Richland, WA, United States
Richland, WA, United States

Time filter

Source Type

Lee J.H.,State University of New York at Stony Brook | McDonnell K.T.,Dowling College | Zelenyuk A.,Pacific Northwest National Laboratory | Imre D.,Imre Consulting | Mueller K.,State University of New York at Stony Brook
IEEE Transactions on Visualization and Computer Graphics | Year: 2014

Although the euclidean distance does well in measuring data distances within high-dimensional clusters, it does poorly when it comes to gauging intercluster distances. This significantly impacts the quality of global, low-dimensional space embedding procedures such as the popular multidimensional scaling (MDS) where one can often observe nonintuitive layouts. We were inspired by the perceptual processes evoked in the method of parallel coordinates which enables users to visually aggregate the data by the patterns the polylines exhibit across the dimension axes. We call the path of such a polyline its structure and suggest a metric that captures this structure directly in high-dimensional space. This allows us to better gauge the distances of spatially distant data constellations and so achieve data aggregations in MDS plots that are more cognizant of existing high-dimensional structure similarities. Our biscale framework distinguishes far-distances from near-distances. The coarser scale uses the structural similarity metric to separate data aggregates obtained by prior classification or clustering, while the finer scale employs the appropriate euclidean distance. © 2014 IEEE.

Abramson E.,University of Washington | Imre D.,Imre Consulting | Beranek J.,Pacific Northwest National Laboratory | Wilson J.,Pacific Northwest National Laboratory | Zelenyuk A.,Pacific Northwest National Laboratory
Physical Chemistry Chemical Physics | Year: 2013

Formation, properties, transformations, and temporal evolution of secondary organic aerosol (SOA) particles depend strongly on SOA phase. Recent experimental evidence from both our group and several others indicates that, in contrast to common models' assumptions, SOA constituents do not form a low-viscosity, well-mixed solution, yielding instead a semisolid phase with high, but undetermined, viscosity. We find that when SOA particles are made in the presence of vapors of semi-volatile hydrophobic compounds, such molecules become trapped in the particles' interiors and their subsequent evaporation rates and thus their rates of diffusion through the SOA can be directly obtained. Using pyrene as the tracer molecule and SOA derived from α-pinene ozonolysis, we find that it takes ∼24 hours for half the pyrene to evaporate. Based on the observed pyrene evaporation kinetics we estimate a diffusivity of 2.5 × 10-21 m2 s -1 for pyrene in SOA. Similar measurements on SOA doped with fluoranthene and phenanthrene yield diffusivities comparable to that of pyrene. Assuming a Stokes-Einstein relation, an approximate viscosity of 108 Pa s can be calculated for this SOA. Such a high viscosity is characteristic of tars and is consistent with published measurements of SOA particle bounce, evaporation kinetics, and the stability of two reverse-layered morphologies. We show that a viscosity of 108 Pa s implies coalescence times of minutes, consistent with the findings that SOA particles formed by coagulation are spherical on the relevant experimental timescales. Measurements on aged SOA particles doped with pyrene yield an estimated diffusivity ∼3 times smaller, indicating that hardening occurs with time, which is consistent with the increase in SOA oligomer content, decrease in water uptake, and decrease in evaporation rates previously observed with aging.© 2013 the Owner Societies.

Zelenyuk A.,Pacific Northwest National Laboratory | Imre D.,Imre Consulting | Beranek J.,Pacific Northwest National Laboratory | Abramson E.,University of Washington | And 2 more authors.
Environmental Science and Technology | Year: 2012

