Rate Of SO2 Oxidation Research Articles

Unexpectedly rapid aerosol formation in the Hunga Tonga plume.

The Hunga Tonga-Hunga Ha'apai (HT-HH) volcanic eruptions on January 13 and 15, 2022, produced a plume with the highest signal in stratospheric aerosol optical depth observed since the eruption of Mt. Pinatubo in 1991. Suites of balloon-borne instruments on a series of launches from Réunion Island intercepted the HT-HH plume between 7 and 10 d of the eruptions, yielding observations of the aerosol number and size distribution and sulfur dioxide (SO2) and water vapor (H2O) concentrations. The measurements reveal an unexpected abundance of large particles in the plume, constrain the total sulfur injected to approximately 0.2 Tg, provide information on the altitude of the injection, and indicate that the formation of sulfuric acid aerosol was complete within 3 wk. Large H2O enhancements contributed as much as ~30% to ambient aerosol surface area and likely accelerated SO2 oxidation and aerosol formation rates in the plume to approximately three times faster than under normal stratospheric conditions.

Quantifying the seasonal variations in and regional transport of PM2.5 in the Yangtze River Delta region, China: characteristics, sources, and health risks

Abstract. Given the increasing complexity of the chemical composition of PM2.5, identifying and quantitatively assessing the contributions of pollution sources has played an important role in formulating policies to control particle pollution. This study provides a comprehensive assessment between PM2.5 chemical characteristics, sources, and health risks based on sampling data conducted over 1 year (March 2018 to February 2019) in Nanjing. Results show that PM2.5 exhibits a distinct variation across different seasons, which is primarily driven by emissions, meteorological conditions, and the chemical conversion of gaseous pollutants. First, the chemical mass reconstruction shows that secondary inorganic aerosols (62.5 %) and carbonaceous aerosols (21.3 %) contributed most to the PM2.5 mass. The increasing oxidation rates of SO2 and NO2 from summer to winter indicate that the secondary transformation of gaseous pollutants is strongly positively correlated with relative humidity. Second, the positive matrix factorization (PMF) method shows that identified PM2.5 sources include secondary inorganic aerosol source (SIS, 42.5 %), coal combustion (CC, 22.4 %), industry source (IS, 17.3 %), vehicle emission (VE, 10.7 %), fugitive dust (FD, 5.8 %), and other sources (1.3 %). The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and the concentration-weighted trajectory (CWT) analysis are used to further explore different spatial distributions and regional transport of sources. The concentrations (10–11 µg m−3) of SIS and CC distribute in Nanjing and central China in winter. The concentrations (8–10 µg m−3) of IS and VE are potentially located north of Jiangsu, Anhui, and Jiangxi. Finally, the health risk assessment indicates that the carcinogenic and non-carcinogenic risks of toxic elements (Cr, As, Ni, Mn, V, and Pb) mainly come from IS, VE, and CC, which are within the tolerance or acceptable level. Although the main source of pollution in Nanjing is SIS at present, we should pay more attention to the health burden of vehicle emissions, coal combustion, and industrial processes.

Getting insight into the oxidation of SO2 to SO3 over P modified VW/Ti catalyst: Effect and inhibition mechanism

Commercial VW/Ti catalyst used in selective catalytic reduction (SCR) process is one of the major sources of SO3 in coal-fired boiler, and modification of VW/Ti catalyst by adding catalytic promoter has been demonstrated to be an effective way to inhibit SO3 generation. In this study, the effect of P addition on the activity of NOx conversion and SO2 oxidation over VW/Ti catalyst was investigated. The results showed that the P-modified VW/Ti catalyst not only enhanced the catalytic activity at low temperature, but also reduced the oxidation rate of SO2. The 1.5PVW/Ti catalyst exhibited the lowest SO2 oxidation rate at 360 °C and achieved about 30 % reduction in SO2 oxidation rate when compared to 0PVW/Ti catalyst, whereas the conversion of NOx was still above 95 %. The physicochemical properties of catalysts were comprehensively characterized with N2 adsorption, XRD, H2-TPR, NH3-TPD, XPS and DRIFTS. The results illustrated that the W-O-W structure was also the main reason for SO2 oxidation on P-modified VW/Ti catalyst, which oxidized SO2 to form intermediate products HSO4− and constantly replenished in the presence of O2. The oxidation of SO2 was weakened by the generation of VOPO4 on P-modified VW/Ti catalyst surface, which inhibited the formation of VOSO4 by reducing the adsorption of SO2 on the catalyst. In addition, the release of P-OH and W=O were promoted with the addition of P, which led to a significant increase in the intensity of the Brønsted and Lewis acid sites, resulting in the increase in the conversion of NOx at low temperatures.

