Light-induced formation of hydroxyl radicals in fog waters determined by an authentic fog constituent,hydroxymethanesulfonate

The determination of the photo-production rate of hydroxyl radical (OH) in atmospheric liquids is of fundamental importance to an understanding of atmospheric aquatic chemistry. Recently, several studies have been performed to examine the photo-chemical formation rate of OH in cloud and fog waters using a free radical quenching technique with addition of a relatively large concentration of organic compounds as an OH scavenger. The addition of free-radical scavenger chemicals may significantly alter the nature of the sample water and its OH production rate. In this paper, an authentic constituent, hydroxymethanesulfonate, is proposed as a free radical probe for the measurement of photo-chemical generation rate of OH in fog water. At 313 nm, an apparent quantum yield for the production of OH in a fog water was found to be 0.012+/-0.001, indicating that aqueous-phase photo-chemical processes could represent a significant and may be a dominant source of OH in atmospheric liquids.     

Fenton试剂生成·OH的动力学研究

通过试验研究确定了Fenton试剂中羟基自由基·OH生成的动力学规律 ,系统考察了Fenton体系中三个主要因素 :H2 O2 浓度、FeSO4 浓度、pH值对羟基自由基·OH生成规律的影响情况 ,结果表明 ,这三个因素对羟基自由基的生成均有较大的影响 ,在实际生产过程中需加以严格控制 ,以保证最佳的处理效果     

Oxidative degradation of dimethylsulfoxide by locally concentrated hydroxyl radicals in streamer corona discharge process

This study systematically investigates the characteristic degradation behaviors of dimethylsulfoxide (DMSO) by the streamer corona discharge process (SCDP) in water. The analysis of the oxidized intermediates of DMSO shows that hydroxyl radical (*OH) is the main oxidant responsible for the degradation of DMSO in the SCDP. The various experiments on the degradation and mineralization of DMSO, and the effect of the *OH scavenger suggest that the SCDP produces locally concentrated *OHs in and around the plasma channel. This explanation was also supported by the formation of H(2)O(2) and the effect of the *OH scavenger on the H(2)O(2) production rate in the SCDP. Based on the kinetic data for the degradation of DMSO and the production of H(2)O(2) in the SCDP, the volume of the active region in which the *OHs are concentrated, and the effective concentration of *OH in that region were estimated to be 0.21 microl and 5.0 x 10(-3)M, respectively. This level of *OH concentration in the SCDP is approximately 10(7)-10(9) times higher than that generated in ordinary advanced oxidation processes using *OH. The ramifications of the results obtained in this study on successful water treatment using the SCDP are also discussed.     

光催化过程中羟基自由基的产生与效能

采用异丙醇淬灭的方法考察了羟基自由基在光催化氧化酸性橙II过程中的产生和效能,研究了TiO2(P-25)的浓度、异丙醇的用量、酸性橙II的初始浓度、初始pH条件和天然共存离子对羟基自由基贡献率的影响。结果表明,在TiO2(P-25)浓度提高时羟基自由基的贡献率逐步提高并稳定在77.6%,异丙醇的投加量对羟基自由基的贡献率影响不大,酸性橙II初始浓度的提高则使羟基自由基的贡献率降低。在中性pH条件下羟基自由基的贡献率最高,酸性或碱性条件下较低。天然共存离子中HCO3-对羟基自由基的淬灭效应最强,F-的淬灭效应最弱。     

The wall as a source of hydroxyl radicals in smog chambers

The role of the wall of a smog chamber as a radical source has been investigated in several ways. From data in the literature evidence is obtained that HNO₃, present on the reactor wall, may react with NO in the gas phase according to the reaction HNO₃(wall) + 2NO + H₂O → 3HNO₂ to give nitrous acid. Nitrous acid may subsequently photolyze to give hydroxyl radicals.Experimental evidence about the occurrence of this reaction was obtained by u.v.-irradiation of propane-NO_x mixtures with and without NH₃. The presence of NH₃ resulted in a drastically reduced photochemical reactivity, suggesting that neutralization of nitric acid prevented the reaction of HNO₃ with NO. Inclusion of the reaction mentioned above into a computer-model gave a good agreement between experimental and calculated concentration profiles of NO, NO₂ and O₃ in experiments with CO-NO_x and propane-NO_x, mixtures. The results of our findings and those from others are discussed.     

