Performance Characteristics of Instrumental Methods for Monitoring Sulfur Dioxide

The performance characteristics of commercially available continuous sulfur dioxide monitors were determined. Conductimetric, colorimetric, and coulometric analyzers were investigated. The study was conducted to develop information on such instrument characteristics as stability, sensitivity, response time, collection efficiency, and response to interfering substances. The methodology and apparatus used to determine each operational parameter are described. The instrument performance data developed in this study should be useful to those involved in selection of instrumental methods for monitoring atmospheric sulfur dioxide.     

Performance Characteristics of Instrumental Methods for Monitoring Sulfur Dioxide

The performance characteristics of commercially available sulfur dioxide monitors were determined. Con-ductimetric, colorimetric, and coulometric analyzers were investigated. During this phase of the study, characteristics that were more closely related to field operation were studied. These included comparability of data among the instruments over a period of time, weekly calibration drift, maintenance requirements (including operating cost), unattended operation performance, and the effect of rotameter changes on calibration. The methodology and apparatus used to determine each operational parameter are described. The results of this study should be useful in the selection of instruments for monitoring sulfur dioxide.     

Improvement of Ambient Sulfur Dioxide Concentrations by Conversion from Low to High Stacks

A study of the “before” and “after” ground-level S0₂ concentrations near the Muskingum River Plant of the American Electric Power System shows that the conversion from low to high stacks has accomplished marked reductions in ambient concentrations. These reductions are in reasonable agreement with theoretical calculations and are most apparent within 5 km of the source. EPA Standards are now being met in this area despite the presence of the 1440 MW power plant burning 5% sulfur fuel with no treatment of the stack gas.     

Ambient Air Monitoring for Sulfur Compounds

The role of sulfur compounds in our environment has been the subject of much speculation during the past two decades. An evaluation of the effect of man-made contributions to the biogeochemical sulfur cycle requires a comprehensive examination of source magnitudes, atmospheric concentrations and removal processes. Many voids exist in our present knowledge of these parameters despite the contributions of numerous researchers. Adequate information is needed concerning the various forms of sulfur as well as other critical constituents which exist in our biosphere so that their interrelationship and role in the mechanisms of the sulfur cycle may be more fully understood.     

The Effectiveness of a Tall Stack for Reduction of Ambient Sulfur Dioxide Concentrations:A Field Investigation

Of many available methods for limiting ground level pollutant concentrations, tall stacks are many times the simplest, most effective, and least costly. Although this is theoretically explicit, field validation of the soundness of this approach is often hampered by lack of comparable "before" and "after" data. In this study at the Alma Power Plant, appropriate air quality and meteorological measurements were made for several years before and after conversion from short to tall stacks. Comparison of these data show that the tall stack has reduced ambient levels of SO₂ by from 50 to 95 % in the vicinity of the plant. This study also found that use of a Turner-Briggs dispersion model in a valley situation gave fairly accurate and reliable estimates of air quality. The model was useful in designing the tall stack, assessing its impact and locating air quality monitors.     

A Comparison of Conductivity And West-Gaeke Analyses For Sulfur Dioxide

A comparison of the two most common methods used by air pollution control agencies for the analyses of sulfur dioxide is discussed in this paper. Samples were collected simultaneously (502 pairs) for an eight month period at eight sites in the City of Chicago, using the West-Gaeke and conductivity methods. These methods are analyzed statistically to ascertain the existence of a factor describing adequately any differences between methods.     