The effect of ash, water vapor, and heterogeneous chemistry on the evolution of a Pinatubo-size volcanic cloud

Abstract. We employ the ECHAM5/MESSy2 atmospheric chemistry general circulation model (EMAC) that incorporates calculations of gas-phase and heterogeneous chemistry coupled with the ozone cycle and aerosol formation, transport, and microphysics to calculate the 1991 Pinatubo volcanic cloud. We considered simultaneous injections of SO2, volcanic ash, and water vapor. We conducted multiple ensemble simulations with different injection configurations to test the evolution of SO2, SO42-, ash masses, stratospheric aerosol optical depth, surface area density (SAD), and the stratospheric temperature response against available observations. We found that the volcanic cloud evolution is sensitive to the altitude where volcanic debris is initially injected and the initial concentrations of the eruption products that affect radiative heating and lofting of the volcanic cloud. The numerical experiments with the injection of 12 Mt SO2, 75 Mt of volcanic ash, and 150 Mt of water vapor at 20 km show the best agreement with the observation aerosol optical depth and stratospheric temperature response. Volcanic water injected by eruptive jet and/or intruding through the tropopause accelerates SO2 oxidation. But the mass of volcanic water retained in the stratosphere is controlled by the stratospheric temperature at the injection level. For example, if volcanic materials are released in the cold point above the tropical tropopause, most of the injected water freezes and sediments as ice crystals. The water vapor directly injected into the volcanic cloud increases the SO42- mass and stratospheric aerosol optical depth by about 5 %. The coarse ash comprises 98 % of the ash injected mass. It sediments within a few days, but aged submicron ash could stay in the stratosphere for a few months providing SAD for heterogeneous chemistry. The presence of ash accelerates the SO2 oxidation by 10 %–20 % due to heterogeneous chemistry, radiative heating, lofting, and faster dispersion of volcanic debris. Ash aging affects its lifetime and optical properties, almost doubling the ash radiative heating. The 2.5-year simulations show that the stratospheric temperature anomalies forced by radiative heating of volcanic debris in our experiments with the 20 km injection height agree well with observations and reanalysis data. This indicates that the model captures the long-term evolution and climate effect of the Pinatubo volcanic cloud. The volcanic cloud's initial lofting, facilitated by ash particles' radiative heating, controls the oxidation rate of SO2. Ash accelerates the formation of the sulfate layer in the first 2 months after the eruption. We also found that the interactive calculations of OH and heterogeneous chemistry increase the volcanic cloud sensitivity to water vapor and ash injections. All those factors must be accounted for in modeling the impact of large-scale volcanic injections on climate and stratospheric chemistry.

Evaluation of reaction between SO2 and CH2OO in MCM mechanism against smog chamber data from ethylene ozonolysis

Environmental context The process of ethylene ozonolysis is an essential source of CH2OO radicals, and the latter is an important oxidant for the atmospheric pollutant SO2. The accuracy of a widely used atmospheric chemistry model (Master Chemical Mechanism, MCM) in quantifying SO2 oxidation has not been evaluated. In this study, this accuracy was evaluated, and optimal parameters underpinned by data from smog chamber experiments. Rationale The oxidation of SO2 by CH2OO radicals in the ethylene-O3 system is one of the important pathways of sulfate aerosol formation, but the accuracy of Master Chemical Mechanism (MCM) simulation for this reaction was not evaluated, although the MCM has been widely used in previous studies. Methodology The oxidation of SO2 in the ethylene-O3 system was performed in detail under different conditions, which were used to evaluate the accuracy of MCM simulation for the reactions in this study. Results The experimental conditions of low RH and high initial SO2 concentration favour the SO2 oxidation in the ethylene ozonolysis, and the yield of CH2OO in the ethylene ozonolysis without irradiations was determined to be 0.43. The n-hexane (C6H14) oxidation intermediates can promote the SO2 oxidation rate by generating sulfur-containing organics in the aerosol water. The original MCM simulated SO2 consumption after 4-h reaction was more than 70% smaller than the measured results. By adjusting the yield of CH2OO and updating the reaction rate constants of CH2OO-related reactions (e.g. with SO2, H2O and organic acid), the difference between experiments and simulations decreased from 70% to 6.6%. Discussion The promotion effects of n-hexane on the oxidation of SO2 suggest that alkanes may be the precursors of sulfur-containing organics in the atmospheric environment. This study further confirms the effect of CH2OO on the oxidation of SO2 in the atmospheric environment and provides information on the performance of MCM simulation.