Rates of production of hydroxyl radicals and singlet oxygen from irradiated compost

The use of organic matter from compost to promote the catalytic photodegradation of micropollutants by solar light appears to be environmentally promising. However, quantitative evaluation of the photodegradation potential of the compost is needed. Our goal was to measure the formation rate of hydroxyl radicals and singlet oxygen, two strongly oxidant species, from irradiated compost organic matter. These two reactive species were photogenerated in all of our extracts regardless of the origin of the compost or the extraction procedure; however, their formation rates increased with composting time. Two herbicides and a fungicide were successfully photodegraded when irradiated with simulated or natural solar light in the presence of the compost organic matter or compost suspensions. For reasons of simplification and ease, the use of the latter is recommended in practice.     

Kinetic studies of the reaction of hydroxyl radicals with trichloroethylene and tetrachloroethylene

Rate coefficients are reported for the gas-phase reaction of the hydroxyl radical (OH) with C2HCl3 (k(1)) and C2Cl4 (k2) over an extended temperature range at 740+/-10 Torr in a He bath gas. These absolute rate measurements were accomplished using a laser photolysis/laser-induced fluorescence (LP/LIF) technique under slow flow conditions. The simple Arrhenius equation adequately describes the low temperature data for k1 (<650 K) and the entire data set for k2 and is given by (in units of cm3 molecule(-1) s(-1)): k1(291 - 650 K) = (9.73+/-1.15) x 10(-13) exp (158.7+/-44.0)/T, k2(293 - 720 K ) = (1.53+/-0.14) x 10(-12) exp (-688.2+/-67.5)/T. Error limits are 2sigma values. The room temperature values for k1 and k2 are within +/-2sigma of previous data using different techniques. The Arrhenius activation energies for k1 and k2 are a factor of 2-3 lower than previously reported values. The experimental measurements for both k1 and k2 in conjunction with transition state and variation transition state theory calculations infer an OH addition mechanism. The lack of a measurable kinetic isotope effect for k1 is consistent with this mechanism. Insight into the subsequent reactions of the chemically activated intermediate are presented in the form of potential energy diagrams derived from ab initio calculations.     

Photochemical ozone formation in the Sydney airshed

The theoretical photostationary state relationship, k₃[O₃][NO]/k₁[NO₂] = 1, was tested in the free atmosphere using data obtained from a series of air mass trajectory experiments which were performed as part of the Sydney Oxidant Study. These data show that in general, the relationship was valid to within a factor of two for the Sydney airshed when three minute averaged concentration measurements were used. The effects of various averaging times upon the experimental photostationary state relationship arc discussed.     

Photochemical particulate formation in sulfur dioxide-air mixtures

Experiments were performed studying the formation of particulates in sulfur dioxide-air mixtures irradiated by ultraviolet light. Measurements were made for five different initial sulfur dioxide concentrations (0.2, 0.3, 0.5, 0.7 and 1 ppm) and for four relative humidities (25, 50, 75 and 100%). The data show that the maximum number of nuclei (particles smaller than 0.1 μm) produced in the mixture is proportional to the initial sulfur dioxide concentration and to the square of the relative humidity. Particles larger than 0.3 μm were not present in measurable amounts in the mixture.     

HQSAR and CoMFA approaches in predicting reactivity of halogenated compounds with hydroxyl radicals

Two quantitative structure–activity relationship (QSAR) methods: hologram QSAR (HQSAR) and comparative molecular field analysis (CoMFa) were evaluated for predicting half-lives of the hydroxyl radicals reaction with substituted aromatic compounds. The HQSAR approach, which is topological in nature, results in a mathematical model which was more stable and has a greater predictive ability than the model derived on the 3-D CoMFA approach. Interpretations of the colour coded results of both methods are in good agreement with the proposed mechanism of the hydroxyl radical oxidation of halogenated aromatic compounds in the atmosphere.     

水中有机物高级氧化过程中的羟基自由基检测方法比较

化学氧化水中有机物过程中的羟基自由基的定量检测是研究高级氧化动力学和过程机理的重要技术手段。本文通过对比整理相关领域羟基自由基的检测技术，分析了目前在医学和化工领域中使用的羟基自由基测量方法的应用特点和适用范围，讨论了其中的便捷式分析方法及其在水处理高级氧化过程研究中的可用性，推荐了可用于多组分水相的Fenton试剂氧化有机物过程中的羟基自由基检测方法。     

水中有机物高级氧化过程中的羟基自由基检测方法比较

化学氧化水中有机物过程中的羟基自由基的定量检测是研究高级氧化动力学和过程机理的重要技术手段.本文通过对比整理相关领域羟基自由基的检测技术,分析了目前在医学和化工领域中使用的羟基自由基测量方法的应用特点和适用范围,讨论了其中的便捷式分析方法及其在水处理高级氧化过程研究中的可用性,推荐了可用于多组分水相的Fenton试剂氧化有机物过程中的羟基自由基检测方法.     

