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1.
This paper presents a novel cleaner production process for producing sodium chlorite by reducing sodium chlorate with hydrogen peroxide. In the new process, chlorine dioxide is generated by reducing chlorate ions with hydrogen peroxide in the presence of sulfuric acid: it then reacts with aqueous sodium hydroxide solution and hydrogen peroxide to produce sodium chlorite. The reaction conditions that were experimentally investigated included: reaction temperatures, concentrations of sodium chlorate solution, molar ratio of NaClO3:H2SO4:H2O2, and acidity. Waste acid in the chlorine dioxide generator is dramatically reduced with recycling in the new process. The by-produced sodium sulfate in sulfuric acid is minimized and reclaimed.  相似文献   

2.
A laboratory-based atmospheric flow chamber, using realistic presentation rates of SO2, NO and NO2 pollutants directed to various dry and wetted surfaces, has been employed to quantify the effects of the individual pollutants and the role of ozone as an oxidant. For the individual pollutant gases reacting with stone surfaces coming to equilibrium with 84% relative humidity (r.h.), chemical reaction in the presence of a moisture film proceeds and the extent of this reaction is related to pollutant gas solubility in the moisture film, i.e. SO2 > NO2 > NO. After dissolution in the moisture film, the pollutant gases are oxidized in the presence of catalysts associated with the stones. The additional presence of ozone promotes oxidation of the pollutant gases and thus their reaction with the stones. For SO2 pollutant, oxidation in the gas phase is not significant compared with that in the moisture film, with enhanced oxidation in the presence of catalysts. Ozone increases oxidation of NO and NO2 pollutant gases in the gas phase and moisture film; however, the oxidation of SO2 in the moisture film is more significant than that of NO or NO2. Wetting of the stone surfaces, in the absence of ozone, reveals the consistently greatest chemical reaction with SO2 compared with NO and NO2, which is related to SO2 solubility, oxidation in the presence of catalysts and production of sulphuric acid. Generally similar behaviour is evident of NO and NO2, but NO shows a reduced extent of chemical reaction, implying that its oxidation in surface water, in the presence of catalytic species, is slow and hence the reactants are lost in the form of run-off. In the additional presence of ozone, the SO2 pollutant gas gives rise to enhanced chemical reaction, whereas both NO and NO2 show lower extents of chemical reaction than for the dry stones. This arises from the relatively slow conversion of N2O5 in the liquid phase to nitric acid, allowing loss of reactants in run-off.  相似文献   

3.
二氧化硫(SO_2)是一种有毒的大气污染物,主要经气孔进入植物体内.目前对于SO_2毒性的研究多集中在氧化损伤方面,关于SO_2对植物脯氨酸代谢的影响及相关分子机制的研究还很少.本文以谷子幼苗为材料,研究了不同浓度SO_2气体暴露对叶片气孔运动、脯氨酸代谢和抗氧化酶系统的影响.结果显示,10 mg·m~(-3) SO_2熏气对谷子幼苗的叶片形态、相对含水量、气孔开度、脯氨酸含量及抗氧化酶活性均无明显影响.30 mg·m~(-3) SO_2暴露24~72 h后,叶片出现明显的受损症状,相对含水量降低,叶面气孔开度减小;30 mg·m~(-3) SO_2熏气导致叶中脯氨酸含量显著增加,脯氨酸脱氢酶(PDH)活性明显升高.同时,长时间的SO_2胁迫可诱导SiPDH基因表达上调,而脯氨酸合成相关基因SiP5CS、SiP5CR表达受到明显抑制.此外,谷子幼苗暴露于30 mg·m~(-3) SO_2时,叶中超氧阴离子(O■)产生速率与对照相比显著提高,诱导超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性增强,从而将过氧化氢(H_2O_2)含量维持在正常水平.以上结果表明,SO_2对谷子的毒性效应具有浓度依赖性.高浓度SO_2暴露下,谷子能够通过控制气孔开放、调节脯氨酸代谢和抗氧化酶活性等过程来适应SO_2胁迫.  相似文献   

4.
The concentrations of aerosols (NH4NO3, (NH4)2SO4 and NH4Cl) and of gases (HCl(g), HNO3(g), NH3(g) were determined by denuder methods under different conditions (in the absence of fog, before, during and after fog events). At this site situated in an urban region, high concentrations of the gaseous strong acids HCl(g) and HNO3(g) are observed. NH4Cl and NH4NO3 aerosols represent a major fraction of the Cl and NO3 aerosols (<2.4 μm)collected by denuders. During a fog event, very high concentrations of SO42− were found in small aerosols, which are attributed to the aqueous phase oxidation of SO2 under the influence of high pH due to the presence of NH3. Differences in SO42− concentrations measured in aerosols (<2.4 μm) and in fog droplets were probably due to mass-transport limitations of the SO2 oxidation. Ammonium sulfate aerosols represent in some cases a significant fraction of the total S present (SO2(g) + SO42−. Soluble aerosols and gases contribute to the composition of fogwater and are released again after fog dissipation.  相似文献   

