SO2 Profiles Research Articles

Activities of Copper Oxide and Cu−V and Cu−Mo Mixed Oxides for H2S Removal in the Presence and Absence of Hydrogen and Predictions of a Deactivation Model

Considering the importance of high-temperature removal of H2S from industrial gases, sorption studies were carried out on copper oxide and Cu−V and Cu−Mo mixed oxides in the absence and presence of hydrogen in a fixed-bed reactor. Experiments were carried out in a wide temperature range between 300 and 700 °C. A significant amount of SO2 was produced with CuO sorbent in the absence of hydrogen. In the case of mixed oxide sorbents, SO2 formation was detected even in the presence of hydrogen. On the basis of the experimental concentration profiles of H2S, SO2, and H2O measured in the reactor effluent and XRD results for the solid products, reaction sequences were proposed in reducing (in hydrogen) and nonreducing atmospheres. A deactivation model proposed for such noncatalytic gas−solid reactions gave excellent predictions of the H2S breakthrough curves. Sorption rate parameters obtained in the absence of hydrogen were found to be larger than the corresponding values in the presence of hydrogen. Partial red...

Optimisation of a wet FGD pilot plant using fine limestone and organic acids

The effects of adding an organic acid or using a limestone with a fine particle size distribution (PSD) have been examined in a wet flue gas desulphurisation (FGD) pilot plant. Optimisation of the plant with respect to the degree of desulphurisation and the residual limestone content of the gypsum has been the aim of the work. In contrast to earlier investigations with organic acids, all essential process parameters (i.e. gas phase concentration profiles of SO 2, slurry pH profiles, and residual limestone in the gypsum) were considered. Slurry concentrations of adipic acid in the range of 0– 7 mM were employed. The overall degree of desulphurisation in the plant increased from 83% at 0 mM to 90% at 3 mM and the residual limestone level was reduced from 4.6 to 1.4 wt% . Increasing the slurry concentration of adipic acid above 3 mM gave only a slightly higher degree of desulphurisation. The wet FGD model of Kiil et al. (Ind. Eng. Chem. Res., 37 (1998) 2792) was extended to include buffer systems and verified against experimental data. Subsequently, the model was used as a tool to identify the optimal organic acid dissociation constants (as pK a values) and concentration levels at different operating conditions. At a holding tank pH of 5.5 and a temperature of 50°C, simulations with Bryozo limestone and a monoprotic buffer suggested that the optimum pK a value is between 4.5–5.5 and 5.5–6.5 with respect to the degree of desulphurisation and the residual limestone level, respectively. Adipic acid has pK a values close to these ranges ( pK 1=4.40 and pK 2=5.41 at 50°C). Changing limestone type (in the absence of organic acids) to one with a lower average particle size (i.e. from 20 to 4 μm ) increased the overall measured degree of desulphurisation from 83 to 87% and reduced the residual limestone level from 4.6 to 1.3 wt% . Increasing the holding tank pH level from 5.5 to 5.8 affected the degree of desulphurisation and the residual limestone level only slightly. At holding tank pH levels between 5.88 and 5.90, a high degree of desulphurisation was observed, but the residual limestone content in the gypsum increased to somewhere between 19 and 30 wt% , making this pH range unsuitable for use in a full-scale plant. The investigations have shown that both the addition of organic acids and the use of a limestone with a fine PSD can be used to optimise wet FGD plants.

Vertical distributions of sulfur species simulated by large scale atmospheric models in COSAM: Comparison with observations

A comparison of large-scale models simulating atmospheric sulfate aerosols (COSAM) was conducted to increase our understanding of global distributions of sulfate aerosols and precursors. Earlier model comparisons focused on wet deposition measurements and sulfate aerosol concentrations in source regions at the surface. They found that different models simulated the observed sulfate surface concentrations mostly within a factor of two, but that the simulated column burdens and vertical profiles were very different amongst different models. In the COSAM exercise, one aspect is the comparison of sulfate aerosol and precursor gases above the surface. Vertical profiles of SO2, SO2−4, oxidants and cloud properties were measured by aircraft during the North Atlantic Regional Experiment (NARE) experiment in August/September 1993 off the coast of Nova Scotia and during the Second Eulerian Model Evaluation Field Study (EMEFSII), in central Ontario in March/April 1990. While no single model stands out as being best or worst, the general tendency is that those models simulating the full oxidant chemistry tend to agree best with observations although differences in transport and treatment of clouds are important as well.

