Nathan F. Dalleska

Chemical Composition of Gas- and Aerosol-Phase Products from the Photooxidation of Naphthalene

The current work focuses on the detailed evolution of the chemical composition of both the gas- and aerosol-phase constituents produced from the OH-initiated photooxidation of naphthalene under low- and high-NO(x) conditions. Under high-NO(x) conditions ring-opening products are the primary gas-phase products, suggesting that the mechanism involves dissociation of alkoxy radicals (RO) formed through an RO(2) + NO pathway, or a bicyclic peroxy mechanism. In contrast to the high-NO(x) chemistry, ring-retaining compounds appear to dominate the low-NO(x) gas-phase products owing to the RO(2) + HO(2) pathway. We are able to chemically characterize 53-68% of the secondary organic aerosol (SOA) mass. Atomic oxygen-to-carbon (O/C), hydrogen-to-carbon (H/C), and nitrogen-to-carbon (N/C) ratios measured in bulk samples by high-resolution electrospray ionization time-of-flight mass spectrometry (HR-ESI-TOFMS) are the same as the ratios observed with online high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), suggesting that the chemical compositions and oxidation levels found in the chemically-characterized fraction of the particle phase are representative of the bulk aerosol. Oligomers, organosulfates (R-OSO(3)), and other high-molecular-weight (MW) products are not observed in either the low- or high-NO(x) SOA; however, in the presence of neutral ammonium sulfate seed aerosol, an organic sulfonic acid (R-SO(3)), characterized as hydroxybenzene sulfonic acid, is observed in naphthalene SOA produced under both high- and low-NO(x) conditions. Acidic compounds and organic peroxides are found to account for a large fraction of the chemically characterized high- and low-NO(x) SOA. We propose that the major gas- and aerosol-phase products observed are generated through the formation and further reaction of 2-formylcinnamaldehyde or a bicyclic peroxy intermediate. The chemical similarity between the laboratory SOA and ambient aerosol collected from Birmingham, Alabama (AL) and Pasadena, California (CA) confirm the importance of PAH oxidation in the formation of aerosol within the urban atmosphere.

Formation and evolution of molecular products in α-pinene secondary organic aerosol

Significance Secondary organic aerosol (SOA) plays a pivotal role in climate and air quality. Characterizing the molecular makeup of SOA has been a major research goal for several decades, yet the chemical dynamics of most anthropogenic and biogenic SOA systems remain poorly resolved. We report here the time-resolved molecular characterization of SOA derived from the canonical α-pinene system, one of the most abundant biogenic emissions in the troposphere. We reveal distinct features of SOA components in terms of molecular structure, abundance, growth rates, evolution patterns, and responses to variations in temperature, relative humidity, and oxidant type. Our findings provide a comprehensive analysis of processes governing α-pinene SOA formation and aging. Much of our understanding of atmospheric secondary organic aerosol (SOA) formation from volatile organic compounds derives from laboratory chamber measurements, including mass yield and elemental composition. These measurements alone are insufficient to identify the chemical mechanisms of SOA production. We present here a comprehensive dataset on the molecular identity, abundance, and kinetics of α-pinene SOA, a canonical system that has received much attention owing to its importance as an organic aerosol source in the pristine atmosphere. Identified organic species account for ∼58–72% of the α-pinene SOA mass, and are characterized as semivolatile/low-volatility monomers and extremely low volatility dimers, which exhibit comparable oxidation states yet different functionalities. Features of the α-pinene SOA formation process are revealed for the first time, to our knowledge, from the dynamics of individual particle-phase components. Although monomeric products dominate the overall aerosol mass, rapid production of dimers plays a key role in initiating particle growth. Continuous production of monomers is observed after the parent α-pinene is consumed, which cannot be explained solely by gas-phase photochemical production. Additionally, distinct responses of monomers and dimers to α-pinene oxidation by ozone vs. hydroxyl radicals, temperature, and relative humidity are observed. Gas-phase radical combination reactions together with condensed phase rearrangement of labile molecules potentially explain the newly characterized SOA features, thereby opening up further avenues for understanding formation and evolution mechanisms of α-pinene SOA.

Plasma enhanced chemical vapor deposition of SiO2 using novel alkoxysilane precursors

This communication describes our results using these novel alkoxysilane precursors for PECVD of SiO_2 films in an inductively coupled rf plasma reactor. The effects of deposition time, rf power, and organosilane pressure on the films’ characteristics are described.

