Ppb SO Research Articles

Comparative evaluation of environment induced cracking of conventional and advanced steam turbine blade steels. Part 2: Corrosion fatigue

Corrosion fatigue crack propagation rates have been determined for two steam turbine blade steels, PH13-8, a candidate steel for advanced turbines, and FV566, typical of conventional turbine blades. The testing was undertaken in simulated condensate environment, 300 ppb Cl − and 300 ppb SO 4 2 - , at 90 °C using trapezoidal loading with a rise time of 20 min to simulate two-shifting (switching on- and off-load on a daily basis). Aerated and deaerated conditions were tested, the former being more representative of the retained aeration in the chamber as the system comes on load. In aerated solution at Δ K = 20 MPa m 1/2 the cyclic crack growth rate for the PH13-8 steel was about a factor of two lower than that for the FV566 steel but the reverse was true for deaerated solution. In both cases, the difference in growth rates diminished with increasing Δ K. Although the cyclic crack growth rate is high the number of cycles per annum is small and the direct impact on overall life may be modest, but not insignificant. The observed cracking behaviour is best explained by a hydrogen assisted cracking mechanism.

A framework for assessing causality and adverse effects in humans with a case study of sulfur dioxide

Following exposure to a substance, several biological events can occur that may eventually, depending on the exposure dose and duration, lead to adverse effects. We developed a framework to evaluate whether an exposure is causally related to an effect and whether that effect is adverse. An exposure is not likely to be causal if an effect is: not statistically significantly different in exposed and non-exposed study subjects; isolated or independent; secondary; observed because of study limitations; or unrelated to the apical effect and not associated with functional impairment. Adaptive effects are not adverse and, although effects that overwhelm homeostasis often are, this may not be the case if they are transient, early precursors of an apical effect, reversible, or of low severity. We applied the framework to a case study of sulfur dioxide (SO 2) and conclude that the available evidence supports a short-term exposure threshold of 400 ppb SO 2 for adverse effects on lung function in sensitive individuals. At this concentration, effects are transient, reversible, and of low severity. Below this concentration, effects are isolated or independent and not statistically different in exposed and unexposed subjects in clinical trials, and study limitations affect interpretation of observational studies.

Detection of ppb level SO 2 in H 2 by an adsorption–desorption gas chromatography method

Some H 2 impurities (e.g., SO 2), even at 10–100 ppb level, can greatly reduce the working life of the proton exchange membrane (PEM) fuel cells. Sulfur compounds such as SO 2 is a typical impurity existing in the coal gas derived H 2 fuel. As a result, detection of near ppb level SO 2 in H 2 for fuel cells has been a focus of many recent studies. In this study, we present a gas chromatography (GC) method integrated with an in-house built adsorption–desorption device that can detect SO 2 at near ppb level. The technique is as follows: sample gas is collected by a SO 2 absorbent at room (or low) temperature, followed by desorption at an elevated temperature prior to gas sampling with GC. Operating conditions are optimized through testing on the absorbent material, adsorption and desorption temperature. Under an optimal condition, a sample gas of 10–20 ppb SO 2 was detected within an hour.

Enhanced tolerance to sulfur dioxide and salt stress of transgenic Chinese cabbage plants expressing both superoxide dismutase and catalase in chloroplasts

To explore the possibility of overcoming the highly phytotoxic effect of SO 2 and salt stress, we introduced the maize Cu/Zn SOD and/or CAT genes into chloroplasts of Chinese cabbage ( Brassica campestris L. ssp. pekinensis cv. Tropical Pride) (referred to as SOD, CAT and SOD + CAT plants). SOD + CAT plants showed enhanced tolerance to 400 ppb SO 2, and visible damage was one-sixth that of wild-type (CK) plants. In addition, when SOD + CAT plants were exposed to a high salt treatment of 200 mM NaCl for 4 weeks, the photosynthetic activity of the plants decreased by only 6%, whereas that of CK plants decreased by 72%. SOD plants had higher total APX and GR activities than CK plants. As expected, SOD plants showed levels of protection from SO 2 and salt stress that were moderately improved compared to CK plants. However, CAT plants showed inhibition of APX activity and provided only limited improvements in plant stress tolerance. Moreover, SOD + CAT plants accumulated more K +, Ca 2+ and Mg 2+ and less Na + in their leaves compared with those of CK plants. These results suggest that the expression of SOD and CAT simultaneously is suitable for the introduction of increased multiple stress protection.

