Hygroscopic Behavior of Multicomponent Aerosols Involving NaCl and Dicarboxylic Acids.

Atmospheric aerosols are usually complex mixtures of inorganic and organic compounds. The hygroscopicity of mixed particles is closely related to their chemical composition and interactions between components, which is still poorly understood. In this study, the hygroscopic properties of submicron particles composed of NaCl and dicarboxylic acids including oxalic acid (OA), malonic acid (MA), and succinic acid (SA) with various mass ratios are investigated with a hygroscopicity tandem differential mobility analyzer (HTDMA) system. Both the Zdanovskii-Stokes-Robinson (ZSR) method and extended aerosol inorganics model (E-AIM) are applied to predict the water uptake behaviors of sodium chloride/dicarboxylic acid mixtures. For NaCl/OA mixed particles, the measured growth factors were significantly lower than predictions from the model methods, indicating a change in particle composition caused by chloride depletion. The hygroscopic growth of NaCl/MA particles was well described by E-AIM, and that of NaCl/SA particles was dependent upon mixing ratio. Compared with model predictions, it was determined that water uptake of the NaCl/OA mixture could be enhanced and could be closer to the predictions by addition of levoglucosan or malonic acid, which retained water even at low relative humidity (RH), leading to inhibition of HCl evaporation during dehydration. These results demonstrate that the coexisting hygroscopic species have a strong influence on the phase state of particles, thus affecting chemical interactions between inorganic and organic compounds as well as the overall hygroscopicity of mixed particles.

Oxygen-sulfur exchange and the gas-phase reactivity of cobalt sulfide cluster anions with molecular oxygen.

We present here a study of gas-phase reactivity of cobalt sulfide cluster anions Co(m)S(n)(-) with molecular oxygen. Nascent Co(m)S(n)(-) clusters were prepared via a laser ablation source and reacted with oxygen in a fast flow reactor under thermal collision conditions. We chose (18)O2 in place of (16)O2 to avoid mass degeneration with sulfur, and a time-of-flight (TOF) mass spectrometer was used to detect the cluster distributions in the absence and presence of the reactant. It was found that oxygen-sulfur exchange occurs in the reactions for those with specific compositions (CoS)(n)(-) and (CoS)(n)S(-) (n = 2-5) according to a consistent pathway, "Co(m)S(n)(-) + (18)O2 → Co(m)S(n-1)(18)O(-) + S(18)O". Typically, for "Co2S2(-) + (18)O2" we have calculated the reaction coordinates by employing the density functional theory (DFT), where both the oxygen-sulfur exchange and SO molecule release are thermodynamically and kinetically favorable. It is noteworthy that the reaction with molecular oxygen (triplet ground state) needs to overcome a spin excitation as well as a large O-O activation energy. This study sheds light on the activation of molecular oxygen by cobalt sulfides on one hand and also provides insight into the regeneration mechanism of cobalt oxides from the counterpart sulfides in the presence of oxygen gas on the other hand.

Consecutive oxygen-for-sulfur exchange reactions between vanadium oxide cluster anions and hydrogen sulfide.

Vanadium oxide cluster anions Vm(16)On(-) and Vm(18)On(-) were prepared by laser ablation and reacted with hydrogen sulfide (H2S) in a fast flow reactor under thermal collision conditions. A time-of-flight mass spectrometer was used to detect the cluster distributions before and after the interactions with H2S. The experiments suggest that the oxygen-for-sulfur (O/S) exchange reaction to release water was evidenced in the reactor for most of the cluster anions: VmOn(-) + H2S → VmOn-1S(-) + H2O. For reactions of clusters VO3(-) and VO4(-) with H2S, consecutive O/S exchange reactions led to the generation of sulfur containing vanadium oxide cluster anions VO3-kSk(-) (k = 1-3) and VO4-kSk(-) (k = 1-4). Density functional theory calculations were performed for the reactions of VO3-4(-) with H2S, and the results indicate that the O/S exchange reactions are both thermodynamically and kinetically favorable, which supports the experimental observations. The reactions of VmOn(+) cluster cations with H2S have been reported previously (Jia, M.-Y.; Xu, B.; Ding, X.-L.; Zhao, Y.-X.; He, S.-G.; Ge, M.-F. J. Phys. Chem. C 2012, 116, 9043), and this study of cluster anions provides further new insights into the transformations of H2S over vanadium oxides at the molecular level.