5.
预处理方法对玉米芯作为反硝化固体碳源的影响   总被引:6,自引:4,他引:2  
分别用1.5%NaOH、1%H2SO4、1.5%H2O2和碱性双氧水(含有1.5%H2O2的NaOH溶液)并联合紫外照射对玉米芯进行预处理,将预处理后玉米芯作为反硝化固体碳源和微生物载体进行静态释碳和静态反硝化实验,考察预处理后玉米芯释碳、反硝化性能及微生物附着情况.结果表明,经过碱和碱性双氧水预处理后的玉米芯碳源可利用性和反硝化效率均有显著的改善,尤其是碱预处理方法,静态反硝化反应至41 d时,仍能保持90%以上的硝酸盐去除率.因此,碱预处理方法可以改善玉米芯释碳性能,有利于微生物的附着和碳源的利用.  相似文献   

6.
Despite the heterogeneous reaction of sulfur dioxide (SO2) on mineral dust particles significantly affects the atmospheric environment, the effect of acidic gases on the formation of sulfite and sulfate from this reaction is not particularly clear. In this work, using the in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) technique, we employed a mineral dust particle model (CaCO3) combined with NO2 and acetic acid to investigate their effects on the heterogeneous reaction of SO2 on CaCO3 particles. It was found that water vapor can promote the formation of sulfite and simulated radiation can facilitate the oxidation of sulfite to sulfate. The addition of NO2 or acetic acid to the reaction system altered the production of sulfate and sulfite accordingly. There was a synergistic effect between NO2 and SO2 that promoted the oxidation of sulfite to sulfate, and a competitive effect between acetic acid and SO2 that inhibited the formation of sulfite. Moreover, light and water vapor can also affect the heterogeneous reaction of SO2 with the coexistence of multiple gases. These findings improve our understanding of the effects of organic and inorganic gases and environmental factors on the formation of sulfite and sulfate in heterogeneous reactions.  相似文献   

7.
A model of the chemical evolution of the droplets in a hill-cap cloud is presented. The chemistry of individual droplets forming on cloud condensation nuclei of differing size and chemical composition is considered, and the take-up of species from the gas phase by the droplets is treated explicity for the droplet population. Oxidation of S(IV) dissolved in cloud droplets is assumed to be dominated by hydrogen peroxide and ozone.Hydrogen peroxide is normally found to be the dominant oxidant for the oxidation of sulphur dioxide (except in the presence of substantial concentrations of ammonia gas, which increases droplet pH and the contribution made by the oxidant ozone). The entrainment of hydrogen peroxide from above the cloud top increases the amount of sulphate produced in conditions where the reaction is otherwise oxidant limited by the availability hydrogen peroxide. These conditions occur when there are high concentrations of sulphur dioxide accompanied by low cloudwater pH values.Within droplets formed on sodium chloride aerosol, reduced levels of acidity lead to an increase in sulphate production as a result of an enhanced reaction between SO2 and the oxidant ozone. This results in an overall higher increase in cloudwater sulphate than would be expected assuming an even distribution of all reactants amongst the droplets. In addition, concentrations of the hydrogen sulphite ion predicted to occur in the cloudwater can be substantially in excess of those predicted from the bulk cloudwater pH. This is consistent with recent observations.  相似文献   

8.
冶炼厂SO2烟气化学催化吸收扩大试验研究   总被引:5,自引:0,他引:5  
在单层塔板泡沫吸收塔中的SO2液相催化氧化进行了扩在试验研究,当SO2净化效率(单板效率)为50%时,得到16%(Wt)H2SO4,硫酸生成速率为18%/h,SO2吸收最佳敢化5L/Nm^3,添加表面活性剂Al2(SO4)3及鼓氧操作对SO2液相催化氧化有明显促进作用,冶炼烟气SO2浓度波动吸收效率影响不大。  相似文献   