Reaction of Zn+ with NO2. The gas‐phase thermochemistry of ZnO

The homolytic bond dissociation energies of ZnO and ZnO^+ have been determined by using guided ion‐beam mass spectrometry to measure the kinetic‐energy dependence of the endothermic reactions of Zn^+ with nitrogen dioxide. The data are interpreted to yield the bond energy for ZnO, D^0_0=1.61±0.04 eV, a value considerably lower than previous experimental values, but in much better agreement with theoretical calculations. We also obtain D^0_0(ZnO^+)=1.67±0.05 eV, in good agreement with previous results. Other thermochemistry derived in this study is D^0_0(Zn^+–NO)=0.79±0.10 eV and the ionization energies, IE(ZnO)=9.34±0.02 eV and IE(NO_2)=9.57±0.04 eV.

A modified molecular beam instrument for the imaging of radicals interacting with surfaces during plasma processing

A new instrument employing molecular beam techniques and laser induced fluorescence(LIF) for measuring the reactivity of gas phase radicals at the surface of a depositing film has been designed and characterized. The instrument uses an inductively coupled plasma source to create a molecular beam containing essentially all plasma species. A tunable excimer pumped dye laser is used to excite a single species in this complex molecular beam.LIF signals are imaged onto a gated, intensified charge coupled device (ICCD) to provide spatial resolution. ICCD images depict the fluorescence from molecules both in the molecular beam and scattering from the surface of a depositing film. Data collected with and without a substrate in the path of the molecular beam provide information about the surface reactivity of the species of interest. Here, we report the first measurements using the third generation imaging of radicals interacting with surfaces apparatus. We have measured the surface reactivity of SiH molecules formed in a 100% SiH_4 plasma during deposition of an amorphous hydrogenated silicon film. On a 300 K Si (100) substrate, the reactivity of SiH is near unity. The substrate temperature dependence (300–673 K) of the reactivity is also reported. In addition, reactivity measurements for OH molecules formed in a water plasma are presented. In contrast to the SiH molecule, the reactivity of OH radicals is 0.55±0.05 on the surface of a Si (100) substrate.

Gas-phase thermochemistry of the group 3 dioxides: SCO2, YO2 and LaO2

Gas-phase ScO_2, YO_2, LaO_2 and the singly charged cations of these species are formed in endothermic reactions between MO+ (M=Sc, Y, and La) and NO_2 in a guided ion beam mass spectrometer. The cross sections of these reactions are measured as a function of kinetic energy and are interpreted to give the following 0 K bond energies (in eV): D^0(OScO)=3.95±0.33, D^0(OYO)=4.14±0.22, D^0(OLaO)=4.20±0.33, D^0(OSc^+O)=1.72±0.19, D^0(OY^+O)=1.76±0.16, and D^0(OLa^+O)=0.99±0.31. Values for the MO_2 ionization energies (in eV) are determined to be IE(ScO_2)=8.66±0.20, IE(YO_2)=8.23±0.16 and IE(LaO_2)=8.11±0.35. The differences between these values and estimates in the literature are discussed by considering the nature of the bonding in MO_2 and MO^+_2.

Nitrate-based niche differentiation by distinct sulfate-reducing bacteria involved in the anaerobic oxidation of methane

Diverse associations between methanotrophic archaea (ANME) and sulfate-reducing bacterial groups (SRB) often co-occur in marine methane seeps; however, the ecophysiology of these different symbiotic associations has not been examined. Here, we applied a combination of molecular, geochemical and Fluorescence in situ hybridization (FISH) coupled to nanoscale secondary ion mass spectrometry (FISH-NanoSIMS) analyses of in situ seep sediments and methane-amended sediment incubations from diverse locations (Eel River Basin, Hydrate Ridge and Costa Rican Margin seeps) to investigate the distribution and physiology of a newly identified subgroup of the Desulfobulbaceae (seepDBB) found in consortia with ANME-2c archaea, and compared these with the more commonly observed associations between the same ANME partner and the Desulfobacteraceae (DSS). FISH analyses revealed aggregates of seepDBB cells in association with ANME-2 from both environmental samples and laboratory incubations that are distinct in their structure relative to co-occurring ANME/DSS consortia. ANME/seepDBB aggregates were most abundant in shallow sediment depths below sulfide-oxidizing microbial mats. Depth profiles of ANME/seepDBB aggregate abundance revealed a positive correlation with elevated porewater nitrate relative to ANME/DSS aggregates in all seep sites examined. This relationship with nitrate was supported by sediment microcosm experiments, in which the abundance of ANME/seepDBB was greater in nitrate-amended incubations relative to the unamended control. FISH-NanoSIMS additionally revealed significantly higher 15N-nitrate incorporation levels in individual aggregates of ANME/seepDBB relative to ANME/DSS aggregates from the same incubation. These combined results suggest that nitrate is a geochemical effector of ANME/seepDBB aggregate distribution, and provides a unique niche for these consortia through their utilization of a greater range of nitrogen substrates than the ANME/DSS.

