Heterogeneous Reaction Products Research Articles

Comparison of the heterogeneous reaction of NO2 on the surface of clay minerals and desert dust particles

Mineral particles in air could provide atmospheric chemical reaction interface for gaseous substances and participate in atmospheric chemical reaction process, and affecting the status and levels of gaseous pollutants in air. However, differences of the heterogenous reaction on the surface minerals particles are not very clear. Considering main mineral composition of ambient particles was from dust emission, therefore, typical clay minerals (chlorite, illite) and desert particles (Taklimakan Desert) were selected to analysize chemical reaction of NO2, one of major gaseous pollutants, on mineral particles by using of In-situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) under different condition. And In situ near-ambient pressure X-ray photoelectron spectroscopy (In situ NAP-XPS) was employed to investigate iron (one of the major metals) species variation on the surface of mineral dust particles during the heterogeneous reactions. Our data show that humidity controlled by deuterium oxide (D2O) has a greater effect on chemical reactions compared to light and temperature. Under dry conditions, the amount of heterogeneous reaction products of NO2 on the particles shows Xiaotang dust > chlorite > illite > Tazhong dust regardless of dark or light conditions. In contrast, under humidity conditions, the order of nitrate product quantity under moderate conditions was chlorite > illite > Xiaotang dust > Tazhong dust. In situ NAP-XPS results demonstrate that specie variation of the Fe could promote the heterogenous reactions. These data could provide useful information for understanding the formation mechanism of nitrate aerosols and removal of nitrogen oxides in the atmosphere.

Smog chamber study of secondary organic aerosol formation from gas- and particle-phase naphthalene ozonolysis

Naphthalene (Nap), one of the most abundant PAHs in the atmosphere, has been shown to be an important secondary organic aerosol (SOA) precursor. In this study, the gas- and particle-phases (Suspended Nap-coated polystyrene latex spheres (PSLs) generated by vaporization condensation) Nap ozonolysis were investigated in a 1000 L volume cubic Teflon smog chamber. Gas-phase products and Nap-SOAs were observed from the gas- and particle-phase Nap ozonolysis via homogeneous and heterogeneous reactions, respectively. The time-dependent size distribution and mass concentration of Nap-SOAs were analyzed using a scanning mobility particle sizer and a laboratory-developed single-particle aerosol mass spectrometry (SPAMS) instrument. The chemical components of the homogeneous and heterogeneous reaction products were analyzed on-line by single photo ionization mass spectrometry (SPIMS), SPAMS, as well as by thermal desorption gas chromatograph-mass spectrometry. The results showed that the chemical components of the gas-and particle-phase Nap ozonolysis were essentially the same, with the dominant products being phthalaldehyde, phthalic anhydride, 2-carboxybenzaldehyde, and benzoic acid; Nap-SOA formation was attributed to the formation of new particles as well as the uptake of homogeneous and heterogeneous Nap oxidation products on the gas-phase or/and the particle surface. Based on the online measurement results, the reaction mechanism of Nap-ozonolysis also exhibits an initial carbon atom or double-bond attacks by O3, and kinetic analysis of Nap-coated PSLs ozonolysis shows a heterogeneous reaction rate constant of 2.55E-4 s−1 with R2 = 0.984. This study provides a systematic approach to characterize the chemical and physical properties of the gas- and particle-phase Nap ozonolysis in real time, which will deepen our understanding of the migration and transformation of PAHs in the atmosphere.

On-line study of the influence of seed particle acidity on ozonation reaction of pyrene