The role of biologically-enhanced pore water transport in early diagenesis: An example from carbonate sediments in the vicinity of North Key Harbor, Dry Tortugas National Park, Florida

Biologically enhanced pore water irrigation affects the course of early diagenesis in shallow marine sediments, as illustrated here for the carbonate sediments from North Key Harbor, Dry Tortugas National Park, Florida. Whereas macrofaunal activity at the study site extends approximately 15 cm below the water-sediment interface, measured O 2 microprofiles only show O 2 penetration to depths of a few mm. This apparent discrepancy can be explained by considering the 3-D O 2 distribution in the burrowed sediments. Calculations based on an idealized tube model for burrow irrigation show that measureable O 2 concentrations are limited to the immediate vicinity of burrows. Given the observed burrow density (705 ± 15 m -2 ), a randomly positioned O 2 microprofile has a high probability (>90%) to fall outside the reach of radial O 2 diffusion from burrows. Hence, the shallow penetration depths recorded at the site do not exclude a much deeper supply of O 2 in the sediment via the burrows. Other characteristic features observed in the upper 15-20 cm of the sediments, in particular, the absence of SO 4 2- depletion and the presence of subsurface maxima in the profiles of NH 4 + and TCO 2 , are also the result of pore water irrigation. These features are reproduced by the multicomponent reactive transport model STEADYSED1. Results of the model simulations indicate that bacterial SO 4 2- reduction is the dominant pathway of organic carbon degradation, but that consumption of SO 4 2- in the sediments is compensated by its enhanced transport by irrigation. Thus, depth profiles of SO 4 2- may be poor indicators of the importance of SO 4 2- reduction in irrigated sediments.

The relationship between regional SO 2 emissions and downwind aerosol sulfate concentrations in the northeastern US

Our research group has been continuously measuring aerosol sulfate at Whiteface Mountain, New York, since 1979 and at Mayville, New York, since 1984. Monthly aerosol SO 2− 4 concentrations for these sites are reported here through 1997. Seasonal and long-term profiles of SO 2− 4 are presented along with SO 2 concentrations. As these sites are directly downwind of the high SO 2 emission region in the Midwestern United States and the same sampling and analytical protocol has been maintained, they are ideally suited to evaluate long-term trends. The recent reductions in SO 2 emissions in response to provisions of the 1990 Clean Air Act provide an excellent opportunity to evaluate the sulfur source–receptor relationship. A linear relationship is demonstrated between aerosol SO 2− 4 and total sulfur (S T, sum of S present as SO 4 and SO 2) concentrations at these sites and SO 2 emissions upwind in the Midwest. This is the most direct evidence to date that deposition of sulfur in the Northeast is linearly related to upwind SO 2 emissions. The results support the possibility of using the ratio of SO 2− 4/SO 2 emissions to develop an empirical source–receptor relationship for the region.

大気中微量物質計測用多波長DIALシステムの開発

A multiwavelength differential absorption lidar system for measuring vertical concentration profiles of atmospheric SO2, NO2, and O3 was developed. The system contains two Nd: YAG pumped dye lasers, each capable of alternate oscillation with two wavelengths, and can emit a sequence of four wavelengths in the ultraviolet and visible regions. The geometrical form factor was calculated for biaxial and coaxial configurations, and the former was adopted for its ability to eliminate scattering from close range during long range measurement. The system can be used for high-resolution, multiwavelength DIAL measurement of a single species or simultaneous two-wavelength DIAL measurement of two species. As a preliminary measurement, O3 concentration was measured in the lower troposphere. The return signals are in agreement with the calculated geometrical form factors, and simultaneous null and DIAL profile measurements show that the instrumental error due to beam misalignment was low.

