Low Concentrations Of SO2 Research Articles

Effects of the surface properties and particle size of hydrated lime on desulfurization

In the gas treatment center in smelters, hydrogen fluoride (HF) is separated from the outlet gases of electrolysis cells, which are used to produce aluminum from alumina. However, SO2 largely remains in the effluent gas. Another method has to be developed to separate this gas which is harmful to the environment. In this study, semi-dry desulfurization of a SO2 containing gas was performed at low SO2 concentrations using hydrated lime [Ca(OH)2] as a catalytic desulfurizer under specific humidity conditions. The low reaction temperature of 100 °C and minimal use of the Ca-based desulfurizer under 17 % relative humidity achieved more than 95 % removal of SO2. The morphological changes and presence of sulfur in different lime samples were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Brunauer–Emmett–Teller (BET) analysis showed changes in the surface properties of hydrated lime after desulfurization. X-ray photoelectron spectroscopy (XPS) analysis provided the phase and composition identification of the sulfur species on hydrated lime and the CaSO3/CaSO4 product ratio. Based on the experimental results, the optimum catalyst surface area with a specific particle size is critical to the effective conversion of Ca(OH)2 into CaSO3 and CaSO4. The practicality of a Ca-based desulfurizer and its ability to convert into the required product may be the key to reducing the overall cost of desulfurization in aluminum industry.

Low-Temperature NH3-SCR Technology for Industrial Application of Waste Incineration: An Overview of Research Progress

Selective catalytic reduction of nitrogen oxides with NH3 (NH3-SCR) was investigated deeper and deeper with poisoning factors such as H2O, SO2, heavy metals, etc. In order to remove the reheating process before the SCR reactor, the application trend of NH3-SCR technology in the non-power industry is concentrated on the condition of low temperature even ultra-low temperature. The present study summarizes the research process of SO2 and H2O resistance of NH3-SCR catalysts under low temperatures related to the working conditions of municipal solid waste incineration plants. In detail, the effects of a high content of H2O and low concentration of SO2 are reviewed. Other factors such as heavy metals, alkali, or alkaline earth metals in the reaction system, synergistic removal of NOx, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are addressed. Finally, the catalytic performance of assembled monolithic catalysts and pilot-scale experiments are also analyzed for the possibility of industrial application. Hopefully, in view of the questions outlined in this study, valuable insights could be taken into consideration for the development of NH3-SCR in waste incineration.

A novel and clean utilization of flue gas desulfurization ash coupled with converter sludge to produce calcium ferrate

To address the environmental pollution from industrial wastes like desulfurization ash (DA) and converter sludge(CS), this study introduces a novel method for synthesizing calcium ferrate. This method involves reacting converter sludge with desulfurization ash at high temperatures, facilitating the concurrent elimination of toxic elements. The solid byproduct is suitable as a sintered ore additive, while the gaseous SO2 serves as a precursor for sulfuric acid production. Additionally, the metal-rich secondary dust offers a source for valuable metal recovery. This research employs simulation software (FactSage 8.1) and thermal analysis to explore the high-temperature reaction dynamics of converter sludge and desulfurization ash. Subsequent in-situ experiments and coupled high-temperature tube furnace-infrared flue gas analysis further elucidated the phase transitions, morphology changes, flue gas emissions, and migration of harmful elements (e.g., S, K, Na, Pb, Zn). Analysis using the Predom dominant zone module calculation indicates that low SO2 concentration and reduced oxygen levels promote the stability of Ca2Fe2O5. Infrared flue gas analysis reveals high concentrations of CO2 and SO2. Sulfur removal rates rose from 62.15 % to 98.48 % between 800 °C and 1100 °C. Removal efficiencies for alkali and heavy metals, namely K, Na, Pb, and Zn, improved significantly, reaching 99.95 %, 99.49 %, 99.71 %, and 86.7 % respectively. At 1100 °C under an N2 atmosphere, the main reaction products from Flue Gas desulfurization ash (FGDA) and converter sludge were CaFe3O5 and Ca2Fe2O5. This study’s comprehensive analysis of synthesizing calcium ferrate from Flue Gas desulfurization ash and converter sludge introduces a novel waste utilization method, offering substantial environmental and economic advantages.

