Sulfate Molar Ratio Research Articles

Fabrication and characterization of starch films containing chitosan nanoparticles using in situ precipitation and mechanoactivation techniques

The aim of this work is to introduce a new environmentally friendly process for the production of starch films containing submicron chitosan particles using mechanoactivated in situ precipitation in the presence of magnesium sulfate as a crosslinker. Mechanoactivation in the rotor-stator device ensures the destruction of swollen starch granules and the embedding of simultaneously formed particles in a gel structure, which prevents their aggregation. The influence of the chitosan: sulfate molar ratio (1.0 and 0.7) on the rheological and film-forming properties of dispersions was evaluated. The composite films were characterized using optical and AFM microscopy and X-ray diffraction. The tensile properties and moisture resistance of the films were also studied. An increase in the particle concentration to 10% had almost no effect on the strength of the films, but caused a 4 time increase, on average, in the elongation. The composite films were smooth, uniformly translucent, and had lower moisture absorption and water vapor permeability than the films made from starch alone.

Global modeling of heterogeneous hydroxymethanesulfonate chemistry

Abstract. Hydroxymethanesulfonate (HMS) has recently been identified as an abundant organosulfur compound in aerosols during winter haze episodes in northern China. It has also been detected in other regions although the concentrations are low. Because of the sparse field measurements, the global significance of HMS and its spatial and seasonal patterns remain unclear. Here, we modify and add to the implementation of HMS chemistry in the GEOS-Chem chemical transport model and conduct multiple global simulations. The model accounts for cloud entrainment and gas–aqueous mass transfer within the rate expressions for heterogeneous sulfur chemistry. Our simulations can generally reproduce quantitative HMS observations from Beijing and show that East Asia has the highest HMS concentration, followed by Europe and North America. The simulated HMS shows a seasonal pattern with higher values in the colder period. Photochemical oxidizing capacity affects the competition of formaldehyde with oxidants (such as ozone and hydrogen peroxide) for sulfur dioxide and is a key factor influencing the seasonality of HMS. The highest average HMS concentration (1–3 µg m−3) and HMS ∕ sulfate molar ratio (0.1–0.2) are found in northern China in winter. The simulations suggest that aqueous clouds act as the major medium for HMS chemistry while aerosol liquid water may play a role if its rate constant for HMS formation is greatly enhanced compared to cloud water.

Spatial and temporal variations of atmospheric chemical condition in the Southeastern U.S.

Animal feeding operations (AFOs) are the largest ammonia (NH3) emission sources in the United States (U.S.). However, the impact of NH3 emissions from AFOs on the formation of secondary inorganic PM2.5 (iPM2.5) has not been well understood and systematically assessed. Under the Southeastern Aerosol Research and Characterization (SEARCH) Network, the hourly concentrations of iPM2.5 chemical compositions and its precursor gases as well as meteorological data were measured at eight urban/nonurban sites labeled as JST/YRK, BHM/CTR, GFP/OAK, and PNS/OLF during 1998–2016. Using the SEARCH data, this research investigated the spatiotemporal variations of atmospheric chemical conditions in those rural and urban areas. The spatiotemporal variations of atmospheric chemical conditions at the eight sites are characterized by four parameters, including (1) gas ratio (GR), (2) gas-phase NH3 molar fraction (NH3/NHx), (3) total available NH3 (gaseous ammonia + aerosol ammonium) to sulfate (SO42−) molar ratio (TA/TS), and (4) PM2.5 ammonium + nitrate to total PM2.5 mass ratio (AN/PM2.5). Results indicate that the NH3 emissions from AFOs may explain the greater values of GR, NH3/NHx, and TA/TS in the wind directions coming from AFOs at YRK and OAK rural sites than the other wind directions. In the wind directions coming from AFOs at YRK and OAK, NH3 was in excess of fully neutralizing acidic gases, more NH3 stayed in gas phase than those in other wind directions, and both ammonium sulfate and ammonium nitrate existed in iPM2.5. The upward trend in NH3/NHx indicates that gas-particle partitioning ofNH3–NH4+shifted toward gas phase, while the downward trend in AN/PM2.5 may implicate that smaller fraction of PM2.5 was directly NH3 sensitive. Understanding of the spatiotemporal variations of atmospheric chemical condition provides insights to improve our understanding of iPM2.5 formation under rural and urban conditions, the reduction in sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions resulted in the reduction of iPM2.5 formation despite the increase in NH3 emissions in the Southeastern U.S.