Experimental and theoretical study of the reactions between MO2- (M = Fe, Co, Ni, Cu, and Zn) cluster anions and hydrogen sulfide.

Transition metal oxide cluster anions M(m)(18)O(n)(-) (M = Fe, Co, Ni, Cu, and Zn) were prepared by laser ablation and reacted with H2S in a fast flow reactor under thermal collision conditions. A time-of-flight mass spectrometer was used to detect the cluster distributions before and after the interactions with H2S. The experiments reveal a suite of oxygen/sulfur (O/S) exchange and oxygen/sulfydryl (O/SH) exchange reactions. The O/S exchange reaction to release water was evidenced for all of the MO2(-) cluster anions: MO2(-) + H2S → MOS(-) + H2O, whereas the O/SH exchange reaction to derive MOSH(-) and OH species was only observed for reactions of NiO2(-), CuO2(-), and ZnO2(-). Density functional theory calculations were performed for reaction mechanisms of MO2(-) + H2S (M = Fe, Co, Ni, Cu, and Zn). The computational results are generally in good agreement with the experimental results. This gas-phase study provides an insight into the metal dependent reactivity in the removal of H2S over metal oxides.

Synergistic effects between SO2 and HCOOH on α-Fe2O3.

Heterogeneous reactions on mineral aerosols remain an important subject in atmospheric chemistry because of their role in altering the properties of particles and the budget of trace gases. Yet, the role of coadsorption of trace gases onto mineral aerosols and potential synergistic effects are largely uncertain, especially synergistic effects between inorganic and organic gas-phase pollutants. In this study, synergistic effects between HCOOH and SO2 were investigated for the first time using in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS). It was found that the heterogeneous reaction of HCOOH is hindered significantly by coexisting SO2. The total amount of formate decreased, whereas the total amount of sulfate was not affected during coadsorption on the surface of α-Fe2O3. Futhermore, part of the formate on the surface was catalytically decomposed to CO2 by α-Fe2O3 with the help of SO2. These results suggest a possible mechanism for the observed correlations between sulfate and carboxylate in the atmosphere.

Conformational transferability of the sulfenyl carbonyl group -SC(O)- in cyclic thioesters.

The molecular and crystal structure of two dithiolactones (formally dimers of ε-caprothiolactone and ω-hexadecathiolactone) have been determined by X-ray diffraction at low temperature, revealing that the thioester group is planar with a synperiplanar orientation of the C═O double bond with respect to the S-C single bond. This conformational behavior is in contrast to that found for the smaller cyclic members of this family, where the antiperiplanar conformation is enforced. It is hypothesized that strain effects play a major role for the energy balance in the conformational preference. In this context, the molecular, vibrational (infrared and Raman), and electronic properties of ε-caprothiolactone have also been analyzed by using a combined experimental, including gas-phase helium I photoelectron spectroscopy, and computational approach.

Temperature dependence of heterogeneous uptake of hydrogen peroxide on silicon dioxide and calcium carbonate.

The heterogeneous kinetic processes of hydrogen peroxide on silicon dioxide (SiO2) and calcium carbonate (CaCO3) have been studied over the temperature range from 253 to 313 K using a Knudsen cell reactor, and the functions of temperature were obtained. The kinetic study indicates that the initial uptake coefficients increase evidently with a temperature decrease. They can be calculated by the equations γBET(SiO2) = [exp(934.5/T - 12.7)]/[1 + exp(934.5/T - 12.7)] and γBET(CaCO3) = [exp(1193.0/T - 11.9)]/[1 + exp(1193.0/T - 11.9)]. On the basis of the temperature dependence of uptake coefficients, the enthalpy (ΔHobs) and entropy (ΔSobs) of uptake progresses were determined to be -(7.77 ± 1.55) KJ mol(-1) and -(105.8 ± 21.2) J K mol(-1) for SiO2 and -(9.92 ± 1.98) KJ mol(-1) and -(98.6 ± 19.7) J K mol(-1) for CaCO3. The activation energies for desorption (Edes) of H2O2 on CaCO3 and SiO2 were calculated to be (5.9 ± 0.9) KJ mol(-1) and (9.15 ± 1.1) KJ mol(-1). The results suggest that hydrogen peroxide could mainly be adsorbed on SiO2 and CaCO3 reversibly in this temperature region, and the quick uptake on these mineral aerosols, especially at low temperature, provides an active surface for further complex reactions.

