Atmospheric Aerosol Chemistry Publications

2009

Liu Y, and A Laskin. 2009. "Hygroscopic Properties of CH3SO3Na, CH3SO3NH4, (CH3SO3)2Mg and (CH3SO3)2Ca Particles Studied by Micro-FTIR Spectroscopy." Journal of Physical Chemistry A 113(8):1531-1538. Abstract The hygroscopic behavior of CH3SO3Na, CH3SO3NH4, (CH3SO3)2Mg and (CH3SO3)2Ca particles as a function of relative humidity (RH) has been studied using microscopic Fourier transform infrared (micro-FTIR) spectroscopy. The approach used exposure of substrate deposited, ~1 μm dry-size particles to humidified nitrogen followed by micro-FTIR spectroscopy over a selected sample area. The results show that CH3SO3Na particles undergo characteristic phase transitions at deliquescence relative humidity (DRH) of 71% and efflorescence relative humidity (ERH) of ~40%. In contrast, CH3SO3NH4, (CH3SO3)2Mg and (CH3SO3)2Ca particles do not undergo phase transitions and exhibit continuous, reversible uptake and evaporation of water under the influence of changing RH. The extent of water uptake is quantified and presented as water-to-solute ratios (WSR) in particles as a function of RH. The WSR values are determined from the integrated absorbance of the water and the solute-specific bands in IR spectra recorded at different RH.
Ferguson MR, KR Minard, and KM Krishnan. 2009. "Optimization of nanoparticle core size for magnetic particle imaging." Journal of Magnetism and Magnetic Materials 321(10):1548-1551. Abstract Magnetic Particle Imaging (MPI) is a powerful new diagnostic visualization platform designed for measuring the amount and location of superparamagnetic nanoscale molecular probes (NMPs) in biological tissues. Promising initial results indicate that MPI can be extremely sensitive and fast, with good spatial resolution for imaging human patients or live animals. Here, we present modeling results that show how MPI sensitivity and spatial resolution both depend on NMP-core physical properties, and how MPI performance can be effectively optimized through rational core design. Monodisperse magnetite cores are attractive since they are readily produced with a biocompatible coating and controllable size that facilitates quantitative imaging.
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, 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.
Yu Y, ML Alexander, V Perraud, E Bruns, S Johnson, M Ezell, and BJ Finlayson-Pitts. 2009. "Contamination from electrically conductive silicone tubing during aerosol chemical analysis." Atmospheric Environment 43(17):2836-2839. Abstract Electrically conductive silicone tubing is used to minimize losses in sampling lines during the analysis of airborne particle size distributions and number concentrations. We report contamination from this tubing using gas chromatography-mass spectrometry (GC-MS) of filter-collected samples as well as by particle mass spectrometry. Comparison of electrically conductive silicone and stainless steel tubing showed elevated siloxanes only for the silicone tubing. The extent of contamination increased with length of tubing to which the sample was exposed, and decreased with increasing relative humidity.