How aerosol pH responds to nitrate to sulfate ratio of fine-mode particulate.

Aerosol acidity (pH), one of key properties of fine-mode particulate (PM2.5), depends largely on nitrate and sulfate in particle. The mass contribution of nitrate relative to sulfate in PM2.5 has tended to increase in many regions globally, but how this change affects aerosol pH remains in debate. In this way, we measured PM2.5 ionic species and oxygen isotopic composition of nitrate in the eastern China, and predicted aerosol pH using the ISORROPIA-II model. When nitrate to sulfate molar ratio increases and thus PM2.5 is gradually enriched in ammonium nitrate (NH4NO3), aerosol pH tends to increase. The oxidation of nitrogen dioxide (NO2) by hydroxyl radical is responsible for most of nitrate formation (generally above 60%). These indicate that nitrate formation through gas-to-particle conversion involving ammonia and nitric acid results in increasing aerosol pH with increasing molar ratio of nitrate to sulfate. Conversely, aerosol pH is expected to decrease with increasing relative abundance of nitrate as ammonia emissions are lowered. Our research concludes that it should be considered to reduce aerosol NH4NO3 by reducing the precursors of nitric oxide and ammonia emissions, to substantially improve the air quality (i.e., reduce PM2.5 levels and potential nitrate deposition) in China.

Optimized Methods for the Production and Bioconjugation of Site-Specific, Alkyne-Modified Glucagon-like Peptide-1 (GLP-1) Analogs to Azide-Modified Delivery Platforms Using Copper-Catalyzed Alkyne-Azide Cycloaddition.

This study aimed to develop and optimize chemistries to produce alkyne-modified glucagon-like peptide-1(7-36)-amide (GLP-1(7-36)-NH2) libraries, which could be rapidly and efficiently conjugated to other components and screened to identify compounds with the best drug delivery properties, as potential treatments for type 2 diabetes or obesity. For this purpose, the Lys26 (K26) side-chain, and the amino (N)- and carboxy (C)-termini of a dipeptidyl peptidase 4 (DPPIV)-resistant GLP-1 sequence (GLP-1(7-36;A8G)-NH2), were modified with an alkyne (4-pentynoic acid or propiolic acid). These analogs were characterized with respect to human GLP-1 receptor (hGLP-1R) agonist activity, effects on cell viability and human serum stability, revealing that these modifications maintained low (N-terminal; EC50 1.5 × 10-9 M) to subnanomolar (C-terminal and K26, ∼4 × 10-10 M) agonist activity toward hGLP-1, had no effect on cell viability, and for the N-terminal and K26 modifications, increased human serum proteolytic stability (t1/2 > 24 h). Copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction conditions were investigated using the C-terminal modified GLP-1 analog and an azide-modified model lipid peptide, with respect to the effects of altering the azide/alkyne ratio, cosolvents, temperature, reducing agents, Cu(I)-stabilizing ligand, copper source, and the concentrations of reagents/reactants, in order to identify general conditions that provide fast reactions and high yields. A 1:2 azide-alkyne (lipid:GLP-1 peptide) and 4:1 sodium ascorbate/copper sulfate molar ratio in 65% v/v DMSO-water at room temperature, in the absence of Cu(I)-stabilizing ligands (THPTA or l-histidine) and buffers (phosphate, pH 7), provided the best yields. This work reports a library of characterized GLP-1 analogs and chemistries for their attachment to other species, providing useful tools to improve GLP-1 delivery and pharmacology (e.g., through conjugation to other species that lower blood glucose, increase the duration of action, or enable delivery via a nonparenteral route).

