EMSL: Alla Zelenyuk's Publications

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.

Zelenyuk A, DG Imre, J Han, and S Oatis. 2008. "Simultaneous Measurements of Individual Ambient Particles Size, Composition, Effective Density, and Hygroscopicity." Analytical Chemistry 80(5):1401-1407. doi:10.1021/ac701723v Abstract The interaction between atmospheric particles and water vapor impacts directly and significantly the effect that these particles exert on the atmosphere. The hygroscopicity of individual particles, which is a quantitative measure of their response to changes in relative humidity, is related to their internal compositions. To properly include atmospheric aerosols in any model requires knowledge of the relationship between particle size, composition and hygroscopicity. Here we demonstrate the capability to conduct in real-time the simultaneous measurements of individual ambient particle hygroscopic growth factors, densities and compositions using a hydrated tandem differential mobility analyzer that is coupled to an ultra-sensitive single particle mass spectrometer. We use as an example the class of particles that are composed of sulfate mixed with oxygenated organics to illustrate how such multidimensional single particle characterization can be used to yield quantitative information about the composition of individual particles. We show that the data provide the relative concentrations of organics and sulfates, the density of the two fractions and particle hygroscopicity.

Song C, RA Zaveri, ML Alexander, JA Thornton, S Madronich, JV Ortega, A Zelenyuk, XY Yu, A Laskin, and AD Maughan. 2007. "Effect of Hydrophobic Primary Organic Aerosols on Secondary Organic Aerosol Formation from Ozonolysis of α-Pinene." Geophysical Research Letters 34(20):Paper # L20803. doi:10.1029/2007GL030720 Abstract Semi-empirical secondary organic aerosol (SOA) models typically assume a well-mixed organic aerosol phase even in the presence of hydrophobic primary organic aerosols (POA). This assumption significantly enhances the modeled SOA yields as additional organic mass is made available to absorb greater amounts of oxidized secondary organic gases than otherwise. We investigate the applicability of this critical assumption by measuring SOA yields from ozonolysis of α-pinene (a major biogenic SOA precursor) in a smog chamber in the absence and in the presence of dioctyl phthalate (DOP) and lubricating oil seed aerosol. These particles serve as surrogates for urban hydrophobic POA. The results show that these POA did not enhance the SOA yields. If these results are found to apply to other biogenic SOA precursors, then the semi-empirical models used in many global models would predict significantly less biogenic SOA mass and display reduced sensitivity to anthropogenic POA emissions than previously thought.

Zelenyuk A, DG Imre, LA Cuadra-rodriguez, and B Ellison. 2007. "Measurements and Interpretation of the Effect of a Soluble Organic Surfactant on the Density, Shape and Water Uptake of Hygroscopic Particles." Journal of Aerosol Science 38(9):903-923. Abstract A large fraction of atmospheric particles are composed of hygroscopic salts that are mixed with variety of organic molecules, of which surfactants represent an interesting and potentially important class. Because of the tendency of surfactant molecules to coat the particles' surface, a monolayer has the potential to completely alter the particles' interactions with the rest of the atmosphere. Given the important role that is played by the interaction of particles with the ambient relative humidity it is critical to develop an understanding of the impact surfactants may exert on particle hygroscopic properties. We present an experimental study of the relationship between the concentrations of a soluble surfactant that is internally mixed with two different hygroscopic salts and particle density, shape and water uptake. We show that the observed particle density provides evidence that the density of the surfactant fraction changes with concentration and that once this is properly taken into account the water uptake data can quantitatively be understood.

Zelenyuk A, and DG Imre. 2007. "On the Effect of Particle Alignment in the DMA." Aerosol Science and Technology 41(2):112-124. Abstract The Differential Mobility Analyzer (DMA) is designed to Measure particle mobility diameter, which for spherical particles is equal to particle volume equivalent diameter. In contrast, the mobility diameter of aspherical particles is a function of the particle shape and orientation. The magnitude of the DMA electric fields is such that it can cause aspherical particles to align preferentially in a specific orientation. The same electric field and the sheath flow rate (qsh) define the particle mobility diameter. But, the fact that particle orientation depends on the electric field makes the dynamic shape factor and hence the mobility diameter depend on qsh. Here, we describe an operating procedure that relies on a tandem DMA system, in which the second DMA is operated at a number of qsh, to obtain information about particle shape by measuring the effect of particle alignment on the particle mobility diameter. We show how the relationship between the mobility diameter and qsh can even be used to physically separate particles according to their shapes. In addition, we explore the use of simultaneous measurements of particle alignment and particle vacuum aerodynamic diameters to gain further information on particle shape and account for particle alignment in the calculations of dynamic shape factor. We first test this approach on doublets and compact triplets of PSL spheres, for which the orientation dependent dynamic shape factors are known. We then investigate applications on a number of polydisperse particle systems of various shapes.

Cai Y, A Zelenyuk, and DG Imre. 2006. "A High Resolution Study of the Effect of Morphology on the Mass Spectra of Single PSL Particles with Na-Containing Layers and Nodules." Aerosol Science and Technology 40(12):1111-1122. doi:10.1080/02786820601001677 Abstract The interpretation and qualification of measurements of particle composition by laser ablation based single particle mass spectroscopy is complex. Among the most difficult system to quantify are internally mixed particles containing alkali metals. The Alkali atoms in such particles tend to suppress the formation of other ions sometimes to below detection limit. Here we present a study of the behavior of the single particle mass spectral peak intensities as a function of the amount of the sodium containing compounds deposited on the surface of 240 nm PSL spheres. We generate three morphologically distinct and well defined coating types: uniform layer, cubic nodules and rounded nodules, and measure the individual particle mass spectra as a function of the vacuum aerodynamic diameter with nanometer resolution. We find that the probability of detecting the PSL spheres depends on the amount of the alkali metal on the PSL sphere surface and the ablation laser power. We also find that the morphological distribution of the sodium containing coating plays a role in determining mass spectral intensities. The data suggest that PSL spheres with localized Na-containing nodules are easier to detect than those completely encapsulated. We show that 80% of PSL spheres with nodules, whose weight fraction is close to 50%, can be detected at high laser power compared with 60% detection of encapsulated PSL particles with the same amount of coating. At low laser powers these detection limits drop to 35% and ~0% respectively.