Electrospun rGO-PVDF/WO3 composite fibers for SO2 sensing

Developing highly selective and sensitive SO2 sensors is essential due to the excessive presence of SO2 in the environment which can cause respiratory illness and acid rain. Semiconducting metal oxides are the materials most used for the development of SO2 sensors; however, they still suffer from sensitivity, selectivity, low-temperature operation, low detection limit, and slow response/recovery time for real-field applications. In this work, rGO-PVDF/WO3 composite fibre-based sensors are developed via electrospinning technique. The electrospun rGO-PVDF/WO3 were characterized for their structural morphology, thermal stability, crystal structure, and their SO2 sensing capability. The results show that the electrospun rGO-PVDF/WO3 sensor (containing 10 mL GO) leads the most improved SO2 sensing performance of all tested sensors in this work, with a response of 11.08 and 22.06 at SO2 concentrations of 60 and 80 ppm, respectively. The 10 mL-rGO-PDVF/WO3 composite nanofibers also demonstrated good selectivity and stability for SO2. The improvement in gas sensitivity is due to the synergistic effect of forming an ohmic contact between the rGO nanosheets, PVDF fibers, and the WO3 nanograins. The good surface properties such as high surface area (10.64 m2/g) and porous structure of 10 mL-rGO-PDVF/WO3 composite nanofibers have also contributed to the SO2 gas sensing performance. The results show that the composite nanofibers rGO-PVDF/WO3 can be used to detect low concentrations of SO2 and could be used to monitor the environment.

Experimental Study on Desulfurization Characteristics of Dry Sorbent Injection at Low SO2 Concentrations

AbstractTo effectively reduce SO2 emissions, flue gas desulfurization methods are widely used in coal‐fired power plants. In desulfurization, the dry sorbent injection (DSI) technology has the advantages of high desulfurization efficiency, simple operation, convenient adjustment, and low initial investment. Here, a pilot‐scale experimental system was designed and built to investigate the desulfurization characteristics of the DSI technology. The influence of the residence time of the desulfurizer, the reaction temperature, the stoichiometric ratio of the desulfurization reaction, the particle size of the desulfurizer, the inlet SO2 concentration, the dust concentration, and the water vapor content in the flue gas on the desulfurization efficiency at low SO2 concentrations was studied by injecting NaHCO3 into the pipeline. The desulfurization efficiency can be significantly improved by reducing the desulfurizer particle size or increasing the water vapor content in the flue gas at low SO2 concentration. An empirical formula describing the dependence of the desulfurization efficiency on experimental parameters is given.

Mathematical modelling of a semi-dry SO2 scrubber based on a Lagrangian-Eulerian approach

Semi-dry desulfurization is an efficient means of SO2 removal from the effluent gases from electrolysis cells in aluminum smelters. These gases are at low temperature and contain low concentrations of SO2, as opposed to thermal power plants. The removal is carried out by injecting powdered alkaline sorbent, hydrated lime (solid particles), into the SO2-containing gas (gas phase) in the presence of humidity. The reaction is controlled by the adsorption of SO2 onto the surface of lime. This study involves the mathematical modelling of a lab-scale scrubber using a Lagrangian-Eulerian approach in order to analyze the desulfurization efficiency. The model was validated based on experimental data. A parametric study was carried out to investigate the effects of particle size, sorbent amount, and relative humidity (RH) on the desulfurization efficiency. The results show that the particle size is the most important parameter; as the particle size decreases, the desulfurization efficiency increases. However, using finer particles may increase the process cost. The loss in SO2 capture efficiency due to the use of coarser particle size could be compensated by increasing the relative humidity (RH) of the gas, another key parameter of the process.

Experimental study on integrated desulfurization and denitrification of low-temperature flue gas by oxidation method

In this paper, TiO2 catalysts doped with different Fe contents (Fe-TiO2 catalysts) were prepared by coprecipitation method and the Fe loading capacity was optimized, and then the integrated pollutant removal experiment was conducted, in which TiO2 doped with Fe as catalyst and H2O2 as oxidant. The results show that under the condition of constant H2O2/(SO2 + NO) molar ratio, low concentration of SO2 can promote the oxidation and removal efficiency of NO, while high concentration of SO2 can inhibit the removal of NOx. The pollutant removal efficiency is proportional to the amount of catalyst, liquid–gas ratio and pH value of the absorbing solution. The optimal experimental conditions are H2O2/(SO2 + NO) molar ratio 1.5, space velocity ratio 10,000 h−1, H2O2 mass fraction 10 wt%, liquid gas ratio 10, pH 10. Correspondingly, NO oxidation efficiency reaches 88%, NOx removal efficiency 85.6%, and SO2 is almost completely removed. The microstructure of the catalyst before and after the reaction was characterized, and the crystal structure did not change obviously. However, with the deepening of the reaction, the specific surface area of the catalyst decreases, and the catalytic effect decreases slightly.