Pollution sources of atmospheric fine particles and secondary aerosol characteristics in Beijing

To investigate the secondary formation and pollution sources of atmospheric particles in urban Beijing, PM2.5 and its chemical components were collected and determined by URG-9000D ambient ion monitor (AIM) from March 2016 to January 2017. Among water-soluble ions (WSIs), NO3−, SO42- and NH4+ (SNA) had the largest proportion (77.8%) with the total concentration of 23.8 μg/m3. Moreover, as fine particle pollution worsened, the NO3−, SO42- and NH4+ concentrations increased basically, which revealed that secondary aerosols were the main cause of particle pollution in Beijing. Furthermore, the particle neutralization ratio (1.1), the ammonia to sulfate molar ratio (3.4) and the nitrate to sulfate molar ratio (2.2) showed that secondary aerosols are under ammonium-rich conditions with the main chemical forms of NH4NO3 and (NH4)2SO4, and vehicle emission could be the main anthropogenic source of secondary aerosols in Beijing. Source analysis further indicated that secondary aerosols, solid fuel combustion, dust and marine aerosol were the principal pollution sources of PM2.5, accounting for about 46.1%, 22.4% and 13.0%, respectively, and Inner Mongolia and Hebei Provinces could be considered as the main potential sources of PM2.5 in urban Beijing. In addition, secondary formation process was closely related with gaseous precursor emission amounts (SO2, NO2, NH3 and HONO), atmospheric ozone concentration (O3), meteorological conditions (temperature and relative humidity) and particle components. Sensitive analysis of the thermodynamic equilibrium model (ISORROPIA II) revealed that controlling total nitrate (TN) is the effective measure to mitigate fine particle pollution in Beijing.

Study of using light-burned dolomite ores as raw material to produce magnesium oxysulfate cement

Magnesium oxysulfate cement (MOS) prepared by light-burned dolomite has excellent performance in terms of light weight, high strength and low carbon dioxide emission. In this research, dolomite ores are used to produce MOS cement at different calcination temperatures and calcination times; the parameters investigated are the rate of loss on ignition, free lime (f-CaO), dihydrate gypsum (CaSO4×2H2O) and impact of active magnesium oxide (α-MgO) content exerted on the setting time and compressive strength of the MOS cement. X-ray diffraction analysis, scanning electron microscopy, the time of colour change for citric acid and hydration-heat release rate were adopted to assess the effects of calcination temperature, calcination time and the molar ratio of α-magnesium oxide/magnesium sulfate on the MOS cement. The experimental results showed that the MOS cement prepared by dolomite ores at the calcination temperature of 850°C for 30 min with the α-magnesium oxide/magnesium sulfate molar ratio of 4 demonstrates better mechanical properties than those made in other circumstances. In addition, the main strength phase of MOS cement with tri-sodium citrate dihydrate (Na3C6H5O7·2H2O) generated by light-burned dolomite ores is the needle-like 5Mg(OH)2·MgSO4·7H2O crystal phase.

Effect of the aniline hydrochloride hydrotrope on the microstructure of SDS/water system: Linear rheological behavior

In this work, the linear viscoelastic properties of the sodium dodecylsulfate/aniline hydrochloride/water system were examined in detail as a function of aniline hydrochloride (AHC) to sodium dodecyl sulfate (SDS) molar ratio (R=[AHC]/[SDS]), SDS concentration and temperature. SDS aqueous solutions undergo a structural transition from sphere to rodlike micelles and subsequently to a viscoelastic network of wormlike micelles induced by the hydrotrope AHC at low and intermediate R molar ratios (i.e., R=0.1–0.6 for 5wt.% SDS), which screens the repulsions between the neighboring charged head groups. The rheological response indicates that at low R molar ratios and constant surfactant concentration, the rheological behavior of the system is predominantly viscous (G′<G″). However, upon increasing R, the elastic behavior predominates (G′>G″) and a maximum of the absolute value of the zero frequency complex viscosity (|η0*|) is observed, which suggest that the micellar length also goes through a maximum. The region of the elastic behavior diminishes at even greater R molar ratios and a predominantly viscous behavior appears again. This drop in |η0*| can be attributed to the transition from linear to branched wormlike micelles that conform the tridimensional viscoelastic network. The dynamic behavior of the system was analyzed in terms of the Granek-Cates theory, which indicates that the viscoelastic network is in the slow-breaking limit. Under these conditions, reptation is found to be the controlling relaxation mechanism for this system.

