle data is shown to provide insights on internal AMS collection efficiencies and ambient mixing state information that augments the ensemble data. Detection of correlated light scattering and chemical ion signals allowed for a detailed examination of the vaporization/ionization process for single particles measured with the AMS instrument. Three particle vaporization event types were identified as a fraction of the total number of particles detected: (1) 23% with prompt vaporization, (2) 26% with delayed vaporization, and (3) 51% characterized as null. Internal consistency checks show that average single particle nonrefractory mass and chemical composition measurements were in reasonable agreement with ensemble measurements and suggest that delayed and null vaporization events are the dominant source of the nonunit collection efficiency of the AMS. Taken together, the simultaneous prompt single particle and aerosol ensemble measurements offer insight into the mixing state and atmospheric transformations of ambient aerosol particles.
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Single particle characterization using a light scattering module coupled to a time-of-flight aerosol mass spectromet
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... The aerosol mass spectrometer (AMS) has revolutionized the observation of non-refractory submicron aerosol particles (Jayne et al. 2000;Jimenez et al. 2003;DeCarlo et al. 2006;Cross et al. 2009). The instrument has four major components. ...
... More recently, light scattering has been added to the PToF region upstream of the vaporizer to permit optical particle sizing and also to permit single-particle detection by triggering mass spectrum data acquisition (light-scattering single-particle mode, LSSP). Using LSSP, individual time-resolved MS signals can be obtained, and furthermore the appearance time of those MS signals can be compared with the expected signal arrival time based on the measured velocity between the chopper and the laser (Cross et al. 2009). ...
... This bias is due to "delayed particles," whose MS signals appear later than expected from the particle time of flight (PToF), and has been attributed to delayed vaporization caused by some particles bouncing off of the vaporizer and subsequently sticking to a nearby surface that is hot enough to cause them to evaporate, but cooler than the vaporizer. It has been proposed that those delayed particles then evaporate more slowly than those that stick promptly to the vaporizer surface (Cross et al. 2009;Huffman et al. 2009). However, as we shall show later, the prompt and delayed particles we measured exhibit time-resolved MS signals with very similar widths. ...
Evaporation rate of particles in the vaporizer of the Aerodyne aerosol mass spectrometer
Article
  • Dec 2016
We present calculations for evaporation rates of particles collected on the vaporizer of the Aerodyne aerosol mass spectrometer (AMS). These calculations provide insight on certain observed phenomena associated with the size-resolved mass spectrum (MS), because the time width of the MS signal from a particle can be limited by its evaporation rate upon contact with the vaporizer. We show that the counterintuitive weak dependence of observed MS signal widths (evaporation rates) on particle volatility is due to suppression of evaporation rates induced by latent heat release, which is more prominent at high volatilities. The same physics is responsible for the observed diminishing returns associated with increasing the vaporizer temperature to achieve narrower single particle pulses. We also show that the vaporizer typical operating temperature of 600°C is sufficient to evaporate extremely low volatility organic compounds (ELVOCs) rapidly enough to obtain reliable measurements for particles smaller than approximately 600 nm. However, the sizing resolution is compromised for large (near-micron) sizes regardless of particle volatility. Finally, our calculations indicate that the observed delayed particle signals, which lead to an artificial tail in AMS mass distributions, are not due to slow evaporation of particles deposited on a surface with lower temperature than the vaporizer, but particles bouncing in the ionizer cage and finally depositing on the vaporizer. Copyright © 2016 American Association for Aerosol Research
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... For particles smaller than 250 nm d mob, only the mass-based method was used for the transmission measurements, since LS module signals are too low for 100% detection efficiency (Cross et al. 2009). For these small sizes, care is required when using Equation (4) for calculating E L , because small particles generated using an atomizer and a differential mobility analyzer (DMA) can have a significant number of multiply charged particles (larger particles with equivalent electrical mobility exiting the DMA). ...
... The bounce of particles off the vaporizer surface was measured using the same experimental setup as described by Cross et al. (2009), shown here in Figure 1a. ...
... Following improvements in the sampling system and the lens, we addressed the other important limiting aspect of the ACSM (and AMS) instruments, i.e., the bounce of particles impacting the particle vaporizer. It is well known that super-micron and sub-micron-sized particles can bounce off collection surfaces and this effect has been observed in the AMS (Matthew et al. 2008;Cross et al. 2009). On average, approximately half of ambient aerosol mass is not captured in the AMS and ACSM, requiring a collection efficiency correction (E B ) due to particle bounce. ...