Polycyclic aromatic hydrocarbons (PAHs), known for their harmful health effects, undergo long-range transport (LRT) when adsorbed on and/or absorbed in atmospheric particles. The association between atmospheric particles, PAHs, and their LRT has been the subject of many studies yet remains poorly understood. Current models assume PAHs instantaneously attain reversible gas-particle equilibrium. In this paradigm, as gas-phase PAH concentrations are depleted due to oxidation and dilution during LRT, particle-bound PAHs rapidly evaporate to re-establish equilibrium leading to severe underpredictions of LRT potential of particle-bound PAHs. Here we present a new, experimentally based picture in which PAHs trapped inside highly viscous semisolid secondary organic aerosol (SOA) particles, during particle formation, are prevented from evaporation and shielded from oxidation. In contrast, surface-adsorbed PAHs rapidly evaporate leaving no trace. We find synergetic effects between hydrophobic organics and SOA - the presence of hydrophobic organics inside SOA particles drastically slows SOA evaporation to the point that it can almost be ignored, and the highly viscous SOA prevents PAH evaporation ensuring efficient LRT. The data show the assumptions of instantaneous reversible gas-particle equilibrium for PAHs and SOA are fundamentally flawed, providing an explanation for the persistent discrepancy between observed and predicted particle-bound PAHs. © 2012 American Chemical Society.

Shrivastava M.,Pacific Northwest National Laboratory | Zelenyuk A.,Pacific Northwest National Laboratory | Imre D.,Imre Consulting | Easter R.,Pacific Northwest National Laboratory | And 3 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2013

We investigate issues related to volatility and multi-generational gas-phase aging parameterizations affecting the formation and evolution of secondary organic aerosol (SOA) in models. We show that when assuming realistic values for the mass accommodation coefficient, experimentally observed SOA evaporation rates imply significantly lower "effective volatility" than those derived from SOA growth in smog chambers, pointing to the role of condensed phase processes and suggesting that models need to use different parameters to describe the formation and evolution of SOA. We develop a new, experimentally driven paradigm to represent SOA as a non-absorbing semi-solid with very low "effective volatility." We modify both a box model and a 3D chemical transport model, to include simplified parameterizations capturing the first-order effects of gas-phase fragmentation reactions and investigate the implications of treating SOA as a non-volatile, non-absorbing semi-solid (NVSOA). Box model simulations predict SOA loadings decrease with increasing fragmentation, and similar SOA loadings are calculated in the traditional, semi-volatile (SVSOA) approach and with the new paradigm (NVSOA) before evaporation reduces loadings of SVSOA. Box-model-calculated O:C ratios increase with aging in both the SVSOA and the NVSOA paradigms. Consistent with box model results, 3D model simulations demonstrate that predicted SOA loadings decrease with the addition of fragmentation reactions. The NVSOA paradigm predicts higher SOA loadings compared to the SVSOA paradigm over nearly the entire 3D modeling domain, with larger differences close to the surface and in regions where higher dilution favors SVSOA evaporation. Low effective volatility of SOA Gas phase fragmentation reaction Box and regional modeling ©2013. American Geophysical Union. All Rights Reserved.

Zelenyuk A.,Pacific Northwest National Laboratory | Imre D.,Imre Consulting | Earle M.,Environment Canada | Easter R.,Pacific Northwest National Laboratory | And 6 more authors.
Analytical Chemistry | Year: 2010

The aerosol indirect effect remains the most uncertain aspect of climate change modeling, calling for characterization of individual particles sizes and compositions with high spatial and temporal resolution. We present the first deployment of our single particle mass spectrometer (SPLAT II) operated in dual data acquisition mode to simultaneously measure particle number concentrations, density, asphericity, and individual particle size and quantitative composition, with temporal resolution better than 60 s, thus yielding all the required properties to definitively characterize the aerosol-cloud interaction in this exemplary case. We find that particles are composed of oxygenated organics, many mixed with sulfates, biomass burning particles, some with sulfates, and processed sea-salt. Cloud residuals are found to contain more sulfates than background particles, explaining their higher efficiency to serve as cloud condensation nuclei (CCN). Additionally, CCN sulfate content increased with time due to in-cloud droplet processing. A comparison between the size distributions of background, CCN, and interstitial particles shows that while nearly all CCN particles are larger than 100 nm, over 80% of interstitial particles are smaller than 100 nm. We conclude that for this cloud, particle size is the controlling factor on aerosol activation into cloud-droplets, with higher sulfate content playing a secondary role. © 2010 American Chemical Society.