Acid-catalyzed heterogeneous reaction can lead to potentially multifold increase in secondary organic aerosol (SOA) generation, which may have a greater impact on climate forcing effects. In this study, single particle aerosol mass spectrometry (SPAMS) and scanning mobility particle sizer (SMPS) were applied to perform an online study of the chemical and physical characteristics of the pyrene-coated inorganic seed particle ozonation in a smog chamber to examine the influence of seed acidity on pyrene-SOA formation. Acidic seed particles are made of ammonium sulfate, ammonium bisulfate and sulfuric acid in different proportions. Fs, the inorganic seed composition number, is defined as a ratio of the molar concentration of SO42− to the total molar concentration of SO42− and NH4+ in this study. Suspended pyrene-coated acidic seed particles were generated by the vaporization-condensation method. Homogeneous and heterogeneous reaction products were identified and assigned. The results show that the seed particle acidity can enhance the mass yield, as well as the chemical diversity of pyrene-SOAs, and also dramatically increase the formation of new smaller particles. Kinetic analysis revealed that the first-order reaction rate constant (K) of acidic seed particles was much higher than that of neutral seed particles, with K values for Fs = 0.77 being 1.47 times that of Fs = 0.50 and 2.58 times that of Fs = 0.33. A mechanism for pyrene-SOA formation was also proposed based on real-time monitoring. For neutral seeds, the pyrene ozonation preferred ‘atom attack’ and mainly formed 1-hydroxypyrene; while for acidic seeds, the pyrene ozonation preferred ‘bond attack’ and formed a Criegee intermediate, followed by broken C–O and C–C bonds, thereby resulting in a variety of semi- and low-volatile products. This study presents a rapid analytical method for the combined use of smog chamber, SPAMS, and SMPS to immediately characterize the effect of seed particle acidity on the formation of polycyclic aromatic hydrocarbon SOA, which may deepen our understanding of new particle formation and particle growth in the atmosphere. Therefore, the present study provides a new insight for an in-depth understanding of haze pollution in China.

Analysis of syngas production and reaction zones in hydrogen oriented underground coal gasification

Underground Coal Gasification (UCG) is an emerging technology that utilizes unmined coals. In UCG process, coal is burned and gasified underground. Produced syngas is collected through drilled wells to be processed or used directly. Syngas comprises mainly CO2, CO, H2 and CH4 and its hydrogen content majorly depends on gasification agents and properties of coal gasified. It is assumed that the combustible components of syngas, such as CO and H2, are products of heterogeneous gasification reactions and oxygen is almost solely consumed by homogeneous combustion reactions of these combustible components. These assumptions are widely used to simplify dynamic UCG models. Here, a lab-scale hydrogen oriented underground coal gasification experiment was performed for Turkish lignite. Using the experimental data, a two-dimensional underground coal gasification computational fluid dynamics (CFD) model was built to investigate cavity formation, reaction zones, reaction rates and the syngas properties. By developing the CFD model, valuable insights regarding which reactions are dominant in which region are gained and UCG process is better understood. Two-stage gasification method was employed in the experiment. Experiments were performed using lignite having high volatile, high ash and moderate moisture contents in a prism-shaped ex-situ reactor. Oxygen and steam were successfully supplied as gasification agents. In the steam-gasification stage with a supply rate of 5 m3/h, hydrogen content and calorific value of syngas were measured up to 40 (vol.) % and 8 MJ/Nm3, respectively. Experimental and CFD model results were compared to validate the mathematical model and assumptions used in UCG syngas production process.

Detecting Intermediates and Products of Fast Heterogeneous Reactions on Liquid Surfaces via Online Mass Spectrometry

One of the research priorities in atmospheric chemistry is to advance our understanding of heterogeneous reactions and their effect on the composition of the troposphere. Chemistry on aqueous surfaces is particularly important because of their ubiquity and expanse. They range from the surfaces of oceans (360 million km2), cloud and aerosol drops (estimated at ~10 trillion km2) to the fluid lining the human lung (~150 m2). Typically, ambient air contains reactive gases that may affect human health, influence climate and participate in biogeochemical cycles. Despite their importance, atmospheric reactions between gases and solutes on aqueous surfaces are not well understood and, as a result, generally overlooked. New, surface-specific techniques are required that detect and identify the intermediates and products of such reactions as they happen on liquids. This is a tall order because genuine interfacial reactions are faster than mass diffusion into bulk liquids, and may produce novel species in low concentrations. Herein, we review evidence that validates online pneumatic ionization mass spectrometry of liquid microjets exposed to reactive gases as a technique that meets such requirements. Next, we call attention to results obtained by this approach on reactions of gas-phase ozone, nitrogen dioxide and hydroxyl radicals with various solutes on aqueous surfaces. The overarching conclusion is that the outermost layers of aqueous solutions are unique media, where most equilibria shift and reactions usually proceed along new pathways, and generally faster than in bulk water. That the rates and mechanisms of reactions at air-aqueous interfaces may be different from those in bulk water opens new conceptual frameworks and lines of research, and adds a missing dimension to atmospheric chemistry.