Laboratory characterization of an Aerosol Chemical Speciation Monitor with PM2.5 measurement capability
Article
Full-text available
  • Oct 2016
The Aerodyne Aerosol Chemical Speciation Monitor (ACSM) is well suited for measuring non-refractory particulate matter up to approximately 1.0 µm in aerodynamic diameter (NR-sub-PM1). However, for larger particles the detection efficiency is limited by losses in the sampling inlet system and through the standard aerodynamic focusing lens. In addition, larger particles have reduced collection efficiency due to particle bounce at the vaporizer. These factors have limited the NR-sub-PM1 ACSM from meeting PM2.5 (particulate matter with aerodynamic diameter smaller than 2.5 µm) monitoring standards. To overcome these limitations, we have redesigned the sampling inlet, the aerodynamic lens, and particle vaporizer. Both the new lens and vaporizer are tested in the lab using a quadruple aerosol mass spectrometer (QAMS) system equipped with light scattering module. Our results show that the capture vaporizer introduces additional thermal decomposition of both inorganic and organic compounds, requiring modifications to the standard AMS fragmentation table, which is used to partition ion fragments to chemical classes. Experiments with mixed NH4NO3 and (NH4)2SO4 particles demonstrated linearity in the NH4⁺ ion balance, suggesting that there is no apparent matrix effect in the thermal vaporization-electron impact ionization detection scheme for mixed inorganic particles. Considering a typical ambient PM2.5 size distribution, we found that 89% of the non-refractory mass is detected with the new system, while only 65% with the old system. The NR-PM2.5 system described here can be adapted to existing Aerodyne Aerosol Mass Spectrometer (AMS) and ACSM systems. Copyright © 2017 American Association for Aerosol Research
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... POA (particularly HOA) levels are usually highest in polluted areas and are quickly diluted when advected away from their sources [50]. When HOA particles are released, they can be coated with secondary aerosol materials such as ammonium nitrate, ammonium sulfate, and secondary organic species [51]. Investigating this process, Canagaratna et al. (2010) verified that the chemical properties of HOA particles rapidly evolved to become OOA-like particles within an advection distance of less than 200 m from the source [52]. ...
Emissions from ships’ activities in the anchorage zone: A potential source of sub-micron aerosols in port areas
Article
  • Jun 2023
  • J HAZARD MATER
Busan Port is among the world's top ten most air-polluted ports, but the role of the anchorage zone as a significant contributor to pollution has not been studied. To assess the emission characteristics of sub-micron aerosols, a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) was deployed in Busan, South Korea from September 10 to October 6, 2020. The concentration of all AMS-identified species and black carbon were highest when the winds came from the anchorage zone (11.9 µg·m-3) and lowest with winds from the open ocean (6.64 µg·m-3). The positive matrix factorization model identified one hydrocarbon-like organic aerosol (HOA) and two oxygenated organic aerosol (OOA) sources. HOAs were highest with winds from Busan Port, while oxidized OOAs were predominant with winds from the anchorage zone (less oxidized) and the open ocean (more oxidized). We calculated the emissions from the anchorage zone using ship activity data and compared them to the total emissions from Busan Port. Our results suggest that emissions from ship activities in the anchorage zone should be considered a significant source of pollution in the Busan Port area, especially given the substantial contributions of gaseous emissions (NOx: 8.78%; volatile organic compounds: 7.52%) and their oxidized moieties as secondary aerosols.
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... The CE measurements in this study were obtained with the AMS PToF mode which allows for counting of individual particles. The quadrupole AMS (Q-AMS) used during the measurements was equipped with a light scattering (LS) module (Cross et al. 2009). Since the light scattering module counts individual particles just before they impact on the AMS vaporizer, it is used to confirm that E L and CE S are close to 1 for the calibrant particles and that the particle concentrations reaching the AMS vaporizer can be compared with those reaching the CPC (CPC S ). ...