Relating Summer Ambient Particulate Sulfur,Sulfur Dioxide,and Light Scattering to Gaseous Tracer Emissions from the MOHAVE Power Project

ABSTRACT

Project MOHAVE was initiated in 1992 to examine the role of emissions from the 1580 MW coal-fired MOHAVE Power Project (MPP) on haze at the Grand Canyon National Park (GCNP), located about 130 km north-northeast of the power plant. Statistical relationships were analyzed between summertime ambient concentrations of a gaseous perfluorocarbon tracer released from MPP and ambient SO₂, particulate sulfur, and light scattering to evaluate whether MPP's emissions could be transported to the GCNP and then impact haze levels there. Spatial analyses indicated that particulate sulfur levels were strongly correlated across the monitoring network, regardless of whether the monitoring stations were upwind or downwind of MPP. This indicates that particulate sulfur levels in this region were influenced by distant regional emission sources. A significant particulate sulfur contribution from a point source such as MPP would result in a non-uniform pattern downwind. There was no suggestion of this in the data.

Furthermore, correlations between the MPP tracer and ambient particulate sulfur and light scattering at locations in the park were virtually zero for averaging times ranging from 24 hr to 1 hr. Hour-by-hour MPP tracer levels and light scattering were individually examined, and still no positive correlations were detected. Finally, agreement between tracer and particulate sulfur did not improve as a function of meteorological regime, implying that, even during cloudy monsoon days when more rapid conversion of SO₂ to par-ticulate sulfur would be expected, there was no evidence for downwind particulate sulfur impacts. Despite the fact that MPP was a large source of SO₂ and tracer, neither time series nor correlation analyses were able to detect any meaningful relationship between MPP's SO₂ and tracer emission “signals” to particulate sulfur or light scattering.     

Relationships Between Sulfur Dioxide Concentration Determined By the West-Gaeke and Electroconductivity Methods

Sulfur dioxide concentrations in the atmosphere are commonly determined by the West-Gaeke and electro-conductivity methods. As a part of the United States-Japan Cooperative Air Pollution Measurement Studies, parallel sampling with a 24-hr bubbler, a 1-hr bubbler, and an electroconductivity instrument was conducted in Kawasaki, Japan, between Jan. 12 and Mar. 25 and between Aug. 19 and Sept. 30, 1966. These time periods were chosen because of the seasonal variation in the air pollution levels. Fair agreement was obtained between the 24-hr sample values and the daily mean values of the 24 hourly samples analyzed by the West-Gaeke method. Sulfur dioxide concentrations determined by the electroconductivity method were greater than those determined by the West-Gaeke method, particularly in the winter season. Relationships between the sulfur dioxide concentrations determined by these two methods are discussed.     

Photo-Oxidation of Sulfur Dioxide

SO₂/O₂ mixtures were photolyzed at 3130 Å and in the range 2500–4000 Å at room temperature. The only product of photolysis was SO₃. Attempts to estimate ф(S0₃) using mass spectrometry, l.R. spectroscopy and pressure change measurements were unsuccessful, because it was not possible to obtain reproducible quantitative estimates of SO₃. ф(SO₂) values were determined by monitoring the 3130 Å absorption for its concentration measurements. ф(SO₂) was independent of SO₂ (11.6 to 50.4 torr) and O₂ (50.0 to 390.6 torr) pressures. At 3130 Å, ф(SO₂) varied between 1.5 × 10^?2 and 2.2 X 10^?2. Over the integrated range 2500–4000 Å ф(SO₂) values of 2.1 X 10^?3 to 2.9 X 10^?3 were obtained. The differences in ф(SO₂) values are explained in terms of wavelength dependence of the rate constants for the two primary reactions: ¹SO₂ + SO₂ → 2SO₂(1) and ¹SO₂ + SO₂ → ³SO₂ + SO₂(2); (k₂/k₁) _{3130 Å} ≈ 10(k₂/k₁)_{2500–4000 Å}.     