Sortaggable liposomes: Evaluation of reaction conditions for single-domain antibody conjugation by Sortase-A and targeting of CD11b+ myeloid cells

Active targeting with ligand coated liposomal drug delivery systems is a means to increase the therapeutic index of drugs. Stable ligand coating requires bilayer anchorage of the commonly proteinaceous ligands and hence a conjugation of lipid structures towards amino acids. This often leads to heterogeneous reaction products especially when chemical coupling methods are employed. Chemoenzymatic Sortase-A mediated transpeptidation (sortagging) is a useful tool to avoid this protein heterogeneity through its site-specific, bioorthogonal ligation mechanism. Manufacturing of such sortaggable, pentaglycine modified liposomes was developed by adaption of a scalable solvent injection technique. The pentaglycine liposomes were prepared with different degrees of PEGylation and steric accessibility of the pentaglycine motif. Comparable hydrodynamic diameters (146–188 nm) of the different formulations were obtained after a flow rate screening. The sortagging reactivity of a single-domain antibody (VHH) towards the pentaglycine liposomes was strongly dependent on the steric accessibility of the pentaglycine nucleophile. Adjusting the pentaglycine to ligand ratio improved conversion rates up to 80%. The liposome bound VHH was accessible for its soluble antigen as shown by a chromatography-based binding assay. Mono- and granulocytes could be selectively targeted in vitro by conjugation of BMX1, a VHH directed towards human myeloid cell surface marker CD11b. Confocal microscopy revealed intracellular localization of the targeted liposomes. The developability of those pentaglycine liposomes as well as their proof of principle for targeted drug delivery shows their potential for further investigation, for example as delivery platform for diagnostics or drugs into the tumor microenvironment.

Effect of the Ni coating thickness on laser welding-brazing of Mg/steel

Dissimilar AZ31B-Mg and Ni-coated Q235A-steel alloys were joined in a lap configuration using a laser welding-brazing process. The effects of the Ni coating thickness on the joint appearance, interfacial reactions and mechanical properties were investigated with the assistance of thermodynamic calculations. In the direct irradiation region, Ni atoms diffused and were accumulated near the interface due to the driving force of the chemical potential. Al atoms from the filler were attracted by the concentrated Ni atoms, which resulted in the formation of the FeAl phase. In the middle region and weld toe region, a Fe(Ni) solid solution formed at the interface. Heterogeneous reaction products were produced at the seam near the interface, varying from only the AlNi phase to the AlNi+(α-Mg+Mg2Ni) eutectic with the increase of the coating thickness. Additionally, a bulky Mg2Ni phase also formed in the matrix of Mg-Ni eutectic with a coating thickness of 40 μm. Strong mutual attraction occurred between the Al and Ni atoms at the seam, resulting in a higher driving force for generating the AlNi phase than for generating the Mg-Ni phase. All joints were finally fractured at the seam. The maximum value of the tensile-shear fracture load approached 230 N/mm with a Ni coating thickness of 20 μm, reaching an 88.5% joint efficiency relative to the Mg base metal.

GAS PRODUCTS OF ARGON PLASMA INTERACTION WITH POLYARAMID AND POLY(ETHYLENE TEREPHTHALATE)