Copper/Nickel/Cobalt modified molybdenum-tungsten-titanium dioxide-based catalysts for multi-pollution control of nitrogen oxide, benzene, and toluene: Enhanced redox capacity and mechanism study

Previous studies have indicated the potential of monometallic-modified TiO2 catalysts in controlling nitrogen oxide (NOx) and volatile organic compounds (VOCs) in coal-fired flue gas. Unfortunately, increasing selective catalytic reduction (SCR) activity under complicated coal-fired flue gas status is tricky. In this study, modified Co-MoWTiO2 catalysts with multiple active sites were synthesized using the wet impregnation method, which exhibited excellent multi-pollution control ability of NO, benzene and toluene under low oxygen and high SO2 concentrations. The modification of Mo and Co achieved high dispersion and electron transfer. The interaction between W5+/W6+ and Co2+/Co3+ promoted gas-phase O2 adsorption on the catalyst surface, forming of reactive oxygen species (Oα). Density functional theory (DFT) calculations informed that the doping of Co effectively enhanced the NH3 and O2 adsorption capacity of the catalyst, and Co possessed the maximum adsorption energy for NH3 and O2. Possible pathways of multi-pollution control of NO, C6H6, and C7H8 were speculated. NH3/NH4+ on the Lewis/Bronsted acid site is reacted with intermediates of NO (e.g., NO2, nitrite, nitrate) via the Langmuir-Hinshelwood and Eley-Rideal mechanism. The introduction of NO and NH3 did not disrupt the oxidation pathways of benzene and toluene. Following the Mars-van Krevelen mechanism, C6H6 and C7H8 were progressively mineralized by Oα into CO2 and H2O.

Enhanced dual-catalytic elimination of NO and VOCs by bimetallic oxide (CuCe/MnCe/CoCe) modified WTiO2 catalysts: Boosting acid sites and rich oxygen vacancy

It remains challenging to remove nitrogen oxides (NOx), benzene (C6H6), and toluene (C7H8) simultaneously under conditions of low oxygen and high SO2 concentration. Herein, CuCe, MnCe, and CoCe doped WTiO2 catalysts were designed. The prepared CuCe-WTiO2 catalyst consistently maintained more than 85% NO, 92% C6H6, and 91% C7H8 removal in 260–420 °C under 3.33% O2 and 1000 ppm SO2. The adequate charge flow between the catalyst surface and the gas molecules was enhanced, promoting SO2 tolerance of CuCe-WTiO2. More NH3, NH4+, and -NH2 were adsorbed with acid sites on the CuCe-WTiO2 surface. The high concentration of adsorption centers and superior redox properties effectively improved the co-catalytic efficiency. The primary intermediates in the reduction processes via the Langmuir-Hinshelwood and Eley-Rideal mechanisms were NO2, bridged nitrite (NO2–), and monodentate nitrite (NO2–). The generation of reactive chemisorbed oxygen (Oα) becomes more accessible with the transfer of electrons from Ce4+ to adsorbed O2. C6H6 and C7H8 are progressively oxidized by Oα and eventually completely mineralized to CO2 and H2O. This study is anticipated to offer a new option for co-catalytic removal of NO, C6H6, and C7H8.