Atmospheric trace gas sounding with SCIAMACHY

Abstract SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY) is a contribution to the ENVISAT-1 satellite, which is to be launched in late 2000. The SCIAMACHY instrument is designed to measure sunlight transmitted, reflected and scattered by the Earth's atmosphere or surface. The instrument measures simultaneously from the UV to the NIR spectral spectral region (240 – 2380 nm). Observations are made in alternate nadir and limb viewing geometries and also for solar sunrise and lunar moonrise occultation. Inversion of the SCIAMACHY measurements will provide the following: the amount and distributions of some important trace gases O3, BrO, OClO, ClO, SO2, H2CO, NO2, CO, CO2, CH4, H2O, N2O, p, T, aerosol, and radiation flux profiles, cloud cover and cloud top height. Combination of the near simultaneous limb and nadir observations enables the tropospheric column amounts of O3, NO2, CO, CH4, H2O, N2O, SO2, and H2CO to be detected. SCIAMACHY will provide new insight into the global behaviour of the troposphere and the stratosphere.

Improved atmospheric trace gas measurements with an aircraft‐based tandem mass spectrometer: Ion identification by mass‐selected fragmentation studies

We have built and employed an aircraft‐borne triple quadrupole mass spectrometer (TQMS) for fragmentation studies of mass‐selected ions in the upper troposphere and lower stratosphere. The fragmentation studies included both ambient and artificially produced ions relevant for the measurement of atmospheric trace gases by ion molecule reaction mass spectrometry (IMRMS) and led to an unambiguous identification of the chemical composition of important ions used for IMRMS measurements. Among these are the product ions of ion molecule reactions of CO3−(H2O)n and H3O+(H2O)n ions with HNO3, SO2, acetone, HCN, and methyl cyanide. These reactions have been studied in the laboratory, and ions having the same masses as the expected product ions have been previously observed in atmospheric IMRMS spectra. The present fragmentation studies are the first to actually identify the chemical composition of these ions during aircraft measurements in the upper troposphere and lower stratosphere and demonstrate that these ions can reliably be used for atmospheric trace gas measurements. Furthermore, the fragmentation studies gave indications for the existence and the possible identification of previously unknown ions. Among these the tentative identification of CO3−H2O2 offers the possibility for sensitive measurements of H2O2 by IMRMS. The fragmentation studies were accompanied by IMRMS measurements of atmospheric trace gases using the TQMS. Altitude profiles of HNO3, SO2, and lower limits for H2O2 are shown.

Modeling study of cloud droplet nucleation and in‐cloud sulfate production during the Sanitation of the Atmosphere (SANA) 2 campaign

Based upon the measurements of vertical profiles of gaseous SO2, H2O2, O3, and meteorological parameters from aircraft and of the aerosol chemical composition and gaseous NH3, HNO3, and SO2 at the surface in southeastern Germany (Melpitz) during the Sanitation of the Atmosphere (SANA) 2 campaign, realistic modeling of cloud droplet nucleation and in‐cloud sulfate production was performed with an explicit microphysical cloud model with size‐resolved chemistry and cloud top entrainment. For the fair weather cumulus observed during the measurements, the calculated cloud droplet number concentrations could be as high as 2000 cm−3 (and precloud aerosol sulfate up to 9.1 μg m−3), indicating strong sulfur pollution at Melpitz during the campaign. The in‐cloud sulfate production is within 1.5–5.0 μg m−3, depending on the initial gaseous NH3 concentration in the parcel. This result shows the necessity of gaseous NH3 vertical profile measurements. Entrainment can reduce the cloud droplet number concentration and cause the distribution of in‐cloud produced sulfate to shift toward larger particle sizes. Under the cases we studied, we do not find a significant effect of cloud top gaseous H2O2 entrainment on the in‐cloud sulfate production. For the adiabatic cases the departure of bulk water H2O2 from the Henry's law equilibrium is very small. When entrainment included, however, bulk water H2O2 concentrations could be clearly less than the equilibrium values, and the deficiencies are higher (>20%) for droplets larger than 10 μm radius. Our results suggest that entrainment could be one of the important factors to account for the measured H2O2 deficiency in cloud water.