9.
Meteorological and chemical conditions during the July 1988 Bermuda-area sampling appear to have been favorable for conversion of sulfur gases to particulate excess sulfate (XSO4). Observed average XSO4 and SO4 concentrations of 11 and 2.1 nmol m−3, respectively, at 15 m a.s.l. in the marine boundary layer (MBL) upwind of Bermuda, indicate that conversion of SO2 to XSO4, over and above homogeneous conversion, may be necessary to explain the > 5.0 average molar ratio of XSO4 to SO2. Given an observed cloud cover of <15% over the region and the <3 nmol m−3 SO3 concentrations observed by aircraft, heterogeneous conversion mechanisms, in addition to cloud conversion of SO2, are necessary to explain the observed 11 nmol XSO4 m−3.Aerosol water content, estimated as a function of particle size distribution plus consideration of SO2 mass transfer for the observed particle size distribution, shows that SO2 was rapidly transferred to the sea-salt aerosol particles. Assuming that aqueous-phase SO2 reaction kinetics within the high pH sea-salt aerosol water are controlled by O3 oxidation, and considering mass-transfer limitations, SO2 conversion to XSO4 in the sea-salt aerosol water occurred at rates of approximately 5% h−1 under the low SO2 concentration, Bermuda-area sampling conditions. All of the 2 nmol XSO4 m−3 associated with sea-salt aerosol particles during low-wind-speed, Bermuda-area sampling can be explained by this conversion mechanism. Higher wind speed, greater aerosol water content and higher SO2 concentration conditions over the North Atlantic are estimated to generate more than 4 nmol XSO4 m−3 by heterogeneous conversion of SO2 in sea-salt aerosol particles.  相似文献   

10.
The reaction between NH3 and SO2 in thin water films was studied with a focus on the formation of sulfate. The reactions were conducted at 5 and 60% relative humidities or partial pressure of water vapor and at 0.04, 0.16 or 0.20 atm O2 for temperatures between 20 and 50°C using a flow reactor and static flask reactors. In the presence of water vapor, the oxidation of SO2 to sulfate was observed only when NH3 was present. The product was primarily (NH4)2SO4. Conversion of as much as 81% of the SO2 to sulfate was observed after 10 min of reaction when the initial concentrations of SO2 and NH3 were 1 ppm and the relative humidity was 60%. Conversion was only 1–3% when NH3 and/or water vapor were absent from the system. The surface of the reactor was found to influence the reaction by providing a place for a film of liquid water to form, and for the first several hours of reaction in the film, th e rate of sulfate formation was observed to be faster than oxidation in liquid water. In general, these results suggest that thin water films on environmental surfaces play a greater role in the deposition of atmospheric gases and the accumulation of their reaction products on surfaces than previously considered.  相似文献   

11.
活性炭催化过氧化氢去除荧光增白剂   总被引:1,自引:1,他引:0  
刘海龙  张忠民  赵霞  焦茹媛 《环境科学》2014,35(6):2201-2208
研究了活性炭(activated carbon,AC)吸附、改性活性炭(activated carbon modified,ACM)吸附、过氧化氢(H2O2)氧化、AC催化H2O2等方法对水体中荧光增白剂VBL的处理效果,并通过自由基俘获剂叔丁醇、催化过程气体分析等探讨了AC催化H2O2分解VBL的机制.结果表明,经硝酸铁[Fe(NO3)3]改性过的ACM对VBL的吸附去除率高于未改性的AC.活性炭催化H2O2对VBL的去除效果明显,但未改性AC催化去除率高于ACM.60 min时,AC催化氧化去除率即可达到95%以上,而ACM仅为58%.叔丁醇的加入降低了AC和ACM催化氧化对VBL的去除率,表明AC催化H2O2氧化能促进H2O2形成羟基自由基(·OH)和原子氧参与反应.AC催化H2O2分解及释放气体分析表明,AC能催化H2O2形成氧气并放热,且ACM明显快于AC.结合催化H2O2去除VBL效率的结果分析,ACM催化反应时活性中间物(自由基和原子氧等)产生速率快于AC,活性中间物自身消耗形成氧气,而不是用于分解VBL.催化反应中活性中间产物的形成速率与反应物供给速率的不匹配可能是导致ACM催化效果弱于AC的重要原因.  相似文献   

12.
Capturing flue gases often require multiple stages of scrubbing, increasing the capital and operating costs. So far, no attempt has been made to study the absorption characteristics of all the three gases (NO, SO2 and CO2) in a single stage absorption unit at alkaline pH conditions. We have attempted to capture all the three gases with a single wet scrubbing column. The absorption of all three gases with sodium carbonate solution promoted with oxidizers was investigated in a tall absorption column. The absorbance was found to be 100% for CO2, 30% for NO and 95% for SO2 respectively. The capture efficiency of sodium carbonate solution was increased by 40% for CO2 loading, with the addition of oxidizer. Absorption kinetics and reaction pathways of all the three gases were discussed individually in detail.  相似文献   