Laboratory evaluation of species-dependent relative ionization efficiencies in the Aerodyne Aerosol Mass Spectrometer
Article
  • Feb 2018
Mass concentrations calculated from Aerodyne's aerosol mass spectrometers depend on particle collection efficiency (CE) and relative ionization efficiency (RIE, relative to the primary calibrant ammonium nitrate). We present new laboratory RIE measurements for a wide range of organic aerosol species (RIEOA). An improved laboratory RIE calibration protocol with size and mass selection of calibrant particles and a light scattering-based detection of CE is used. Simpler calibrations of alcohol RIEs using binary mixtures with NH4NO3 are demonstrated. Models that account for only thermal velocity and electron ionization of vaporized molecules do not reproduce RIEOA measurements, confirming that other processes are significant. The relationship between RIEOA and average carbon oxidation state ( ), a metric used to describe atmospheric OA, is investigated. An average RIEOA of 1.6 ± 0.5 (2σ) is found for −1.0 < < 0.5, a range consistent with most ambient OA except hydrocarbon-like organic aerosol (HOA) and cooking organic aerosol (COA). RIEOA from 2 to 7 are found for below and above this range. The RIEOA typically used for ambient OA (1.4 ± 0.3) is within the laboratory RIEOA measurement uncertainty of oxidized organic species, but is a factor of 2 to 5 lower than that of reduced species. Such biases in OA mass concentrations have not been observed in published field analyses. Chemically reduced ambient OA may have composition, phase states, or compensating CE effects that are not mimicked well in the laboratory. This work highlights the need for further ambient OA studies to better constrain the composition dependence of ambient RIEOA, and the need to always calibrate with the OA under study for laboratory experiments. Copyright © 2018 American Association for Aerosol Research
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... During the measurements in Zurich, a second HR-ToF-AMS instrument equipped with a standard PM 1 aerodynamic lens was used on the same sampling line for comparison. In Payerne, the PM 2.5 -HR-ToF-AMS was additionally equipped with a light scattering module for an accurate detection of single particles diameters and their corresponding mass spectra (Cross et al., 2007(Cross et al., , 2009. AMS sampling alternated between mass spectrum (MS) mode in V-mode configuration (30 s), particle time-of-flight mode (pToF, 30 s) and light scattering single particle mode (LSSP, 30 s). ...
Contribution of bacteria-like particles to PM 2.5 aerosol in urban and rural environments
Article
Full-text available
  • Apr 2017
  • ATMOS ENVIRON
We report highly time-resolved estimates of airborne bacteria-like particle concentrations in ambient aerosol using an Aerodyne aerosol mass spectrometer (AMS). AMS measurements with a newly developed PM2.5 and the standard (PM1) aerodynamic lens were performed at an urban background site (Zurich) and at a rural site (Payerne) in Switzerland. Positive matrix factorization using the multilinear engine (ME-2) implementation was used to estimate the contribution of bacteria-like particles to non-refractory organic aerosol. The success of the method was evaluated by a size-resolved analysis of the organic mass and the analysis of single particle mass spectra, which were detected with a light scattering system integrated into the AMS. Use of the PM2.5 aerodynamic lens increased measured bacteria-like concentrations, supporting the analysis method. However, at all sites, the low concentrations of this component suggest that airborne bacteria constitute a minor fraction of non-refractory PM2.5 organic aerosol mass. Estimated average mass concentrations were below 0.1 μg/m3 and relative contributions were lower than 2% at both sites. During rainfall periods, concentrations of the bacteria-like component increased considerably reaching a short-time maximum of approximately 2 μg/m3 at the Payerne site in summer.
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A new method to quantify mineral dust and other aerosol species from aircraft platforms using single particle mass spectrometry
Article
Full-text available
  • Apr 2019
Single-particle mass spectrometer (SPMS) instruments characterize the composition of individual aerosol particles in real time. Their fundamental ability to differentiate the externally mixed particle types that constitute the atmospheric aerosol population enables a unique perspective into sources and transformation. However, quantitative measurements by SPMS systems are inherently problematic. We introduce a new technique that combines collocated measurements of aerosol composition by SPMS and size-resolved absolute particle concentrations on aircraft platforms. Quantitative number, surface area, volume, and mass concentrations are derived for climate-relevant particle types such as mineral dust, sea salt, and biomass burning smoke. Additionally, relative ion signals are calibrated to derive mass concentrations of internally mixed sulfate and organic material that are distributed across multiple particle types. The NOAA Particle Analysis by Laser Mass Spectrometry (PALMS) instrument measures size-resolved aerosol chemical composition from aircraft. We describe the identification and quantification of nine major atmospheric particle classes, including sulfate/organic/nitrate mixtures, biomass burning, elemental carbon, sea salt, mineral dust, meteoric material, alkali salts, heavy fuel oil combustion, and a remainder class. Classes can be sub-divided as necessary based on chemical heterogeneity, accumulated secondary material during aging, or other atmospheric processing. Concentrations are derived for sizes that encompass the accumulation and coarse size modes. A statistical error analysis indicates that particle class concentrations can be determined within a few minutes for abundances above ~ 10 ng m−3. Rare particle types require longer sampling times. We explore the instrumentation requirements and the limitations of the method for airborne measurements. Reducing the size resolution of the particle data increases time resolution with only a modest increase in uncertainty. The principal limiting factor to fast time response concentration measurements is statistically relevant sampling across the size range of interest, in particular, sizes D 2 μm for coarse mode analysis. We demonstrate the use of a virtual impactor to enhance sampling statistics for the inherently sparse coarse mode. Performance is compared to other airborne and ground-based composition measurements, and examples of atmospheric mineral dust concentrations are given. The wealth of information afforded by composition-resolved size distributions for all major aerosol types represents a new and powerful tool to characterize atmospheric aerosol properties in a quantitative fashion.
