Effect of CH3OOH on the atmospheric concentration of OH radicals

Methyl hydroperoxide (CH₃OOH, MHP) is known to be a significant sink and reservoir of HO_x and RO_x radicals in the atmosphere. In order to investigate the impact of MHP on the concentration of atmospheric OH radicals, two key gas-phase reactions of MHP, i.e. the reactions with OH radicals and with UV photolysis, have been simulated at temperature of 293±2 K and total pressure of 1.01×10⁵ Pa, using the long path Fourier transform infrared (LP-FTIR) spectrometry. OH radicals are generated by the photolysis of O₃ in the presence of water vapor. Combined with the relative rate method, the reaction rate constant of MHP with OH radicals is determined to be (3.99±0.15)×10^-12 cm³?molecule^-1?s^-1, and thus the atmospheric lifetime of MHP is estimated at 2.9 days. Furthermore, from detailed analysis of the UV photolysis of MHP, the yield of OH radicals is obtained to be 0.91±0.04. Based on the MHP atmospheric lifetime and the yield of OH radicals, it is concluded that MHP plays an essential role in the redistribution of OH radicals in the troposphere.     

Effect of CH3OOH on the atmospheric concentration of OH radicals

Methyl hydroperoxide (CH₃OOH, MHP) is known to be a significant sink and reservoir of HO_x and RO_x radicals in the atmosphere. In order to investigate the impact of MHP on the concentration of atmospheric OH radicals, two key gas-phase reactions of MHP, i.e. the reactions with OH radicals and with UV photolysis, have been simulated at temperature of 293±2 K and total pressure of 1.01×10⁵ Pa, using the long path Fourier transform infrared (LP-FTIR) spectrometry. OH radicals are generated by the photolysis of O₃ in the presence of water vapor. Combined with the relative rate method, the reaction rate constant of MHP with OH radicals is determined to be (3.99±0.15)×10^-12 cm³?molecule^-1?s^-1, and thus the atmospheric lifetime of MHP is estimated at 2.9 days. Furthermore, from detailed analysis of the UV photolysis of MHP, the yield of OH radicals is obtained to be 0.91±0.04. Based on the MHP atmospheric lifetime and the yield of OH radicals, it is concluded that MHP plays an essential role in the redistribution of OH radicals in the troposphere.     

UV/H2O2作用下冰中苯酚的光转化及其与羟基自由基的关系

在UV和H₂O₂作用下考察pH值、 光强、 H₂O₂初始浓度和无机离子等对冰中苯酚光解的影响, 并利用二甲基亚砜（DMSO）捕获体系中生成的
羟基自由基（·OH）研究·OH对冰中苯酚光解的影响. 实验结果表明: H₂O₂可显著促进冰中产生·OH及苯酚光解; 改变光强、 pH值和H₂O₂的初始浓度, 苯酚的光解率随体系中·OH浓度的增加而增大; 加入NO^-₂和NO^-₃可抑制体系中产生·OH及苯酚光解; 加入SO^2-₄不影响体系中·OH的产生及苯酚光解; 加入CO^2-₃和HCO^-₃可抑制体系中产生·OH, 但对苯酚光解影响较小, 这是由于体系中产生了其他自由基所致.     

Measurement of rate constant for gas-phase reaction of DDVP with OH radical by using LP-FTIR

：Pollution caused by organic pesticides has received increasing attention. Until now, studies on organic pesticides pollution are mainly focused on soil and water. For reactions of organic pesticides in gas-phase, there are very little research results reported. Using a long path quartz reactor to simulate the atmospheric reaction of dimethyl_dichloro_vinyl_phosphate(DDVP) with OH radicals, the rate constant for the reaction at room temperature is measured at (3.06±0.46)×10-11 cm3 s-1 with Fourier transform infrared spectrograph.The result indicates that DDVP degrades relatively fast in the atmosphere and is unlikely to cause persistent pollution.     

Determination of Henry''s Law constant for methyl hydroperoxide by long path FTIR

Methyl hydroperoxide (MHP, CH3OOH) is one of the main organic peroxides in the atmosphere. In order to understand how MHP partitions in atmospheric gas and liquid phases, the Henry's Law constant for its aqueous solution is determined. A novel technique is established for measuring gas-phase MHP concentration, I.e. The gas phase is collected by a gas-bag and then analyzed by long path Fourier transform infrared (LP-FTIR) spectrometry. At 283 K～303 K, the temperature dependence of the Henry's Law constant for MHP can be expressed as lnKH= a/T - b, a = 4386 ± 140, b = 9.19 ± 0.48, where KH is in unit of molar concentration per atm,and T is in degrees Kelvin. The standard heat of solution is 36.45 ± 1.16 kJ? K- 1? mol-1.     

