Low Concentrations Of SO2 Research Articles

Promotion of Ni/H-BEA by Fe for NOx Reduction with Propane in a Lean-Burn Condition

The effect of iron addition to Ni/H-BEA on selective catalytic reduction of NOx with propane (C3H8–SCR) was investigated under a lean-burn condition. The addition of iron significantly lowered the optimum reaction temperature of Ni/H-BEA from 623 to 573 K. The 3Ni–1Fe/H-BEA catalyst had the highest activity among samples with different bimetal loading. NOx conversion of 100% was obtained at 573 K. Oxygen played an important role in activating NO and propane during the C3H8–SCR reaction. NOx conversion increased as the C3H8/NO molar ratio increased. A complete conversion of NOx was achieved with C3H8/NO = 1.25 at 573 K. The catalytic activity was inhibited slightly at a low SO2 concentration (100 ppm) but decreased dramatically at a high SO2 concentration (600 ppm) over different catalysts. The introduction of 10% water also exhibited a negative impact on the reduction of NOx. The catalytic activity of Ni–Fe/H-BEA represented only a slight drop in the presence of 100 ppm SO2 and 10% H2O. The addition of ir...

簡易モデルによる脱硝触媒の劣化再生予測 -第1報：劣化モデルの構築

Selective catalytic reduction (SCR) is an effective technique to reduce nitrogen oxides (NOx) from diesel engine emissions. In this study, a simple reaction model for predicting DeNOx performance deactivation and NH3 slip on a vanadia-based commercial catalyst is developed to evaluate the effects of the gas component and temperature, and NH3/NO feed ratio. This model predicted that NOx conversion rate does not depend on the catalyst temperature when the feed ratio becomes small. The calculation results at 250 deg. indicated that high excess air ratios and low NO and SO2 concentrations suppress the DeNOx performance deactivation. It was also shown that keeping the NH3/NO feed ratio small is necessary to avoid NH3 slip.

An analysis of CH4/N2 rich biogas production, fuel treatment process and microturbine application

Biogas usually contains CH4 and CO2 as main components with the ratio of 6 : 4, and its composition varies with wide range depending on digester conditions. In addition to concentration change of each constituent, biogas com- position could be changed due to the variations in the organic matter treatment process. The aim of the study is to analyze the production and application to a microturbine system of CH4/N2 rich biogas produced from Gong-Ju wastewater treatment plant. CH4/N2 rich biogas is produced due to the internal wastewater recirculation. The internal wastewater recirculation is intended to enhance NO3 − removal without additional carbon source input. As a result, the digester was shown to be the highest contributor for nitrogen removal and average CH4 concentration was lowered compared to the typical biogas composition. Nitrate removal rate was influenced by the internal recirculation ratio. Content of N2 has no effect on biogas clean-up system performance. Besides, adaptability of CH4/N2 rich biogas to microturbine was satisfactory with very low NOx and SO2 concentration in microturbine exhaust gas. Influence of high N2 concentra- tion of biogas on NOx concentration was limited due to the low combustion temperature.

Analysis of the concentration–respiratory response among asthmatics following controlled short-term exposures to sulfur dioxide

Some of the most compelling evidence of sulfur dioxide (SO2)-induced respiratory morbidity is derived from a large body of studies involving controlled short-term exposures among groups of asthmatic volunteers. These studies were extensively cited in the recently completed review of the primary National Ambient Air Quality Standards for SO2. Although it is clear from these investigations that exposure to SO2 may result in a significant increase in bronchoconstriction, there is uncertainty regarding the range of concentrations over which this respiratory response occurs. The objective of this study was to better characterize the concentration–response relationship between SO2 and measures of bronchoconstriction using individual subject lung function response data. In reviewing studies of asthmatics exposed to SO2 during 5- to 10-min periods of elevated ventilation, we observed clear and consistent evidence of an increase in the bronchoconstrictive response to SO2 with increasing exposure concentrations between 0.2 and 1.0 ppm. In a subsequent analysis of individual subject data, it was found that those asthmatics experiencing SO2-induced respiratory effects at relatively high exposure concentrations are also more likely than nonresponders to experience similar effects after exposure to lower SO2 concentrations (≤0.4 ppm). Although the clinical significance of these effects is unsettled, the findings provide additional support to epidemiologic evidence of an association between ambient SO2 concentration and various measures of respiratory morbidity in the general population.