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Following Particle-Particle Mixing in Atmospheric Secondary Organic Aerosols by Using Isotopically Labeled Terpenes
Article
  • Feb 2018
We used unlabeled and deuterium-labeled precursors to generate and characterize secondary organic aerosol (SOA), a class of atmospheric constituents that rank among the least understood in the climate system, while circumventing the typical problems caused by spectral similarity of SOA mass fragments in aerosol mass spectrometry. We used highly sensitive single-particle mass spectrometers to measure mixing via semi-volatile gas-phase exchange between SOA from biogenic precursors (terpenes) and an anthropogenic precursor (toluene). These are common laboratory mimics for ambient SOA. The experiments showed that particles derived from isoprene and α-pinene ozonolysis undergo fast exchange via evaporation and condensation of semi-volatile constituents without any signs of diffusion limitations, even when the relative humidity (RH) is <10%. Particles derived from limonene ozonolysis showed slower exchange than those from α-pinene because of their more polar constituents and resulting lower diffusivity. Finally, particles derived from β-caryophyllene ozonolysis showed limited vapor uptake even for RH ≫ 30%.
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Characterization of a large biogenic secondary organic aerosol event from eastern Canadian forests
Article
Full-text available
  • Sep 2009
  • ACP
Biogenic secondary organic aerosol levels many times larger than past observations have been measured 70 km north of Toronto during a period of increasing temperatures and outflow from Northern Ontario and Quebec forests in early summer. A regional chemical transport model approximately predicts the event timing and accurately predicts the aerosol loading, identifying the precursors as monoterpene emissions from the coniferous forest. The agreement between the measured and modeled biogenic aerosol concentrations contrasts with model underpredictions for polluted regions. Correlations of the oxygenated organic aerosol mass with tracers such as CO support a secondary aerosol source and distinguish biogenic, pollution, and biomass burning periods during the field campaign. Using the Master Chemical Mechanism, it is shown that the levels of CO observed during the biogenic event are consistent with a photochemical source arising from monoterpene oxidation. The biogenic aerosol mass correlates with satellite measurements of regional aerosol optical depth, indicating that the event extends across the eastern Canadian forest. This regional event correlates with increased temperatures, indicating that temperature-dependent forest emissions can significantly affect climate through enhanced direct radiative forcing and higher cloud condensation nuclei numbers.
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A Study on Chemical Characteristics of Aerosol Composition at West Inflow Regions in the Korean Peninsula I. Characteristics of PM Concentration and Chemical Components
Article
  • Oct 2016
HR-ToF-AMS was applied for a seasonal and size-distributional measurements for inorganic (SO{_4}^{2-}, NO_3{^-}, NH_4{^ }, Cl^-) and organic components in Baegryung Island Super Site. The average concentration of PM_{1.0} remarks 12.9?g/m^3 while 14.5?g/m^3 in Spring time, 14.2?g/m^3 in Winter, 13.1?g/m^3 in Summer and 9.86?g/m^3 in Autumn. The mass of measured PM_{1.0} shows 54.6% of PM_{2.5} which is similar to those of Beijing and Lanzhou, China. The highest portion of Chemical composition is SO{_4}^{2-} marking 41.0%, 31.8% by organics, 13.5% by NH_4{^ }, 12.8% by NO_3{^-} and 1% by Cl^-. In every seasons, except winter, SO{_4}^{2-} remarks the highest level, organic components take place the highest in winter time. The size-distribution of PM_{1.0} components scattered at accumulation mode of 200 nm~800 nm which means the influence of primary emission is low. In case of air stream from the industrialized area of Sandung, Shanghai, China, the concentrations of such components were distributed a bit higher.