The Effect of Aniline Hydrochloride Hydrotrope on the Phase Behavior of SDS/Water System

AbstractThe aim of this work was to determine the detailed phase behavior of the sodium dodecyl sulfate/aniline hydrochloride/water system as a function of concentration of sodium dodecyl sulfate (SDS), aniline hydrochloride (AHC) to sodium dodecyl sulfate molar ratio (R = [AHC]/[SDS]) and temperature. Phase behavior information was obtained via polarizing microscopy, differential scanning calorimetry (DSC), cryo‐scanning electron microscopy (Cryo‐SEM) and oscillatory linear rheological measurements with good agreement among these techniques. It is well known that SDS in water forms spherical micelles at concentrations lower than 40 wt% and temperatures above its Krafft temperature (Tk = 16–21 °C). In this region, the SDS/water system exhibits Newtonian rheological behavior, which is characteristic of spherical micellar solutions. The addition of the hydrotrope, aniline hydrochloride, to SDS aqueous solutions produces a viscosity increase in this system as R augments, and a maximum of about five orders of magnitude was found at R = 0.47 for 5 wt% SDS at 20 °C. Moreover, the system shows a transition from viscous to strong viscoelastic behavior. These changes in the rheological behavior are produced by the transitions from sphere to rodlike micelles, which are induced by the hydrophobicity of AHC causing it to be absorbed into the core and the hydrophilic interface of the micelles, which screens the repulsions between the charged head groups.

The "Parade Blue": effects of short-term emission control on aerosol chemistry.

The strict control on emissions implemented in Beijing, China, during the 2015 China Victory Day Parade (V-day Parade) to commemorate the 70(th) Anniversary of Victory in World War II, provided a good opportunity to investigate the relationship between emission sources and aerosol chemistry in a heavily polluted megacity. From August 11 to September 3, 2015, an Aerosol Chemical Speciation Monitor was deployed in urban Beijing, together with other collocated instruments, for the real-time measurement of submicron aerosol characteristics. The average PM1 mass concentration was 11.3 (±6.7) μg m(-3) during the V-day Parade, 63.5% lower than that before the V-day Parade. Differently to the relatively smaller decrease of organics (53%), secondary inorganic aerosols (sulfate, nitrate and ammonium) showed significant reductions of 65-78% during the V-day Parade. According to the positive matrix factorization results, primary organic aerosol (POA) from traffic and cooking emissions decreased by 41.5% during the parade, whereas secondary organic aerosol (SOA) presented a much greater reduction (59%). The net effectiveness of emission control measures was investigated further under comparable weather conditions before and during the parade. By excluding the effects of meteorological parameters, the total PM1 mass was reduced by 52-57% because of the emission controls. Although the mass concentrations of aerosol species were reduced substantially, the PM1 bulk composition was similar before and during the control period as a consequence of synergetic control of various precursors. The emission restrictions also suppressed the secondary formation processes of sulfate and nitrate, indicated by the substantially reduced SOR and NOR (molar ratios of sulfate or nitrate to the sums of the sulfate and SO2 or nitrate and NO2) during the event. The study also explored the influence of emission controls on the evolution of organic aerosol using the mass ratios of SOA/POA and oxygen-to-carbon ratios. The results showed that for northwesterly airflows, emission restrictions during the V-day Parade also reduced the oxidation degree of organic aerosol.