Urban and rural limestone weathering; the contribution of dust to black crust formation

A novel approach of studying dust, black crust and host limestones by using various techniques is presented in this paper. Samples were collected from limestone monuments located in rural, urban and industrial areas in Germany and Hungary. The paper focuses on differences in the mineralogical composition, major and trace element distribution of materials and their total polyaromatic hydrocarbons (PAH) concentration having different exposure to air pollutants. High concentration of gypsum was found in laminar and dendritic black crusts and even in the dust of both urban and rural areas, despite the low concentration of SO2 in rural atmospheric environments. The black crusts show a typical microfabric with distinct layers of various gypsum–calcite mineral associations, silt-sized mineral fragments and black particle content. In dust, newly formed gypsum crystals were found along with mineral fragments, and siliceous and, less frequently, carbonaceous fly ash particles. High concentration of lead was found both in the samples of urban and rural areas of Germany and Hungary. Lead mostly accumulates in dust and also in the black crust. Highest lead concentrations were found not on the surface of the black crust, but close to the crust/limestone boundary according to LA-ICPMS analyses. It indicates that despite the ban of leaded petrol, lead is still present in the dust and the in the soiled zones of the built environment. Similarly to lead, no significant difference in the total PAH content of dust and crust samples were found in the two countries. Dusts are equally enriched in PAH in both countries, whereas black crusts contain fewer amounts. Most of the aqueous extracts of the samples were saturated with respect to sulphate, which also indicate the presence of gypsum, whilst in some German samples unsaturated conditions were detected. In summary, by using a combination of these analytical techniques, it was possible to distinguish rural and urban samples and to outline the role of dust in bringing pollutants to the stone surface. It is suggested that the analysed dust and stone samples indicate not only present, but also the past, pollution fluxes and as a consequence stones similar to sediments or surface waters can be used as environment indicators.

Improving the SO2 absorption rate of CeFeMg-based sorbent promoted with titanium promoter

To improve the poor SO2 absorption rate of CeFeMgTi sorbent with high sulfur removal capacity and fast regeneration, a new sorbent, CeFeMgTi-sol was prepared by the modified co-precipitation method and tested in a packed bed reactor at RFCC conditions (sulfation of MgO to MgSO4 in the presence of low concentration of SO2 at 973 K, regeneration of MgSO4 to MgO and H2S in the presence of H2 at 803 K). The CeFeMgTi-sol sorbent showed excellent SO2 absorption and sulfur removal capacity (46.2 sulfur g/g absorbent×100). It was found that the SO2 absorption rates were related to the structure of the Mg and Ti and the textural properties such as surface area and pore volume. In the case of the fresh state of CeFeMgTi sorbent, CeO2, MgO and MgTiO3 structures were observed. But the new CeFeMgTisol sorbent before SO2 absorption, showed a separated MgO and TiO2 peak only. These differences in the sorption rates were discussed by the difference in the XRD pattern, surface area and pore volume.

Absorption kinetics of NO from simulated flue gas using Fe(II)EDTA solutions

The absorption of NO encountering flue gases in aqueous solutions of Fe(II)EDTA was determined using a semi-batch stirred tank with a plane gas–liquid interface at 50 °C. The concentrations of NO, SO 2 and O 2 in the feeding stream were 300–800 ppm, 500–2200 ppm and 0–20%, respectively. The pH value of the Fe(II)EDTA solutions varied from 3 to 11. The concentrations of Fe(II)EDTA were maintained between 0.01 and 0.05 M. Experiments were performed to evaluate the effect of operating parameters on the NO absorption rate, the reaction kinetics of the reactants in gas and liquid phases, and the effect of competition between various reactants on the mass transfer rate in the NO removal system. Results indicate that the average reaction rate constant is 3.70 × 10 7 M −1 s −1. Adding NaOH does not increase the absorption capability of Fe(II)EDTA. The presence of O 2 decreases the NO absorption rate with Fe(II)EDTA. The absorption rate of NO with Fe(II)EDTA decreases at low concentrations of SO 2, but increases at high concentrations.