13.
Aircraft measurements of hydrogen peroxide (H2O2) were performed during the TROPOZ II meridional campaign. A specially designed automatic H2O2 analyser on board the airplane allowed us to obtain more than 43,000 H2O2 measurements. The data set covers a latitude range from 60°N to 60°S and altitudes up to 11 km. Concentration of H2O2 ranged from 0.42 ppb (percentile 5) to 6.31 ppb (percentile 95) and exhibited a variability factor of as much as 15. Hydrogen peroxide concentration was typically low (<2 ppb) in the boundary layer of both hemispheres except for the inter-tropical belt, even in America, as well as Africa where the mean mixing ratio reached 5 ppb. In the northern uppermost troposphere a significant increase in H2O2 (>3 ppb) could be noticed. Some episodes of high hydrogen peroxide mixing ratio were encountered in the vicinity of cloud systems probably by exchange of H2O2 from the liquid phase to the gas phase.  相似文献   

14.
A commercial Differential Optical Absorption Spectrometer (DOAS), measuring trace gases absorbing in the u.v./vis region was used for obtaining information on aerosol parameters (e.g. total surface) based on the observed Mie scattering. This procedure allows simultaneous measurements of trace gas concentrations and aerosol parameters within the same air volume. A series of measurements of HNO2, NO2, NO, SO2 and aerosol parameters was performed at Ispra in northern Italy. The observations show a rapid formation of gaseous HNO2 during foggy episodes and give direct evidence of an important contribution of reactions on wet aerosols to the transformation of tropospheric NOx into HNO2.  相似文献   

15.
Ozone (O3) is an important atmospheric oxidant. Black carbon (BC) particles released into the atmosphere undergo an aging process via O3 oxidation. O3-aged BC particles may change their uptake ability toward trace reducing gases such as SO2 in the atmosphere, leading to different environmental and health effects. In this paper, the heterogeneous reaction process between O3-aged BC and SO2 was explored via in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Combined with ion chromatography (IC), DRIFTS was used to qualitatively and quantitatively analyze the sulfate product. The results showed that O3-aged BC had stronger SO2 oxidation ability than fresh BC, and the reactive species/sites generated on the surface had an important role in the oxidation of SO2. Relative humidity or 254 nm UV (ultraviolet) light illumination enhanced the oxidation uptake of SO2 on O3-aged BC. The oxidation potentials of the BC particles were detected via dithiothreitol (DTT) assay. The DTT activity over BC was decreased in the process of SO2 reduction, with the consumption of oxidative active sites.  相似文献   

16.
UV/H2O2氧化对硝基酚实验表明,H2O2光解产生·OH自由基是对硝基酚降解的直接原因,12min内25mg/L的对硝基酚去除率达到98%以上.溶液中TOC变化与对硝基酚的去除并不同步,说明对硝基酚的降解中生成了一系列的中间产物,然后再达到完全矿化的.体系中H2O2浓度变化显示产生的中间产物对H2O2光解没有明显影响.研究中还对对硝基酚起始质量浓度、H2O2浓度及pH影响进行了考察.研究认为UV/H2O2是对硝基酚脱毒的一种有效方法.   相似文献   

17.
为研究近年来福建省SO2污染的时空动态特征,利用臭氧观测仪(ozone monitoring instrument,OMI)卫星遥感反演的PBL(planetary boundary layer,大气边界层)SO2柱含量数据,分析了2005-2017年福建省PBL SO2柱含量的时空间分布特征.结果表明:①在长时间尺度上,PBL SO2柱含量的变化趋势可分为2个时段,其中,2005-2011年PBL SO2柱含量呈逐渐上升趋势,6 a增加了约0.027 DU,增长率约为6.12%;2011-2017年PBL SO2柱含量呈下降趋势,7 a减少了约0.018 DU,下降率约为3.89%.②PBL SO2柱含量呈明显的周期性变化特征,最小值和最大值分别出现在6月和12月,多年平均值分别约为0.383和0.555 DU.③PBL SO2柱含量的3个高值区分别出现在沿海的福州市,厦门市、漳州市东部和泉州市西部,三明市和南平市部分地区,这3个高值区多年平均PBL SO2柱含量分别约为0.505、0.495和0.485 DU.从城市尺度上来看,PBL SO2柱含量最大值出现在厦门市,其多年平均值为(0.486±0.015)DU;其次为福州市,PBL SO2柱含量多年平均值为(0.465±0.026)DU;最低值出现在漳州市,PBL SO2柱含量多年平均值为(0.429±0.020)DU.④福建省PBL SO2柱含量变化趋势在空间分布上存在明显的差异,不同时期、不同区域变化趋势不一致.2005-2011年PBL SO2柱含量的变化范围为-0.13~0.18 DU,变化率范围为-25%~50%,PBL SO2柱含量出现增长的区域主要是在高值区,如龙岩市西部、厦门市北部以及三明市东部等区域;2011-2017年PBL SO2柱含量的变化范围为-0.13~0.15 DU,变化率范围为-29%~34%.2011-2017年福州市和厦门市PBL SO2柱含量下降最为明显,减少了约0.10 DU,下降率约为25%.研究显示,卫星遥感估算的PBL SO2柱含量具有一定的可靠性,可以用于区域SO2污染的研究.   相似文献   