Killer yeasts used as starter cultures to modulate the behavior of potential spoilage non-Saccharomyces yeasts during Malbec wine fermentation

Yeast contamination is an important problem that affects wine production worldwide. In the present work, fermentative and biocontrol properties under winemaking conditions of the two killer strains, Saccharomyces cerevisiae Cf8 and Wickerhamomyces anomalus Cf20, were evaluated. S. cerevisiae Cf8 and its combination with W. anomalus Cf20 were able to effectively control the growth of Meyerozyma guilliermondii Cd6 at low SO2 concentrations during Malbec must fermentation. Although the killer strain Cf8 alone exerted lower inhibitory activity, it modulated the growth of the strain Cd6, which positively influenced on wine aroma and complexity without being detrimental to product quality. Malbec wine produced by mixed culture Cf8 and Cd6 was the preferred one by the judges in the sensory analysis. To our knowledge, this is the first study made on red wines produced with indigenous killer yeasts from the Northwest Region of Argentina, as well as the first report of the modulation of potential spoilage yeasts into positive starters using killer yeasts in wine production. These results suggest that killer yeasts could be utilized as starter cultures to produce regional wines using low concentrations of SO2.

Variability of sulfur and oxygen isotope values within wet precipitation and its correlation with diminished anthropogenic sulfur dioxide (SO2) emission

Atmospheric sulfate (SO42−) aerosols have the capacity to scatter solar radiation, thus exerting a cooling effect on the climate. It is widely acknowledged that SO42− deposition significantly contributes to ecosystem effect in aquatic and terrestrial environments worldwide. Over the course of several decades, considerable efforts have been undertaken to mitigate anthropogenic sulfur dioxide (SO2) emissions in China, leading to remarkably low SO2 concentrations. Nevertheless, the implications of reduced anthropogenic SO2 emission on atmospheric sulfate transformation and compositions of isotope values (δ34S-SO42–, δ18O-SO42–) remain inadequately understood. To address this knowledge gap, we conducted multiple rainfall sampling instances between 2010 and 2022 (n = 191), encompassing the period of transitioning anthropogenic SO2 emission from high to low levels. Remarkably, we observed a significant reduction in the volume-weighted mean value (VWMV) of SO42− concentrations, declining from 20.86 mg L−1 in 2010 to 2.41 mg L−1 in 2022, and the VWMV of SO42−/NO3− molar ratios also decreased from 12.90 in 2010 to 0.55 in 2022, reflecting the synchronously decreasing annual SO2 emissions and annual SO2 concentrations from 2010 to 2022. In contrast to the declining trends in VWMV of SO42− concentrations, the VWMV of δ34S-SO42– values exhibited a different pattern from 6.6‰ in 2010 to −0.1‰ in 2017 and slightly increased to 2.5‰ in 2022. Furthermore, the VWMV of δ18O-SO42– values demonstrated an increase from 8.8‰ in 2010 to 14.5‰ in 2018, but subsequently decreased to 5.4‰ in 2022. We attributed the sharply dropping VWMV of δ34S-SO42– values to the reduction in the input of primary sulfate with enriched δ34S-SO42– values. The strict desulfurization reduced SO2 emissions, leading to oxidation of these trace SO2 with negative δ34S values, resulting in low sulfate concentrations and negative δ34S-SO42– values. In addition, the monthly average δ18O-SO42– values exhibited a positive correlation with monthly mean δ18O-H2O values (p < 0.05), strongly indicating the water incorporation during SO2 heterogeneous oxidation. More importantly, during spring rainfall, positive δ18O-SO42– values but relatively negative δ34S-SO42– values were influenced by SO2 heterogeneous oxidation facilitated by air oxygen catalyzed under metal ions in dry weather condition, attributed to the low relative humidity (RH) coupled with high deuterium excess (dexcess) values. Conversely, in summer, negative δ18O-SO42– values but relatively positive δ34S-SO42– values resulted from the SO2 heterogeneous oxidation with H2O2 due to high RH and low dexcess values. Moreover, the VWMV of δ18O-H2O exhibited variations from −3.7‰ in 2019 to −9.7‰ in 2021, and displayed a positive correlation with annual temperature (p < 0.01) and a negative correlation with annual precipitation (p < 0.05), making it a valuable indicator of climate change alongside δ18O-SO42– values. Our findings underscore the importance of continued monitoring of atmospheric wet depositions in response to changes in anthropogenic SO2 emission activities. Furthermore, they highlight the substantial impact of variations in δ34S values of SO2 and primary sulfate on rainwater sulfate concentrations and isotope values.