Experimental Investigation and Modeling of a Wet Flue Gas Desulfurization Pilot Plant

A detailed model for a wet flue gas desulfurization (FGD) pilot plant, based on the packed tower concept, has been developed. All important rate-determining steps, absorption of SO2, oxidation of HSO3-, dissolution of limestone, and crystallization of gypsum were included. Population balance equations, governing the description of particle size distributions of limestone in the plant, were derived. Model predictions were compared to experimental data such as gas-phase concentration profiles of SO2, slurry pH profiles, solids content of the slurry, liquid-phase concentrations, and residual limestone in the gypsum. Simulations were found to match experimental data for the two limestone types investigated. A parameter study of the model was conducted with the purpose of validating assumptions and extracting information on wet FGD systems. The modeling tools developed may be applicable to other wet FGD plants.

Infrared heating rates in the stratosphere due to volcanic sulphur dioxide

AbstractA narrow‐band radiative‐transfer model is used to assess potential infrared cooling rates due to SO2 injected into the stratosphere by volcanic eruptions. In addition to SO2 profiles representing the eruptions of El Chichón and Pinatubo, two hypothetical SO2 profiles following a massive volcanic eruption are used. The net radiative impact of the SO2 depends on the vertical distribution as well as the altitude and magnitude of its injection. For broader distributions the magnitudes of the infrared heating rates are comparable with those due to heating caused by the absorption of solar ultraviolet by SO2 tending to enhance the heating of the lower stratosphere and reduce it in the upper stratosphere. These results are explained in terms of the relative strengths of the SO2 bands and of those of H2O and O3 overlapping in the same spectral regions.

On the scavenging of gaseous nitrogen compounds by large and small rain drops: II. Wind tunnel and theoretical studies of the simultaneous uptake of NH3, SO2 and CO2 by water drops

An experimental investigation of the simultaneous absorption of NH3 and SO2 from the ambient atmosphere by freely falling water drops has been carried out in the Mainz vertical wind tunnel. The experimental results were found to be in good agreement with the results derived from computations with the Kronig-Brink convective diffusion model and also with a model which assumes a drop to be well mixed at all times. Encouraged by this agreement, these computation schemes for the uptake of gas by single drops where incorporated in a pollution washout model with realistic SO2, NH3 and CO2 gas profiles. This model allows an entire raindrop size distribution to fall through a gas layer. The results of this ‘plume-model’ show that the SO2 uptake is strongly dependent on the NH3 concentration in the atmosphere and on the rainrate. We also find that the small drops contribute more towards the washout of these gases. In the case of simultaneous presence of NH3 and SO2, desorption of these gases is negligible.

VEGA 1 and VEGA 2 entry probes: An investigation of local UV absorption (220–400 nm) in the atmosphere of Venus (SO2 aerosols, cloud structure)