Influence of temperature on the heterogeneous reaction of formic acid on α-Al2O3.

Despite increased awareness of the role played by heterogeneous reactions of formic acid on mineral aerosol, the experimental determination of how these atmospheric reaction rates vary with temperature remain a crucially important part of atmosphere science. Here we report the first measurement of heterogeneous uptake of formic acid on α-Al(2)O(3) as a function of temperature (T = 240-298 K) at ambient pressure using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). From the analysis of the spectral features, crystalline HCOOH was identified at low temperature besides common product (formate ions) on the surface. It was also interesting to find that crystalline HCOOH can continue to react with α-Al(2)O(3). The reaction mechanisms at both room and low temperature were discussed. Furthermore, the reactive uptake coefficients were acquired and found to increase with decreasing temperature. Finally, the atmospheric lifetime of formic acid because of heterogeneous loss on mineral aerosol was estimated at temperatures related to the upper troposphere.

Uptake of methacrolein into aqueous solutions of sulfuric acid and hydrogen peroxide.

Multiphase acid-catalyzed oxidation by hydrogen peroxide has been suggested to be a potential route to secondary organic aerosol (SOA) formation from isoprene and its gas-phase oxidation products, but the kinetics and chemical mechanism remain largely uncertain. Here we report the first measurement of uptake of methacrolein into aqueous solutions of sulfuric acid and hydrogen peroxide in the temperature range of 253-293 K. The steady-state uptake coefficients were acquired and increased quickly with increasing sulfuric acid concentration and decreasing temperature. Propyne, acetone, and 2,3-dihydroxymethacrylic acid were suggested as the products. The chemical mechanism is proposed to be the oxidation of carbonyl group and C═C double bonds by peroxide hydrogen in acidic environment, which could explain the large content of polyhydroxyl compounds in atmospheric fine particles. These results indicate that multiphase acid-catalyzed oxidation of methacrolein by hydrogen peroxide can contribute to SOA mass in the atmosphere, especially in the upper troposphere.

Vibrational and valence photoelectron spectroscopies, matrix photochemistry, and conformational studies of ClC(O)SSCl.

ClC(O)SSCl was prepared by an improved method by the reaction of [(CH(3))(2)CHOC(S)](2)S with SO(2)Cl(2) in hexane. The photoelectron spectra in the gas phase present four distinct regions, corresponding to ionizations from electrons formally located at the S, O, and Cl atoms and at the C═O bond. The vibrational IR and Raman spectra of the liquid were interpreted in terms of the most stable syn-gauche conformer (the O═C double bond syn with respect to the S-S single bond and the C-S single bond gauche with respect to the S-Cl single bond) in equilibrium with the less stable anti-gauche form, both occurring in two enantiomeric forms. The randomization process between the conformers was induced by broad-band UV-visible irradiation in matrix conditions, and several photoproducts were identified by FTIR spectroscopy. The experimental results were complemented by theoretical calculations.

[X-ray fluorescence spectrum studies on bioorganic carbon in cereals and carbon chemical circulation].