高级氧化技术研究现状及其发展趋势

 中国面临环境保护的重大压力,高级氧化技术(AOT)是解决环境污染的理想绿色技术,而高级氧化技术是指·OH制备以及诱发一系列的攻击污染物及微生物反应,从源头上解决了治理污染过程中再污染的问题。高级氧化技术规模制备·OH是其标志性核心关键问题。基于此,学术界进行了一系列羟基自由基制备研究工作。本文介绍了在水中制备·OH的方法,主要介绍O₃/H₂O₂、O₃/UV、H₂O₂/UV、Fenton、光催化氧化、电子辐射和水激励等方法;也介绍了在气体中制备·OH的方法,主要有脉冲电晕放电法、电子束和强电离放电法等。强电离放电法有望同时解决在水、气中规模制备·OH过程中存在的问题。     

Quantitative relationship between production and removal of OH and HO<Subscript>2</Subscript> radicals in urban atmosphere

Atmospheric oxidizing capacity is the essential feature of urban and regional air. And OH and HO2 radicals are the key species indicating atmospheric oxidizing capacity. Using Guangzhou City as a case, this work has conducted field measurements of photochemistry relevant pollutants including O3, NOx, VOCs, H2O2, HNO2 and CO,SO2. The concentrations of OH radical are measured simultaneously by impregnated filter trapping and HPLC (IFTHPLC) method. The factors influencing OH levels are assessed. Based on understanding of OH and HO2 air chemistry, the production and removal rates of these 2 radicals are calculated. The results show that the budget of OH and HO2 can generally be closed, the radical transformation between OH and HO2 dominates the sources and sinks of them, and also the photolysis of HNO2 and HCHO is the significant source of OH and HO2 respectively.     

Atmospheric oxidation capacity sustained by a tropical forest

Terrestrial vegetation, especially tropical rain forest, releases vast quantities of volatile organic compounds (VOCs) to the atmosphere, which are removed by oxidation reactions and deposition of reaction products. The oxidation is mainly initiated by hydroxyl radicals (OH), primarily formed through the photodissociation of ozone. Previously it was thought that, in unpolluted air, biogenic VOCs deplete OH and reduce the atmospheric oxidation capacity. Conversely, in polluted air VOC oxidation leads to noxious oxidant build-up by the catalytic action of nitrogen oxides (NO(x) = NO + NO2). Here we report aircraft measurements of atmospheric trace gases performed over the pristine Amazon forest. Our data reveal unexpectedly high OH concentrations. We propose that natural VOC oxidation, notably of isoprene, recycles OH efficiently in low-NO(x) air through reactions of organic peroxy radicals. Computations with an atmospheric chemistry model and the results of laboratory experiments suggest that an OH recycling efficiency of 40-80 per cent in isoprene oxidation may be able to explain the high OH levels we observed in the field. Although further laboratory studies are necessary to explore the chemical mechanism responsible for OH recycling in more detail, our results demonstrate that the biosphere maintains a remarkable balance with the atmospheric environment.     

Pulse radiolysis studies of functionally substituted imidazolium-based ionic liquids

The reactions of imidazolium-based ionic liquids having different substituent groups on the ring with hydrated electrons (eaq-),hydroxyl radicals (·OH),and sulfate anion radicals (SO4·-) were investigated using nanosecond pulse radiolysis techniques.The spectra of these ionic liquids on reaction with eaq-all exhibited a similar peak at about 320 nm,and a typical peak for eaq-in aqueous ionic liquid solutions.The reaction rate constants for 1,3-disubstituted imidazolium-based ionic liquid hexafluorophosphates (BMIPF 6) with eaq-were deduced to be 10 10 L mol-1s-1,however the values were lower for trisubstituted ionic liquids.For example,the rate constant for 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMMIBF 4) was 5.5×10 9 L mol-1s-1.Imidazolium-based ionic liquids reacted with hydroxyl radicals via adducts to produce a mixture of isomeric OH adducts,and the pk a value of the OH adducts was deduced to be 8.4±0.4 for 1-butyl-3-methylimdazolium tetrafluoroborate (BMIBF 4).Moreover,imidazolium cations were also oxidized by SO4·-to produce bivalent cation radicals,which exhibit a peak at 320 nm,and these rate constants are of the same order of magnitude,i.e.,10 9 L mol-1s-1,except that for 1-(2-hydroxyethyl)-3-methylimdazolium tetrafluoroborate with SO4·-(k=2.8×10 8 L mol-1 s-1).Theoretical calculations were carried out to estimate the structures of the products of reduction by eaq- and the results were related to the experimental data.     