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Collection efficiency of α-pinene secondary organic aerosol particles explored via light scattering single particle aerosol mass spectrometry
Article
Full-text available
  • Sep 2016
We investigated the collection efficiency and effective ionization efficiency for secondary organic aerosol (SOA) particles made from α-pinene + O3 using the single-particle capabilities of the Aerosol Mass Spectrometer (AMS). The mean count-based collection efficiency (CEp) for SOA across these experiments is 0.30 (±0.04 S.D.), ranging from 0.25 to 0.40. The mean mass-based collection efficiency (CEm) is 0.49 (±0.07 S.D.). This sub-unit collection efficiency and delayed vaporization is attributable to particle bounce in the vaporization region. Using the coupled optical and chemical detection of the light scattering single-particle (LSSP) module 5 of the AMS, we provide clear evidence that ''delayed vaporization'' is somewhat of a misnomer for these particles: SOA particles that appear within the chopper window do not vaporize at a slow rate; rather, they flash-vaporize, but often not on the initial impact with the vaporizer, and instead upon a subsequent impact with a hot surface in the vaporization region. We also find that the effective ionization efficiency (defined as ions per particle, IPP) decreases with delayed arrival time. CEp is not a function of particle size (for the mobility diameter range investigated, 170–460 nm), but we did see a decrease in CEp with thermodenuder temperature, implying that oxidation state and/or volatility can affect CEp for SOA.
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Source apportionment of fine organic aerosol in Mexico City during the MILAGRO Experiment 2006
Article
Full-text available
  • Jul 2007
  • ACP
Organic carbon (OC) comprises a large fraction of fine particulate matter (PM<sub>2.5</sub>) in Mexico City. Daily and select 12-h PM<sub>2.5</sub> samples were collected in urban and peripheral sites in Mexico City from 17–30 March 2006. Samples were analyzed for OC and elemental carbon (EC) using thermal-optical filter-based methods. Real-time water-soluble organic carbon (WSOC) was collected at the peripheral site. Organic compounds, particularly molecular markers, were quantified by soxhlet extraction with methanol and dichloromethane, derivitization, and gas chromatography with mass spectrometric detection (GCMS). A chemical mass balance model (CMB) based on molecular marker species was used to determine the relative contribution of major sources to ambient OC. Motor vehicles, including diesel and gasoline, consistently accounted for 49% of OC in the urban area and 32% on the periphery. The daily contribution of biomass burning to OC was highly variable, and ranged from 5–26% at the urban site and 7–39% at the peripheral site. The remaining OC unapportioned to primary sources showed a strong correlation with WSOC and was considered to be secondary in nature. Comparison of temporally resolved OC showed that contributions from primary aerosol sources during daylight hours were not significantly different from nighttime. This study provides quantitative understanding of the important sources of OC during the MILAGRO 2006 field campaign.
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Performance of a Single Ultrafine Particle Mass Spectrometer
Article
Full-text available
  • May 2002
We report on the performance of a rapid single particle mass spectrometer (RSMS-II), designed to obtain the size and composition of individual ultrafine particles. Particles are sized aerodynamically at the inlet using a dynamic focusing mechanism to transmit particles to the source region of a time-of-flight mass spectrometer. Since the target particles are too small to be detected optically, an excimer laser is pulsed at high frequency so that data are acquired only when a particle coincides with a laser pulse within the source region. The instrument is tested with sodium chloride and oleic acid particle standards of various sizes and the hit rate efficiency is monitored as the normalized number of particle hits per unit time. The hit rate efficiency depends on the particle flux through the active region of the laser beam, in addition to the particle size and composition, and may thus be used to determine the relative transmission efficiency and size selectivity of the inlet.