Combination effect of activated carbon with TiO 2 for the photodegradation of binary pollutants at typical indoor air level

Previously we identified that residence time and water vapor are the vital parameters that affect the photodegradation of indoor air pollutants at parts-per-billion (ppb) levels using TiO 2. The presence of water vapor competes with pollutants for adsorption sites on TiO 2 thus reducing the pollutant removal rate. By immobilizing TiO 2 on activated carbon (AC), a satisfactory pollutant removal rate is achieved even at high water vapor levels. This study further examines the effect of TiO 2 immobilized on AC by co-injecting binary pollutants simultaneously since the presence of other pollutants might have an inhibition effect on the photocatalytic activity under different humidity levels. 200 parts-per-billion NO, 20 ppb BTEX and 200 ppb SO 2 were co-injected under different residence time and humidity levels to investigate their mutual effect on TiO 2 and TiO 2 immobilized on AC. Results showed that no significant pollutant removal difference was observed between TiO 2 and TiO 2 immobilized on AC at longer residence time. The presence of BTEX only reduced NO conversion by 5%. At evaluated humidity levels, however, a significant different pollutant removal rate was observed. The presence of BTEX reduced NO conversion by more than 10%. The use of TiO 2 on AC, reduced both the competition effect of the pollutant and water vapor on TiO 2. The inhibition effect of BTEX and SO 2 on NO conversion was significantly reduced when TiO 2 immobilized on AC compared to TiO 2 only. The by-product, NO 2, from the photodegradation of NO, was also reduced despite the presence of SO 2 and BTEX under high humidity level.

Multianalytical in-situ investigations of the early stages of corrosion of copper, zinc and binary copper/zinc alloys

Abstract A new experimental infrared reflection absorption spectroscopy (IRRAS) set-up for in-situ investigation of corrosion phenomena occurring in the metal–atmosphere interface was developed. It was applied in combination with in-situ tapping-mode atomic force microscopy (TM-AFM) and phase detection imaging (PDI) to study the early stages of corrosion of pure copper and pure zinc as well as to determine the influence of increasing zinc contents in brass. Additionally, ex-situ secondary ion mass spectrometry (SIMS) investigations were carried out on the samples after exposure. The investigations were accomplished in synthetic air with 80% relative humidity (RH) and synthetic air with 80% RH and 250 ppb SO 2 . The experiments showed that an increase of the zinc content in the brass alloy yields to an increase of the dimension of the corrosion features formed on the metal surface during weathering. Large features on top of smaller features were observed with TM-AFM on the surfaces exposed to SO 2 -containing humidified air, which could be identified by IRRAS as metal sulphur compounds. Furthermore, an increased amount of physisorbed water on the metal surfaces was determined with IRRAS in dependence of the increasing zinc content in the brass samples.

In situ TM-AFM investigations of the influence of zinc and tin as alloy constituents of copper to the early stages of corrosion

To obtain information about the changes in the topography of sample surfaces during weathering, in situ tapping mode atomic force microscopy (TM-AFM) was used for the investigation of the early stages of corrosion of binary copper/zinc (brass) and copper/tin (bronze) alloys. The emphasis of these investigations is to state the shape and lateral distribution of the corrosion products grown within the first 1300 min of weathering. Investigations were carried out in synthetic air with 80% relative humidity (RH) and 80% RH with 250 ppb SO 2. While brass shows a homogeneous growth of features forming a surface film during weathering in 80% RH, the features on the bronze surface reveal a higher growth rate of a few sparsely distributed features.

Influence of increasing zinc contents in brass in the early stages of corrosion investigated by in-situ TM-AFM and SIMS.