Bruns E.A.,University of California at Irvine | Perraud V.,University of California at Irvine | Zelenyuk A.,Pacific Northwest National Laboratory | Ezell M.J.,University of California at Irvine | And 5 more authors.
Environmental Science and Technology | Year: 2010

While multifunctional organic nitrates are formed during the atmospheric oxidation of volatile organic compounds, relatively little is known about their signatures in particle mass spectrometers. High resolution time-of-flight aerosol mass spectrometry(HR-ToF-AMS) and FTIR spectroscopy on particles impacted on ZnSe windows were applied to NH4NO3, NaNO 3, and isosorbide 5-mononitrate (IMN) particles, and to secondary organic aerosol (SOA) from NO3 radical reactions at 22 °C and 1 atm in air with α- and β-pinene, 3-carene, limonene, and isoprene. For comparison, single particle laser ablation mass spectra (SPLAT II) were also obtained for IMN and SOA from the α-pinene reaction. The mass spectra of all particles exhibit significant intensity at m/z 30, and for the SOA, weak peaks corresponding to various organic fragments containing nitrogen [C xHyNzOa]+ were identified using HR-ToF-AMS. The NO+/NO2 + ratios from HR-ToF-AMS were 10-15 for IMN and the SOA from the α- and β-pinene, 3-carene, and limonene reactions, ∼5 for the isoprene reaction, 2.4 for NH4NO3 and 80 for NaNO3. The N/H ratios from HR-ToF-AMS for the SOA were smaller by a factor of 2 to 4 than the -ONO 2/ C-H ratios measured using FTIR. FTIR has the advantage that it provides identification and quantification of functional groups. The NO +/NO2 + ratio from HR-ToF-AMS can indicate organic nitrates if they are present at more than 15-60% of the inorganic nitrate, depending on whether the latter is NH4NO3 or NaNO3. However, unique identification of specific organic nitrates is not possible with either method. © 2010 American Chemical Society.

Beranek J.,Pacific Northwest National Laboratory | Imre D.,Imre Consulting | Zelenyuk A.,Pacific Northwest National Laboratory
Analytical Chemistry | Year: 2012

Particle shape is an important attribute in determining particle properties and behavior, but it is difficult to control and characterize. We present a new portable system that offers, for the first time, the ability to separate particles with different shapes and characterize their chemical and physical properties, including their dynamic shape factors (DSFs) in the transition and free-molecular regimes, with high precision, in situ, and in real-time. The system uses an aerosol particle mass analyzer (APM) to classify particles of one mass-to-charge ratio, transporting them to a differential mobility analyzer (DMA) that is tuned to select particles of one charge, mobility diameter, and for particles with one density, one shape. These uniform particles are then ready for use and/or characterization by any application or analytical tool. We combine the APM and DMA with our single-particle mass spectrometer, SPLAT II, to form the ADS and demonstrate its utility to measure individual particle compositions, vacuum aerodynamic diameters, and particle DSFs in two flow regimes for each selected shape. We applied the ADS to the characterization of aspherical ammonium sulfate and NaCl particles, demonstrating that both have a wide distribution of particle shapes with DSFs from approximately 1 to 1.5. © 2011 American Chemical Society.

Earle M.E.,Environment Canada | Liu P.S.K.,Environment Canada | Strapp J.W.,Environment Canada | Zelenyuk A.,Pacific Northwest National Laboratory | And 4 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2011

