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The modern chemical industry uses heterogeneous catalysts in almost every production process (1).They commonly consist of nanometre-size active components (typically metals or metal oxides) dispersed on a high-surface-area solid support, [...]

Aluminum coordination in the framework of USY and ZSM-5 zeolites containing charge-compensating cations {N[H.sub.4][.sup.+], [H.sup.+], or [Cu.sup.+]} was investigated by Al K-edge EXAFS and X-ray absorption near edge spectroscopy (XANES). Al K-edge XANES of hydrated H-USY and H-ZSM-5 showed evidence for both tetrahedrally and octahedrally coordinated Al and EXAFS data indicated that the Al-O bond distance for tetrahedrally coordinated Al in dehydrated USY and ZSM-5 as 1.67 Angstrom.

The rate coefficients are measured for the removal of OH(v=1) and OD(v=1) by HNO3 and DNO3 as a function of temperature from 253 to 383 K. OH(v=1) and OD(v=1) were produced by photolysis of HNO3/DNO3 at 248nm and laser induced fluorescence was used to monitor the kinetics of the vibrationally excited radicals.

The rate coefficient for the reaction OH + BrO are determined by monitoring OH temporal profiles in an excess of BrO, generated in a flow tube and measured via its UV -vis absorption. Quoted uncertainties include estimated uncertainties in the BrO concentration and that to the unavoidable concurrent reaction of OH with Br2.

The rate coefficient, k(sub 1), for the reaction OH+CF3I --> products was measured under pseudo-first-order conditions in hydroxyl radical, OH temporal profiles were monitored by laser-induced fluorescence (LIF) and CF3I were determined by UV/Visible absorption. The heat of formation of HOI is deduced to be less than -16 kcal mole(super -1) that supports that OH with CF3I plays a negligibly small role in the atmospheric removal of CF3I.

A study relating to OH reactions with ClO presents results from the study of the temperature dependence of the rate coefficient for the reactions OH + ClO -- HO2 + Cl and OH + ClO -- HCl + O2. These reactions were examined under pseudo-first-order conditions in OH. ClO was generated via the reaction Cl + O3 -- ClO + O2 under conditions where excess O3 was present, or where O3 was completely depleted during ClO production. Experimental methodology is presented.

An analysis of the photoelectron spectra of monofluorovinyldene and difluorovinyldene anions is presented. Transition to the neutral singlet states show extensive vibrational progressions suggesting a large change in equilibrium geometry between the anion and the neutral ground state. Analysis of the ground-state singlet spectrum of monofluorovinyldene and results of the ab initio calculations proves that the straightening of the CCF bond angle in the CCF bending mode in a vital part of the isometrization process.

Long-range transport of continental emission has far reaching influence over remote regions resulting in substantial change in the size, morphology, and composition of the local aerosol population and cloud condensation nuclei (CCN) budget. Here, we investigate the physiochemical properties of atmospheric particles collected onboard a research aircraft flown over the Azores during the winter 2018 Aerosol and Cloud Experiment in the Eastern North Atlantic (ACE-ENA) campaign. Particles were collected within the marine boundary layer (MBL) and free troposphere (FT), after long-range atmospheric transport episodes facilitated by dry intrusion (DI) events. Chemical and physical properties of individual particles were investigated using complementary capabilities of computer-controlled scanning electron microscopy and X-ray spectro-microscopy to probe particle external and internal mixing state characteristics in the context of real-time measurements of aerosol size distribution, cloud condensation nuclei (CCN) concentration, and back trajectory calculations. While carbonaceous particles were found to be the dominant particle-type in the region, changes in the percent contribution of organics across the particle population (i.e., external mixing) shifted from 68% to 43% in the MBL and from 92% to 46% in FT samples during DI events. This change in carbonaceous contribution is counterbalanced by the increase of inorganics from 32% to 57% in the MBL and 8% to 55% in FT. The quantification of organic volume fraction (OVF) of individual particles derived from X-ray spectro-microscopy, which relates to the multi-component internal composition of individual particles, showed a factor of 2.06±0.16 and 1. 11±0.04 increase in the MBL and FT, respectively, among DI samples. We show that supplying particle OVF into the K-Kohler equation can be used as a good approximation of field measured in-situ CCN concentrations. We also report changes in the k values between kmbl, non-DI = 0.48 to kmbl, DI = 0.41 and kft, non-DI = 0.36 to kft, di = 0.33, which is consistent with enhancements in OVF followed by the DI episodes. Our observations suggest that entrainment of particles from long-range continental sources alters the mixing state population and CCN properties of aerosol in the region. The work presented here provides field observation data that can inform atmospheric models that simulate sources and particle composition in the Eastern North Atlantic. [ABSTRACT FROM AUTHOR]

A study was carried out to measure the oxygen K-edge X-ray absorption spectrum (XAS) of aqueous sodium halide solutions, demonstrating that ions significantly perturb the electronic structure of adjacent water molecules. The addition of halide salts to water engenders an increase in the preedge intensity and a decrease in the postedge intensity of the XAS.