In-situ tapping mode atomic force microscopy (TM-AFM), a powerful, high-resolution imaging technique for determining the structure of surfaces and ex-situ secondary ion mass spectroscopy (SIMS), a multielement, high-depth-resolution method, were used to examine the influence of increasing zinc contents in brass in the early stages of corrosion. Four different samples (pure Cu, pure Zn, Cu/Zn=90/10 wt% and Cu/Zn=70/30 wt%) were studied in order to determine their chemical behaviour under various atmospheric conditions. The in-situ TM-AFM investigations were carried out in synthetic air with 60% relative humidity (RH) and 80% RH with 250 ppb SO(2). The samples for the ex-situ SIMS experiments were weathered over a period of 60 h in 80% RH and 250 ppb SO(2). The in-situ TM-AFM investigations have shown that an increasing Zn content in brass increases the corrosion rate.

Comparison of the early stages of corrosion of copper and iron investigated by in situ TM-AFM

Tapping mode atomic force microscopy (TM-AFM) was used for the investigation of the early stages of atmospheric corrosion of pure copper and pure iron. The information obtained by this method is the change of the topography of the sample surfaces with emphasis on the shape and lateral distribution of the corrosion products grown within the first 1300 min of weathering. Investigations were carried out in synthetic air at 80 and 90% relative humidity (RH) with additions of 250 ppb SO 2 and 250 ppb NO 2. On a polished copper surface the growth of corrosion products could be observed already at 80% RH and 250 ppb SO 2, whereas an iron surface had to be exposed to 90% RH with 250 ppb SO 2 and 250 ppb NO 2 to produce detectable changes on the surface.

Multianalytical in situ investigation of the initial atmospheric corrosion of bronze

Atomic force microscopy (AFM) and infrared reflection absorption spectroscopy (IRAS) were used for in situ investigations of the initial atmospheric corrosion of bronze. In addition ex situ XPS investigations were carried out on the samples before and after the exposure, as well as on the sputtered bronze sample. Investigations were carried out in synthetic air with 80% relative humidity (RH) and synthetic air with 80% RH with 250 ppb SO 2. At 80% RH, small features covering the surface were observed with AFM, whereas IRAS detected that more water is adsorbed on the bronze sample surface compared to pure copper. Large features on top of smaller features were observed with AFM on the bronze surface exposed to SO 2-containing humidified air. These large features were identified as copper sulfite. Furthermore, cuprous oxide was detected approximately 500 min after the introduction of SO 2. This fact and the XPS results indicate the formation of a protective lead oxide layer already during the preparation of the sample, which is destroyed by the SO 2-containing environment and leads to the formation of cuprous oxide and copper sulfite.

Design of hollow fibre membrane modules for soluble gas removal

Asymmetric PVDF hollow fibre modules coupled with a concentrated alkaline solution were investigated both experimentally and theoretically for soluble gas removal such as H 2S or SO 2 from gas streams. Each of the modules used consisted of a bundle of hollow fibres having a skin layer at the outer edge of the hollow fibre. A gas mixture containing either 17.2 ppm H 2S or 3000 ppb SO 2 in balance of N 2 was fed into the fibre lumen and was in countercurrent contact with a 10% NaOH solution fed in the shell side of the modules. Laminar parabolic velocity profile was adopted to characterize the flow of the gas mixture in the hollow fibre lumen. Effects of membrane pore structure parameters such as pore size, pore size distribution and effective surface porosity on the membrane's coefficient were examined theoretically. Subsequently, studies on the module performance and design analysis were also carried out with consideration of the membrane pore structure parameters and the predicted values agreed very well with the experimental data in most cases. Finally, a graphic method is outlined, which enables a quick estimate of the design parameters of such systems for soluble gas removal.