In 1985 the VEGA 1 and VEGA 2 spacecraft dropped two descent probes into the nightside of Venus. Onboard was the French‐Russian ISAV ultraviolet spectroscopy experiment, consisting of a UV light source absorbed by atmospheric constituents circulating freely into a tube attached outside the pressurized modules. ISAV generated a wealth of absorption spectra in the 220‐ to 400‐nm range with an unprecedented vertical resolution (60–170 m) from 62 km of altitude down to the ground. On the basis of known instrument properties and a careful examination of the light curves recorded in 13 wavelength intervals in the UV, we show that most of the recorded differential absorption (at each wavelength with respect to 394 nm) can be explained by a combination of gaseous SO2 absorption and absorption by aerosols deposited on the mirrors during the crossing of Venus' lower cloud. The spectral signature of this absorber, termed X, was obtained, thanks to an unexpected shock on VEGA 1 which removed this absorber from the mirrors at 18 km of altitude. The UV spectral signature of X resembles that of croconic acid, C5O5H2, whose absorbing power as a contaminant of H2SO4 droplets at 2.5% dilution is compatible with the observations. However, the nonidentity of the spectral signature, together with stability arguments, makes this identification less plausible. Whatever its nature, the relevance of this new absorber X is discussed in connection with the albedo of Venus and the IR variable leak windows. If this absorber X detected by ISAV in the lower cloud were also present in the upper cloud, it would be a good candidate to explain the UV part (λ < 400 nm) of the Venus albedo. Three layers of absorbing material, called b, c, and d, are identified in the data of both ISAV 1 and 2 in the altitude range 49–43 km. The higher layer b is inside the lower cloud identified by the nephelometer of Pioneer Venus, while the two other layers are well below the lower cloud boundary as measured by Pioneer Venus. The SO2 profile (from 60 km down to 10 km) is characterized for ISAV 1 by a double peak of the mixing ratio (150 ppmv at 51.5 km, 125 ppmv at 42.5 km) separated by a deep trough at 30 ppmv at 45.6 km. For ISAV 2 there is a single peak at 43 km. Both SO2 profiles are quite compatible with recent ground‐based measurements, showing 130 ± 40 ppmv in the altitude range of 35 –45 km [Bézard et al., 1993]. Below the clouds the measured SO2 mixing ratio decreases steadily on both probes, down to 25 ± 2 ppmv at 10 km for ISAV 1, which is lower than previously reported values from gas chromatograph measurements (shown to be incompatible with ISAV measurements). The variation of SO2 mixing ratio with altitude implies a strong vertical transport which is given as a function of altitude, showing the source and sink regions of SO2 from 10 to 60 km of altitude. These data should impose severe constraints on future chemical models of the atmosphere of Venus, occurring after volcanic episodes or impact cratering events. The total SO2 column density (0–60 km) was measured to be 4 × 1022 molecules cm−2 or 4.2 g cm−2, a factor of 5 below previous estimates. With an average reaction rate of 4.6 × 1010 molecules cm−2 s−1 with calcite, CaCO3, estimated by Fegley and Prinn [1989], it would take only 27,000 years to get rid of SO2 and associated H2SO4 droplets if calcite were present all over the surface of Venus. Therefore SO2 and its associated ubiquitous cloud cover may only be transient phenomena in the life of Venus.

Kinetics of the Thermal Decomposition of the CH3SO2 Radical and Its Reaction with NO2 at 1 Torr and 298 K

The kinetics and mechanism of the thermal decomposition of CH3SO2 and its reaction with NO2 have been investigated in a discharge flow reactor at 298 K and 1 Torr pressure using Cl/Cl2/CH3SH/NO2/He mixtures: CH3SO2 + NO2 → CH3SO3 + NO (3); CH3SO2 + M → CH3 + SO2 + M (4). The rate constants k3 and k4 were derived from the fitting of calculated and experimental kinetic profiles of CH3O and SO2 monitored by laser-induced fluorescence (LIF) analysis. CH3 produced in reaction 4 was rapidly converted into CH3O by reaction with NO2. The values obtained were k3 = (2.2 ± 1.1) × 10-12 cm3 molecule-1 s-1 and k4 = 510 ± 150 s-1. Errors are 1 standard deviation. The role of these reactions in the atmospheric oxidation mechanism of dimethyl sulfide is discussed.

New UV tunable solid-state lasers for lidar applications

We present the first lidar/DIAL system based on an Ultra Violet (UV) vibronic laser. A Nd:YAG-pumped Ce:LiSAF laser has been developed for this purpose, providing high pulse energy (5 mJ at 10 Hz), very high slope efficiency (33%), and a tuning range from 284 to 299 nm. Simultaneous measurements of SO2 and O3 concentration profiles are presented using this frequency-agile Ce:LiSAF-based lidar system.

H2SO4 photolysis: A source of sulfur dioxide in the upper stratosphere

Numerous absorption lines of stratospheric sulfur dioxide (SO2) have been identified in solar occultation spectra recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Atmospheric Laboratory for Applications and Science (ATLAS)‐1 shuttle mission (March 24‐April 2, 1992). Based on their analysis, a volume mixing ratio profile of SO2 increasing from (13 ± 4) p.p.t.v. (parts per 10−12 by volume) at 16 mbar (∼ 28 km) to 455 ± 90 p.p.t.v. at 0.63 mbar (∼ 52 km) has been measured with no significant profile differences between 20°N and 60°S latitude. The increase in the SO2 mixing ratios with altitude indicates the presence of a source of SO2 in the upper stratosphere. Profiles retrieved from ATMOS spectra recorded during shuttle flights in April‐May 1985 and April 1993 show similar vertical distributions but lower concentrations. Two‐dimensional model calculations with SO2 assumed as the end product of H2SO4 photolysis produce SO2 profiles consistent with the ATMOS measurements to within about a factor of 2.