MoO3/TiO2 catalyst with atomically dispersed O-Mo-O structures toward improving NH4HSO4 poisoning resistance for selective catalytic reduction of nitrogen oxides

Slow progress in discovering new catalysts to circumvent the problem of ammonium bisulfate (NH4HSO4, ABS) poisoning has hindered further development of selective catalytic reduction (SCR) technology of NOx with ammonia (from numerous industrial processes) in afterburning systems at temperatures below dew point of ABS (typically between 280 °C and 320 °C). Recently, we have explored the use of atomically dispersed Mo species on TiO2 particles (hereafter denoted as MoO3/TiO2) as highly efficient catalyst for NH3-SCR reaction. In the present study, it will be shown that this type of catalyst is highly resistant to ABS poisoning for NH3-SCR reaction, overcoming a major issue afflicting the application of commercial V2O5-WO3/TiO2 catalyst at temperatures below the dew point of ABS. Aberration-corrected scanning transmission electron microscopy (STEM) suggests that most of the Mo species are present in atomically dispersed form in the MoO3/TiO2 catalyst. SO2 oxidation measurements show that the MoO3/TiO2 catalyst exhibits a substantially lower SO2 oxidation rate compared to the commercial V2O5-WO3/TiO2, mitigating ABS formation. Furthermore, decomposition of ABS on MoO3/TiO2 surface is found to be extremely facile. Temperature-programmed surface reaction (TPSR) with NO shows that the decomposition temperature of ABS over MoO3/TiO2 is 70 °C lower than that found on the commercial V2O5-WO3/TiO2 catalyst. Our investigations provide valuable information for the development of NH3-SCR catalysts with exceptional resistance to ABS poisoning for NOx emission control.

Effects of Trace Components in Reclaimed Water Sludge on Wet Flue Gas Desulfurization Process

The paper designed and built a simulation reaction system for the Wet Flue Gas Desulfurization(WFGD) process to analyze the effects of factors on the Oxidation reaction of SO2 for the reuse of reclaimed water sludge. Six trace components including magnesium, iron, chloride, aluminum, PAM and PFS in reclaimed water sludge from reclaimed water softening were selected for analysis factors. The effects of six factors on the oxidation reaction were tested by single factor experiments. The multi-factor effects on the oxidation reaction was studied by adding different proportion of reclaimed water sludge to the desulfurizer of the simulated reaction system. In addition, the effect of reclaimed water sludge on the crystallization and dehydration of desulfurization slurry was analyzed. The results show that six factors have little effects on the SO2 oxidation rate in the test range. The addition of reclaimed water sludge has a significant effect on the crystalline form and dehydration of gypsum.

Simultaneous removal of SO2, NOx and Hg0 by O3 oxidation integrated with bio-charcoal adsorption

Simultaneous removal of SO2, NOx and Hg0 using O3 and corn stalk bio-charcoal (CR)/coconut shell activated carbon (CS) was compared in a fixed bed. The effects of temperature, adsorption time and ratio of O3/NO on the removal efficiency of NO, Hg0 and SO2 by CR/CS were studied, and the CR and CS was characterized and analyzed. The results indicated that the oxidation rate of NO and Hg0 increased with the increase of O3/NO ratio, while the oxidation rate of SO2 first increased and then decreased slightly. The increase of temperature inhibits the oxidation of NO but promotes the oxidation of Hg0 and SO2. At 140°C and O3/NO ratio was 1.4, the oxidation rate of NO, Hg0 and SO2 is 99%, 78.6% and 3.5%, respectively. As O3/NO ratio increased from 0.4 to 1.4, the removal efficiency of CR for NOx increased from 4.6% to 93%, and CS increases from 4.5% to 79%. CR and CS can reduce part of NO2 and increase NO concentration at the outlet. NOx adsorption performance on CR is relatively better, while those of Hg0 and SO2 on CS are relatively stronger. CS has stronger physical adsorption capacity than CR. The relative content of oxygen-containing functional groups C-O and C=O on the surface of CR is higher than that of CS, while its relative content of COOH and O=C-O is lower.