Effect of Low Concentration of SO x on NO Reduction with Propene Over Ag/Al2O3

Catalytic activity for NO reduction with propene was investigated at 0–80 ppm SO2. NO was reduced more efficiently by propene on SO2-treated than untreated catalyst. Simultaneously, combustion of reductant was observed to lower NO reduction efficiency. Thus, the role of surface-adsorbed SOx species was regarded as depressing reductant combustion. NH3 adsorption revealed that SO2 treatment increased Bronsted acidity of the Ag/Al2O3 catalyst, which promoted propene activation. Reductant activation is a more important step, compared with NO activation to oxidative nitrate species. The NCO species, an index intermediate in NOx reduction, was produced on SO2-adsorbed Ag/Al2O3 at a lower temperature (473 K) than on the untreated catalyst. The reductive intermediates at low temperature are suggested to be alcohol, or aldehyde-adsorbed species, based on observed C=O band.

Applying size segregation to relate the surrounding aerosol pollution to its source

Size segregated sampling of aerosol particles at the coal-fired power station Sostanj, Slovenia was performed by a newly developed system. In addition, simultaneous sampling of particles was performed at two locations, Velenje and Veliki vrh, chosen on the basis of long term monitoring of SO2 in the influential area of power plant. The signature of the power plant (e.g. characteristic size distributions of some typical trace elements) was identified. For elements, like As, Mo, Cd and Ga, which are typical for coal combustion, the highest concentrations were observed in the size range between 1 and 4 μm. For Se and sometimes for Ga two modes were identified, first between 0.1 and 0.5 μm and second between 1 and 4 μm. Ratios between the average concentrations of selected elements in fine and coarse particles collected at Veliki vrh (the most influenced location) and Velenje (usually not influenced by the thermo power station) were significantly higher than 1 in the case of Mo and Se for coarse and fine size range, while for As the ratio was higher than 1 for the coarse fraction. Consequently, Mo, Se and As were found as the most important tracers for the emissions from the investigated source. On the basis of the ratios between the concentrations of elements measured in particles at low and high SO2 concentrations at Veliki vrh, Cd was shown to be a typical tracer as well. Our results definitely showed that size segregated measurements of particles at the source and in the influenced area give more precise information on the influence of source to the surrounding region. It was found that patterns of size distributions for typical trace elements observed at the source are found also in the influenced area, i.e. Veliki vrh.

Spatiotemporal Modeling of Ambient Sulfur Dioxide Concentrations in Rural Western Canada

The provinces of Saskatchewan, Alberta, and British Columbia are major oil- and gas-producing regions in western Canada. With increasing oil and gas production activities, there has been a growing concern of the effect of oil and gas industry emissions on health. Nevertheless, lack of proper tools to estimate the exposure to these emissions has been a hindrance to epidemiological studies and risk assessment. This paper presents a spatiotemporal modeling approach to estimating ambient sulfur dioxide (SO2) levels based on environmental monitoring data (N = 10,295), which were collected at rural sites (591 per month on average) of this region from June 1, 2001 to May 31, 2002. Based on the model, illustrative maps consistently revealed high and low SO2 concentration sub-regions. The sub-regions with elevated SO2 concentrations had increased levels during the winter months from December 2001 to March 2002 and then decreased during the spring of 2002. This statistical modeling approach may help researchers estimate the SO2 levels within the study area for their epidemiological studies or risk assessment.

