Atmospheric sulfur dioxide using sulfation

Summary of Non-Marine Sulfur Emissions. S S values for continental sources of atmospheric sulfur dioxide vary, ranging between -32 and +10 0/00. This makes it difficult to use sulfur isotope ratios to distinguish sulfate from these individual sources. It appears that the f S value for marine biogenic sulfur is much more enriched in the heavier isotope than sulfur from continental origins. Therfore, it should be possible to isotopically distinguish between marine biogenic and continentally-derived sulfur. 

Sulfur is assimilated by plants as the sulfate ion, S04 . In addition, in areas where the atmosphere is contaminated with SOj, sulfur may be absorbed as sulfur dioxide by plant leaves. Atmospheric sulfur dioxide levels have been high enough to kill vegetation in some areas (see Chapter 11). However, some experiments designed to show SO2 toxicity to plants have resulted in increased plant growth where there was an unexpected sulfur deficiency in the soil used for the experiment. 

A smaller factor in ozone depletion is the rising levels of N2O in the atmosphere from combustion and the use of nitrogen-rich fertilizers, since they ate the sources of NO in the stratosphere that can destroy ozone catalyticaHy. Another concern in the depletion of ozone layer, under study by the National Aeronautics and Space Administration (NASA), is a proposed fleet of supersonic aircraft that can inject additional nitrogen oxides, as weU as sulfur dioxide and moisture, into the stratosphere via their exhaust gases (155). Although sulfate aerosols can suppress the amount of nitrogen oxides in the stratosphere... 

Titanium Sulfates. Solutions of titanous sulfate [10343-61-0] ate readily made by reduction of titanium(IV) sulfate ia sulfuric acid solutioa by electrolytic or chemical means, eg, by reduction with ziac, ziac amalgam, or chromium (IT) chloride. The reaction is the basis of the most used titrimetric procedure for the determination of titanium. Titanous sulfate solutions are violet and, unless protected, can slowly oxidize ia coatact with the atmosphere. If all the titanium has been reduced to the trivalent form and the solution is then evaporated, crystals of an acid sulfate 3 Ti2(S0 2 [10343-61-0] ate produced. This purple salt, stable ia air at aormal temperatures, dissolves ia water to give a stable violet solutioa. Whea heated ia air, it decomposes to Ti02, water, sulfuric acid, and sulfur dioxide. 

Health effects attributed to sulfur oxides are likely due to exposure to sulfur dioxide, sulfate aerosols, and sulfur dioxide adsorbed onto particulate matter. Alone, sulfur dioxide will dissolve in the watery fluids of the upper respiratory system and be absorbed into the bloodstream. Sulfur dioxide reacts with other substances in the atmosphere to form sulfate aerosols. Since most sulfate aerosols are part of PMj 5, they may have an important role in the health impacts associated with fine particulates. However, sulfate aerosols can be transported long distances through the atmosphere before deposition actually occurs. Average sulfate aerosol concentrations are about 40% of average fine particulate levels in regions where fuels with high sulfur content are commonly used. Sulfur dioxide adsorbed on particles can be carried deep into the pulmonary system. Therefore, reducing concentrations of particulate matter may also reduce the health impacts of sulfur dioxide. Acid aerosols affect respiratory and sensory functions. 

The deleterious effect of sulfur dioxide and sulfites in domestic water is increased corrosivity owing to the lowered pH. However, oxidation of sulfite to sulfate in aqueous solutions uses dissolved oxygen, and lliis may retard corrosion. While llte oxichition of sulfite and sulfiirous acid to sulfate and sulfuric acid in the atmosphere is an environmental concern, this reaction is too... 

Further studies are needed to give better dose-response information and to provide a frequency distribution of the population response to oxidants alone and in combination with other pollutants at various concentrations. Such studies should include the effects of mixed pollutants over ranges corresponding to the ambient atmosphere. With combinations of ozone and sulfur dioxide, the mixture should be carefully characterized to be sure of the effects of trace pollutants on sulfate aerosol formation. The design of such studies should consider the need to use the information for cost-benefit analysis and for extrapolation from animals to humans and from small groups of humans to populations. Recent research has indicated the possibility of human a ptation to chronic exposure to oxidants. Further study is desirable. 

While hexavalent chromium is reduced to its trivalent form in treatment systems mainly so that the metal can be precipitated, this also lowers its toxicity by a factor of 1000. Ferrous sulfate can be used for this reduction, but is not popular due to its inefficiency, high sludge generation rate, and expense. Sulfur dioxide gas is a far more economical reducing agent, although it is efficient only at low pH, preferably below 2. There can also be problems with atmospheric emission of S02 in this process. 

A possible function of this intracellular sulfur cycle is to buffer, i.e. to homeostatically regulate, the cysteine concentration of the cells. Irrespective of whether sulfate, cysteine, or sulfur dioxide is available as sulfur source, the intracellular sulfur cycle would allow a plant cell to use as much of these compounds as necessary for growth and development. At the same time, it would give a plant cell the possibility to maintain the cysteine pool at an appropriate concentration by emitting excess sulfur into the atmosphere. Thus, emission of hydrogen sulfide may take place when the influx of sulfur in the form of sulfate, cysteine, or sulfur dioxide exceeds the conversion of these sulfur sources into protein, glutathione, methionine, and other sulfur-containing components of the cell. 