Responses of Agrostis capillaris to gaseous pollutants and wet nitrogen deposition

Agrostis capillaris L. plants were exposed to combinations of gaseous pollutants and wet nitrogen mist in Solardome glasshouses. Gaseous pollution treatments were (a) charcoal-filtered air (control), (b) 10 ppb SO 2 + 10 ppb NO 2, (c) 20 ppb SO 2 + 20 ppb NO 2, (d) 40 ppb SO 2 + 40 ppb NO 2. Within each Solardome, four plant blocks were allocated different wet deposition treatments which provided a North Wales maritime rain with the equivalent of 0, 20, 40 or 60 kg N per hectare per year without changes in hydrogen ion concentration. Progressive senescence of leaves in the gaseous pollution treatments correlated well with leaf dry weight data, showing increasing injury with time. Growth analysis was performed after 11, 13 and 15 weeks exposure to pollutants. Gaseous pollution treatments resulted in substantial reductions in leaf areas and dry weights of A. capillaris in both the 20 ppb SO 2 + 20 ppb NO 2 and the 40 ppb SO 2 + 40 ppb SO 2 + 40 ppb NO 2 treatments compared with the plants exposed to charcoal filtered air and the 10 ppb SO 2 + 10 ppb NO 2 treatment. Adverse effects of the gaseous pollution treatments were greater on shoots than roots. Additions of wet nitrogen caused reductions in the numbers of tillers and leaf areas of A. capillaris compared with plants with zero nitrogen application. There were no effects of wet nitrogen treatments on total plant dry weights but all nitrogen additions above zero application resulted in a reduction in root dry weights at the final harvest which was reflected in a decrease in root/shoot ratio in the 60 N treatment.

Weathering Rates of Marble in Laboratory and Outdoor Conditions

In the modern urban atmosphere SO{sub 2} and NO{sub 2} attack calcite (CaCO{sub 3}) in marble exposed at rain-sheltered surfaces creating largely gypsum (CaSO{sub 4}{center_dot}2H{sub 2}O) crusts that eventually exfoliate. In combination with CO{sub 2} these gases erode the marble at unsheltered surfaces. the authors report the development of mathematical models to predict the rate of growth of crust and the rate of surface recession. To determine the rate of growth of crust the kinetic rate constant, diffusion rate, and the order of reaction were determined by the application of the shrinking-core model applied to data generated in laboratory experiments. Based on these parameters /and average ambient levels of 10 parts per billion (ppb) SO{sub 2} and 25 ppb NO{sub 2} in Louisville, Ky., the rate of crust formation for this metro area was calculated to be 1.8 {micro}m in the first year. However, the rate of recession was modeled from data obtained by exposing marble slabs to rainfalls. A surface recession of 15 {micro}m/yr was calculated. The models predicted well the rate of growth of crust observed at several sites in Louisville and the predicted surface recession compared well with values reported in the literature.

Interactive effects of gaseous air pollutants and acid mist on two major pasture grasses

Plants of Lolium perenne L. (perennial ryegrass) and Agrostis capillaris L. (common bent-grass) were exposed, for 18 and 22 weeks respectively, to combinations of gaseous pollutants and acid mists. The gaseous pollutant treatments were (a) charcoal filtered air, (b) 40 ppb SO 2 + 40 ppb NO 2, (c) 40 ppb O 3 with additional peaks of 2 × 3 h at 80 ppb and 1 × 1 h at 110 ppb O 3 and (d) SO 2 + NO 2 + O 3 (a combination of treatments (b) and (c)) and the mist treatments were 6 mm per week of solutions at pH 2.5, 3.5, 4.5 and 5.6. All gaseous pollution treatments resulted in substantial reductions in the dry weights of plants of L. perenne but there were less than additive effects of O 3 and SO 2 + NO 2 in the SO 2 + NO 2 + O 3 treatment. There was a stimulation in the growth of L. perenne exposed to pH 2.5 compared with less acid mists in the charcoal filtered air and O 3, but not in the SO 2 + NO 2 and SO 2 + NO 2 + O 3, gas treatments. Plants of A. capillaris were more resistant to the gas × mist treatments. There were no significant differences ( P ≤ 0.05) in the weights of total shoots for plants grown in the gas exposure treatments compared with those grown in charcoal-filtered air. There was a growth stimulation for plants of A. capillaris exposed to pH 2.5, compared with less acid mists, in all gas treatments. For both species, all gaseous pollution treatments caused a reduction in green shoots and an increase in dead ones. The data are discussed in relation to critical levels and loads of pollutants. It is concluded that these concepts need some refinement for assessing the threat of pollutants to vegetation.