Aerosol chemical component: Simulations with WRF-Chem and comparison with observations in Nanjing

Secondary inorganic aerosols, including sulfate, nitrate, and ammonium (SNA), are the predominant components of fine particles (PM2.5). Reasonable representations of SNA formation in numerical models can largely improve the predictions of PM2.5 concentrations and effectively help implement emission control strategies. Despite the Atmospheric Pollution Prevention and Control Action Plan has been implemented since 2013, PM2.5 concentration during 2017 in Nanjing, one of the megacities in China, still exceeded the World Health Organization-recommended safe level (35 μg m−3). In this study, WRF-Chem model was applied to simulate aerosol chemical components in PM2.5 during April 2016 and January 2017 in Nanjing, and the simulations are evaluated with in-situ observations. Our results show that the model can reasonably reproduce the temporal variability of PM2.5 in two seasons, but significantly underestimate the sulfate concentrations by 71% (84%) in April (January), and overestimate the nitrate concentrations by 67% (45%) in April (January). The simulated ammonium is overall consistent with the observations. Meanwhile, the model tends to overestimate SO2 concentrations by 20% (74%) in April (January). Several sensitivity studies are conducted to explore the mechanisms for underestimation of sulfate and overestimation of nitrate, and found that the conversion rate of SO2 to sulfate is significantly underestimated in the model. Tripling the gas-phase oxidation rate of SO2 by OH only enhances sulfate by 67% (72%) in April (January), indicating gas-phase oxidation is not the main causes for the underestimations in the model. However, inclusion of SO2 heterogeneous oxidation in aerosol water can largely increase the simulated sulfate by 84% (196%) in April (January), and also better reproduce the diurnal variations of sulfate compared to the reference run. It should be noted that the simulated sulfate is still 47% (53%) lower than the observations in April (January), though inclusion of heterogeneous reaction can substantially improve the simulation performance of SNA.

Catalytic conversion of mercury over Ce doped Mn/SAPO-34 catalyst: Sulphur tolerance and SO2/SO3 conversion

A series of Mn-Ce/SAPO-34 catalysts were prepared to study the catalytic oxidisation of elemental mercury (Hg0). Sulphur tolerance and SO3 formation over the catalyst were studied further. Hg0 was transported by compressed air from PSA Cavkit. NO, SO2, and NH3 are standard gases, and H2O is produced by gas carrying. Mn could incorporate into the cerium oxide lattice to form capping oxygen and well-dispersed high valance manganese ions after the addition of Ce, which was conducive to NO removal and Hg0 oxidisation. 9 Mn-9Ce showed the best performance regarding Hg0 conversion, achieving more than 92% Hg0 conversion efficiency at 50–300 °C. The sulphur resistance of the Mn-based catalyst was significantly improved after the addition of cerium due to the high affinity of Ce for SO2, and the relative content of HgSO4 was exceeded 72% on the 9 Mn-9Ce catalyst with SO2; SO3 formation over the 9 Mn-9Ce decreased by 17% compared with the 9 Mn. H2O not only reduced the available active site, but also decreased the oxidation rate of SO2. The active sites were preferentially occupied by NH3 rather than Hg0 and SO2, generated NH4+ occupied cation vacancies. Therefore, both H2O and NH3 have inhibitory effects on Hg0 conversion and SO3 formation.

Rates of Wintertime Atmospheric SO2 Oxidation based on Aircraft Observations during Clear‐Sky Conditions over the Eastern United States