The bioorganic carbon contents and chemical element compositions in six kinds of cereals: paddy (rice), wheat (flour), soybean, millet, sorghum and corn were determined by X-ray fluorescence (XRF) spectrum, meanwhile a new method was established to probe their protein contents. In the cereals, the average bioorganic carbon content is about 440%. The highest protein content is 42.74% from soybean, and other protein content is 28.56% in millet, 27.57% in wheat, 24.99% in corn, 22.21% in sorghum, but only 20.31% in rice. Based on our new definition of carbon chemical circulation presented in the current work, the authors have found that in 2009 humankind used bioorganic carbon to discharge CO2 into the earth's atmosphere that accounts for one percent of the total CO2 discharge, and consumed organic carbon to release CO2 into the earth's atmosphere, accounting for 10.73% of the total CO2 discharge. The clear definition of carbon chemical circulation and the discharged CO2 content from the distinct types of carbon compounds would advance the study on carbon chemical circulation and the atmospheric CO2 greenhouse effect. Our work further found that it takes eight years to circulate the total earth's atmospheric CO2. The short period shows the sensitivity for CO2 to keep its dynamical equilibrium in the earth's atmosphere. However, no experimental data has been reported to prove a heavy destructive greenhouse effect of CO2 existing in the earth's atmosphere.

Molecular and electronic structure of δ-valerothiolactone.

The crystal structure of the six-member heterocyclic δ-valerothiolactone (1-thiocycloalkan-2-one) compound has been determined by X-ray diffraction at low temperature, revealing that its skeleton adopts a half-chair conformation. The conformation around the thioester group is almost planar with an anti orientation of the C=O double bond with respect the S-C single bond [C(2)-S(1)-C(6)-O(1) = 176.26(8)°]. The skeletal parameters, especially valence angles [∠C5-C6-S = 121.19(6)°, ∠O=C6-C5 = 122.25(8)°, ∠C6-S-C2 = 106.80(4)°], differ from those typically found in acyclic thioester compounds, symptomatic of the presence of strain effects. The conventional ring strain energy was determined to be 7.5 kcal/mol at the MP2/6-311++G(d,p) level of calculation within the hyperhomodesmotic model approximation. Moreover, the valence electronic structure was investigated by HeI photoelectron spectroscopy assisted by quantum chemical calculations at the OVGF/6-311++G(d,p) level of theory. The first three bands at 9.35, 9.50, and 11.53 eV denote ionizations related with the n(S), n(O), and π(C=O) orbitals, respectively, demonstrating the importance of the -SC(O)- group in the outermost electronic properties.

Matrix photochemistry at low temperatures and spectroscopic properties of gamma-butyrothiolactone.

The five-membered heterocyclic gamma-butyrothiolactone was isolated in a low-temperature, inert Ar matrix, and the UV-visible (200

Conformational behavior of CH3OC(O)SX (X = CN and SCN) pseudohalide congeners. A combined experimental and theoretical study.

Pure methoxycarbonylsulfenyl cyanide, CH(3)OC(O)SCN (I), and methoxycarbonylsulfenyl thiocyanate, CH(3)OC(O)SSCN (II), were prepared by reacting liquid CH(3)OC(O)SCl with either AgCN or AgSCN, respectively. Compounds I and II were characterized by (1)H NMR, CG-MS, and vibrational (FTIR and FT-Raman) techniques. The conformational properties have been studied by using vibrational spectroscopy [infrared (gaseous, liquid, and Ar matrix isolated), Raman (liquid) spectroscopy] together with quantum chemical calculations at the B3LYP and MP2 methods with the extended 6-311++G** and aug-cc-pVTZ basis sets. Compound I exhibits a conformational equilibrium at room temperature having the most stable form C(s) symmetry with a synperiplanar (syn) orientation of the carbonyl double bond (C=O) with respect to both the CH(3)O- and -SCN groups (syn-syn). Several bands assigned to a second conformer have been observed in the IR matrix spectra. This rotamer presents an antiperiplanar orientation of the thiocyanate group (syn-anti). Evaluating the equilibrium compositions at different temperatures by quenching the gas phase mixtures as Ar matrices allowed us to determine the conformational enthalpy difference DeltaH(0) = H(0)((syn-anti)) - H(0)((syn-syn)) = 0.80(18) kcal mol(-1). A similar conformational behavior has been determined for compound II. Thermodynamic properties were also computed at the high-level G2MP2 and G3 model chemistry methods. The importance of mesomeric (resonance) and anomeric (hyperconjugation) electronic interaction in the conformational behavior is evaluated by using the NBO approach for both species.