Characterization of aerosol composition, concentrations, and sources at Baengnyeong Island, Korea using an aerosol mass spectrometer

To improve understanding of the sources and chemical properties of particulate pollutants on the western side of the Korean Peninsula, an Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) measured non-refractory fine (PM1) particles from May to November, 2011 at Baengnyeong Island, South Korea. Organic matter and sulfate were generally the most abundant species and exhibited maximum concentrations of 36 μg/m3 and 39 μg/m3, respectively. Nitrate concentrations peaked at 32 μg/m3 but were typically much lower than sulfate and organic matter concentrations. May, September, October, and November featured the highest monthly average concentrations, with lower concentrations typically observed from June through August. Potential source contribution function (PSCF) analysis and individual case studies revealed that transport from eastern China, an area with high SO2 emissions, was associated with high particulate sulfate concentrations at the measurement site. Observed sulfate aerosol sometimes was fully neutralized by ammonium but often was acidic; the average ammonium to sulfate molar ratio was 1.49. Measured species size distributions revealed a range of sulfate particle size distributions with modes between 100 and 600 nm. Organic aerosol source regions were widespread, including contributions from eastern China and South Korea. Positive matrix factorization (PMF) analysis indicated three “factors,” or types of organic aerosol, comprising one primary, hydrocarbon-like organic aerosol (HOA) and two oxidized organic aerosol (OOA) components, including a more oxidized (MO-OOA) and a less oxidized (LO-OOA) oxidized organic aerosol. On average, HOA and OOA contributed 21% and 79% of the organic mass (OM), respectively, with the MO-OOA fraction nearly three times as abundant as the LO-OOA fraction. Biomass burning contributions to observed OM were low during the late spring/early summer agricultural burning season in eastern China, since airflow into eastern China during the Asian Monsoon generally prevents transport of emissions eastward to the Korean Peninsula. Concentrations of the m/z 60 AMS biomass burning marker were more abundant in autumn, when transport patterns appeared to bring some smoke from fires in northern Asia to the island.

Recovery of rare earth from ion-adsorption rare earth ores with a compound lixiviant

The present research investigates the use of ammonium nitrate and ammonium sulfate as a compound lixiviant, and ammonium acetate as an inhibitor for aluminum in the recovery of rare earth elements from ion-adsorption rare earth ores. It is previously shown that rare earth ions, adsorbed physically on ion-adsorption rare earth ores, could be easily recovered via an ion exchange mechanism with inorganic monovalent salt solutions. A standardized desorption procedure was established to systematically investigate the effects of elution conditions such as compound lixiviant concentration, ammonium nitrate/ammonium sulfate molar ratio, particle size, elution flow rate, pH and inhibitor concentration on the leaching of rare earth and aluminum. It was determined that the leaching rate of rare earth exceeded 80% under the optimum elution conditions: particle size <74μm, compound lixiviant concentration 2.0%, ammonium nitrate/ammonium sulfate molar ratio 4:1, pH 5.5, ammonium acetate concentration 0.05%, elution flow-rate 0.5ml/min and room temperature. At these conditions, the inhibition rate of aluminum exceeded 80%.

Using hourly measurements to explore the role of secondary inorganic aerosol in PM2.5 during haze and fog in Hangzhou, China

This paper explores the role of the secondary inorganic aerosol (SIA) species ammonium, NH 4 + , nitrate, NO 3 − , and sulfate, SO 4 2− , during haze and fog events using hourly mass concentrations of PM2.5 measured at a suburban site in Hangzhou, China. A total of 546 samples were collected between 1 April and 8 May 2012. The samples were analyzed and classified as clear, haze or fog depending on visibility and relative humidity (RH). The contribution of SIA species to PM2.5 mass increased to ∼50% during haze and fog. The mass contribution of nitrate to PM2.5 increased from 11% during clear to 20% during haze episodes. Nitrate mass exceeded sulfate mass during haze, while near equal concentrations were observed during fog episodes. The role of RH on the correlation between concentrations of SIA and visibility was examined, with optimal correlation at 60%–70% RH. The total acidity during clear, haze and fog periods was 42.38, 48.38 and 45.51 nmol m−3, respectively, indicating that sulfate, nitrate and chloride were not neutralized by ammonium during any period. The nitrate to sulfate molar ratio, as a function of the ammonium to sulfate molar ratio, indicated that nitrate formation during fog started at a higher ammonium to sulfate molar ratio compared to clear and haze periods. During haze and fog, the nitrate oxidation ratio increased by a factor of 1.6–1.7, while the sulfur oxidation ratio increased by a factor of 1.2–1.5, indicating that both gaseous NO2 and SO2 were involved in the reduced visibility.

