The oxidation of sulfur dioxide to sulfate aerosols in the plume of a coal-fired power plant

Instrumented aircraft have been used to determine the rate of oxidation of sulfur dioxide to sulfate aerosols within the dispersing plume of a coal-fired power plant. Measurements have been made in the stack and from 10 to 105 km downwind of a 2600-MW power plant. Sampling experiments were conducted during the winter of 1975–1976 and in the fall of 1976. Average temperatures and relative humidities varied from −5 to 17°C and 22 to 71% respectively. Data were also collected on sulfate production at night.An average of 1.1% and a maximum of 4.3% of the plume sulfur was in the form of sulfate. Most of the atmospheric oxidation that was observed appeared to occur in the immediate vicinity of the power plant. The average oxidation rate, beyond 10km, was found to be 0.2% h⁻¹. Analyses of individual particles showed that the sulfur found in plume particles is usually associated with submicron fly ash particles.     

Lagrangian measurements of sulfur dioxide to sulfate conversion rates

On the basis of Project MISTT data and proposed homogeneous gas phase oxidation mechanisms for sulfur dioxide, it has been suggested that the degree of mixing with background air, the chemical composition of the background air, and the intensity of the sunlight available are key factors determining the rate of sulfur dioxide to sulfate conversion. These hypotheses are examined in light of Lagrangian measurements of conversion rates in power plant plumes made during the Tennessee Plume Study and Project Da Vinci. It is found that the Lagrangian conversion rate measurements are consistent with these hypotheses. It has also been suggested that the concentration of ozone may serve as a workable surrogate for the concentrations of the free radicals involved in the homogeneous gas phase mechanism. The night-time Lagrangian data remind one that the gross difference in mean lifetime of ozone and free radicals can lead to situations in which the ozone concentration is not a good surrogate for the free radical concentrations.     

Airborne sulfur dioxide to sulfate oxidation studies of the INCO 381M chimney plume

Investigations of the rate of oxidation of SO₂ in the plume of the INCO 381 m chimney at Sudbury, Ontario, Canada were carried out using an instrumented helicopter. Over a wide range of experimental conditions, the SO₂ → SO²⁻₄ conversion rate was found to be relatively low — typically less than 0.5% h⁻¹. The paniculate sulfur found in the plume appeared to be mainly in the form of sulfuric acid and was less than 4% of the total plume sulfur. All results apply to distances within roughly 100 km from the chimney. No quantitative conclusion can be drawn regarding the reaction mechanism. There is evidence in the data for both homogeneous and heterogeneous processes.     

Atmospheric oxidation of sulfur dioxide: A review as viewed from power plant and smelter plume studies

An overview is presented of significant historical, recent, and new power plant and smelter plume studies which have been directed at understanding the atmospheric oxidation of sulfur dioxide. It can be concluded that the average rate of oxidation of sulfur dioxide in plumes entering into and mixing with clean air is generally less than 1 %h⁻¹ but with polluted urban air the rate can be at least twice as fast. In addition, a diurnal variation in the rate is sometimes observed that is near zero at night and approx. 3% during mid-day. Although there is a tendency for some scientific observers to select the homogenous over the hetrogenous mechanism as the dominant pathway for the oxidation, the basis for choice is not definitive and most likely both mechanisms are at times operative. Suggestions are advanced for new and important studies that can be performed with technologies just becoming available.     

Project mistt: Kinetics of particulate sulfur formation in a power plant plume out to 300 km

As part of the 1976 field program of Project MISTT, the plume of the coal-fired Labadie power plant near St Louis was positively identified and sampled from aircraft over a range exceeding 300 km and 10 h of transport during day and night on July 9 and July 18. Measurements were made of SO₂, NO_x, ozone, particulate sulfur and various other pollutant and meteorological parameters. For both days, it is found that the gas-to-particle conversion of sulfur occurred mostly during daylight hours. The ratio of particulate to total sulfur was related linearly with the total solar radiation dose experienced by the plume. The maximum rate of paniculate sulfur formation was less than 3%h⁻¹ on both days. Production of ozone was also observed within the plume on both occasions. Ground removal of total sulfur was found to be about 25% in the first 200 km, and its magnitude is compared to that of the gas-to-particle conversion.     

Formation of sulfate,ammonium and nitrate in an oil-fired power plant plume

A series of experiments was performed at the oil-fired Anclote power plant of the Florida Power Corp., Tarpon Springs, Florida. Plume samples at varying downwind locations were obtained by means of a high-volume filter pack. Operational oxygen levels during fuel combustion were varied experimentally; particulate sulfate and sulfuric acid concentrations in both flue gas and plumes increased directly with excess O₂ levels. Plume dropout of paniculate sulfate was found to occur during some experiments. A generalized trend toward increasing ammonium content of plume particulates with time was observed. Particulate nitrate formation did not indicate a similar trend. Oxidation of SO₂ to sulfate within a time frame of up to 100 min and 50 km ranged within 1–3 %, with but two runs exceeding 3 %. No correlation was found between any individual meteorological parameter and extent of oxidation. A significant difference between conversions during summer and winter runs was observed, conceivably attributable to differences in the vanadium content of the fuel oils and to some extent the combination of higher temperature, relative humidity, water partial pressure and unstable weather during the summer.     