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Transmission Efficiency of an Aerodynamic Focusing Lens System: Comparison of Model Calculations and Laboratory Measurements for the Aerodyne Aerosol Mass Spectrometer
Article
Full-text available
  • Jul 2007
The size-dependent particle transmission efficiency of the aerodynamic lens system used in the Aerodyne Aerosol Mass Spectrometer (AMS) was investigated with computational fluid dynamics (CFD) calculations and experimental measurements. The CFD calculations revealed that the entire lens system, including the aerodynamic lens itself, the critical orifice which defines the operating lens pressure, and a valve assembly, needs to be considered. Previous calculations considered only the aerodynamic lens. The calculations also investigated the effect of operating the lens system at two different sampling pressures, 7.8 × 10 Pa (585 torr) and 1.0 × 10 Pa (760 torr). Experimental measurements of transmission efficiency were performed with size-selected diethyl hexyl sebacate (DEHS), NH4NO3, and NaNO3 particles on three different AMS instruments at two different ambient sampling pressures (7.8 × 10 Pa, 585 torr and 1.0 × 10 Pa, 760 torr). Comparisons of the measurements and the calculations show qualitative agreement, but there are significant deviations which are as yet unexplained. On the small size end (30 nm to 150 nm vacuum aerodynamic diameter), the measured transmission efficiency is lower than predicted. On the large size end (> 350 nm vacuum aerodynamic diameter) the measured transmission efficiency is greater than predicted at 7.8 × 10 Pa (585 torr) and in good agreement with the prediction at 1.0 × 10 Pa (760 torr).
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Numerical Characterization of Particle Beam Collimation: Part II Integrated Aerodynamic-Lens–Nozzle System
Article
  • Jun 2004
As a sequel to our previous effort on the modeling of particle motion through a single lens or nozzle, flows of gas–particle suspensions through an integrated aerodynamic-lens–nozzle inlet have been investigated numerically. It is found that the inlet transmission efficiency (ηt) is unity for particles of intermediate diameters (Dp ∼ 30–500 nm). The transmission efficiency gradually diminishes to ∼40% for large particles (Dp > 2500 nm) because of impact losses on the surface of the first lens. There is a catastrophic reduction of ηt to almost zero for very small particles (Dp ≤ 15 nm) because these particles faithfully follow the final gas expansion. We found that, for very small particles, particle transmission is mainly controlled by nozzle geometry and operating conditions. A lower upstream pressure or a small inlet can be used to improve transmission of very small particles, but at the expense of sampling rate, or vice versa. Brownian motion exacerbates the catastrophic reduction in ηt for small particles; we found that the overall particle transmission efficiency can be roughly calculated as the product of the aerodynamic and the purely Brownian efficiencies. For particles of intermediate diameters, Brownian motion is irrelevant, and the modeling results show that the transmission efficiency is mainly controlled by the lenses. Results for an isolated lens or nozzle are used to provide guidance for the design of alternative inlets. Several examples are given, in which it is shown that one can configure the inlet to preferentially sample large particles (with ηt > 50% for Dp = 50–2000 nm) or ultrafine particles (with ηt > 50% for Dp = 20–1000 nm). Some of the results have been compared with experimental data, and reasonable agreement has been demonstrated.
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Single Particle Laser Ablation Time-of-Flight Mass Spectrometer: An Introduction to SPLAT
Article
  • Jun 2005
We present our single particle mass spectrometer we call SPLAT. SPLAT was designed to make possible the detection and characterization of particles down to 100 nm, generate reproducible single particle mass spectra, and collect data at a high rate. The final instrument presented here is capable of characterizing individual particles down to 50 nm at the rate of 20 particles per second. In SPLAT mass spectra are generated by a two-step process, that uses a pulsed infrared laser to heat the particle and a time delayed pulsed UV laser to create ions. We describe a mode of operation that makes it possible to take advantage of the gas phase ionization of the semivolatile components of the particle, while also generating mass spectral signatures of the nonvolatile fraction, thereby providing complete particle mass spectra. We present some sample results from two field deployments of SPLAT.
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Field-deployable, high-resolution, time-of-flight aerosol mass spectrometer
Article
  • Jan 2006
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Key factors influencing the relative humidity dependence of aerosol light scattering
Article
  • Mar 2006
We have measured the relative humidity dependence of aerosol light extinction (fsigma(ep)(80%RH, Dry)) at 532 nm for non-absorbing surrogate atmospheric aerosols to determine the influence of particle size, composition (inorganic vs. organic), and mixing state (internal vs. external) on aerosol light scattering. We present results for mixtures of NaCl and (NH4)2SO4 with a few dicarboxylic acids. For atmospheric conditions the variability in the RH dependence of aerosol light scattering (fsigma(sp)(RH, Dry)) is most sensitive to aerosol composition and size. The influence of the mixing state on fsigma(sp)(RH, Dry) is small. These laboratory results imply that fsigma(sp)(RH, Dry) can be reasonably estimated from the aerosol size distribution and composition (inorganic/organic) using the mass-weighted average of fsigma(sp)(RH, Dry) for the individual components.
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