Gas-sensing properties and first-principles comparative study of metal (Pd, Pt)-decorated MoSe2 hierarchical nanoflowers for efficient SO2 detection at room temperature

The online detection and control of concentration for agricultural greenhouse gas SO2 is an important technology to ensure normal agricultural production. This paper reports on a facile hydrothermal method to synthesis Pd-decorated and Pt-decorated MoSe2 nanomaterials, i.e. multistage flower-like structures with attached nanometallic particles and nanosheets hierarchical structures. The Pd/MoSe2 and Pt/MoSe2 hierarchical materials were characterized for the nanostructure, microscopic morphology and elemental compositions. The gas-sensing properties results show that the Pd/MoSe2 and Pt/MoSe2 nanofilm sensors have good sensitivity, stability and response rate to SO2 gas. The response values for the metal Pd and Pt decorated samples to 20 ppm SO2 were 2.04 and 3.42 times higher than those for the intrinsic MoSe2 samples at room temperature. The hierarchical flower-like structure proved to be beneficial in providing more adsorption drop points. In addition, based on the first-principles, the geometrical parameters and electronic properties of the metal-decorated modified structures were calculated to comparatively investigate the enhanced sensing mechanism of SO2 by nanoflower materials. The Pt-MoSe2 nanofilm sensor achieves a high sensitivity detection with a response value of 2.89 for low concentration (1 ppm) of SO2, which is confirming the promotion of charge transfer by metal decorating. This study suggests that Pd-MoSe2 and Pt-MoSe2 hierarchical structures may be recommended for the detection of the agricultural greenhouse gas SO2.

Effect of additives on sulfur resistance of catalytic filter material during denitrification and synergistic decomposition of 1,2-DCBz.

Modified Mn-Ce/P84 catalytic filter material can be used to achieve high removal efficiency of NOx and 1,2-DCBz in bag-filtering dust precipitator synergistic removal of multiple pollutants. However, the presence of SO2 in the actual industrial flue gas has an adverse impact on the catalytic performance of the catalytic filter material. In this paper, a kind of Mn-Ce catalytic filter material was prepared by the impregnation method, which was modified by Fe, Cu, and Co, respectively. As a result, the sulfur resistance of the catalytic filter material was improved. The change of catalytic activity of the three kinds of modified catalytic filter material at different concentrations was compared in the SO2 flue gas fixed bed system. And the modified catalytic filter materials were characterized by SEM, BET, XPS, XRD, and H2-TPR. When the temperature was over 80 °C, different concentrations of SO2 were injected into the simulated flue gas to test the denitrification activity of the catalytic filter material. The results showed that under the low SO2 concentration of 150 ppm, the denitrification activity and 1,2-DCBz activity of Fe, Co, and Cu-modified filter material were increased, and the sulfur resistance of Fe was better under the flue gas conditions of 300 ppm and 450 ppm SO2. Under the condition of 450 ppm SO2 and 200 °C reaction, 93.4% denitrification efficiency and 96.1% 1,2-DCBz removal efficiency could be achieved by using modified Fe-Mn-Ce catalytic filter material.

Hg0 removal performance of magnetic raffinate slag-based sorbents: Mechanism study on oxidation modification

The sulfur-containing carbon-based sorbent was regarded as potential sorbent for the removal of toxic elemental mercury (Hg0). However, due to its lower reaction temperature and the stronger Hg0 oxidation capacity of oxides at higher temperature, oxidation modification on sulfur-containing raffinate slag-based sorbents was proposed in the study. The effects of O2, H2O2 and KMnO4 oxidation modification on Hg0 removal performance and physicochemical properties of sorbents were investigated. The oxidation modification had little effect on pore structure of sorbents, but mainly affected the content and valence state of sulfur and oxygen elements. Compared with H2O2 oxidation, KMnO4 oxidation was more conducive to forming active lattice oxygen (Oα). The valence state of manganese bound with Oα influenced Hg0 capture a lot, and Oα in MnO2 showed strong oxidation capacity to Hg0. Active S22−and Oα in A850-0.1KMnO4-12h sorbent could both promote the Hg0 removal with HgS and HgO formed in used sorbent. The saturated magnetization of A850-0.1KMnO4-12h sorbent was 5.39 emu·g−1, making it possible to separate mercury-containing sorbents from fly ash. It showed good resistance to low concentration of SO2, and NO could promote its Hg0 removal ability. Meanwhile, KMnO4 oxidation successfully improved the Hg0 removal performance at higher reaction temperature and gas hourly space velocity.