Availability of H 2O 2 for oxidation of SO 2 in clouds in the Northeastern United States

A technique using inert tracers was used to determine SO 4 formed from in situ oxidation of SO 2 by H 2O 2 in 20 summer clouds at Whiteface Mountain, New York. The amount of in situ SO 4 formed, along with H 2O 2 present in cloud water, was used to determine the total available H 2O 2. In 11 of the clouds, for which SO 2 concentration was < 1 ppb, total available H 2O 2 could oxidize about 0.5 ppb SO 2. In the other nine clouds, in which SO 2 varied from 1 to 13 ppb with a weighted mean of 2.9 ppb, total available H 2O 2 could oxidize only 0.9 ppb SO 2 or 31 % of the SO 2 present. These results unequivocally show a deficiency of H 2O 2 in the atmosphere in the Northeastern U.S. that would result in a non-linear response between reductions in SO 2 emissions and downwind acid deposition, for scenarios where the aqueous-phase oxidation by H 2O 2 is the dominant mechanism for forming sulfuric acid in this region.

Measurement of Gases by a Suppressed Conductometric Capillary Electrophoresis Separation System

This paper describes the direct measurement of soluble ionogenic atmospheric gases by a suppressed conductometric capillary electrophoresis separation system (SuCCESS). A small circular wire loop is incorporated at the sampling end of a fused silica capillary located immediately at the tip in the same plane as the capillary. When the loop is dipped into a solution and withdrawn, a liquid film is formed on it. The film is in fluid communication with the capillary and acts as a microreservoir. When the film end is lifted relative to the destination side, all or part of the film contents can be injected into the capillary. To perform gas sampling, a series of automated operations are conducted with a commercial CE instrument modified in a minor fashion : the film-bearing loop is lowered into a sample chamber, and air is sampled for a preset period of time at a preselected flow rate (typically 1 min at 100 cm 3 /min). The capillary is then lifted to introduce an aliquot from the film for analysis and then dipped into the running electrolyte source vial, and electrophoresis is commenced. Under the above sampling conditions, 1 ppb SO 2 can be detected. The system should be applicable for use with other detection modes and nonaqueous electrolytes.

Growth responses of N and S deficient white clover and burr medic to SO 2, NO and NO 2

White clover and burr medic plants were exposed to SO 2, NO and NO 2 under conditions of probable nitrogen and sulphur deficiency in open top chambers for 4 h day −1, 7 days week −1 for 149 days to determine if the growth changes in nitrogen and sulphur deficient plants resulting from long term exposure to SO 2 could be ameliorated by NO and NO 2. Burr medic was very sensitive to SO 2, as 80 ppb SO 2 decreased shoot weight by about 70%, and stem length by 30%. The halving of shoot weight of white clover by exposure to 29 ppb NO and NO 2 for 4 h day −1 for 149 days suggests a very high sensitivity to NO and NO 2. Although the unexposed plants were deficient or marginal in sulphur nutrition, exposure to SO 2 did not result in a corresponding improvement in plant growth. This is despite exposure to SO 2 causing a substantial increase in leaf sulphur concentrations, and an improvement in nutrition to adequate or high levels. A linear decrease in shoot weight with increase in SO 2 concentration suggests that the toxic effects of SO 2 overwhelmed any potential beneficial effects. The toxic effects of SO 2 on vegetative growth were found to be additively increased by the additional presence of NO and NO 2. Although they were probably nitrogen-deficient, when the white clover plants were fumigated with NO and NO 2, shoot weight was halved but the rate of sulphur accumulation by leaves was doubled. Nitrogen deficiency may induce partial closure of stomata, but, ironically, the uptake of NO 2 may partially relieve the nitrogen deficiency increasing stomatal conductance, causing enhanced uptake of SO 2 and growth inhibition.