2008

Hopkins RJ, Y Desyaterik, AV Tivanski, RA Zaveri, CM Berkowitz, T Tyliszczak, MK Gilles, and A Laskin. 2008. "Chemical Speciation of Sulfur in Marine Cloud Droplets and Particles: Analysis of Individual Particles from the Marine Boundary Layer Over the California Current." Journal of Geophysical Research. D. (Atmospheres) 113(D4):D04209. doi:10.1029/2007/JD008954 Abstract Detailed chemical speciation of the dry residue particles from individual cloud droplets and interstitial aerosol collected during the Marine Stratus Experiment (MASE) was performed using a complementary combination of microanalysis techniques. Techniques include computer controlled scanning electron microscopy with energy dispersed analysis of X-rays (CCSEM/EDX), time-of-flight secondary ionization mass spectrometry (TOFSIMS), and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). Samples were collected at the ground site located in Point Reyes National Seashore, approximately 1 km from the coast. This manuscript focuses on the analysis of individual particles sampled from an air mass that originated over the open ocean and then passed through the area of the California current located along the northern California coast. Based on composition, morphology, and chemical bonding information, two externally mixed, distinct classes of sulfur containing particles were identified: chemically modified (aged) sea salt particles and secondary formed sulfate particles. The results indicate substantial heterogeneous replacement of chloride by methanesulfonate (CH3SO3 -) and non-sea salt sulfate (nss-SO4 2-) in sea-salt particles with the characteristic ratios of CH3SO3 −/nss-SO4 2−> 0.6. Although this value seems too high for a mid-latitude site, our model calculations suggest that high CH3SO3 -/nss-SO4 2- ratios are expected during the early stages of dimethyl sulfide (DMS) oxidation when CH3SO3H forms more rapidly than H2SO4.
Liu Y, ER Gibson, JP Cain, H Wang, VH Grassian, and A Laskin. 2008. "Kinetics of Heterogeneous Reaction of CaCO3 Particles with Gaseous HNO3 Over a Wide Range of Humidity." Journal of Physical Chemistry A 112(7):1561-1571. doi:10.1021/jp076169H Abstract Heterogeneous reaction kinetics of gaseous nitric acid (HNO3) with calcium carbonate (CaCO3) particles was investigated using the Particle-on-Substrate Stagnation Flow Reactor (PS-SFR). The technique utilizes the exposure of substrate deposited, isolated, and narrowly dispersed particles to a gas mixture of HNO3/H2O/N2 followed by microanalysis of individual reacted particles using computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM/EDX). The first series of experiment was conducted at atmospheric pressure, room temperature and constant relative humidity (40%) with a median dry particle diameter pD = 0.85 μm, particle loading densities 2×104 ≤ Ns ≤ 6×106 cm–2 and free stream HNO3 concentrations of 7, 14 and 25 ppb. The apparent, pseudo first-order rate constant for the reaction was determined from oxygen enrichment in individual particles as a function of particle loading. Quantitative treatment of the data using a diffusion-kinetic model yields lower limit to the net reaction probability γnet ≥ 0.06 (×3/÷2). In the second series of experiments, HNO3 uptake on CaCO3 of the same particle size was examined over a wide range of relative humidity, from 10 to 80%. The lower limit for the net reaction probability was found to increase with an increase in the relative humidity, from γnet ≥ 0.003 at RH = 10% to 0.21 at 80%.
Walser ML, Y Dessiaterik, J Laskin, A Laskin, and S Nizkorodov. 2008. "High-Resolution Mass Spectrometric Analysis of Secondary Organic Aerosol Produced by Ozonation of Limonene." Physical Chemistry Chemical Physics. PCCP 10(7):1009-1022. doi:10.1039/b712620d Abstract Secondary organic aerosol (SOA) particles formed from the ozone-initiated oxidation of limonene are characterized by high-resolution electrospray ionization mass spectrometry in both the positive and negative ion modes. The mass spectra reveal a large number of both monomeric (m/z < 300) and oligomeric (m/z > 300) products of oxidation. A combination of high resolving power (m/Δm ~60,000) and Kendrick mass defect analysis makes it possible to unambiguously determine the composition for hundreds of individual compounds in SOA samples. Van Krevelen analysis shows that the SOA compounds are heavily oxidized, with average O:C ratios of 0.43 and 0.50 determined from the positive and negative ion mode spectra, respectively. An extended reaction mechanism for the formation of the first generation SOA molecular components is proposed. The mechanism includes known isomerization and addition reactions of the carbonyl oxide intermediates generated during the ozonation of limonene, and numerous isomerization pathways for alkoxy radicals resulting from the decomposition of unstable carbonyl oxides. The isomerization reactions yield numerous products with a progressively increasing number of alcohol and carbonyl groups, whereas C-C bond scission reactions in alkoxy radicals shorten the carbon chain. Together these reactions yield a large number of isomeric products with broadly distributed masses. A qualitative agreement is found between the number and degree of oxidation of the predicted and measured reaction products in the monomer range.
Kassianov EI, and M Ovtchinnikov. 2008. "On Reflectance Ratios and Aerosol Optical Depth Retrieval in the Presence of Cumulus Clouds ." Geophysical Research Letters 35(6):Art. No. L06807. doi:10.1029/2008GL033231 Abstract The traditional conversion of satellite-observed reflectances to the aerosol optical depth (AOD) is highly conjectural in the vicinity of clouds due to the 3D cloud-induces enhancement of the apparent reflectance. This study uses 3D Monte Carlo radiative transfer calculations and simulated cloud and aerosol fields to illustrate that for clear pixels the reflectance ratios for two pairs of wavelengths (660, 470 nm and 870, 470 nm) are less sensitive to the 3D cloud effects than the reflectances themselves. We develop a new algorithm for converting these two ratios to three spectral values of AOD and show that it is accurate to within 10% for the majority of clear pixels in our model-inverse problem. This preliminary study suggests that the proposed approach can be used to significantly improve the accuracy of the AOD retrieved from spectral satellite observations under partly cloudy conditions.
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.

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