A novel robust phosphate-functionalized metal–organic framework for deep desulfurization at wide temperature

The need to decrease environmental pollution, reduce energy consumption and produce high-purity chemicals has become an increasingly important driving force for sulfur dioxide (SO2) capture. The efficient capture of low concentrations of SO2, a highly corrosive acid gas that is not typically present in high concentrations in industrial settings, is a major challenge. Herein, a novel phosphate-functionalized metal–organic framework, ZU-801, is designed with precisely controlled pore sizes and chemical environment to achieve excellent adsorption capacity for SO2 (1.44 mmol g−1 at 0.002 bar, 2.00 mmol g−1 at 0.01 bar) and high IAST selectivities for SO2/CO2 (145), which provides great potential for selective capture of SO2. ZU-801 shows excellent stability to air, water, SO2, strong acid and strong base solutions, and it is thermally stable up to 733 K. Additionally, ZU-801 exhibits outstanding separation ability in removing SO2 from SO2/CO2 mixtures at temperature as high as 383 K or in humid environments. This work demonstrates the potential of designing ion-functionalized ultramicroporous materials with tailored pore sizes and porous chemical environments for efficient capture and separation of SO2 and sheds light on designing stable high-performance materials that operate at high temperatures.

Impact of Gaseous Pollutants Reduction on Fine Particulate Matter and Its Secondary Inorganic Aerosols in Beijing–Tianjin–Hebei Region

A reduction in gaseous pollutants is an important method for mitigating PM2.5 concentration in the atmosphere, and the reduction in SO2/NH3/NOx is beneficial to control secondary inorganic aerosols in PM2.5. In this study, the Weather Research and Forecasting model with Chemistry model (WRF-Chem) was applied to study the impact on the PM2.5 and its secondary inorganic aerosols using the scenario simulation method in the Beijing–Tianjin–Hebei (BTH) region. The results showed that the BTH region is characterized by being NH3-rich and having a higher [NH4+]/[SO42−] ratio in southern BTH, with a ratio of more than 6.0. Source contribution to PM2.5 was highest in the 30%_SO2_40%_NH3_40%_NOx scenario, with a contribution ratio of 6.8%, followed by 3.8% contribution in the 30%_SO2_40%_NH3 scenario, and a 3.4% contribution in the 30%_SO2_60%_NH3_60%_NOx scenario. These results indicate that synergistic reduction measures may be suitable for controlling PM2.5 concentrations. A lower sensitivity factor, β value between PM2.5 and NH3 suggests that solely reducing NH3 emissions is not beneficial for the BTH region. However, this study indicates that the sensitivity of NO3− would improve significantly if NH3 emissions are reduced sharply. A slight reduction in NH3 was found to be beneficial for controlling NO3− in medium and small cities, while a significant decrease in NH3 would be more suitable for mega-cities. The study also observed that SO42− and its constituents continued to decrease with a consistent β value of approximately 0.14 in the 30%_SO2_%_NH3 scenario and between 10.5 and 12.8 in the 30%_SO2_%_NH3_%_NOx scenario. These findings suggest that a synergistic reduction in SO2-NH3-NOx emissions may be more effective in reducing PM2.5 concentrations and its secondary inorganic aerosols (SIAs). However, it is important to ensure that the reduction in NH3 and NOx exceeds 60% in low SO2 concentration conditions.

Efficient removal of Hg0 from cement kiln flue gas using CexFeyOz composite catalyst.

In this study, a kind of CexFeyOz composite with oxygen vacancy structure and strong oxygen storage capacity was prepared by coprecipitation method. Under the condition of no HCl of flue gas, the Hg0 in the flue gas of cement kiln was efficiently and economically removed by using 6-8% oxygen. The results showed that the optimum preparation conditions of the catalyst were Ce-Fe molar ratio of 1-11 and calcination temperature of 550°C. In addition, the reaction temperature, space velocity, the concentration of O2, SO2, and NO had significant effects on the removal efficiency of Hg0 at different rates. More precisely, at the reaction temperature of 350°C, low airspeed, high concentration of O2, and low concentration of SO2 and NO, the efficiency reached the highest value. According to XPS results, the elemental valence of the CexFeyOz composite changed after the reaction. The redox pairs of Ce3+-Ce4+ and Fe3+-Fe2+ had the ability to transfer electrons, which enabled more oxygen adsorbed on the catalyst surface to be converted into O2-, leading to the improvement of the oxidation efficiency of Hg0.