Gas-phase photolytic production of hydroxyl radicals in an ultraviolet purifier for air and surfaces

We have measured the concentration of hydroxyl radicals (OH) produced in the gas phase by a commercially available purifier for air and surfaces, using the time rate of decay of n-heptane added to an environmental chamber. The hydroxyl generator, an Odorox® BOSS? model, produces the OH through 185-nm photolysis of ambient water vapor. The steady-state concentration of OH produced in the 120 m³ chamber is, with 2σ error bars, (3.25 ± 0.80) × 10⁶ cm^?3. The properties of the hydroxyl generator, in particular the output of the ultraviolet lamps and the air throughput, together with an estimation of the water concentration, were used to predict the amount of OH produced by the device, with no fitted parameters. To relate this calculation to a steady-state concentration, we must estimate the OH loss rate within the chamber owing to reaction with the n-heptane and the 7 ppb of background hydrocarbons that are present. The result is a predicted steady-state concentration in excellent agreement with the measured value. This shows we understand well the processes occurring in the gas phase during operation of this hydroxyl radical purifier.

Implications: Hydroxyl radical air purifiers are used for cleaning both gaseous contaminants, such as volatile organic compounds (VOCs) or hazardous gases, and biological pathogens, both airborne and on surfaces. This is the first chemical kinetic study of such a purifier that creates gas-phase OH by ultraviolet light photolysis of H₂O. It shows that the amount of hydroxyls produced agrees well with nonparameterized calculations using the purifier lamp output and device airflow. These results can be used for designing appropriate remediation strategies.     

响应面法对泡沫铜阴极电芬顿产H2O2与·OH性能优化

泡沫金属因其三维结构及优良导电性,使其作为电芬顿阴极开始引起学者关注。选择泡沫铜为阴极、石墨棒为阳极,搭建微孔曝气均匀的玻璃反应器,提高体系传质效率,并通过响应面探索体系产H2O2和·OH的机理。用响应面设计3因素(pH、电流、Fe2+初始浓度)3水平实验,得到体系产H2O2和·OH与3种因素之间的非线性回归方程,得到最优条件:当pH=2、电流0.25 A、Fe2+初始浓度为15 μmol·L-1时H2O2产量最大,为457.27 μmol·L-1;当pH=2、电流0.25 A、Fe2+初始浓度为20 μmol·L-1时·OH产量最多,可达18.56 μmol·L-1。根据方差分析,二次模型显著性很高(R2H2O2=0.977 8,R2·OH=0.964 2),能够很好地模拟实验结果。通过铜溶出实验分析得出铜溶出量在0.4~1.8 mg·L-1之间,符合现行污水排入城镇下水道水质标准(CJ 343-2010)。     

Photochemical generation rates of hydroxyl radical in aqueous solutions containing Fe(III)-hydroxy complex

The rates of photochemical generation of hydroxyl radical at 313 nm in aqueous solutions containing ferric ion at acidic pH were measured by the competitive kinetic method using 2-chlorophenol as a test compound and 1-octanol as a radical scavenger. The quantum yield of hydroxyl radical generation calculated from the rates was about 0.02. From the results, it was suggested that this system could be used as a method of wastewater treatment.     

Photochemical formation and transport of ozone in Athens,Greece

An evaluation of the diurnal variation of the hourly ozone concentrations measured at five sites in Greater Athens from June until early September 1984 indicates that photosmog episodes in Greater Athens are associated with the sea breeze circulation. Due to local air circulation in the Athens basin, precursors of O₃ are transported to and accumulated in the Saronikos Bay during the morning hours while the land breeze is blowing. At noon, when the sea breeze sets in, the O₃ formed over the sea is brought back to the coast and to central Athens where it increases the local O₃ concentration by a factor of 3–5 within a few hours. The O₃ levels often remain high throughout the night. During the photochemical smog episodes, all of them accompanied by well-developed sea breezes, the U.S. Air Quality Standard of 120 ppb O₃ was exceeded for 4–7 h day⁻¹. Peak O₃ concentrations up to nearly 200 ppb were recorded in the smog episodes.Relatively high O₃ concentrations were measured on the island of Aegina. They tend to remain high during the night and can be attributed only to primary pollutant transport from Greater Athens advected by the land breeze. The O₃ values obtained at Mount Immitos (1000 m above MSL) suggest that, first, the sea breeze inhibits the influence of vertical thermal convection up to heights above 600 m, and second, no O₃ is noticeable from above the tropopause to ground level or from long-range transport.