Kinetics of Degradation of 4-Chlorophenol by Fenton Oxidation

In this paper, the degradation of 4-chlorophenol contaminated water by Fenton process was investigated. It was found that 4-chlorophenol could be removed efficiently by Fenton process, and rapidly be degraded into low molecular weight organics under an optimum concentration of hydrogen peroxide to ferrous sulfate ([H2O2]/[FeSO4]) molar ratio of 20:1. Based on the reaction characteristics of the contaminant oxidized by Fenton, degradation kinetics model of 4-chlorophenol was constructed, kinetics equation of 4-chlorophenol degradation was eventually obtained through experiments, which could be expressed as: dW/dt = kC(H2O2)(0.282) W-0.273, where: dW/dt is the reaction rate, k is the rate constant, CH2O2 is the concentration of H2O2, W is the concentration decrease of 4-chlorophenol. The results showed that the reaction rate could be significantly increased when the concentration of H2O2 increased, and temperature increased in favor of the degradation of 4-chlorophenol. The reaction mechanisms of degradation of 4-chlorophenol were analyzed based on the kinetics equation, and the entire degradation process could be divided into two stages of rapid reaction and slow reaction.

Carbothermal Reduction of Barium Sulfate-Rich Sludge from Acid Mine Drainage Treatment

The alkali–barium–calcium (ABC) desalination process is basically an integrated lime/limestone neutralisation process combined with a sulfate removal stage using barium carbonate (BaCO3), and a sludge processing stage. The BaSO4/CaCO3 sludge generated during the desalination stage is treated to recover BaS and CaO by dewatering and thermal processes, with the ultimate goal of producing sulfur and recovering BaCO3. BaCO3 is the main raw material used for sulfate removal and its recovery ensures that the ABC process is environmentally and financially sustainable. South Africa is also a large importer of sulfur. We evaluated the optimum conditions for the thermal treatment of BaSO4/CaCO3 sludge to recover by-products. A high temperature tube furnace was used to reduce BaSO4/CaCO3 sludge obtained from a pilot plant test conducted at a gold mine shaft. We used response surface methodology to investigate the combined effects of relevant process variables (time, temperature, and the carbon/barium sulfate (C/BaSO4) molar ratio to maximize the reduction of BaSO4/CaCO3 sludge. At optimal process conditions (T = 1,028 °C; molar ratio of C/BaSO4 = 2.8 mol/mol), the tube furnace yield of BaS from waste sludge was over 78.5 % after 35 min. Furthermore, the results were similar to those generated by roasting a laboratory-grade mixture of barite and calcite concentrates.

Atmospheric aerosol episodes over Lithuania after the May 2011 volcano eruption at Grimsvötn, Iceland