Ground state structures of Fe(2)O(4-6)(+) clusters probed by reactions with N(2).

Reactions of small cationic iron oxide clusters (Fe(2)O(4-6)(+)) with N(2) are investigated by experiments and first principle calculations. The cationic iron oxide clusters are generated by reaction of laser ablated iron plasma with O(2) in a supersonic expansion, and are reacted with N(2) in a fast flow reactor at near room temperature conditions. Cluster cations are detected by a time-of-flight mass spectrometer. The substitution reaction Fe(2)O(n)(+) + N(2) --> Fe(2)O(n-2)N(2)(+) + O(2) is observed for n = 5 but not for n = 4 and 6. Density functional theory calculations predict that the low-lying energy structures of Fe(2)O(4-6)(+) are with side-on (eta(1)-O(2)) or end-on (eta(2)-O(2)) bonded molecular oxygen unit(s). The calculations further predict that the substitution of eta(1)-O(2) and eta(2)-O(2) in Fe(2)O(4,6)(+) clusters by N(2) is exothermic and subject to negative and positive overall reaction barriers, respectively, at room temperature. We thus propose that the ground state structures of Fe(2)O(4)(+) and Fe(2)O(6)(+) contain eta(2)-O(2). In contrast, both the experiment and theory favor a eta(1)-O(2) in the ground state structure of Fe(2)O(5)(+).

Matrix photochemistry, photoelectron spectroscopy, solid-phase structure, and ring strain energy of beta-propiothiolactone.

The four-membered heterocyclic beta-propiothiolactone compound was isolated in a low-temperature inert Ar matrix, and the UV-visible (200 < or = lambda < or = 800 nm) induced photochemistry was studied. On the basis of the IR spectra, the formation of methylketene (CH(3)CHCO) was identified as the main channel of photodecomposition. The formation of ethene and thiirane, with the concomitant elimination of OCS and CO, respectively, was also observed as minor decomposition channels. The valence electronic structure was investigated by HeI photoelectron spectroscopy assisted by quantum chemical calculations at the OVGF/6-311++G(d,p) level of theory. The first three bands at 9.73, 9.87, and 12.06 eV are ascribed to the n''(S), n'(O), and pi''(CO) orbitals, respectively, denoting the importance of the -SC(O)- group in the outermost electronic properties. Additionally, the structure of a single crystal, grown in situ, was determined by X-ray diffraction analysis at low temperature. The crystalline solid [monoclinic system, P21/c, a = 8.1062(1) A, b = 10.3069(2) A, c = 10.2734(1) A, beta = 107.628(1) degrees, and Z = 8] consists of planar molecules arranged in layers. The skeletal parameters, especially the valence angles [angleC2-C1-S = 94.55(7) degrees, angleOC-C = 134.20(11) degrees, angleC-S-C = 77.27(5) degrees], differ from those typically found in acyclic thioester compounds, suggesting the presence of strong strain effects. The conventional ring strain energy was determined to be 16.4 kcal/mol at the G2MP2 level of calculation within the hyperhomodesmotic model.

Acetylene cyclotrimerization catalyzed by TiO2 and VO2 in the gas phase: a DFT study.

Density functional theory (DFT) calculations have been used to investigate acetylene cyclotrimerization catalyzed by titanium and vanadium dioxides. The calculated results illustrate that the overall process is highly favorable at room temperature from both thermodynamic and kinetic points of view. The mechanism of C2H2 cyclotrimerization over MO2 (M = Ti, V) can be understood as four steps: (1) a four-membered ring (-O-M-C=C-) formation that coordinates and activates the first C2H2 molecule; (2) the second C2H2 insertion into the M-C bond to form a six-membered ring (-O-M-C=C-C=C-); (3) the third C2H2 insertion into the M-C bond to form an eight-membered ring (-O-M-C=C-C=C-C=C-); and (4) contraction of the eight-membered ring and benzene formation and desorption. All of the reaction steps are overall barrierless with respect to the separated reactants (MO2C2xH2x + C2H2, x = 0, 1, 2). This theoretical study predicts that the M=O double bond in MO2 is very catalytic toward the C2H2 cyclotrimerization. The metal center in this study can be considered always in the same +4 oxidation state (Ti4+ and V4+). In contrast, two-electron cycling of the metal center is present in the documented mechanism for the C2H2 cyclotrimerization. The C2H2 cyclotrimerization over the Ti atom and TiO molecule is also studied, and the documented mechanism applies in this case. The new mechanism is suggested to apply to reactions using titanium and vanadium oxides as catalysts.