Non-equilibrium plasma is widely used for surface modification of polymer materials. Reactions of plasma active species with polymers lead not only to the surface modification, but to the formation of gaseous products, which change the plasma composition and internal plasma parameters. It results in the dependence of surface etching and modification kinetics on the quantity of material been treated (on sample sizes in a reactor). These phenomena are known as so called “loading effect” and have been studied for the treatment of polypropylene and polyimide films, poly(ethylene terephthalate) films and fabrics in oxygen and air plasma. It can be expected that gas products of noble gas plasma action on polymers will change strongly plasma parameters and modification results. In this paper, experimental data are represented on composition of gas products and their evolution rates at the treatment of polyaramid films, fibers and poly(ethylene terephthalate) fabric in low-pressure argon plasma. Poly(ethylene terephthalate) textile fabric (PET) made of monofilament yarns (SAATI, S.p.A., Italy) and polyaramide (PA) films and complex yarns “Rusar®” (Termotex, Russia) were used in experiments. Direct current discharge was excited in a flow of argon (technical grade) in a glass tube reactor with 3 cm inner diameter. Fabric samples were placed as cylinders on the reactor wall in the discharge positive column. Square of PET samples was varied from 18 to 111 cm2. The PA yarns with the total length of 550 or 1020 cm were placed in the reactor on special holder with the length of 20 cm. Total gas pressure in reactor was varied from 30 to 300 Pa at discharge current of 20 – 110 mA. Gas flow rate in the reactor was kept constant and equal to 30 cm´s-1. Gas phase analysis was carried out by the methods of plasma emission spectroscopy and mass-spectrometry. Plasma emission spectra and mass-spectra show evolution of H2, CO and H2O molecules at the treatment of PA and PET in argon plasma. Evolution rates for different gas products and their mole fractions have been obtained as functions of total gas pressure. Increase in polymer sample square has been shown to result in changing the ratios between evolution rates for different gas products. Sum of CO, H2 and H2O mole fractions increases with polymer sample square and decreases with gas pressure. Dissociation of molecular gas products results in the changing plasma active species. Oxygen and hydrogen atom lines and OH emission bands are observed in plasma emission spectra. Alteration of intensity ratio for О(3p3P ® 3s3S0) and Ar (4p3D3 ® 4s3P2) lines (IO/IAr) versus time after discharge starting shows the possible participation of oxygen atoms in heterogeneous reactions with polymers. Evolution of molecular gas products of heterogeneous reactions influences plasma properties and rates of plasma chemical reactions. The data obtained will be used for the further analysis of mechanisms of heterogeneous reactions of plasma active species with polymers.

The effect of gas-phase polycyclic aromatic hydrocarbons on the formation and properties of biogenic secondary organic aerosol particles.

When secondary organic aerosol (SOA) particles are formed by ozonolysis in the presence of gas-phase polycyclic aromatic hydrocarbons (PAHs), their formation and properties are significantly different from SOA particles formed without PAHs. For all SOA precursors and all PAHs, discussed in this study, the presence of the gas-phase PAHs during SOA formation significantly affects particle mass loadings, composition, growth, evaporation kinetics, and viscosity. SOA particles formed in the presence of PAHs have, as part of their compositions, trapped unreacted PAHs and products of heterogeneous reactions between PAHs and ozone. Compared to 'pure' SOA particles, these particles exhibit slower evaporation kinetics, have higher fractions of non-volatile components, like oligomers, and higher viscosities, assuring their longer atmospheric lifetimes. In turn, the increased viscosity and decreased volatility provide a shield that protects PAHs from chemical degradation and evaporation, allowing for the long-range transport of these toxic pollutants. The magnitude of the effect of PAHs on SOA formation is surprisingly large. The presence of PAHs during SOA formation increases mass loadings by factors of two to five, and particle number concentrations, in some cases, by more than a factor of 100. Increases in SOA mass, particle number concentrations, and lifetime have important implications to many atmospheric processes related to climate, weather, visibility, and human health, all of which relate to the interactions between biogenic SOA and anthropogenic PAHs. The synergistic relationship between SOA and PAHs presented here are clearly complex and call for future research to elucidate further the underlying processes and their exact atmospheric implications.

Chemisorption binding of gold(III) from solutions with bismuth dipropyldithiocarbamate: Supramolecular self-assembly (role of the secondary Au…S and aurophilic interactions) and thermal behavior of the solvated heteropolynuclear ionic type complex ([Au{S2CN(C3H7)2}2]3[Bi2Cl9] • 0.5CO(CH3)2 • 0.5HCl) n