AbstractSulfur dioxide (SO2) is emitted in large quantities from coal‐burning power plants and leads to various harmful health and environmental effects. In this study, we use plume intercepts from the Wintertime INvestigation of Transport, Emission and Reactivity (WINTER) campaign to estimate the oxidation rates of SO2 under wintertime conditions and the factors that determine SO2 removal. Observations suggest that OH governs the rate SO2 oxidation in the eastern United States during winter. The range of mean oxidation rates during the day from power plants were 0.22–0.71%/hr, producing SO2 lifetimes of 13–43 days, if SO2 consumption is assumed to occur during 10.5 hr of daylight in cloudless conditions. Though most nighttime rate measurements were zero within uncertainty, there is some evidence of nighttime removal, which suggests alternate oxidation mechanisms. The fastest nighttime observed SO2 oxidation rate was 0.25±0.07%/hr, producing a combined day/night SO2 lifetime of 8.5–21 days. The upper limit of the oxidation rate (the mean+1σ of the fastest day and night observations) is 16.5%/day, corresponding to a lifetime of 6.1 days. The analysis also quantifies the primary emission of sulfate from power plants. The median mole percentage of SO4‐2 from observed plumes was 1.7% and the mean percentage sulfate was 2.8% for intercepts within 1 hr of transit to power plants. The largest value observed from close intercepts was over 7% sulfate, and the largest extrapolated value was 18%, based on intercepts further from their source and fastest observed oxidation rate.

Parameterization of heterogeneous reaction of SO2 to sulfate on dust with coexistence of NH3 and NO2 under different humidity conditions

Sulfate plays an important role in atmospheric haze in China, which has received considerable attention in recent years. Various types of parameterization methods and heterogeneous oxidation rates of SO2 have been used in previous studies. However, properly representing heterogeneous sulfate formation in air quality models remains a big challenge. In this study, we quantified the heterogeneous oxidation reaction using experimental results that approximate the haze conditions in China. Firstly, a series of experiments were conducted to investigate the heterogeneous uptake of SO2 with different relative humidity (RH) levels and the presence of NH3 and NO2 on natural dust surfaces. Then the uptake coefficients for heterogeneous oxidation of SO2 to sulfate at different RH under NH3 and NO2 coexistence were parameterized based on the experimental results and implemented in the Community Multiscale Air Quality modeling system (CMAQ). Simulation results suggested that this new parameterization improved model performance by 6.6% in the simulation of wintertime sulfate concentrations for Beijing. The simulated maximum growth rate of SO42− during a heavy pollution period increased from 0.97 μg m−3 h−1 to 10.11 μg m−3 h−1. The heterogeneous oxidation of SO2 in the presence of NH3 contributed up to 23% of the sulfate concentration during heavy pollution periods.

Formation of sulfur trioxide during the SCR of NO with NH3 over a V2O5/TiO2 catalyst.

The oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3) is an undesirable reaction that occurs during the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia (NH3), which is a process applied to purify flue gas from coal-fired power plants. The objectives of this work were to establish the fundamental kinetics of SO3 formation over a V2O5/TiO2 catalyst and to illustrate the formation mechanism of SO3 in the presence of NOx, H2O and NH3. A fixed-bed reactor was combined with a Fourier transform infrared (FTIR) spectrometer and a Pentol SO3 analyser to test the outlet concentrations of the multiple components. The results showed that the rate of SO2 oxidation was zero-order in O2, 0.77-order in SO2 and -0.19-order in SO3 and that the apparent activation energy for SO2 oxidation was 74.3 kJ mol−1 over the range of studied conditions. Based on in situ diffuse reflectance infrared Fourier transform (in situ DRIFT) spectroscopy, X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) tests, the SO3 formation process is described here in detail. The adsorbed SO2 was oxidized by V2O5 to produce adsorbed SO3 in the form of bridge tridentate sulfate, and the adsorbed SO3 was desorbed to the gas phase. NOx promoted the oxidation of the adsorbed SO2 due to the promotion of the conversion of low-valent vanadium to high-valent vanadium. In addition, the desorption of the adsorbed SO3 was inhibited by H2O or NH3 due to the conversion of tridentate sulfate to the more stable bidentate sulfate or ammonium bisulfate. Finally, the mechanism of the influence of NOx, H2O and NH3 on the formation of gaseous SO3 was proposed.

SO2 Oxidation Across Marine V2O5-WO3-TiO2 SCR Catalysts: a Study at Elevated Pressure for Preturbine SCR Configuration

The undesired oxidation of SO2 was studied experimentally at elevated pressures of up to 4.5 bar across two commercial vanadium-based (1.2 and 3 wt% V2O5) selective catalytic reduction (SCR) catalysts. This pressure range is of interest for preturbine SCR reactor configuration for NOx reduction on ships. The residence time in the catalyst was kept constant, independent on pressure, by adjusting the total flow rate. The conversion of SO2 was of the order 0.2–3% at temperatures of 300–400 °C and was independent of the pressure. Based on the measured conversion of SO2, the kinetics were fitted using an nth order rate expression. The reaction order of SO2 was found close to 1, and the reaction order of SO3 was found close to 0, also at increased pressures of up to 4.5 bar. The rate of SO2 oxidation was clearly promoted by the presence of 1000 ppm NOx at elevated pressure; however, at atmospheric pressure, the effect was within experimental uncertainty. The promoting effect is explained by a catalyzed redox reaction between SO2 and NO2, and since more NO2 is formed at elevated pressure, a higher degree of promotion by NOx is observed at elevated pressures.