18.
Controlled exposure of ice to a reactive gas, SO2, demonstrated the importance of the chemical composition of the ice surface on the accumulation of acidity in snow. In a series of bench-scale continuous-flow column experiments run at four temperatures (−1, −8, −30 and −60°C), SO2 was shown to dissolve and to react with other species in the ice-air interfacial region at temperatures approaching the melting point of ice. Experiments consisted of passing air containing SO2 through glass columns packed with 100μm ice spheres of varying bulk composition (0–5μM H2O2, and 0–1 mM NaCl), and analysing SO2 in the air and SO42− in the ice. At all temperatures (−60 to −1°C), increased retention volumes were found for increasing ionic strength and oxidant concentration. At the coldest temperatures and with no NaCl, increased retention volumes for −60 vs −30°C are consistent with SO2 uptake by physical adsorption. At warmer temperatures, −8 and −1°C, the observed tailing in the sorption curves indicated that other processes besides physical adsorption were occurring. The desorption curves showed a rapid decrease for the warmer temperatures, indicating the sorbed SO2 is irreversibly oxidized to SO42−. Results indicate that aqueous-phase reactions can occur below −8°C (i.e. −30 and −60°C). Results for different salt concentrations show that increasing ionic strength facilitates SO2 oxidation at colder temperatures, which is consistent with freezing point depression. One environmental implication is that snowpacks in areas with background SO2, can accumulate acidity during the winter months. As acidity accumulates, the solubility of SO2 will decrease causing a concomitant decrease in the air-to-surface flux of SO2. Modeling dry deposition of gases to snow surfaces should incorporate the changing composition of the ice surface.  相似文献   

19.
The influence of wind velocity, air temperature and vapour pressure deficit of the air (VPD) on NH3 and SO2 transfer into bean leaves (Phaseolus vulgaris L.) was examined using a leaf chamber. The measurements suggested a transition in the properties of the leaf boundary layer at a wind velocity of 0.3–0.4 ms−1 which corresponds to aRecrit value of about 2000. At higher wind velocities the leaf boundary layer resistance (rb) was 1.5–2 times lower than can be calculated from the theory. Nevertheless, the assessed relationships betweenrb and wind velocity appeared to be similar to the theoretical derived relationship forrb. The NH3 flux and in particular the SO2 flux into the leaf strongly increased at a VPD decline. The increase of the NH3 flux could be attributed to an increase of the stomatal conductance (gs). However, the increase of the SO2 flux could only partly be explained by an increase ofgs. An apparent additional uptake was also observed for the NH3 uptake at a low temperature and VPD. The SO2 flux was also influenced by air temperature which could be explained by a temperature effect ongs. The results suggest that calculation of the NH3 and SO2 flux using data ofgs gives a serious understimation of the real flux of these gases into leaves at a low temperature and VPD.  相似文献   

20.
SO2 oxidation in the presence of NH3 was studied in a mixing-type continuous-flow cloud chamber. NaCl and soot particles (∼5–15 μ m−3) were used as cloud condensation nuclei. Cloud liquid water content was varied between 0.2 and 3 g m−3. SO2 and NH3 concentrations were 0.6 and 1.1 ppm, respectively. The contact time between the SO2 and the cloud drops was varied from 8 s to 3 min. Up to 80% of the input SO2 can be oxidized within short contact times in the presence of NH3 and when the water is in the condensed cloud-drop phase. Negligible sulfate formation was observed in the absence of the liquid phase regardless of the presence or absence of NH3. No significant dependence of the oxidation on the cloud condensation nuclei type nor the contact time was found. This in-cloud SO2 oxidation is much faster than predicted by S(IV) oxidation by molecular oxygen measured in bulk solutions.  相似文献   

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