Sulfur budget of a power plant plume

As part of the Midwest Interstate Sulfur Transformation and Transport (MISTT) study, the summer sulfur budget of the plume of the 2400 MW coal-fired Labadie power plant near St. Louis, Missouri is assessed via aircraft data, ground monitoring network data and a two-box model. The paniculate sulfur (S_p) formation rate is obtained from three-dimensional plume mapping combined with a high time-resolution S_p sampling technique. During noon hours the SO₂ conversion rate is found to be 1–4% per hour, compared to night rates below 0.5% per hour. Plume excess light scattering coefficient (b_scat) and excess S_p correlated well (r = 0.87), indicating most S_p is formed in the light-scattering size range.During daytime the well-mixed plume is transported at 5ms⁻¹ on the average; at night the July average wind speed at plume height is 12ms⁻¹ due to the low-level jet The nocturnal plume is less than 100 m thick at 400 m above ground and is decoupled from the surface until morning. Ground monitoring data from the Regional Air Pollution Study (RAPS) show that plume entrainment into the rising mixing layer is completed by 1000 Central Daylight Time (CDT). Due to daytime vertical mixing and nocturnal decoupling, the dry removal rate for the elevated plume is highest near noon. In a daily cycle, the plume sequentially passes through a reservoir regime, dissociated from delivery to the ground and then enters the mixing-removal regime.A two-box model representing the two regimes, with diurnally periodic rate constants for transformation and removal, is employed to estimate plume sulfur budgets. Ignoring wet removal, 30–45% of the SO₂ is estimated to be converted to S_p, half within the first day. Particulate sulfur is formed unevenly: the afternoon plume contributes more than its share because it rises so high that it has more time to react before removal begins. In short: transformation and removal occur mainly during the daytime, while transport is fastest at night. After a hard day of convection, reaction and deposition, the lower atmosphere relaxes at dusk while the midwestern plume takes off overnight on a jetstream and begins the next day's work 300–400 km from the stack.     

Atmospheric conversion of sulfur dioxide to particulate sulfate and nitrogen dioxide to particulate nitrate and gaseous nitric acid in an urban area

Sulfur dioxide, nitrogen dioxide, particulate sulfate and nitrate, gaseous nitric acid, ozone and meteorological parameters (temperature and relative humidity) were measured during the winter season (1999-2000) and summer season (2000) in an urban area (Dokki, Giza, Egypt). The average particulate nitrate concentrations were 6.20 and 9.80 microg m(-3), while the average gaseous nitric acid concentrations were 1.14 and 6.70 microg m(-3) in the winter and summer seasons, respectively. The average sulfate concentrations were 15.32 microg m(-3) during the winter and 25.10 microg m(-3) during the summer season. The highest average concentration ratio of gaseous nitric acid to total nitrate was found during the summer season. Particulate sulfate and nitrate and gaseous nitric acid concentrations were relatively higher in the daytime than those in the nighttime. Sulfur conversion ratio (Fs) and nitrogen conversion ratio (Fn) defined in the text were calculated from the field measurement data. Sulfur conversion ratio (Fs) and nitrogen conversion ratio (Fn) in the summer were about 2.22 and 2.97 times higher than those in the winter season, respectively. Moreover, sulfur conversion ratio (Fs) and nitrogen conversion ratio (Fn) were higher in the daytime than those in the nighttime during the both seasons. The sulfur conversion ratio (Fs) increases with increasing ozone concentration and relative humidity. This indicates that the droplet phase reactions and gas phase reactions are important for the oxidation of SO2 to sulfate. Moreover, the nitrogen conversion ratio (Fn) increases with increasing ozone concentration, and the gas phase reactions are important and predominant for the oxidation of NO2 to nitrate.     

Cloud nucleus formation in a power plant plume

A rate of production of ca 10¹⁶ particles s⁻¹ of H₂SO₄ aerosol that acts as cloud condensation nuclei at 1% supersaturation has been estimated to take place in the emission plume from the Four Comers power plant near Farmington, N.M. This generating plant produces about 2175MW at full capacity and emits about 3.7kgs⁻¹ of SO₂, 2.2 kgs⁻¹ of NO_x, and 0.9 kgs⁻¹ of particulates. The site area is desert; annual precipitation averages around 15cm, daytime relative humidity is typically 10–20% and annual sunshine is 75% of possible.An instrumented aircraft was utilized during five investigative periods over a 2-year span to measure plume parameters and to collect plume aerosol samples.The estimated production rate of 10¹⁶ particles s⁻¹ in the plume is equivalent to a gas phase oxidation of SO₂ and homogeneous nucleation-condensation of about 5 μg m⁻³h⁻¹ of H₂SO₄ and is consistent with this mechanism being the primary route for removal of SO₂.     