The pilot demonstration of a honeycomb catalyst for the DeNOx of low-temperature flue gas from an industrial coking plant

The practical low-temperature DeNOx catalyst has a huge market demand for the flue gas purification of the widespread small-scale boilers. In this work, the modified V-based low-temperature honeycomb catalyst was produced through the hydrothermal process of metatitanic acid, which exhibited high strength and low SO2 oxidation rate. The pilot test of flue gas from a coking plant demonstrated that the honeycomb catalyst could endure the high content of SOx (400–600 ppm) and H2O (>15 vol%) in flue gas at 300 °C and work stably with adjustable NO removal efficiency and little ammonia slip. After dry desulphurization and dedusting processes, the catalytic activity could still keep stable during the three-week test at as low as 220 °C, and the catalyst showed none deactivation. But the obvious deactivation of catalyst was observed at 270 °C before dry desulphurization and dedusting processes. The characterization of spent catalyst revealed that the deactivation of catalyst mainly resulted from the covering of catalytic surface by ammonium sulfate and ferric sulfate species, which formed through the gas reaction of inherent SO3 with NH3 for ammonium sulfate species and the corrosion/stripping of Fe based pipe for ferric sulfate species, respectively. After the re-calcination process, the deactivated catalyst could be regenerated with the decomposition of sulfate species.

Research progress on ammonium bisulfate formation and control in the process of selective catalytic reduction

The formation mechanism of ammonium bisulfate (ABS) in the process of SCR flue gas denitrification and some research progresses on ABS are reviewed in the paper. The main factors affecting the formation of ABS are investigated, the formation temperature of ABS is in the range of about 190°C−240°C; ABS exists in vapor phase at temperature between 320°C and 345°C, and begins to decompose when the temperature is higher than 345°C; the formation of the ABS can be reduced by reducing the amount of NH3 slip and SO3, in the flue gas. The adverse effects of ABS on catalyst and air preheater are discussed: ABS will cover the surface of catalyst and Bronsted acid sites, decreasing denitrification efficiency; it will deposit in the air preheater, fouling and corroding the air preheater and reduce its operational effectiveness; it also can reduce the resistivity of fly ash and the quality of the fly ash as well. The methods to control ABS formation and the measures to reduce its negative effects are proposed: Select appropriate operating temperature to reduce the ABS deposition over the SCR catalyst; replace the material of the air preheater components from steel to ceramic coating type and change the structure of the air preheater; Take proper methods to reduce NH3 slip and the oxidation rate of SO2, etc. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1664–1672, 2016

Aqueous phase oxidation of sulphur dioxide by ozone in cloud droplets

Abstract. The growth of aerosol due to the aqueous phase oxidation of sulfur dioxide by ozone was measured in laboratory-generated clouds created in the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN). Experiments were performed at 10 and −10 °C, on acidic (sulfuric acid) and on partially to fully neutralised (ammonium sulfate) seed aerosol. Clouds were generated by performing an adiabatic expansion – pressurising the chamber to 220 hPa above atmospheric pressure, and then rapidly releasing the excess pressure, resulting in a cooling, condensation of water on the aerosol and a cloud lifetime of approximately 6 min. A model was developed to compare the observed aerosol growth with that predicted using oxidation rate constants previously measured in bulk solutions. The model captured the measured aerosol growth very well for experiments performed at 10 and −10 °C, indicating that, in contrast to some previous studies, the oxidation rates of SO2 in a dispersed aqueous system can be well represented by using accepted rate constants, based on bulk measurements. To the best of our knowledge, these are the first laboratory-based measurements of aqueous phase oxidation in a dispersed, super-cooled population of droplets. The measurements are therefore important in confirming that the extrapolation of currently accepted reaction rate constants to temperatures below 0 °C is correct.