The rate coefficient for the reaction of OH with acetone, k1, is measured by producing OH via pulsed laser photolysis and detecting it via laser-induced fluorescence to be k1 (T) = 1.38 x 10(super -13) + 3.86 x 10(super -11) exp (-1997/T) cm(super 3) molecule(super -1) s(super -1). The results showed that the reaction of (super 18)OH with acetone does not produce (super 16)OH.

The 351 nm photoelectron spectra of FO-, ClO-, BrO-, IO-, OClO-, and OIO- are reported. The spectra of the halogen monoxides display transitions to both spin–orbit states of the 2Πi ground state neutrals. Anion vibrational frequencies are observed in the spectra and bond lengths are obtained for the anions from Franck–Condon simulations. Spectra of the halogen dioxides display two active vibrational modes—the symmetric stretch and the bend. Anion symmetric stretching frequencies and normal coordinate displacements from the corresponding neutral are reported. Adiabatic electron affinities found for the halogen oxides are 2.272(6) eV (FO), 2.276(6) eV (ClO), 2.353(6) eV (BrO), 2.378(6) eV (IO), 2.140(8) eV (OClO), and 2.577(8) eV (OIO). The difference between the neutral and anion dissociation energies [D0(XO)-D0(XO-)] is reported for each of the halogen monoxides. Anion heats of formation (298 K) are also determined. [ABSTRACT FROM AUTHOR]

The ultraviolet negative ion photoelectron spectrum of Pd-2 is presented for electron binding energies up to 3.35 eV. The anion is prepared by sputtering in a flowing afterglow ion source. Multiple low-lying electronic states of Pd2, all unidentified previously, are observed with resolved vibrational structure. The spectrum shows two strong electronic bands, each with similar vibrational progressions. Franck–Condon analyses are carried out on the two transitions and molecular constants are extracted for the anion and the two neutral electronic states. With the help of simple molecular orbital arguments and ab initio calculations, these two electronic bands are assigned as the triplet ground state (3Σ+u) and a singlet excited state (1Σ+u). The adiabatic electron affinity is E.A.(Pd2)=1.685±0.008 eV and the singlet excitation energy T0(1Σ+u) is 0.497±0.008 eV (4008±65 cm-1 ). The bonding in the palladium dimers is discussed and we find that the anion bond strength is 1.123±0.013 eV stronger than that of the neutral. Related studies of Pd- yield an improved electron affinity of E.A.(Pd)=0.562±0.005 eV. [ABSTRACT FROM AUTHOR]

Rate coefficient measurements for the reaction of OH + bromopropane isotopomers: CH3CH2CH2Br (k1), CD3CH2CH2Br (k2), CD3CH2CD2Br (k3), CH3CD2CD2Br (k4), and CD3CD2CD2Br (k5) over the range of 230-360 K are presented. The hydroxyl was produced by pulsed laser photolysis and detected via laser induced fluorescence.

Pulsed laser photolysis-laser-induced fluorescence method is used to quantify the rate coefficients for the reaction OH + chloral (CCl3CHO) over a temperature range 233-415 K. UV absorption cross sections of CCl3CHO and quantum yield of O, H, and Cl atoms generated from CCl3CHO photolysis are reported in order to analyze the tropospheric lifetime of CCl3CHO and the significance of chlorine transport from methylchlorofom degradation to the lower stratosphere.

Two complementary techniques, Scanning Transmission X-ray Microscopy/Near Edge Fine Structure spectroscopy (STXM/NEXAFS) and Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDX), have been quantitatively combined to characterize individual atmospheric particles. This pair of techniques was applied to particle samples at three sampling sites (ATTO, ZF2, and T3) in the Amazon basin as part of the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) field campaign during the dry season of 2014. The combined data was subjected to k-means clustering using mass fractions of the following elements: C, N, O, Na, Mg, P, S, Cl, K, Ca, Mn, Fe, Ni, and Zn. Cluster analysis identified 12 particle types across different sampling sites and particle sizes. Samples from the remote Amazon Tall Tower Observatory (ATTO, also T0a) exhibited less cluster variety and fewer anthropogenic clusters than samples collected at the sites nearer to the Manaus metropolitan region, ZF2 (also T0t) or T3. Samples from the ZF2 site contained aged/anthropogenic clusters not readily explained by transport from ATTO or Manaus, possibly suggesting the effects of long range atmospheric transport or other local aerosol sources present during sampling. In addition, this data set allowed for recently established diversity parameters to be calculated. All sample periods had high mixing state indices (Χ) that were >0.8. Two individual particle diversity (Di) populations were observed, with particles <0.5 μm having a Di of ~2.4 and >0.5 μm particles having a Di of ~3.6, which likely correspond to fresh and aged aerosols, respectively. The diversity parameters determined by the quantitative method presented here will serve to aid in the accurate representation of aerosol mixing state, source apportionment, and aging in both less polluted and more developed environments in the Amazon Basin. [ABSTRACT FROM AUTHOR]