The reaction of binuclear bismuth(III) N,N-dipropyldithiocarbamate [Bi2{S2CN(C3H7)2}6] with a solution of AuCl3 in 2 M HCl was studied. Crystallization of the heterogeneous reaction products from an acetone solution afforded the polymeric solvated heteropolynuclear gold(III)–bismuth complex, ([Au{S2CN(C3H7)2}2]3[Bi2Cl9] · 1/2CO(CH3)2 · 1/2HCl)n (I). According to X-ray diffraction data (CIF file CCDC no. 1050766), the structure of I comprises four isomeric [Au{S2CN(C3H7)2}2]+ cations in 1: 1: 2: 2 ratio, namely: cation “A” with the Au(1) atom, cation “B” with the Au(2) atom, cation “C” with the Au(3) atom, and cation “D” with the Au(4) atom, and the discrete binuclear [Bi2Cl9]3– anions. The isomeric gold(III) complex cations are involved in the construction of two types of cationic triads, [“C”···“A”···“C”] and [“D”···“B”···“D”], through secondary bonds and short Au···S contacts. The cation types differ by both the nature of binding and the Au–Au distances. The weak aurophilic binding between the cationic triads (Au···Au 3.5416(2) A) gives rise to zigzag-like polymeric chains (···[“C”···“A”···“C”]···[“D”···“B”···“D”]···)n extended along the y axis. In turn, the [Bi2Cl9]3– anions located on one side of polymer chains are held by the secondary Cl···S bonds. The outer-sphere CO(CH3)2 and HCl solvate molecules joined by hydrogen bonds are located in the space between bismuth anions. The thermal behavior of I was studied by simultaneous thermal analysis. The thermal destruction of the complex includes desolvation and thermolysis of the dithiocarbamate moiety and [Bi2Cl9]3– with liberation of gold metal and bismuth chloride (which is subsequently evaporated) and partial formation of Bi2S3. In the temperature range of 712–828°C, bismuth sulfide is oxidized to (BiO)2SO4, which decomposes above 828°C to give Bi2O3. Bismuth(III) oxide and reduced gold are the final products of thermal transformations.

A New Method of Synthesis Carbon with Onion-Like Structure with High (10-13%) Content of Nitrogen from Pyridine

The new method of pyridine pyrolysis is created, the some part of pyrolytic soot of which contains onion-similar carbon with high (10-13%) contents of nitrogen (or “pyridine carbon”). Nanoparticles of this “pyridine carbon” are formed only in a gas phase at the expense of reactions of polymerization and polycondensation of molecules of pyridine and by reactionary flow in a low-temperature zone of reactionary space are taken out. Onion-structures of the greater size and with the small contents of nitrogen (~1.0 %) together with nanotubes and filaments are products of heterogeneous reactions between carbon fragments of destruction of pyridine molecules, which mainly on the most high-temperature surface of quartz reactor are carried out. Nitrogen-containing fragments of a destruction of a molecule С 5 H 5 N mainly as НCN in a gas flow from sphere of reaction are removed. The growth of carbon nanostructures is realized at the expense of heterogeneous reactions but in absence of the metallic catalyst. The products were characterized by methods X-ray photoelectron and IR spectroscopy, scanning, transmission and high resolution transmission electron microscopy, X-ray diffraction and chemical analysis.

Kinetics and Products of Heterogeneous Reaction of HONO with Fe2O3 and Arizona Test Dust.

Kinetics and products of the reaction of HONO with solid films of Fe2O3 and Arizona Test Dust (ATD) were investigated using a low pressure flow reactor (1 - 10 Torr) combined with a modulated molecular beam mass spectrometer. The reactive uptake of HONO was studied as a function of HONO concentration ([HONO]0 = (0.6 - 15.0) × 10(12) molecules cm(-3)), relative humidity (RH = 3 × 10(-4) - 84.1%) and temperature (T = 275 - 320 K). Initial reactive uptake coefficients were found to be similar under dark conditions and in the presence of UV irradiation (JNO2 = 0.012 s(-1)) and independent of the HONO concentration and temperature. In contrast, the relative humidity (RH) was found to have a strong impact on the uptake coefficients: γ (ATD) = 3.8 × 10(-6) (RH)(-0.61) and γ (Fe2O3) = 1.7 × 10(-6) (RH)(-0.62) (γ calculated with BET surface area, 30% conservative uncertainty). In both reactions of HONO studied, NO2 and NO were observed as gaseous products with yields of (60 ± 9) and (40 ± 6) %, respectively, independent of relative humidity, temperature, concentration of HONO and UV irradiation intensity. The observed data point to minor importance of the HONO uptake on mineral aerosol compared with other known sinks of HONO in the atmosphere, which are its dry deposition and photolysis in night-time and during the day, respectively.