Fe3+ and amino functioned mesoporous silica: preparation, structural analysis and arsenic adsorption.

Two novel adsorbents to remove excess arsenate and arsenite in the drinking water were prepared for the first time by grafting monoamine and diamine, respectively, and then coordinating Fe(3+) on silica gel that was obtained using sol-gel method with two-step acid-base catalysis. It was found that both adsorbents had mesoporous structure, large specific surface, and high amino and iron content according to N(2) adsorption isotherms, FTIR, XPS, and NMR analysis. The removal ability and adsorption rate of the adsorbents were very high for both As(V) and As(III). Langmuir and Freundlich models were used to fit the adsorption isotherm and investigate the adsorption mechanism. The effects of chloride and sulfate anion on the removal of arsenate and arsenite for the two adsorbents were also studied.

[Kinetic studies on the gas-phase reactions of NO3 radicals with three cyclic ethers].

Kinetics of the reaction of NO3 radicals with tetrahydrofuran, 1, 3-dioxolane and 1, 4-dioxane at 298 K +/- 1 K and 1.01 x 10(5) Pa were investigated using a relative rate method in a self-made Teflon chamber. The objective of this study was to assess the possible impact of these volatile organic compounds (VOCs) on the environment by studying their atmospheric degradation kinetics. Using gas chromatograph with a flame ionization detector(GC/FID), the measured reaction rate constant for NO3 with tetrahydrofuran was (5.36 +/- 1.93) x 10(-3) cm (molecule x s)(-1), which is in good agreement with the reported values, indicating the reliability of our experiment setup and methods. The reactions of NO3 radicals with 1, 3-dioxolane and 1, 4-dioxane were studied for the first time and the measured rate constants were (1.84 +/- 0.70) x 10(-15) cm3 x (molecule x s)(-1) and (3.20 +/- 0.67) x 10(16) cm3 x (molecule x s)(-1), respectively. The atmospheric lifetimes of these compounds have also been estimated based on the measured rate constants, which indicate that emissions of these compounds may have an impact on regional atmospheric environment.

[Uptake of 3-methyl-3-buten-1-ol into aqueous mixed solution of sulfuric acid and hydrogen peroxide].

Multiphase acid-catalyzed oxidation with hydrogen peroxide (H2O2) has been suggested recently to be a potential route to SOA formation, but the kinetics and chemical mechanism of this process have not been well-known yet. In this work, the uptake of 3-methyl-3-buten-1-ol (MBO331) into aqueous mixed solutions of H2O2, and sulfuric acid (H2SO4) was performed using a rotated wetted-wall reactor coupled to a VUV single-photon ionization time of flight mass spectrometer (VUV-SPI-TOFMS). The reactive uptake coefficients (gamma) were acquired for the first time and the reaction pathways were deduced according to products information. The uptake of MBO331 into H2SO4/H2O2 was fast, resulting in gamma reaching 2.52 x 10(-4)-1.05 x 10(-2) for 40%-60% H2SO4. Acetaldehyde, acetone and 3-methyl-3, 4-expoxybutane-1-ol were suggested as gas-phase products in this process. 3-methyl-3,4-expoxybutane-1-ol can transform into polyhydroxy compounds while the further reactions of the carbonyl products can occur in acidic solution, which may play a role in SOA formation. Thus, the heterogeneous acid-catalyzed oxidation of MBO331 with H2O2 might be a significant contributor to SOA loading.