SO2 in Beirut: air quality implication and effects of local emissions and long-range transport

While sulfur dioxide (SO2) emissions have been dramatically restricted in the past few decades, some cities in developing countries still encounter high pollution levels. This makes it essential to implement an air quality monitoring network in these sensitive regions. Results from a program of measuring ground-level concentration of SO2 (from December 2004 till July 2006) at 22 curbside and background sites within the city of Beirut (Lebanon) are presented for the first time. Four-week sampling period measurements were made over 20 periods for all sites by passive sampling. Low SO2 concentrations were observed (3.1 parts per billion on average for the whole period). This value is among the lowest observed in urban areas worldwide. Thus, Beirut is not polluted by SO2 on an annual basis. Highest concentrations were measured in winter time, resulting from low height of the boundary layer and higher emissions of SO2 (e.g., heating). Cluster analysis revealed two different SO2 variation patterns over the city (high- and low-level patterns), highlighting the effects of local sources location and wind direction variability on SO2 distribution. Analysis of seasonal variations pointed out a springtime SO2 maximum in 2005. Beside local sources, long-range transport can account for an important source of SO2 in Beirut, explaining around 50% of SO2 levels within the city.

Geochemistry and stable sulfur and oxygen isotope ratios of the Podwiśniówka pit pond water generated by acid mine drainage (Holy Cross Mountains, south-central Poland)

Abstract The paper presents the results of a geochemical and isotopic study of acidic pond water in the abandoned Podwiśniowka quarry (Poland). The scope of investigations also encompassed mineralogical and isotopic studies of pyrite and related supergene minerals. Compared to similar sites throughout the world, the pit pond water examined is characterized by a very low pH averaging 2.64 ± 0.33 and simultaneously very low concentrations of SO 4 2 - (geometric mean of 237 ± 57 mg L−1), Fe(II) (4.8 ± 3.4 mg L−1), Fe(III) (10.0 ± 6.2 mg L−1) and other trace elements. This acidity has been generated by complex processes of As-rich pyrite oxidation combined primarily with hydrolysis, precipitation, and transformation of Fe oxyhydroxysulfates and oxyhydroxides into goethite. The specific mineralogy of ore and gangue minerals, but especially the lack of acid–buffering constituents, has additionally contributed to the very low pH and element concentrations. Of the toxic elements, the high content of As (1111–1879 mg kg−1) in the western part of pit pond sediment may be of great concern, especially when using lime as a neutralizing agent of the acidic water. The δ34S of soluble SO4 varied from −19.8‰ to −11.1‰ and was different from that of efflorescent sulfates (−25.7‰ to −25.4‰) and host pyrite (−25.4 ± 2.5‰). The comparison of the δ18O– SO 4 2 − (−2.0 ± 1.2‰) and δ18O–H2O (−6.2 ± 3.5‰) values indicated that the pyrite underwent bacterially catalyzed oxidation by two natural oxidants, primarily by Fe3+ and to a lesser extent O2.

Palaeo-hydrogeological control on groundwater As levels in Red River delta, Vietnam

To study the geological control on groundwater As concentrations in Red River delta, depth-specific groundwater sampling and geophysical logging in 11 monitoring wells was conducted along a 45 km transect across the southern and central part of the delta, and the literature on the Red River delta's Quaternary geological development was reviewed. The water samples (n=30) were analyzed for As, major ions, Fe 2+ , H 2 S, NH 4 , CH 4 , δ 18 Ο and 8D, and the geophysical log suite included natural gamma-ray, formation and fluid electrical conductivity. The SW part of the transect intersects deposits of grey estuarine clays and deltaic sands in a 15-20 km wide and 50-60m deep Holocene incised valley. The NE part of the transect consists of 60-120 m of Pleistocene yellowish alluvial deposits underneath 10-30m of estuarine clay overlain by a 10-20m veneer of Holocene sediments. The distribution of δ 18 O-values (range -12.2‰ to -6.3%o) and hydraulic head in the sample wells indicate that the estuarine clay units divide the flow system into an upper Holocene aquifer and a lower Pleistocene aquifer. The groundwater samples were all anoxic, and contained Fe 2+ (0.03-2.0mM), Mn (0.7-320μM), SO 4 (<2.1μM-0.75mM), H 2 S (<0.1-7.0μM), NH 4 (0.03-4.4 mM), and CH 4 (0.08-14.5 mM). Generally, higher concentrations of NH 4 and CH 4 and low concentrations of SO 4 were found in the SW part of the transect, dominated by Holocene deposits, while the opposite was the case for the NE part of the transect. The distribution of the groundwater As concentration (<0.013-11.7 μM; median 0.12 μM (9μg/L)) is related to the distribution of NH 4 , CH 4 and SO 4 . Low concentrations of As (≤0.32μM) were found in the Pleistocene aquifer, while the highest As concentrations were found in the Holocene aquifer. PHRE-EQC-2 speciation calculations indicated that Fe 2+ and H 2 S concentrations are controlled by equilibrium for disordered mackinawite and precipitation of siderite. An elevated groundwater salinity (Cl range 0.19-65.1 mM) was observed in both aquifers, and dominated in the deep aquifer. A negative correlation between aqueous As and an estimate of reduced SO 4 was observed, indicating that Fe sulphide precipitation poses a secondary control on the groundwater As concentration.