Fast Mapping of Biomolecular Interfaces by Random Spin Labeling (RSL)

Random spin labeling (RSL) is a method for rapid mapping of biomolecular interaction surfaces using an interaction partner with SL and an interaction partner enriched in 13C or 15N nuclei for paramagnetic relaxation enhanced NMR-based detection. The SL reaction is conducted in a manner resulting in a heterogeneous reaction product consisting of different populations of the protein carrying a varying number of spin labels at different positions. Preparation of the paramagnetic probe is complete within a few hours and hence much faster than site selective SL. RSL is applicable to tightly interacting systems but shows its particular strength when applied to systems involving weak or transient contacts.

Capillary Electrophoresis Assisted Flow System for In Situ Analysis of Products of Heterogeneous Electrocatalytic and Catalytic Processes: Application to the Oxidation of Glycerol

AbstractAnalysis by capillary electrophoresis (CE) of nanoliter samples taken 0.05 mm away from the electrode/solution interface assisted in the evaluation of glycerol electrooxidation on noble metals (Pt, Au and Pd). The fully automated all electrochemical flow system generates a conductometric electropherogram every few minutes, while exploring experimental parameters. Products like glycerate, glycolate, formate and hydroxymalonate were observed in different ratios by changing the electrocatalyst and the applied potential. On Pd, dissolved oxygen oxidizes glycerol at zero current. This new approach holds promise for fast in situ study of reaction products of heterogeneous catalysis reactions and electrode processes in general.

Heterogeneous reaction of formaldehyde on the surface of γ-Al2O3 particles

Abstract Formaldehyde is one of the most important carbonyl organic compounds. Heterogeneous reactions of formaldehyde on the surface of oxides of crustal elements could be an important sink for formaldehyde in the atmosphere. In this study, the kinetics of the heterogeneous reaction of formaldehyde on the surface of γ-Al 2 O 3 was investigated in situ by diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) combined with ion chromatography (IC), X-ray diffraction (XRD), and field emission environmental scanning electron microscope (ESEM). The adsorbed species, formate, dioxymethylene, polyoxymethylene, and formaldehyde, on γ-Al 2 O 3 particles, were identified by infrared spectroscopy. On the surface of γ-Al 2 O 3 particles, formaldehyde is first oxidized to dioxymethylene, which is further oxidized to formate. The reaction order was determined as 0.74 ± 0.05, and the initial reactive uptake coefficients at room temperature were calculated with the geometric and Brunauer–Emmett–Teller specific surface areas as (3.6 ± 0.8) × 10 −4 and (1.4 ± 0.31) × 10 −8 , respectively. The influences of oxygen concentration, humidity, and temperature on the reaction products and reactive uptake coefficients were studied. The results indicated the reaction is independent of the O 2 concentration within the range used in this experiment, and humidity is negatively correlated with the uptake of formaldehyde by the particles. Temperature not only plays a role on the heterogeneous reaction products but also is positively correlated with the uptake rate of formaldehyde by γ-Al 2 O 3 particles in the troposphere. The apparent activation energy of the reaction was determined.

Characteristics of a Confined Impinging Jet Reactor: Energy Dissipation, Homogeneous and Heterogeneous Reaction Products, and Effect of Unequal Flow

The confined impinging jet reactor (CIJR) has attracted wide interest in the past few years because of the efficient micromixing that it offers. In this work, the CIJR is characterized over a wide range of mixing conditions, using three measures of performance: estimates of the energy dissipation rate, micromixing efficiency based on the yield of a homogeneous reaction, and particle size resulting from a heterogeneous precipitation reaction. The energy dissipation results showed very good agreement between four methods, with values up to 100 times greater than those observed in stirred tanks. The reactions showed a higher sensitivity to mixing conditions at higher concentrations, with less effect of mixing at high flow rates. The operation of the CIJR was very robust to changes in flow rate, with stable performance for up to a 30% difference in the inlet flows.