During the eruption of the volcano at Grimsvötn in Iceland (21 May 2011), an inflow of volcanic pollutants to the atmospheric surface layer of Vilnius, Lithuania from 0700 UTC 24 May until the end of 29 May 2011 was observed. A cloud of volcanic plume rose up from Grimsvötn and reached an altitude of 19km. The analysis of possible volcanic origin PM1 aerosol sources was supplemented with forward and backward air mass trajectories, concentration and composition measurements and size distribution calculations of aerosol particles. According to the forward air mass trajectories from the volcano at Grimsvötn, the plume from the layer of 3000–4500m was advected southeastward from Iceland towards the British Isles and the Baltic Sea. The plume reached Vilnius and descended from the troposphere to the surface after about 86h. After data analysis, four episodes selected in the time series of the atmospheric submicron aerosol particle (PM1) concentration of chemical components (sulfate, ammonium, nitrate and organics) were analyzed with the Aerodyne Quadrupole Aerosol Mass Spectrometer, and calculations of the size-resolved distribution spectra were made. Two clear episodes were detected when the main source of aerosols was the volcano, with well-defined size distribution spectra of PM1 chemical components in the accumulation mode. The ammonium to sulfate molar ratio (ASR) during Episodes 1 and 2 is 0.81, suggesting that sulfate particles were partially neutralized by ammonium and determined by volcanic eruptions. However, during Episodes 3 and 4 the ASR was higher (1.0) and determined by both volcanic and non-volcanic origin components. This study shows that the sulfate emissions from the volcano at Grimsvötn in Iceland reached distances farther than 3000km, and they can have an influence on the local concentration and size distribution spectra of PM1 chemical components. Over the period of the volcanic eruption (Episode 1) the sulfate concentrations increased by a factor of 3 and reached 90% of PM1, while the nitrate and organic levels remained low and unchanged. The volcanic sulfate contribution made up about 250% of the average concentration of anthropogenic sulfate in Vilnius.

Effect on the Formation of Fe_3O_4 with Ferrous Sulfate/Ferric Sulfate Molar Ratio

The effect of ferrous/ferric molar ratio on the formation of nano-sized magnetite particles was investigated by a co-precipitation method. Ferrous sulfate and ferric sulfate were used as iron sources and sodium hydroxide was used as a precipitant. In this experiment, the variables were the ferrous/ferric molar ratio (1.0, 1.25, 2.5 and 5.0) and the equivalent ratio (0.10, 0.25, 0.50, 0.75, 1.0, 2.0 and 3.0), while the reaction temperature (25 o C) and reaction time (30 min.) were fixed. Argon gas was flowed during the reactions to prevent the Fe 2+ from oxidizing in the air. Single-phase magnetite was synthesized when the equivalent ratio was above 2.0 with the ferrous/ferric molar ratios. However, goethite and magnetite were synthesized when the equivalent ratio was 1.0. The crystallinity of magnetite increased as the equivalent ratio increased up to 3.0. The crystallite size (5.6 to 11.6 nm), median particle size (15.4 to 19.5 nm), and saturation magnetization (43 to 71 emu.g �1 ) changed depending on the ferrous/ferric molar ratio. The highest saturation magnetization (71 emu.g �1 ) was obtained when the equivalent ratio was 3.0 and the ferrous/ferric molar ratio was 2.5.

Competition and coexistence of sulfate-reducing bacteria, acetogens and methanogens in a lab-scale anaerobic bioreactor as affected by changing substrate to sulfate ratio

The microbial population structure and function of natural anaerobic communities maintained in lab-scale continuously stirred tank reactors at different lactate to sulfate ratios and in the absence of sulfate were analyzed using an integrated approach of molecular techniques and chemical analysis. The population structure, determined by denaturing gradient gel electrophoresis and by the use of oligonucleotide probes, was linked to the functional changes in the reactors. At the influent lactate to sulfate molar ratio of 0.35 mol mol−1, i.e., electron donor limitation, lactate oxidation was mainly carried out by incompletely oxidizing sulfate-reducing bacteria, which formed 80–85% of the total bacterial population. Desulfomicrobium- and Desulfovibrio-like species were the most abundant sulfate-reducing bacteria. Acetogens and methanogenic Archaea were mostly outcompeted, although less than 2% of an acetogenic population could still be observed at this limiting concentration of lactate. In the near absence of sulfate (i.e., at very high lactate/sulfate ratio), acetogens and methanogenic Archaea were the dominant microbial communities. Acetogenic bacteria represented by Dendrosporobacter quercicolus-like species formed more than 70% of the population, while methanogenic bacteria related to uncultured Archaea comprising about 10–15% of the microbial community. At an influent lactate to sulfate molar ratio of 2 mol mol−1, i.e., under sulfate-limiting conditions, a different metabolic route was followed by the mixed anaerobic community. Apparently, lactate was fermented to acetate and propionate, while the majority of sulfidogenesis and methanogenesis were dependent on these fermentation products. This was consistent with the presence of significant levels (40–45% of total bacteria) of D. quercicolus-like heteroacetogens and a corresponding increase of propionate-oxidizing Desulfobulbus-like sulfate-reducing bacteria (20% of the total bacteria). Methanogenic Archaea accounted for 10% of the total microbial community.

