EMSL: Alla Zelenyuk's Publications

Yang J, M Stewart, GD Maupin, DR Herling, and A Zelenyuk. 2009. "Single Wall Diesel Particulate Filter (DPF) Filtration Efficiency Studies Using Laboratory Generated Particles." Chemical Engineering Science 64(8):1625-1634. Abstract Diesel offers higher fuel efficiency, but produces higher exhaust particulate matter. Diesel particulate filters are presently the most efficient means to reduce these emissions. These filters typically trap particles in two basic modes: at the beginning of the exposure cycle the particles are captured in the filter holes, and at longer times the particles form a "cake" on which particles are trapped. Eventually the "cake" removed by oxidation and the cycle is repeated. We have investigated the properties and behavior of two commonly used filters: silicon carbide (SiC) and cordierite (DuraTrap® RC) by exposing them to nearly-spherical ammonium sulfate particles. We show that the transition from deep bed filtration to "cake" filtration can easily be identified by recording the change in pressure across the filters as a function of exposure. We investigated performance of these filters as a function of flow rate and particle size. The filters trap small and large particles more efficiently than particles that are ~80 to 200 nm in aerodynamic diameter. A comparison between the experimental data and a simulation using incompressible lattice-Boltzmann model shows very good qualitative agreement, but the model overpredicts the filter’s trapping efficiency.

Zelenyuk A, J Yang, DG Imre, and EY Choi. 2009. "Achieving Size Independent Hit-Rate in Single Particle Mass Spectrometry." Aerosol Science and Technology 43(4):305-310. Abstract Recent improvements in single particle mass spectrometers make it possible to optically detect, size, and characterize the compositions of individual particles with diameters larger than a micron and smaller than 100 nm. Based on particle detection in two stages of optical detection these instruments generate a precisely timed trigger pulse, which is used to fire the ion generation laser or lasers. Practical experience shows that the wide size range results in small, but significant differences in laser trigger timing between small and large particles. If not treated, the instrument hit-rate becomes size dependent and instrument operator is forced to optimize the instrument for the desired size range, while having to contend with a lower hit-rate for the other. The present paper presents an analysis of the problem, demonstrating that size dependence of laser trigger timing stems from the differences in the particle position within the detection laser beam at the instant of detection. It shows that it is possible to compensate for these differences by generation a laser trigger delay coefficient for individual particles as a function of particle time of flight, i.e. its size. The study also shows that a single function can be used to characterize particles with a wide range of densities.

Zelenyuk A, and D Imre. 2009. "Beyond single particle mass spectrometry: multidimensional characterisation of individual aerosol particles." International Reviews in Physical Chemistry 28(2):309-358. Abstract The behavior of small aerosol particles depends on a number of their physical and chemical properties, many of which are strongly coupled. The size, internal composition, density, shape, morphology, hygroscopicity, index of refraction, activity as cloud condensation nuclei and ice nuclei, and other attributes of individual particles - all play a role in determining particle properties and their impacts. The traditional particle characterization approaches rely on separate parallel measurements that average over an ensemble of particles of different sizes and/or compositions and later attempt to draw correlations between them. As a result such studies overlook critical differences between particles and bulk and miss the fact that individual particles often exhibit major differences. Here we review the recently developed methods to simultaneously measure in-situ and in real time several of the attributes for individual particles using single particle mass spectrometer, SPLAT or its second generation SPLAT II. We also discuss novel approaches developed for classification, visualization and mining of large datasets produced by the multidimensional single particle characterization.

Zelenyuk A, J Yang, and DG Imre. 2009. "Comparison Between Mass Spectra of Individual Organic Particles Generated by UV Laser Ablation and in the IR/UV Two-Step Mode." International Journal of Mass Spectrometry 282(1-2):6-12. Abstract One of the most fundamental aspects of single particle mass spectrometry is that the individual particle mass spectra are first classified and only then averaged. When ions are generated by ablation with a UV laser the mass spectra of particles with identical compositions exhibit large particle to particle fluctuations in the mass spectral intensity pattern. This is particularly true when it comes to particles containing organic molecules. At laser fluence that is sufficient to ionize sulfates many of the organic molecules exhibit high degree of fragmentation, often to the point where they cannot be distinguished from elemental carbon. In contrast, when ion generation is separated into two steps, in which the first step uses infra red to evaporate the semi-volatile components and the second, time delayed UV pulse to ionize the evaporating plume, the quality of the individual particle mass spectra are significantly improved. We present an experimental investigation of the properties and behavior of individual particle mass spectra of organic particles that are generated by ablation and in two steps. We investigate the effect of UV laser fluence and the delay between the two lasers. The study shows that the two step approach yields highly reproducible mass spectra that contain sufficient detail to allow clear molecular assignments. The two step approach also produces 10 times as many ions, and the mass spectral intensity can be related to the amount of organics in the particle. In contrast, ablation generated mass spectra were found to exhibit high degree of fragmentation and particle-to-particle fluctuations.