Nashville Sulfur Dioxide Emission Inventory and the Relationship of Emission to Measured Sulfur Dioxide

A detailed inventory of sulfur dioxide emissions was prepared as part of the Nashville Community Air Pollution Study conducted by the Public Health Service during 1958–59. The primary purpose of the inventory was to provide data for a study of the relationship between the emission of sulfur dioxide and measured ambient levels. The development of the inventory, data collection methods, and calculations are described. Ambient levels of sulfur dioxide were related to average emissions of sulfur dioxide in such a way (correlation coefficient = 0.81) that mean seasonal concentrations of atmospheric sulfur dioxide in square-mile areas could be predicted with fairly good confidence from a knowledge of sulfur dioxide emissions. For these long-period {average) predictions meteorological variables can be disregarded. On a square-mile basis, on the average, one ton of sulfur dioxide emitted per day produced a mean atmospheric sulfur dioxide concentration of 0.022 ppm, and 10 tons of sulfur dioxide per day produced a concentration of 0.067 ppm.     

Sulfur Dioxide and Material Damage

Whereas most estimates of material damage are based on industrial surveys, the estimates produced in this study were derived from material damage experiments and ambient air quality data. Air quality data on SO₂ were obtained from 200 or more monitoring sites primarily located in heavily populated or polluted areas. Material threshold damage function data were then compared with SO₂ levels, and an estimate of losses, as reflected in increased maintenance and replacement costs, was determined. Estimates of the total stock of various materials in use were derived from census and industry data and allocated geographically according to population. A substantial decrease in the ambient SO₂ levels, particularly in larger urban areas, has occurred during the past five years. From 1968 to 1972, the estimated amount of material damage from SO₂ in the U. S. decreased from $900 million/yr to less than $100 million. During this period, the estimated percentage of man made materials exposed to SO₂ levels exceeding the proposed secondary annual average standard (60 μg/m³) and primary annual average standard (80 μg/m³) in the U. S. fell respectively, from 20% to less than 5% and from more than 10% to less than 1%. Most of the present loss is attributed to corrosion damage of metallic surfaces that are normally exposed to the ambient environment.     

Flash Photolysis of Sulfur Dioxide

The body of information presented in this paper is directed to photochemists and air pollution scientists interested in species which result from the interaction of SO₂ and light. When SO₂ at low pressures is subjected to an intense photolysis flash, the characteristic, very structured SO₂absorption spectrum disappears immediately after the flash and is replaced by a continuous absorption. The continuous absorption gradually decays and the normal SO₂ absorption spectrum returns. The initial absorbance of the continuous absorption is proportional to the square of the SO₂ pressure and the square of the flash irradiance. From these facts we propose the formation of a metastable dimer of SO₂ formed by the collision of two excited molecules. Some properties of this dimer are: natural lifetime = 2 sec; energy above separated monomers = 4 kcal; lifetime at atmospheric pressure = 1 sec (quenching coefficients with several foreign gases = 10^-20 cm³/sec molecule); absorption of ultraviolet light results in photode-composition of the dimer into monomeric SO₂. The long lifetime of this species and its low quenching cross section may make it an important intermediate in photochemical reactions of SO₂. The relatively low excitation energy of the metastable species indicates it may also be an intermediate in thermally excited reactions and perhaps an important component of smoke stack effluent.     

Alternative Strategies for Control of Sulfur Dioxide Emissions

Achievement of air quality goals now more than ever requires careful consideration of alternative control strategies in view of national concerns with energy and the economy. Three strategies which might be used by coal-fired steam electric plants to achieve ambient air quality standards for sulfur dioxide have been compared, and the analysis shows that the desired objective can be achieved using the intermittent control strategy with substantially less impact on the environment, less consumption of energy, and at a much lower economic cost than using either stack gas scrubbing or low-sulfur coal.     

Solid Absorbent Method for Sampling and Analysis of Nitrogen Dioxide in Ambient Air

A sampling and analysis system was developed for measuring concentrations of nitrogen dioxide in ambient air. Copper shot was found to be an effective absorbent for collecting samples at ambient levels. The analytical system was based on the desorption of the sample from the copper by heating in a hydrogen carrier stream. The desorbed sample was then determined by a combination of catalytic pyrolysis, which converted it to ammonia, and a Coulson Conductivity Detector. Data are presented showing overall recovery, effects of storage of collected samples, results for 24-hour sampling and interferences. Studies indicated the feasibility of the method for short time sampling as well as for 24-hour sampling periods. The detection limit was shown to be as little as 100 ng NO₂ in laboratory studies. This solid absorbent method provides a simple, convenient, and compact means for air sampling.     