Influence of dust composition on cloud droplet formation

Previous studies suggest that interactions between dust particles and clouds are significant; yet the conditions where dust particles can serve as cloud condensation nuclei (CCN) are uncertain. Since major dust components are insoluble, the CCN activity of dust strongly depends on the presence of minor components. However, many minor components measured in dust particles are overlooked in cloud modeling studies. Some of these compounds are believed to be products of heterogeneous reactions involving carbonates. In this study, we calculate Kohler curves (modified for slightly soluble substances) for dust particles containing small amounts of K +, Mg 2+, or Ca 2+ compounds to estimate the conditions where reacted and unreacted dust can activate. We also use an adiabatic parcel model to evaluate the influence of dust particles on cloud properties via water competition. Based on their bulk solubilities, K + compounds, MgSO 4·7H 2O, Mg(NO 3) 2·6H 2O, and Ca(NO 3) 2·4H 2O are classified as highly soluble substances, which enable activation of fine dust. Slightly soluble gypsum and MgSO 3·6H 2O, which may form via heterogeneous reactions involving carbonates, enable activation of particles with diameters between about 0.6 and 2 μm under some conditions. Dust particles>2 μm often activate regardless of their composition. Only under very specialized conditions does the addition of a dust distribution into a rising parcel containing fine (NH 4) 2SO 4 particles significantly reduce the total number of activated particles via water competition. Effects of dust on cloud saturation and droplet number via water competition are generally smaller than those reported previously for sea salt. Large numbers of fine dust CCN can significantly enhance the number of activated particles under certain conditions. Improved representations of dust mineralogy and reactions in global aerosol models could improve predictions of the effects of aerosol on climate.

Investigating the composition of organic aerosol resulting from cyclohexene ozonolysis: low molecular weight and heterogeneous reaction products

Abstract. The composition of organic aerosol formed from the gas phase ozonolysis of cyclohexene has been investigated in a smog chamber experiment. Comprehensive gas chromatography with time of flight mass spectrometric detection was used to determine that dicarboxylic acids and corresponding cyclic anhydrides dominated the small gas phase reaction products found in aerosol sampled during the first hour after initial aerosol formation. Structural analysis of larger more polar molecules was performed using liquid chromatography with ion trap tandem mass spectrometry. This indicated that the majority of identified organic mass was in dimer form, built up from combinations of the most abundant small acid molecules, with frequent indication of the inclusion of adipic acid. Trimers and tetramers potentially formed via similar acid combinations were also observed in lower abundances. Tandem mass spectral data indicated dimers with either acid anhydride or ester functionalities as the linkage between monomers. High-resolution mass spectrometry identified the molecular formulae of the most abundant dimer species to be C10H16O6, C11H18O6, C10H14O8 and C11H16O8 and could be used in some cases to reduce uncertainty in exact chemical structure determination by tandem MS.

Markers of heterogeneous reaction products in α-pinene ozone secondary organic aerosol

A gas chromatograph iontrap mass spectrometer (GC-ITMS) was used to analyze the gas-and particle-phase products of α-pinene ozone oxidation in the presence of three different inorganic seed aerosols: sodium chloride, ammonium sulfate only, and ammonium sulfate with sulfuric acid. Products of α-pinene ozone oxidation common to the literature showed little difference in gas or particle-phase concentrations between seed types within the precision of the measurements even though significantly different aerosol yields were found between seed types. Small amounts of ring-opening products of four-membered cyclic oxygenates and markers of aldol condensation products were tentatively identified in the particle-phase for all seed types. These tentatively identified products are thought to be the result of acid-catalyzed heterogeneous reactions in the particle-phase or during sampling processes or analysis. The mechanisms for their formation are also proposed in this study.

Desorption Dynamics of the Products of Heterogeneous Catalytic Reactions

A review of experimental data on the desorption of excited molecules that are the products of heterogeneous catalytic reactions is given. It is shown that the sharply peaked spatial distributions of desorption flows (SDDFs) are observed in many systems. The translational energies of the products (T tr) are much higher than the surface temperatures. A correlation of SDDF parameters and T tr is found. The excitation of internal degrees of freedom (vibrations and rotations) is weaker. The vibrational and rotational temperatures (T vib and T rot) obey the following inequalities: T tr > T vib > T rot or T tr ≥ T vib > T rot, and T rot ≈ T surf. Models for the description of the desorption of excited molecules are considered. New data on the active sites for anisotropic and stepped surfaces, from which desorption occurs, are discussed.