Effect of Selective Catalytic Reduction System on Fine Particle Emission Characteristics

Based on commercial catalysts (V2O5–WO3/TiO2), the effects of a selective catalytic reduction (SCR) system on the emission characteristics of fine particles were investigated. The size distribution, morphology, element compositions, and chemical compositions of fine particles at the outlet of the SCR system were measured by an electrical low pressure impactor (ELPI), particulate matter (PM10/PM2.5) samplers, field emission scanning electron microscopy/energy dispersive spectrometry (FSEM–EDS), X-ray diffraction (XRD), etc. The influences of reaction conditions and flue gas components on fine particle formation were also studied. The results reveal that a large number of fine particles can be generated during the SCR process. These fine particles are mostly in the submicrometer size range and appear to be nonuniform. The main components of these fine particles are ammonium sulfate or ammonium bisulfate. There is a good correlation between the formation of fine particles and the SO2 oxidation rate. Fine par...

Atmospheric evolution of sulfur emissions from Kı̅lauea: real-time measurements of oxidation, dilution, and neutralization within a volcanic plume.

The high atmospheric concentrations of toxic gases, particulate matter, and acids in the areas immediately surrounding volcanoes can have negative impacts on human and ecological health. To better understand the atmospheric fate of volcanogenic emissions in the near field (in the first few hours after emission), we have carried out real-time measurements of key chemical components of the volcanic plume from Kı̅lauea on the Island of Hawai'i. Measurements were made at two locations, one ∼ 3 km north-northeast of the vent and the other 31 km to the southwest, with sampling at each site spanning a range of meteorological conditions and volcanic influence. Instrumentation included a sulfur dioxide monitor and an Aerosol Chemical Speciation Monitor, allowing for a measurement of the partitioning between the two major sulfur species (gas-phase SO2 and particulate sulfate) every 5 min. During trade wind conditions, which sent the plume toward the southwest site, sulfur partitioning exhibited a clear diurnal pattern, indicating photochemical oxidation of SO2 to sulfate; this enabled the quantitative determination of plume age (5 h) and instantaneous SO2 oxidation rate (2.4 × 10(-6) s(-1) at solar noon). Under stagnant conditions near the crater, the extent of SO2 oxidation was substantially higher, suggesting faster oxidation. The particles within the plume were extremely acidic, with pH values (controlled largely by ambient relative humidity) as low as -0.8 and strong acidity (controlled largely by absolute sulfate levels) up to 2200 nmol/m(3). The high variability of sulfur partitioning and particle composition underscores the chemically dynamic nature of volcanic plumes, which may have important implications for human and ecological health.

The influence of microporosity creation in highly mesoporous N-containing carbons obtained from chitosan on their catalytic and electrochemical properties

Highly mesoporous novel nitrogen-containing, silica templated carbons, obtained from chitosan were described in the present study to demonstrate the effects of ZnCl2, KOH and CO2, widely used carbon activators, on the development of their micro/mesoporsity by means of nitrogen sorption, elemental analysis, X-ray diffraction, cyclic voltammetry and SO2 oxidation reaction. The latter two activation methods were post-synthesis treatments as opposite to the first one in which ZnCl2 was added directly to the solution of colloidal silica template and chitosan. We confirmed that chemical activation using KOH or ZnCl2 generates microporosity as opposite to physical activation which only slightly enhances micro/mesoporosity. All the activation methods studied resulted in a wider mesopore size distribution. The KOH was the most effective activator for the creation of narrow micropores with the diameter of ca. 0.6nm, and it was the most widely used one.The microporosity development was also reflected in capacitance measured in 6M KOH solution and high rate of catalytic SO2 oxidation in solution. The higher the activation temperature the less the nitrogen was preserved in the structure modified with KOH. No significant changes in nitrogen percentage have been found after two other activation treatments.Microporosity development reflects in an improvement of the ability to accumulate the charge and an increase in a rate of SO2 oxidation in solution. The studied carbons exhibited a specific surface area up to 1800m2/g, and a quite high capacitance up to 245F/g, as for carbons having such a low microporosity contribution of up to 32% to the overall pore volume, and SO2 oxidation rate up to 4.42μmol/s/g.A creation of appropriate microporosity is extremely important for a particular process/reaction. The diameter of pores within the range of 0.7–0.9nm is demanded for SO2 oxidation. However, slightly smaller pores (0.6nm) improve the ability to store the charge in 6M KOH.