Photoelectron spectroscopy of terpenoids and prediction of their rate constants in atmospheric oxidation reactions

The electronic structures of six mono-terpenoids and two of their oxygenated derivatives were studied by He I photoelectron spectroscopy (PES). The observed bands were interpreted on the basis of empirical arguments and theoretical calculations. The first vertical ionization potentials for β-pinene, α-terpinene, terpinolene, γ -terpinene, limonene, myrcene, citral, and terpinene-4-ol were determined to be 8.73, 7.57, 8.26, 8.30, 8.53, 8.68, 8.71, and 8.77 eV, respectively. Most of these values have not been determined by PES before. The correlations of the first vertical ionization potentials of these compounds to the natural logarithms of rate constants for their reactions with the radicals OH, NO3, and O3 were determined. The correlation coefficients for their reactions with OH, NO₃, and O₃ were 0.97, 0.91, and 0.95, respectively. This method is a powerful technique for predicting the rate constants for the atmospheric oxidation reactions of terpenoids.     

Novel synergic combinatorial photoelectrochemical technology for degradation of trace of 2-chlorophenol in drinking water

A novel combinatorial photoelectrochemical(CPE) technology with combination of ultraviolet (UV)-photolysis and direct current (DC) electrolysis is studied and discussed for drinking water purification. In the self-madecompositive photo-electrolysis incorporate reactor, removal rate of the 2-chlorophenol as model environmental pollutants has been investigated experimentally in terms of applied voltage, pH value, flow velocity, temperature, and aeration conditions. A primary analysis of the combinatorial photoelectric synergic effect on the degradation of organic pollutants has been carried out. It is found that the best performance of CPE oxidation is achieved by the following conditions: DC voltage of 5.0 V combined with UV_254-raidatiou,near neutral of pH 8 with aeration of pure oxygen. The influences of circular velocity, temperature, and initial concentration of the pollutant are minor. Under the optimal conditions, removal ratio of 2-CP is higher than 50% in 30 min,and 100% removal ratio of 2-CP (5 x 10-6) can be reached and TOC removal ratio reached above 90% in 2.5 h. Complete mineralization is achieved eventually. It shows in our investigation that under the studied conditions the synergic effect of UV photolysis and DC electrolysis on the degradation of the model pollutant is remarkable and validated,which may be derived from the coexistence of mutual complementary mechanisms of photoelectrochemical action, and the radicals chain reactions resulted from photo activation and electrolysis excitation in the process of CPE oxidation.     

苯二氮类药物地西泮的水相光解转化机制

模拟紫外光解和太阳光解水相中典型苯二氮?类镇静催眠药物地西泮，对其去除效率、转化产物及毒性进行了实验研究. 地西泮可以被紫外光（波长254 nm）有效去除，其紫外光解的光量子产率为2.32(0.17)10-3 mol/Einstein. 地西泮对模拟太阳光解（波长300~400 nm）具有较强的稳定性，在90 min光照时间内无任何降解. 采用高分辨飞行时间质谱监测到65个地西泮紫外光解产物，其中49个紫外光解产物在电喷雾离子化正模式下检出，16个在负模式下检出. 根据产物鉴定的结果和光解反应的特性，地西泮在紫外光解作用下可能会发生8种转化途径，反应机制主要包括羟基取代反应、水解反应、脱甲基反应、脱苯基反应、七元杂环开环反应以及环化反应. 通过计算毒理学模型预测，生成的主要紫外光解产物对鱼、水蚤和绿藻的水生生物毒性增加.     

SO_2,NO 等离子体净化中自由基行为的分析

建立一个简单而合理的化学反应模型，对等离子体条件下活性自由基在ＳＯ２和ＮＯ净化中的行为和作用进行化学动力学分析．结果表明，ＯＨ，Ｏ和ＨＯ２基在ＳＯ２和ＮＯ气相氧化脱除中起主导作用，在整个净化机制中，气相反应的贡献仅占２０％左右；气溶胶表面的催化作用加强了ＳＯ２和ＮＯ的氧化速度，异相反应对ＳＯ２和ＮＯ净化有重要贡献，一个气溶胶可提供１０７ｃｍ－３的自由基．动力学模拟结果与实验结果定性相符．动力学研究结果为等离子体过程的优化提供依据     