The evolution of photochemical smog in a power plant plume

The evolution of photochemical smog in a plant plume was investigated with the aid of an instrumented helicopter. Air samples were taken in the plume of the Cumberland Power Plant, located in central Tennessee, during the afternoon of 16 July 1995 as part of the Southern Oxidants Study – Nashville Middle Tennessee Ozone Study. Twelve cross-wind air sampling traverses were made at six distance groups from 35 to 116 km from the source. During the sampling period the winds were from the west–northwest and the plume drifted towards the city of Nashville TN. Ten of the traverses were made upwind of the city, where the power plant plume was isolated, and two traverses downwind of the city when the plumes were possibly mixed. The results revealed that even six hours after the release, excess ozone production was limited to the edges of the plume. Only when the plume was sufficiently dispersed, but still upwind of Nashville, was excess ozone (up to 109 ppbv, 50–60 ppbv above background levels) produced in the center of the plume. The concentrations image of the plume and a Lagrangian particle model suggests that portions of the power plant plume mixed with the urban plume. The mixed urban power plant plume began to regenerate O₃ that peaked at 120 ppbv at a short distance (15–25 km) downwind of Nashville. Ozone productivity (the ratio of excess O₃ to NO_y and NO_z) in the isolated plume was significantly lower compared with that found in the city plume. The production of nitrate, a chain termination product, was significantly higher in the power plant plume compared to the mixed plume, indicating shorter chain length of the photochemical smog chain reaction mechanism.     

Conversion of sulfur dioxide to sulfate during the da vinci flights

Simultaneous measurements of atmospheric particulate sulfate and SO₂ were made by tandem filter sampling during manned balloon flights. The balloon permitted measurement of chemical species evolution while following a given air mass. On the June 8, 1976, flight, the balloon encountered a relatively stagnant air mass, remaining above St. Louis County for most of the day before being carried off by nocturnal winds. Concentrations of sulfate and SO₂ remained relatively constant during an eight-hour period. Processes responsible for concentration changes were examined to set bounds upon the oxidation rate of SO₂. The data are consistent with an oxidation rate as low as zero and no greater than 4% h⁻¹.     

碱式硫酸铝溶液吸收二氧化硫

为了探讨碱式硫酸铝对二氧化硫的吸收效果,对所需试剂硫酸铝和碳酸钙的适宜比例（碱度）,以及碱式硫酸铝能稳定存在的铝量范围等进行了研究,测定了不同铝量和碱度的碱式硫酸铝对二氧化硫的吸收量以及pH值,并分析每种吸收液的饱和吸收量,最后将其与乙二胺/磷酸溶液的吸收情况进行对比。结果表明,碱度为40%时,铝量要保持在70 g/L以下才能在加热时不产生沉淀,吸收过程pH由4.5左右一直下降到2.0左右保持稳定,饱和吸收时间控制在140~160 min为宜,较为理想的方案是铝量32 g/L,碱度35%。     

Importance of deposition velocity for sulfur gas to sulfate particle transformation rates at the four corners power plant

Sulfate (SO₄) is known to contribute to visibility degradation. The rate of sulfur dioxide (SO₂) transformation to SO₄ in the real atmosphere is, therefore, a very important measurement parameter and model component. The rate of deposition or deposition velocity (v_d) to the ground influences the determination of the SO₂→SO₄ rate, and must therefore be carefully stated. v_d has rarely been consistently defined or carefully considered in transformation rate estimations.This paper will discuss the effect of uncertainty in our knowledge of v_d values on previously estimated transformation rates. Emphasis will be placed on a data base for the Four Corners power plant located in Farmington, New Mexico. This power plant is situated in the broad valley of the San Juan River having relative humidity rarely above 40% and with the power plant being the predominant source of anthropogenic particles in the valley. Thus, transformation rates are expected to be less variable than in environments subject to wide fluctuations in relative humidity and background pollution. Calculation of the transformation rate using earlier field studies but with the v_d range for SO₂ of 0.3, 0.8 and 1.2 cm s⁻¹ as low confidence, mean and high confidence values, results in a range of possible transformation rates from 0 to as much as 8.2% h⁻¹. It appears that uncertainty in v_d for SO₂ may hamper attempts to specify transformation rates in which plume loss to the ground is present. Given this, it is recommended that direct SO₄ measurements be taken in the plume.     

Oxidation of sulfur dioxide in aqueous ammonium sulfate aerosols containing manganese as a catalyst

The pseudo-first order reaction rate coefficient for the oxidation of SO₂ in air-borne water droplets containing (NH₄)₂SO₄ and MnSO₄ H₂O has been evaluated in a laminar gas flow apparatus. The sulfate and bisulfate formed in the reaction were detected using ³⁵S as a radioactive tracer. Droplet diameters ranged from 1 to 10 μm. The gas phase SO₂ concentrations ranged from 0.1 to 1.0 ppm. Initial measurements yielded a value of the rate coefficient as defined in Equation (2) of about 0.04s⁻¹ for the Mn²⁺ catalyzed reaction system at a manganese concentration of about 0.1 mol dm⁻³, at a temperature of 25°C, and at a relative humidity of 90%.