The energy flows in Earth's natural and modified climate systems are strongly influenced by the concentrations of atmospheric particulate matter (PM). For predictions of concentration, equilibrium partitioning of semivolatile organic compounds (SVOCs) between organic PM and the surrounding vapor has widely been assumed, yet recent observations show that organic PM can be semisolid or solid for some atmospheric conditions, possibly suggesting that SVOC uptake and release can be slow enough that equilibrium does not prevail on timescales relevant to atmospheric processes. Herein, in a series of laboratory experiments, the mass liabilities of films of secondary organic material representative of similar atmospheric organic PM were directly determined by quartz crystal microbalance measurements of evaporation rates and vapor mass concentrations. There were strong differences between films representative of anthropogenic compared with biogenic sources. For films representing anthropogenic PM, evaporation rates and vapor mass concentrations increased above a threshold relative humidity (RH) between 20% and 30%, indicating rapid partitioning above a transition RH but not below. Below the threshold, the characteristic time for equilibration is estimated as up to 1 wk for a typically sized particle. In contrast, for films representing biogenic PM, no RH threshold was observed, suggesting equilibrium partitioning is rapidly obtained for all RHs. The effective diffusion rate Dorg for the biogenic case is at least 103 times greater than that of the anthropogenic case. These differences should be accounted for in the interpretation of laboratory data as well as in modeling of organic PM in Earth's atmosphere. [ABSTRACT FROM AUTHOR]

The occurrence of non-liquid and liquid physical states of submicron atmospheric particulate matter (PM) downwind of an urban region in central Amazonia was investigated. Measurements were conducted during two Intensive Operating Periods (IOP1 and IOP2) that took place during the wet and dry seasons, respectively, of the GoAmazon2014/5 campaign. Air masses representing variable influences of background conditions, urban pollution, and regional and continental scale biomass burning passed over the research site. As the air masses varied, particle rebound fraction, which is an indicator of the mix of physical states in a sampled particle population, was measured in real time at ground level using an impactor apparatus. Micrographs collected by transmission electron microscopy confirmed that liquid particles adhered while non-liquid particles rebounded. Relative humidity (RH) was scanned to collect rebound curves. When the apparatus RH matched ambient RH, 95% of the particles were liquid as a campaign average, although this percentage dropped to as low as 60% during periods of anthropogenic influence. Secondary organic material, produced for the most part by the oxidation of volatile organic compounds emitted from the forest, was the largest source of liquid PM. Analyses of the mass spectra of the atmospheric PM by positive-matrix factorization (PMF) and of concentrations of carbon monoxide, total particle number, and oxides of nitrogen were used to identify time periods affected by anthropogenic influences, including both urban pollution and biomass burning. The occurrence of non-liquid PM correlated with these indicators of anthropogenic influence. A linear model having as output the rebound fraction and as input the PMF factor loadings explained up to 70% of the variance in the observed rebound fractions. Anthropogenic influences appear to favor non-liquid PM by providing molecular species that increase viscosity when internally mixed with background PM, by contributing non-liquid particles in external mixtures of PM, and a by combination of these effects under real-world conditions. [ABSTRACT FROM AUTHOR]

Aerosol absorption is strongly dependent on the internal heterogeneity (mixing state) and morphology of individual particles containing black carbon (BC) and other non-absorbing species. Here, we examine an extensive microscopic data set collected in the California central valley during the CARES 2010 field campaign. During a period of high photochemical activity and pollution buildup, the particle mixing state and morphology were characterized using Scanning Transmission X-ray Microscopy (STXM) at the carbon K-edge. Observations of compacted BC core morphologies and thick organic coatings at both urban and rural sites provide evidence of the aged nature of particles. Based on the observation of thick coatings and more convex BC inclusion morphology, the contribution of fresh BC emissions at the urban site was relatively small. These measurements of BC morphology and mixing state provide important constraints for the morphological effects on BC optical properties expected in aged urban plumes. [ABSTRACT FROM AUTHOR]