Branched Polymeric Media: Boron-Chelating Resins from Hyperbranched Polyethylenimine

Extraction of boron from aqueous solutions using selective resins is important in a variety of applications including desalination, ultrapure water production, and nuclear power generation. Todays commercial boron-selective resins are exclusively prepared by functionalization of styrene-divinylbenzene (STY-DVB) beads with N-methylglucamine to produce resins with boron-chelating groups. However, such boron-selective resins have a limited binding capacity with a maximum free base content of 0.7 eq/L, which corresponds to a sorption capacity of 1.16 ± 0.03 mMol/g in aqueous solutions with equilibrium boron concentration of ∼70 mM. In this article, we describe the synthesis and characterization of a new resin that can selectively extract boron from aqueous solutions. We show that branched polyethylenimine (PEI) beads obtained from an inverse suspension process can be reacted with glucono-1,5-D-lactone to afford a resin consisting of spherical beads with high density of boron-chelating groups. This resin has a sorption capacity of 1.93 ± 0.04 mMol/g in aqueous solution with equilibrium boron concentration of ∼70 mM, which is 66% percent larger than that of standard commercial STY-DVB resins. Our new boron-selective resin also shows excellent regeneration efficiency using a standard acid wash with a 1.0 M HCl solution followed by neutralization with a 0.1 M NaOH solution.

Cerebrospinal fluid sodium rhythms

BackgroundCerebrospinal fluid (CSF) sodium levels have been reported to rise during episodic migraine. Since migraine frequently starts in early morning or late afternoon, we hypothesized that natural sodium chronobiology may predispose susceptible persons when extracellular CSF sodium increases. Since no mammalian brain sodium rhythms are known, we designed a study of healthy humans to test if cation rhythms exist in CSF.MethodsLumbar CSF was collected every ten minutes at 0.1 mL/min for 24 h from six healthy participants. CSF sodium and potassium concentrations were measured by ion chromatography, total protein by fluorescent spectrometry, and osmolarity by freezing point depression. We analyzed cation and protein distributions over the 24 h period and spectral and permutation tests to identify significant rhythms. We applied the False Discovery Rate method to adjust significance levels for multiple tests and Spearman correlations to compare sodium fluctuations with potassium, protein, and osmolarity.ResultsThe distribution of sodium varied much more than potassium, and there were statistically significant rhythms at 12 and 1.65 h periods. Curve fitting to the average time course of the mean sodium of all six subjects revealed the lowest sodium levels at 03.20 h and highest at 08.00 h, a second nadir at 09.50 h and a second peak at 18.10 h. Sodium levels were not correlated with potassium or protein concentration, or with osmolarity.ConclusionThese CSF rhythms are the first reports of sodium chronobiology in the human nervous system. The results are consistent with our hypothesis that rising levels of extracellular sodium may contribute to the timing of migraine onset. The physiological importance of sodium in the nervous system suggests that these rhythms may have additional repercussions on ultradian functions.

Guided ion beam studies of reactions of alkaline earth ions with O2

The endothermic reactions of Mg^+ and Sr^+ with O_2 are studied in a guided ion beam mass spectrometer. Analysis of the reaction thresholds are used to obtain 0 K bond dissociation energies of MgO^+ (2.50 ± 0.10 eV) and SrO^+ (3.47 ± 0.06 eV), which are compared with other literature values. Analysis of these reaction cross sections and those previously published for the reaction of Ca^+ with O_2 [E.R. Fisher, J.L. Elkind, D.E. Clemmer, R. Georgiadis, S.K. Loh, N. Aristov, L.S. Sunderlin, and P.B. Armentrout, J. Chem. Phys., 93 (1990) 2676] suggests that there are both thermodynamic and impulsive reaction pathways. The latter play an increasingly important role in the reaction dynamics as the mass of the alkaline earth ion increases.