Tropospheric lifetimes of halogenated anaesthetics

Concern has been expressed over the use of the halogenated anaesthetics halothane (CF3CClBrH), enflurane (CF2HOCF2CFClH) and isoflurane (CF2HOCHClCF3) because of their potential for stratospheric ozone destruction. Halogenated species also contribute to global warming. The significance of the anaesthetics in stratospheric ozone loss or in 'greenhouse' heating depends on their atmospheric lifetimes. Because reaction with hydroxyl (OH) radicals is likely to be the main homogeneous sink for these species in the troposphere, we have measured absolute rates of reaction with OH. Comparison with a one-dimensional model indicates that the lifetimes of halothane, enflurane and isoflurane with respect to this reaction are 2, 6 and 5 years, respectively. Thus the small production of the anaesthetics is not offset by anomalously long atmospheric lifetimes to give a large atmospheric burden of the compounds. The anaesthetics will contribute at most a fraction of approximately 5 x 10(-4) to the total atmospheric content of chlorine-containing species.     

CH3SH与简单自由基反应的研究现状

含硫有机化合物在对流层大气化学中起着重要的作用.目前在实验和理论上对CH3SH,CD3SH及CD3SD的反应进行了很多研究,主要集中在CH3SH与原子(O,H,F,Cl,Br等)、双原子分子和双原子自由基(NO,OH,OD,BrO,CN等)、三原子分子和自由基及多原子(O3,NO3等)的反应.本文中,笔者对CH3SH与原子和双原子自由基的反应进行了综述.     

铁-草酸盐配合物光催化降解对苯二酚的研究

Fe(Ⅲ)-草酸盐配合物在光照条件下,能产生有活性的强氧化剂H2O2和OH自由基以氧化水中的有机化合物.研究了在高压汞灯(λ≥300nm)照射下,对苯二酚在Fe(Ⅲ)-草酸盐配合物体系中的光催化降解.结果表明:溶液pH值、对苯二酚初始浓度、铁与草酸盐浓度比和光照强度均对降解结果产生影响.在pH=4.0,Fe(Ⅲ)溶液浓度为10.0μmol/L,草酸盐浓度为100.0μmol/L的实验条件下,10.0mg/L的对苯二酚的降解率为99.0%.     

无声放电场作用下产生OH自由基的实验研究

用一种无声放电方法，使反应器中Ｎ２－Ｈ２Ｏ介质在高频高压电场作用下产生ＯＨ，以促进燃烧反应，抑制碳烟生成，并开发一种追踪化学反应的分子物理测量手段，用共振吸收光谱法测定ＯＨ浓度。     

气体放电/高效混溶协同制取·OH的pH影响

羟基自由基(·OH)对海洋微小生物有很强的杀灭效果,因此可以用来预防由船舶压载水引发的外来生物入侵性传播对海洋环境造成的危害.为提高·OH的产量以及提高压载水处理的效果,采用·OH探针化合物法研究了去离子水、海水中pH变化对强电场电离放电/高效混溶协同制取·OH的影响.结果表明:OH-是臭氧分解链反应的引发剂和促进剂,适当提高pH值能够提高系统·OH的产量.以亚心形扁藻(Platymonas subcorodiformis),小新月菱形藻(Nitzschia closterum)为处理对象,进一步研究了水体pH值对压载水处理效果的影响.pH值越高,藻的杀灭率越高.     

紫外光照射下钴钼杂多酸降解有机染料SRB

制备了不同配比的钴钼杂多酸（CoMox Heteropoly acids,CoMox）,在紫外光（λ≤387 nm）照射下,以有机染料酸性桃红（Sulforhodamine B,SRB）的光催化降解为探针反应,研究了CoMox杂多酸不同配比及用量和体系介质pH值对其降解行为的影响.结果表明,最佳配比的钴钼杂多酸为CoMo12,在pH=3.0,CoMo12用量为1.0 g/L时,对SRB降解效果最好.在紫外光照射下,CoMo12活化O2,3.5 h内SRB脱色率达到96%.通过紫外-可见吸收光谱（UV-vis absorption spectrum）,红外光谱（FTIR）和总有机碳（TOC）测定分析钴钼杂多酸对SRB的降解特性,同时采用苯甲酸荧光光度法跟踪测定降解过程中产生的活性氧化物种,表明CoMo12多酸对SRB的光催化降解过程主要涉及.OH氧化历程.     

戊唑醇在水中光解特性研究

以氙灯为人工光源,研究戊唑醇在水中的光化学降解速率。结果表明,戊唑醇在氙灯下的光降解符合化学反应一级动力学方程。试验期间光照度为3 720~4 300 lux,紫外强度59.8~62.4μw/cm2,试验在25±2℃恒温条件下进行。通过试验测得戊唑醇的光解半衰期为29.1 h。