Deposition of sulfur dioxide to building stones: the influence of the ambient concentration on the deposition velocity

We report on extensive deposition measurements of sulfur dioxide (SO2) on three types of commonly used building stones (Obernkirchen sandstone, Sand sandstone, Ihrlerstein sandstone). The deposition velocities on the three materials were determined in a number of measuring campaigns at different sites with different levels of air pollution. The measurements clearly imply that there is a strong influence of SO2 concentration on the deposition velocity. With increasing concentration there is a strong decrease in the deposition velocity. To understand this deposition behavior a simple model with a single rate constant as the only adjustable parameter was established. Rate constants for the three stone materials were determined by least squares analysis and good agreement between experimental and calculated deposition velocities was obtained. According to the model treatment the surface resistance of stone materials increases with increasing SO2 concentration due to a decrease of the pH in surface films. It follows from the concentration dependence of the deposition velocity that emission control measures for the reduction of ambient SO2 concentrations do not lead to a proportional reduction of the SO2 deposition. At low SO2 concentrations the differences in the deposition behavior of different stone materials diminish and stone surfaces behave like ideal absorbers under such conditions, i.e., the deposition velocity is controlled by the aerodynamic resistance.

Analyzing SO 2 concentrations and wind directions during a short monitoring campaign at a site far from the industrial pole of La Plata, Argentina

This article presents and discusses SO2 air quality concentrations (ppbv) together with wind velocities and directions measurements carried out between September 1st and December 21st 2005 at a site located 8.5 km away from the Industrial Pole of La Plata area. As the city and its surroundings have no official monitoring network, the current work enlarges the air quality information available from the zone and sets some initial considerations to the future siting of monitoring stations. The statistical analysis of the data was performed using techniques of tests for outliers and trends, dissimilarity measures and robust regression. In relation to SO2 concentrations, low values were found during this short campaign considering daily averages (with a maximum of 8.5 ppbv) and hourly averages (with a maximum of 25.9 ppbv); World Health Organization guidelines were never surpassed. Nevertheless, a strong dependence between wind directions carrying air pollutants from the Industrial Pole and hourly concentration peaks were found. Due to low monthly SO2 concentrations and because a decreasing time trend was found, the authors propose, as an example, the implementation of an alternative discontinuous method to the continuous analyzer used in the current campaign. Our results state that sampling every 7 days at 13:00-13:59 hours (local time) would be enough to get representative values of the air quality. As a general remark it is possible to highlight that longer and systematic studies should be encouraged to confirm the seasonal wind pattern and to evaluate the air quality.