Relevance and Reliability of Outdoor SO2 Monitoring in Low-Income Countries Using Low-Cost Sensors

In the Western world, the SO2 concentration in ambient air dropped to low levels, but some emission sources (e.g., merchant ships) and some regions (e.g., low-income countries) still emit substantial amounts of SO2. At those locations, SO2 monitoring is critical. However, low-income countries do not have much access to expensive reference instruments. Low-cost gas sensors might be an alternative, but it is unclear how reliable such measurements are. To evaluate the performance of the low-cost alternative, the same SO2 gas sensor has been subjected to three different calibration methods: (1) low-cost calibration performed in the tropical climate of Cuba; (2) high-end calibration performed in Belgium; (3) a field calibration at an air quality measuring station in Belgium. The first two methods showed similar trends, suggesting that the gas sensor can be calibrated with a low-cost method. The field calibration was hampered by the low SO2 concentrations. For the monitoring campaign in Cienfuegos, Cuba, the low-cost SO2 sensor calibrated by the low-cost method appeared to be sufficiently reliable. The reliability of the sensor increases with the increase in SO2 concentration, so it can be used in Cuba instead of Belgium.

Efficient SO2 capture at ultra-low concentration using a hybrid absorbent of deep eutectic solvent and ethylene glycol

Deep eutectic solvents (DESs) are considered as the highly effective absorbents for sulfur dioxide (SO2) capture. However, the high viscosity of DESs and the resulting slow absorption rate as well as low absorption capacity at low SO2 concentration seriously hinder their industrial application. In this study, DES of N-methyldiethanolamine (MDEA) and imidazole (Im) is simply blended with ethylene glycol (EG) forming a hybrid absorbent, namely MDEA/Im-EG, which exhibits extremely high SO2 capture capacity at low concentration. In particular, SO2 capture capacity in MDEA/Im-EG (molar ratio = 1:1) reaches 0.446 g SO2/g absorbent at 293.2 K with SO2 concentration of 2000 ppm. Moreover, the corresponding desorption enthalpy is only −40.67 kJ/mol. To well understand the results, thermodynamic analysis of SO2 capture is performed and the SO2 capture mechanism is speculated by nuclear magnetic resonance and Fourier transform infrared spectroscopy.

Secondary aerosol formation drives atmospheric particulate matter pollution over megacities (Beijing and Seoul) in East Asia

Atmospheric particulate matter (PM) pollution in Beijing and Seoul is an urgent concern because of the dense population and the role of the capital city. This study aimed to understand haze formation over East Asia during winter by simultaneously measuring the in situ aerosol chemical composition in the two megacities. During the sampling period, a similar pollution situation characterized by extremely low SO2 (approximately 1 ppbv) and high NOx (approximately 20 ppbv) concentrations and secondary inorganic aerosol (SIA)-dominated PM was found in both cities. Nitrate dominated the inorganic components in the submicron particles in both cities and was more pronounced in Seoul than in Beijing. The enhanced SIA mass concentrations during pollution episodes were observed to be associated with an increased local atmospheric oxidation capacity (indicated by O3+NO2=Ox concentration) and ambient relative humidity under similar stagnant weather conditions. Regarding the thermodynamic equilibrium, abundant aerosol liquid water promoted the partitioning of gaseous HNO3 into its particle phase when pollution events occurred. This result emphasized the importance of local secondary aerosol formation for atmospheric PM pollution in East Asian megacities. The box model simulation of nitrate formation indicated that the homogeneous oxidation of NO2 by OH radicals was the major nitrate formation pathway in both megacities. The downward transport of nitrate from the residual layer also significantly contributed to nitrate concentrations. NOx and volatile organic compounds (VOCs) exhibited a non-linear relationship with nitrate formation. Reducing VOCs concentrations was an efficient approach to mitigate nitrate in both megacities. A reduction of more than 50% in NOx concentrations was required for the effective reduction of nitrate. This study highlighted that Beijing and Seoul were experiencing similar PM pollution situations, and nitrate reduction should be considered to improve their air quality.