Effects of SO 2 and salinity on nitrogenase activity, nitrogen concentration and growth of young soybean plants

Young soybean plants ( Glycine max L.) were exposed to three SO 2 concentrations (2, 110 and 250 ppb) and two levels of soil salinity (no added NaCl and 27 mM NaCl) in a factorial experiment for 16 days. SO 2 exposure was for 5 hr day −1. Exposure to 250 pbb (high) SO 2 decreased the number and weight of root nodules, suppressed nitrogenase activity, and reduced shoot and root nitrogen concentrations, whereas 110 ppb (low) SO 2 usually had no effect on these parameters. High and low SO 2 concentrations increased the shoot-to-root ratios by reducing root growth and stimulating shoot growth, respectively. Soil salinity decreased root nodulation and N-fixation, but it ameliorated SO 2-induced injury. Twelve days after exposure to SO 2, foliar injury was apparent in the treatment of high SO 2 alone but was negligible in the high SO 2 and salinity treatment. The reduced SO 2 injury under saline conditions was probably achieved by decreasing SO 2 uptake through stomatal closure.

Studies on the effects of air pollution on limestone degradation in Great Britain

The CEGB and the Cathedrals Advisory Commission for England formed a Joint Working Party in 1985 to promote a research programme aimed at improving the understanding of the relationships between stone decay, atmospheric pollution and other factors. The programme has included exposure of limestone samples at York Minster and eight other sites in England and Scotland selected to give a mix of urban, marine and rural locations. All of the sites have comprehensive air pollution and meteorological monitoring and measurement of rainfall chemistry. At two sites samples have been fumigated with controlled levels of sulphur dioxide. Over all sites, there was a significant trend to increased weight loss with increase in average sulphur dioxide concentration, but a negative trend with total nitrogen oxides and with nitrogen dioxide. For sample exposures longer than 200 days, the sulphur dioxide dependence at the inland Liphook fumigation site was about half that found near the coast at Littlehampton. There was no significant trend to increase weight loss with total rainfall amount for the complete data set, but the analysis was dominated by the very wet Scottish site, which experienced the lowest average concentrations of air pollutants. A theoretical model for the chemical dissolution of rainwashed limestone has been derived from consideration of the ion and mass balances between the incident rain water and run-off water. The model has been fitted to the measured loss rates from the stonework field trials. With the exception of the very wet Scottish site, the difference between the stone loss rate, calculated from the model, and the mean measured loss rate for any particular exposure was generally smaller than the variation between the triplicate samples. Variation in the dry deposition velocity between sites and exposure periods does not appear to have been a very significant factor, and no residual effect due to the concentrations of nitrogen oxides was found. The natural solubility of limestone in water was the dominant term in describing the stone loss, and neutralization of the rainfall acidity the least significant. The volume of the intercepted rainfall and the variation in the pH of the run-off water with rainfall intensity have been identified as the two most significant terms which require more precise quantification. The data from the inland fumigation site used in the model predict a stone loss due to sulphur dioxide in the air of less than 1 μm yr −1 surface recession per ppb SO 2.

Phytotoxicity of sea-water aerosols on forest plants with special reference to the role of surfactants

Experiments were conducted in a wind tunnel to investigate the impact of synthetic sea-water aerosols, with or without the addition of sodium linear-alkylbenzene-sulfonate (LAS), a common pollutant of sea-water, on young plants of Pinus pinea and Quercus ilex. LAS had a minor direct toxic effect, but its presence was correlated with a greater absorbance of salts into leaf tissues. Sodium was the principal noxious agent in Q. ilex; in P. pinea the contributions of sodium and chloride were not different. Potassium levels decreased in both species as a consequence of saline stress; the levels of calcium and magnesium did not show any major variation. By using a gradient of LAS concentrations in sea-water (from 0 to 240 ppm), it was possible to identify a significant linear regression for sodium and chloride absorbed by the leaves. Total free amino acid content was significantly increased by the saline treatment in P. pinea and a consistent accumulation of proline took place; no such metabolic changes were observed in Q. ilex, which proved to be more salt stress tolerant. An exposure for 10 days of plants to 110 ppb SO 2 (a concentration which does not cause any macroscopic injury) before and/or after the spray induced a significant increase in toxicity of the saline treatment.