Pyrolysis of High Sulfur Indian Coals

Pyrolysis experiments under laboratory conditions for five numbers of high sulfur coal samples from the states of Meghalaya and Nagaland, India, were carried out at temperatures of 450, 600, 850, and 1000{sup o}C, respectively. The yield of products and thermal release of sulfur from these coals are investigated. The distribution of sulfur in the pyrolyzed products, i.e., char/coke, gas, and tar, is also reported. Hydrocarbon and sulfurous gases released at different temperatures were analyzed by a gas chromatograph (GC) with an FID (flame ionized detector) and an FPD (flame photometric detector), respectively. H{sub 2}S evolution during coal pyrolysis was found to be a function of temperature up to 850{sup o}C. The low concentration of SO{sub 2} detected for some of the samples is due to decomposition of inorganic sulphates present. Evolution of methane for the coals tested increases with the increase of temperature. Maximum sulfur release was found in the range of 600-850{sup o}C and has a decreasing tendency from 850-1000{sup o}C, which might be due to the incorporation of sulfur released into the coal matrix. Activation energies for sulfur release were found in the range of 38-228 kJ mol{sup -1}, which were higher than the reported activation energies formore » lignites and bituminous coals mainly due to highly stable organic sulfur functionalities. 52 refs., 9 figs., 6 tabs.« less

Investigation of Mercury Transformation by HBr Addition in a Slipstream Facility with Real Flue Gas Atmospheres of Bituminous Coal and Powder River Basin Coal

An investigation of speciated mercury transformation with the addition of hydrogen bromide (HBr) at elevated temperatures was conducted in a slipstream reactor with real flue gas atmospheres. A real flue gas atmosphere is composed of bituminous coal (with high sulfur and high chlorine contents) and Powder River Basin (PRB) coal (with lower sulfur and chlorine contents). The average sulfur, chlorine, and mercury contents in the tested bituminous coal were 1.31% and 1328 and 0.11 ppm and 0.61% and 170 and 0.08 ppm, respectively, for tested PRB coal. The average CaO, Fe2O3, and loss on ignition in collected fly ash contents of tested bituminous coal were 1.71, 17.51, and 7.13% and 22.95, 4.91, and 0.64%, respectively, for tested PRB coal. The different contents of coal chlorine, CaO, and Fe2O3 in fly ash can be attributed to the different mercury speciations at baseline tests for these two coals in this study. The addition of HBr concentrations into the flue gas was controlled in the 3−15 ppm range. Semi-continuous mercury emission monitors were used to check the variation of mercury speciation at sampling locations. The Ontario Hydro Method (ASTM D6784-02) was used for data validation or comparison. For both methods, a high temperature inertial sampling probe was used to minimize the interference between vapor phase mercury and fly ash. Its temperatures were controlled consistently with flue gas temperatures at their installation locations in the slipstream reactor. Test results indicated that adding HBr into the flue gas at several parts per million strongly impacted the mercury oxidation and adsorption, which were dependent upon temperature ranges. Higher temperatures (in the range of 300−350 °C) promoted mercury oxidation by HBr addition but did not promote mercury adsorption. Lower temperatures (in a range of 150−200 °C) enhanced mercury adsorption on the fly ash by adding HBr. Test results also verified effects of flue gas atmospheres on the mercury oxidation by the addition of HBr, which included concentrations of chlorine and sulfur in the flue gas. Chlorine species seemed to be involved in the competition with bromine species in the mercury oxidation process. With the addition of HBr at 3 ppm at a temperature of about 330 °C, the additional mercury oxidation could be reached by about 55% in a flue gas atmosphere by burning PRB coal in the flue gas and by about 20% in a flue gas by burning bituminous coal. These are both greater than the maximum gaseous HgBr2 percentage in the flue gas (35% for PRB coal and 5% for bituminous coal) by thermodynamic equilibrium analysis predictions under the same conditions. This disagreement may indicate a greater complexity of mercury oxidation mechanisms by the addition of HBr. It is possible that bromine species promote activated chlorine species generation in the flue gas, where the kinetics of elemental mercury oxidation were enhanced. However, SO2 in the flue gas may involve the consumption of the available activated chlorine species. Thus, the higher mercury oxidation rate by adding bromine under the flue gas by burning PRB coal may be associated with its lower SO2 concentration in the flue gas.