Zelenyuk A, J Yang, EY Choi, and DG Imre. 2009. "SPLAT II: An Aircraft Compatible, Ultra-Sensitive, High Precision Instrument for In-Situ Characterization of the Size and Composition of Fine and Ultrafine Particles." Aerosol Science and Technology 43(5):411-424. Abstract The properties of aerosols depend on the size and internal compositions of the individual particles. The vast majority of atmospheric aerosols are smaller than 200 nm, yet the single particle mass spectrometers, the only instruments that can characterize the size and internal compositions of individual particles, typically detect these small particles with extremely low efficiencies. In this paper we describe a new instrument called SPLAT II that provides unparalleled sensitivity to small particles, detecting 100% of particles that are larger than 125 nm and 40% of 100 nm particles. This instrument also brings an increase by a factor of 10 in temporal resolution, sizing up to 500 particles per second and characterizing the composition of up to 100 of them. SPLAT II uses a two-laser, two-step process to evaporate the particles and generate ions, producing high quality, reproducible mass spectra of the refractive and non-refractive aerosol fractions to yield the complete compositions of individual particles. The instrument control board provides for size dependent delays for lasers’ triggers to eliminate a size dependent hit rate. The mass spectra are recorded with 14-bit vertical resolution and analyzed using custom software packages. The instrument’s high sizing resolution and sensitivity makes it possible to combine it with the differential mobility analyzer(s) and measure particle size, composition, density, dynamic shape factor, hygroscopicity, and fractal dimension.

Yu Y, MJ Ezell, A Zelenyuk, DG Imre, ML Alexander, JV Ortega, JL Thomas, K Gogna, DJ Tobias, B D'Anna, CW Harmon, S Johnson, and BJ Finlayson-Pitts. 2008. "Nitrate Ion Photochemistry at Interfaces: A New Mechanism for Oxidation of alpha-Pinene." Physical Chemistry Chemical Physics. PCCP 10(21):3063-3071. doi:10.1039/b719495a Abstract The photooxidation of 0.6 - 0.9 ppm α-pinene in the presence of a deliquesced thin film of NaNO3, and for comparison increasing concentrations of NO2, was studied in a 100 L Teflon® chamber at relative humidities from 70 − 88% and temperatures from 296 − 304 K. The loss of α-pinene and the formation of gaseous products were followed with time using proton transfer mass spectrometry. The yields of gas phase products were smaller in the NaNO3 experiments than in NO2 experiments. In addition, pinonic acid, pinic acid, trans-sobrerol and other unidentified products were detected in the extracts of the wall washings only for the NaNO3 photolysis. These data indicate enhanced loss of α-pinene at the NaNO3 thin film during photolysis. Supporting the experimental results are molecular dynamics simulations which predict that α-pinene has an affinity for the surface of the deliquesced nitrate thin film, enhancing the opportunity for oxidation of the impinging organic gas during the nitrate photolysis. This new mechanism of oxidation of organics may be partially responsible for the correlation between nitrate and the organic component of particles observed in many field studies, and may also contribute to the missing source of SOA needed to reconcile model predictions and field measurements. In addition, photolysis of nitrate on surfaces in the boundary layer may lead to oxidation of co-adsorbed organics.

Yu Y, MJ Ezell, A Zelenyuk, DG Imre, ML Alexander, JV Ortega, B D'Anna, CW Harmon, S Johnson, and BJ Finlayson-Pitts. 2008. "Photooxidation of Alpha-Pinene at High Relative Humidity in the Presence of Increasing Concentrations of NOx." Atmospheric Environment 42(20):5044-5060. doi:10.1016/j.atmosenv.2008.02.026 Abstract The photooxidation of ~1 ppm alpha-pinene in the presence of increasing concentrations of NO2 was studied in a Teflon chamber at relative humidities from 70 - 88% and temperatures from 296 - 304 K. The loss of alpha-pinene and formation of gas phase products were followed using proton transfer reaction mass spectrometry (PTR-MS). Gas phase reaction products measured by PTR-MS and their yields include formaldehyde (5 + 1%), formic acid (2.5 + 1.4%), methanol (0.6 + 0.3%), acetaldehyde (3.9 + 1.7%), acetic acid (10 + 2%), acetone (11.5 + 3.1%), pinonaldehyde (22 + 6%), and pinene oxide (0.9 + 0.1%). There was evidence of organic nitrates in the gas phase and small peaks were tentatively assigned to norpinonaldehyde, 4-oxopinonaldehyde, propanedial, 2,3-dioxobutanal and 3,5,6-trioxoheptanal or 3-hydroxymethyl-2,2-dimethylcyclobutylethanone. The formation and growth of new particles were followed using a scanning mobility particle sizer (SMPS), and their chemical composition was probed using single particle mass spectrometry (SPLAT II). SPLAT II analysis also provided measurements of the vacuum aerodynamic diameters of the newly formed secondary organic aerosol (SOA) particles and, in combination with the electrical mobility diameter, a particle density of 1.21 + 0.02 g cm-3 was calculated, 20% larger than often assumed in calculating SOA yields. SPLAT II showed that the suspended SOA consisted of a complex mixture of organic nitrates and organics, possibly including pinonic acid, pinic acid and trans-sobrerol. Three-wavelength light scattering measurements made using an integrating nephelometer were consistent with particles having a refractive index characteristic of organic compounds, but the data could not be well matched at all three wavelengths with a single refractive index. The effect of addition of cyclohexane or NO on particle formation showed that ozonolysis was the major mechanism of SOA formation in this system. However, unlike simple ozonolysis, organic nitrates are formed in both the gas and particle phases. Identifying and measuring specific organic nitrates in both the gas and particle phases in air may help to elucidate why SOA formation has been reported in field studies to be associated with polluted urban areas, yet the carbon in these particles is largely contemporary, i.e., non-fossil fuel carbon.