Simultaneous Sulfur Dioxide and Nitrogen Dioxide Removal by Calcium Hydroxide and Calcium Silicate Solids

ABSTRACT

At conditions typical of a bag filter exposed to a coal-fired flue gas that has been adiabatically cooled with water, calcium hydroxide and calcium silicate solids were exposed to a dilute, humidified gas stream of nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) in a packed-bed reactor. A prior study found that NO₂ reacted readily with surface water of alkaline and non-alkaline solids to produce nitrate, nitrite, and nitric oxide (NO). With SO₂ present in the gas stream, NO₂ also reacted with S(IV), a product of SO₂ removal, on the exterior of an alkaline solid. The oxidation of S(IV) to S(VI) by oxygen reduced the availability of S(IV) and lowered removal of NO₂. Subsequent acidification of the sorbent by the removal of NO₂ and SO₂ facilitated the production of NO. However, the conversion of nitrous acid to sulfur-nitrogen compounds reduced NO production and enhanced SO₂ removal. A reactor model based on empirical and semi-empirical rate expressions predicted rates of SO₂ removal, NO₂ removal, and NO production by calcium silicate solids. Rate expressions from the reactor model were inserted into a second program, which predicted the removal of SO₂ and NO_x by a continuous process, such as the collection of alkaline solids in a baghouse. The continuous process model, depending upon inlet conditions, predicted 30-40% removal for NO and 50-90% removal for SO₂. These x 2 results are relevant to dry scrubbing technology for combined SO₂ and NO_x removal that first oxidizes NO to NO₂ by the addition of methanol into the flue duct.     

Modification of Sulfur Dioxide Injury to Tobacco and Tomato by Varying Nitrogen and Sulfur Nutrition

The body of information presented in this paper is directed to plant scientists who are concerned with factors which modify the susceptibility of plants to air pollutants.

Tobacco and tomato plants grown in sand-solution culture with varying levels of nitrogen or sulfur were exposed to injurious levels of sulfur dioxide. Plants of both species which were deficient in either nutrient exhibited decreased susceptibility to the gas compared with plants grown at optimal levels of each nutrient. Foliage of these plants was also found to have increased stomatal resistance as measured by a porometer and decreased total sulfur accumulations. Plants grown at optimum levels of each nutrient showed increased susceptibility over that of the deficient plants. Stomatal resistance was lower and sulfur accumulation was greater than in the deficient plants. At the supra-optimal nitrogen and sulfur levels, there were differences in susceptibility. Over-abundant nitrogen appeared to decrease susceptibility whereas over-supplies of sulfur increased it.

The response of plants with deficient or optimal supplies of either nutrient might be explained by the effects of nutrition on stomatal activity and hence on ability to absorb SO₂S from the atmosphere, mineral deficiency being known to increase stomatal resistance, and mineral sufficiency, to decrease stomatal resistance by virtue of increased efficiency of water use. The difference in response between plants overfertilized with respect to nitrogen or sulfur is explained by the fact that sulfur is both nutrient and phytotoxicant at the same time. Having already been oyersupplied with sulfur by absorption from the nutrient substrate, the high-sulfur plants were unable to withstand additional sulfur accumulation from the atmosphere and hence were more severely injured.

Increased carbohydrate accumulation in the nitrogen- and sulfur-deficient plants might play an additional role in protection from SO2-injury.     

从空气中捕集CO_2的研究现状

从空气中捕集CO2是一项有前途的新CO2减排技术,具有传统CO2减排技术所没有的多项优势。文中首先介绍了从空气中捕集CO2的意义、可行性、吸收剂选择和捕集器设计原则;然后介绍了最新的原型设计及成本预计;最后讨论了该技术的现存问题和对其他技术的启发。