Aircraft measurements during the Indirect and Semi-Direct Aerosol Campaign (ISDAC) in April 2008 are used to investigate factors influencing the microphysics and radiative properties of springtime Arctic clouds. The analysis is focused on low-level, liquid-dominated clouds in two separate regimes with respect to cloud and aerosol properties: single-layer stratocumulus with below-cloud aerosol concentrations (Na) less than 250 cm-3 (clean cases); and layered stratocumulus with Na > 500 cm -3 below cloud base, associated with a biomass burning aerosol (polluted cases). For each regime, vertical profiles through cloud are used to determine cloud microphysical and radiative properties. The polluted cases were correlated with warmer, geometrically thicker clouds, with higher droplet number concentrations (Nd), liquid water paths (LWP), optical depths and albedo (A) relative to clean cases. The mean cloud droplet effective radii (reff), however, were similar (μ5.7 m) for both aerosol-cloud regimes. This discrepancy resulted mainly from the higher LWP of clouds in polluted cases, which can be explained by both meteorological (temperature, dynamics) and microphysical (precipitation inhibition) factors. Adiabatic parcel model simulations demonstrate that differences in droplet activation between the aerosol-cloud regimes may play a role, as the higher Na in polluted cases limits activation to larger and/or more hygroscopic particles. The observations and analysis presented here demonstrate the complex interactions among environmental conditions, aerosol, and the microphysics and radiative properties of Arctic clouds. Copyright 2011 by the American Geophysical Union.

Vaden T.D.,Pacific Northwest National Laboratory | Imre D.,Imre Consulting | Beranek J.,Pacific Northwest National Laboratory | Zelenyuk A.,Pacific Northwest National Laboratory
Aerosol Science and Technology | Year: 2011

Single particle mass spectrometers have traditionally been deployed to measure the size and composition of individual particles. The relatively slow sampling rates of these instruments are determined by the rate at which the ionization lasers can fire and/or mass spectra can be recorded. Under most conditions, our single particle mass spectrometer, SPLAT, can detect and size particles at much higher rates than it can record mass spectra. We therefore developed a dual data acquisition mode, in which particle number concentrations, size distributions, and asphericity are measured at a rate determined by particle concentration and the particle detection efficiency, all while the instrument generates and records individual particle sizes and mass spectra at an operator-set rate. Particle number concentrations are calculated from the particle detection rate at the first optical stage and the measured sampling flow rate. We show that SPLAT measured particle number concentrations are in very good agreement with independent measurements by the passive cavity aerosol spectrometer probe (PCASP). Particle asphericity is based on the ratio of the particle detection rates at the first and second optical stages. Particle size is based on the measurement of particle time of flight between the two detection stages. We illustrate the artifact in the measured size distributions that can be introduced by high particle concentrations and present a method to remove it and correct the size distributions. Particle number concentration and asphericity are measured with 1 s resolution and particle vacuum aerodynamic size distributions are measured with 4 to 60 s resolution. Copyright © American Association for Aerosol Research.

Vaden T.D.,Pacific Northwest National Laboratory | Imre D.,Imre Consulting | Beranek J.,Pacific Northwest National Laboratory | Zelenyuk A.,Pacific Northwest National Laboratory
Aerosol Science and Technology | Year: 2011

Particle density is an important and useful property that is difficult to measure because it usually requires two separate instruments to measure two particle attributes. As density measurements are often performed on size-classified particles, they are hampered by low particle numbers, and hence poor temporal resolution. We present here a new method for measuring particle densities using our single particle mass spectrometer, SPLAT. This method takes advantage of the fact that the detection efficiency in our single particle mass spectrometer drops off very rapidly as the particle size decreases below ∼ 100 nm creating a distinct sharp feature on the small particle side of the vacuum aerodynamic size distribution. Thus, the two quantities needed to determine particle density, the particle diameter and vacuum aerodynamic diameter, are known. We first test this method on particles of known compositions and densities to find that the densities it yields are accurate. We then apply the method to obtain the densities of particles that were characterized during instrument field deployments. We illustrate how the method can also be used to measure the density of chemically resolved particles. In addition, we present a new method to characterize the instrument detection efficiency as a function of particle size that relies on measuring the mobility and vacuum aerodynamic size distributions of polydisperse spherical particles of known density. We show that a new aerodynamic lens used in SPLAT II improves instrument performance, making it possible to detect 83 nm particles with 50% efficiency. Copyright © American Association for Aerosol Research.

Loading Imre Consulting collaborators
Loading Imre Consulting collaborators