Zelenyuk A, J Yang, C Song, RA Zaveri, and DG Imre. 2008. ""Depth-Profiling" and Quantitative Characterization of the Size, Composition, Shape, Density, and Morphology of Fine Particles with SPLAT, a Single-Particle Mass Spectrometer." Journal of Physical Chemistry A 112(4):669-677. doi:10.1021/jp077308y Abstract A significant fraction of atmospheric particles are composed of inorganic substances that are mixed or coated with organics. The behavior of these particles depends on the particle internal composition and on the arrangement of the specific constituents in each particle. It is important to know which constituent is on the surface and whether it entirely covers the particle surface. We present a study that demonstrates that an instrumental system that includes an ultra-sensitive single particle mass spectrometer that is coupled with a differential mobility analyzer can be used to quantitatively measure in real-time individual particle composition, size, density, shape and determine which substance is on the surface and whether it entirely covers the particle. Here we use liquid dioctyl phthalate to coat NaCl seeds and generate spherical particles that are encapsulated with the organic coat and pyrene, a solid poly aromatic hydrocarbon, to produce aspherical particles with pyrene nodules and exposed NaCl cores. We show that the behavior of the mass spectral intensities as a function of laser fluence yields information that can be used to determine the morphological distribution of individual particles constituents.

Zelenyuk A, J Yang, C Song, RA Zaveri, and DG Imre. 2008. "A New Real-Time Method for Determining Particles Sphericity and Density: Application to Secondary Organic Aerosol Formed by Ozonolysis of alpha-Pinene." Environmental Science & Technology 42(21):8033-8038. doi:10.1021/es8013562 Abstract Particle volumes are most often obtained by measuring particle mobility size distributions and assuming that the particles are spherical. These volumes are then converted to mass loads by using particle densities that are commonly either assumed or estimated from the measured mobility and vacuum aerodynamic diameters assuming again that the particles are spherical. Depending on the system, these assumptions can introduce significant errors. We present a new method that can be applied to any particle system to determine in real-time whether the particles are spherical or not. We use our 2nd generation single particle mass spectrometer (SPLAT II) to measure with extremely high precision the vacuum aerodynamic size distributions of particles classified by differential mobility analyzer (DMA) and demonstrate that the line shape of these distributions provide a way to unambiguously distinguish between spherical and aspherical particles. Moreover, the very same experimental system is used to obtain in addition to individual particle size, its density, composition and dynamic shape factor. We illustrate the application of this method to secondary organic aerosols formed as a result of ozonolysis of α-pinene in the presence and absence of an OH scavenger and find these particles to be spherical with densities of 1.198±0.004 gcm-3 and 1.213±0.003 gcm-3 respectively.

Zelenyuk A, DG Imre, EJ Nam, Y Han, and K Mueller. 2008. "ClusterSculptor: Software for Expert-Steered Classification of Single Particle Mass Spectra." International Journal of Mass Spectrometry 275(1-3):1-10. doi:10.1016/j.ijms.2008.04.033 Abstract To take full advantage of the vast amount of highly detailed data acquired by single particle mass spectrometers requires that the data be organized according to some rules that have the potential to be insightful. Most commonly statistical tools are used to cluster the individual particle mass spectra on the basis of their similarity. Cluster analysis is a powerful strategy for the exploration of high-dimensional data in the absence of a-priori hypotheses or data classification models, and the results of cluster analysis can then be used to form such models. More often than not, when examining the data clustering results we find that many clusters contain particles of different types and that many particles of one type end up in a number of separate clusters. Our experience with cluster analysis shows that we have a vast amount of non-compiled knowledge and intuition that should be brought to bear in this effort. We will present new software we call ClusterSculptor that provides comprehensive and intuitive framework to aid scientists in data classification. ClusterSculptor uses k-means as the overall clustering engine, but allows tuning its parameters interactively, based on a non-distorted compact visual presentation of the inherent characteristics of the data in high-dimensional space. ClusterSculptor provides all the tools necessary for a high-dimensional activity we call cluster sculpting. ClusterSculptor is designed to be coupled to SpectraMiner, our data mining and visualization software package. The data are first visualized with SpectraMiner and identified problems are exported to ClusterSculptor, where the user steers the reclassification and recombination of clusters of tens of thousands particle mass spectra in real-time. The resulting sculpted clusters can be then imported back into SpectraMiner. Here we will greatly improved single particle chemical speciation in an example of application of this new tool to a number of particle types of atmospheric importance.