Vertical Sulfur Dioxide, Ozone, and Heavy Metal Concentration Profiles Above the Southern Bight of the North Sea

AbstractVertical profiles of SO2 and O3 concentrations were measured continuously within the lower atmosphere during 18 flights over the Southern Bight of the North Sea. The average SO2 concentration below the temperature inversion layer ranged from 1.9 to 19.5 ppb. The highest levels were observed when the air masses came from the southeast‐east and under variable wind sector conditions: 15.2 and 12.0 ppb, respectively. The highest SO2 concentrations were found at altitudes between 100 and 200 m. The overall average O3 concentration was 46 ppb, with values of 30–40 ppb at sea level to 60–70 ppb at altitudes above 100 m. Low O3 concentrations reflect O3 depletion through reaction with freshly emitted pollutants, while high O3 concentrations are an indication of photochemical activity. O3 concentrations are primarily dependent on seasonal influences, while SO2 levels are dictated more by the history of the sampled air mass. The results are discussed in relation to the heavy metal concentrations, measured within the same experiment. In spite of some differences, SO2 and trace metals showed similar trends. The individual SO2 and O3 profiles clearly illustrated the high variability in vertical concentration distributions.

Project aguila: In situ measurements of Mexico City air pollution by a research aircraft

Measurements of aerosol concentrations, chemical species and meteorological quantities in the air above Mexico City were obtained from an instrumented research aircraft. Concentrations of particles in the size range between 0.12 and 3.12 μm were nearly invariant with height, and typical values were of the order of 5000 cm −3. However, particles smaller than 0.12 μm were confined to the lowest few hundred meters of the atmosphere until the morning temperature inversion dissipated, after which time those particles, together with newly formed particles created by secondary processes, mixed to a greater height above the city. Total particle concentrations near the surface attained values in excess of 60,000 cm −3. An examination of the corresponding profiles of SO 2 suggests that combustion processes are likely sources for the additional small particles.

Latitude structure of upper clouds of Venus

Some new results of interpretation of IR spectra of Venus obtained in 1983 by orbiter Venera-15 for spectral range 270–1650 cm −1 are given. Temperature and aerosol profiles which were obtained by self-consistent retrieval are presented and used to analyze vertical profiles of SO 2, its mixing ratio at 40 mb level and scale height. In low latitudes of planet a scale height of SO 2 is 2–3 times less than that of the clouds. In cold collar this values are nearly equal, and in polar region scale height of SO 2 as a rule is 2–4 times larger.

An improved filter pack technique for airborne measurement of low concentrations of SO2

Recent improvements to the carbonate‐impregnated filter technique for measuring low‐level SO2concentrations have resulted in dramatically improved performance. The improvements are (1) a better cleaning procedure for the paper filter substrates, resulting in approximately 60% reduction of their sulfate blank, (2) the use of an ion‐exchange resin to remove the carbonate matrix from the sample extract, resulting in a 100% increase in the signal‐to‐noise ratio, (3) the use of high‐purity glycerol in the filter impregnate, resulting in approximately 10% further reduction of blanks, and (4) improved Chromatographic and standardization procedures for more accurate quantification of sample peaks. Combined, these improvements allow measurements to be made of SO2 concentrations in marine background air with a 2σ uncertainty of ±6 parts per trillion by volume (pptv) and, based on this, a 3σ detection limit of 9 pptv for air volumes of 4 m3 (which can be collected in 15 min aboard our research aircraft). Measurements in polluted air show better than 95% collection efficiency, even at concentrations as high as 100 ppbv. Vertical profiles of SO2 measured during three research flights off the Washington coast (one in clean marine air) showed concentrations ranging from 15 to 86 pptv in the mixed layer and from 40 to 93 pptv in the free troposphere.