Anatomical and functional responses of Calendula officinalis L. to SO 2 stress as observed at different stages of plant development

Growth responses of field-grown marigold ( Calendula officinalis L.) plants to SO 2 (0.5, 1.0 and 2.0 ppm) stress were studied at pre-flowering, flowering and post-flowering stages. Low concentrations of SO 2 did not cause any noticeable difference in shoot length, flowers and fruits per plant, and in seeds per fruit, but enhanced leaf number, leaf area and root length. With higher concentrations, however, all these parameters declined. Compared with controls, dry mass of leaves and roots was higher with 0.5 ppm SO 2 but significantly lower with higher doses at each stage. With a high SO 2 dose stomatal pore size increased on adaxial epidermis but decreased on abaxial epidermis. The net photosynthetic rate significantly increased, whereas stomatal conductance and intercellular CO 2 concentration decreased with 0.5 ppm SO 2 treatment, the reverse being the case with higher concentrations. The photosynthetic pigments declined significantly under high SO 2 stress at each stage of plant development, although 0.5 ppm concentration had a stimulatory effect. SO 2 stress delayed the development of interfascicular cambium and altered the proportion of the component tissues in the plant axis. The areas of cortex and vasculature in stems and roots decreased, while pith area increased in the treated plants. The length of fibres and vessel elements increased in the stem and decreased in the root, compared with the control. Vessel density and diameter declined in large vascular bundles and increased in small vascular bundles of the stem. In roots, both the parameters gained under heavy SO 2 stress.

Comparative XPS Study of Silver and Copper Surfaces Exposed to Flowing Air Containing Low Concentration of Sulfur Dioxide

Sulfur dioxide (SO2) is a typical gas affecting the atmospheric corrosion of metals, particularly outdoors. Although many studies have investigated the effect of SO2 on the atmospheric corrosion of silver and copper, little is known about the early stage of their corrosion behavior. In this study we analyzed the chemical state of sulfur on silver and copper plates exposed to flowing air containing low concentrations (18 and 148 ppb) of SO2 using X-ray photoelectron spectroscopy (XPS). The shapes of the spectra were the same for both concentrations, indicating that the chemical state of the analyzed elements did not depend on the SO2 concentration. There was a difference in the chemical state of the sulfur between the silver and copper. Three peaks were observed in the S 2p XPS spectra for the silver originating from bisulfite, S2O52-, S2O32-, and S2-. The bisulfite resulted from SO2 dissolution into the surface electrolyte, and the others resulted from the reduction of sulfurous acid. In contrast, only bisulfite was observed in the S 2p XPS spectra for the copper. It also originated from the dissolution of SO2 into the surface electrolyte. The difference in the chemical state of the sulfur between the silver and copper is attributed to the presence of native oxides on the surface, which may have impeded the reduction of bisulfite.

Single photon ionization of van der Waals clusters with a soft x-ray laser: (SO2)n and (SO2)n(H2O)m

van der Waals cluster (SO2)n is investigated by using single photon ionization of a 26.5 eV soft x-ray laser. During the ionization process, neutral clusters suffer a small fragmentation because almost all energy is taken away by the photoelectron and a small part of the photon energy is deposited into the (SO2)n cluster. The distribution of (SO2)n clusters decreases roughly exponentially with increasing cluster size. The photoionization dissociation fraction of I[(SO2)(n-1)SO+] / I[(SO2)n+] decreases with increasing cluster size due to the formation of cluster. The metastable dissociation rate constants of (SO2)n+ are measured in the range of (0.6-1.5) x 10(4) s(-1) for cluster sizes 5< or =n< or =16. Mixed SO2-H2O clusters are studied at different experimental conditions. At the condition of high SO2 concentration (20% SO2 partial pressure), (SO2)n+ cluster ions dominate the mass spectrum, and the unprotonated mixed cluster ions (SO2)nH2O+ (1< or =n< or =5) are observed. At the condition of low SO2 concentration (5% SO2 partial pressure) (H2O)nH+ cluster ions are the dominant signals, and protonated cluster ions (SO2)(H2O)nH+ are observed. The mixed clusters, containing only one SO2 or H2O molecule, SO2(H2O)nH+ and (SO2)nH2O+ are observed, respectively.