Modeling the methanesulfonate to non‐sea‐salt sulfate molar ratio and dimethylsulfide oxidation in the atmosphere

A photochemical box model is used to examine the latitudinal and seasonal variations of the methanesulfonate (MSA, CH3SO3−) to non‐sea‐salt sulfate (nss‐SO42−) molar ratio in NOx‐poor environments of the remote marine atmosphere. Reasonable agreement between observed and modeled results was obtained. The unimolecular decomposition rates of both CH3SO2 and CH3SO3 are assumed to strongly depend on air temperature. These radicals are thought to be produced through the hydrogen abstraction reaction and the addition reaction of dimethylsulfide (DMS, CH3SCH3) with both OH and NO3. In this model, the production of MSA is assumed to occur through the OH addition reaction of DMS along with the hydrogen abstraction reaction. If the MSA production through the OH addition reaction is neglected, the predicted MSA to nss‐SO42− molar ratios are not in agreement with the latitudinal and seasonal variations observed in the atmosphere. Assuming a MSA production yield of 10% through the OH addition reaction in addition to the further oxidation of CH3SO3 without breaking the C‐S bond, the model calculations can reproduce MSA/nss‐SO42− molar ratios similar to the observed latitudinal and seasonal variations. Since the reaction of DMS with OH is the most important sink of DMS in the summer the addition and abstraction reactions appear to control the MSA production during this season. At middle and high latitudes during the winter, DMS is mainly oxidized by reaction with NO3. Therefore MSA in the winter may primarily be produced from the further oxidation of CH3SO3. It appears that competition between the decomposition and the further oxidation of CH3SO3 is a determining factor of the winter MSA/nss‐SO42− molar ratio.

Simulations of seasonal variations of sulfur compounds in the remote marine atmosphere

A photochemical box model is used to simulate seasonal variations in concentrations of sulfur compounds at latitude 40° S. It is assumed that the hydroxyl radical (OH) addition reaction to sulfur in the dimethyl sulfide (DMS) molecule is the predominant pathway for methanesulfonic acid (MSA) production, and that the rate constant increases as the air temperature decreases. Concentration of the nitrate radical (NO3) is a function of the DMS flux, because the reaction of DMS with NO3 is the most important loss mechanism of NO3. While the diurnally averaged concentration of OH in winter is a factor of about 8 smaller than in summer, due to the weak photolysis process, the diurnally averaged concentration of NO3 in winter is a factor of about 4–5 larger than in summer, due to the decrease of DMS flux. Therefore, at middle and high latitudes in winter, atmospheric DMS is mainly oxidized by the reaction with NO3. The calculated ratio of the MSA to SO2 production rates is smaller in winter than in summer, and the MSA to non-sea-salt sulfate (nssSO4 2-) molar ratio varies seasonally. This result agrees with data on the seasonal variation of the MSA/nssSO4 2- molar ratio obtained at middle and high latitudes. The calculations indicate that during winter the reaction of DMS with NO3 is likely to be a more important sink of NOx (NO+NO2) than the reaction of NO2 with OH, and to serve as a significant pathway of the HNO3 production. If dimethyl sulfoxide (DMSO) is produced through the OH addition reaction and is heterogeneously oxidized in aqueous solutions, half of the nssSO4 2- produced in summer may be through the oxidation process of DMSO. It is necessary to further investigate the oxidation products by the reaction of DMS with OH, and the possibility of the reaction of DMS with NO3 during winter.