Simultaneous materials-deterioration and aerometric measurements are made at one location. Correlations of deterioration parameters with varying atmospheric physical and chemical parameters will be examined using multivariate statistical methods when sufficient data are accumulated. Deterioration parameters being measured include rates of surface erosion, surface chemical changes, and microstructural alterations. Atmospheric monitoring includes particulate sulfate, nitrate, and sulfur dioxide concentrations, as well as temperature, relative humidity, and parameters of wind and water erosion. 

This oxidation is of third order and its reaction rate is independent of the temperature. Using reaction rate values measured under laboratory conditions and the concentrations of M and O for different levels of the atmosphere, Cadle and Powers calculated that this process can be significant only above 10 km if the S02 concentration is 1 /ig m 3 STP. The residence time of sulfur dioxide molecules is estimated to be 103 hr at an altitude of 10 km, while at 30 km the corresponding figure ranges from 5 hr to 10 hr. Hence it seems probable that this reaction is not important in the troposphere. However, it may play an important role in the formation of the stratospheric sulfate layer (Subsection 4.4.3). 

Another interesting example of the biological influence on atmospheric chemistry is provided by sulfur. Under natural conditions, sulfur compounds in the atmosphere are provided by the oceanic emission of dimethyl disulfide (DMS). This biogenic emission results from the breakdown of sulfoniopropionate (DMSP), which is thought to be used by marine phytoplankton to control their osmotic pre.ssure. The oxidation of DMS leads to the formation of sulfur dioxide, which is further converted to sulfate particles. As indicated above, these particles, by scattering back to space some of the incoming solar radiation, tend to cool the earth s surface. Their presence also affects the optical properties of the clouds, which introduces an indirect climatic effect. 

The second method involves measurement of the temperature, time of wetness, amount of sulfur in the atmosphere, md the amoimt of chloride in the atmosphere. Temperature and hiunidity information can be used to estimate the time of wetness. This estimation is based on the percentage of time that the temperature is above freezing, O C, and the relative humidity is at the same time above 80 %. Once the time of wetness is known, it is then possible to determine a time of wetness class (Table 2). Sulfur dioxide content of the atmosphere can be estimated either by measurement of the concentration in the atmosphere over some period of time or by means of the sulfation plate or candle. This information is then used to develop a sulfur dioxide class or P class (Table 3). The chloride dry plate or wet candle method is used to obtain the chloride deposition rate of the atmosphere that is then converted to a chloride class or S class (Table 3). The corrosion class or C class can be obtained for the time of wetness, chloride, and sulfur dioxide classes (Table 4). Once the corrosion class is known, it is possible to estimate the corrosion damage that will occur in either short-term or long-term exposures for the five metals, steel, weathering steel, aluminum, copper, and zinc (Table 5). The detailed information on this method is discussed in Tables 2-5. 

There are two accepted methods for determining the sulfur dioxide (SO2) concentration in the atmosphere of interest. Both employ the affinity of lead oxide for sulfur dioxide. The most common technique uses sulfation plates. This procedure is covered in dqtail in ASTM G 91, Test Method for Monitoring Atmo heric SO2 Using the Sulfation Plate Technique. These devices are no longer available for purchsise, but must be prepared in the laboratory. The second method is the peroxide candle, similar in its function to the chloride candle. The procedure suggests a 30-day exposure, followed by a standard sulfate analysis. This procedure is covered by ASTM D 2010, Test Methods for Evaluation of Total Sulfation Activity in the Atmosphere by the Lead Dioxide Technique. In both cases, the results are calculated as the capture rate of SO2 per unit area, normally per m. ... 

Coal ash corrosion is a widespread problem for superheater and reheater tubes in coal fired power plants that bum high-sulfur coals. The accelerated corrosion is caused by liquid sulfates on the surface of the metal beneath an over-lying ash deposit. Coal ash corrosion is very severe between 540 and 740°C (1000°F and 1364°F) because of the formation of molten alkali iron-trisulfate. Considerable work has been done to predict corrosion rates based on the nature of the coal (its sulfur and ash content). This was accomplished by the exposure of various alloys to synthetic ash mixtures and synthetic flue gases. The corrosion rates of various alloys were repotted in the form of iso-corrosion curves for various sulfur dioxide, alkali sulfiite, and temperature combinations. An equation was developed to predict corrosion rates for selected alloys from details of the nature of ash by analyzing deposits removed from steam generator tubes and from test probes installed in a boiler [33]. Then laboratory tests were conducted using coupons of various tdloys coated with synthetic coal ash that was exposed to simulated combustion gas atmospheres. 

There are two widely used methods for determining the sulfur dioxide (SO ) concentration in the atmosphere of interest Both employ the affinity of lead oxide to react with gaseous SO to form lead sulfate. The most common method used in corrosion work is the sulfation. These devices can be either purchased or prepared in the laboratory. They consist of small disks of lead oxide that are exposed facing the ground under a small shelter to prevent the reactive paste from being removed by the elements [15]. 

---