氯氟烃替代物大气化学研究

大气平流层臭氧（大气臭氧层）由于能够吸收太阳辐射中的高能量紫外线,对人类和生物起着非常重要的保护作用,氯氟烃类化合物（ＣＦＣｓ）已被认为是造成大气平流层臭氧耗损的主要原因,淘汰ＣＦＣｓ和使用替代物日趋紧迫,目前,最有应用前景的替代物是含氢氧氟烃类化合物（ＨＣＦＣｓ）和氢氟烃类化合物（ＨＦＣｓ）,其中有些已投入工业使用,本文总结 了ＨＣＦＣｓ和ＨＦＣｓ在气中的光化学降解机制及其产物,以及产物对环境的     

氯氟烃及其替代物

近年来,臭氧衰竭比原先预料的更严重,对人类健康和环境构成了严重威胁。“蒙特利尔议定书”和“大气清洁法案”要求2000年要完全清除致臭氧衰竭物质——氯氟烃(CFCs)的生产和使用。目前,世界各地积极开发CFCs的替代物,以加速转换。虽然已开发的氧氯氟烃(HCFCs)、氢氟烃(HFCs)等替代物与CFCs相比还有一定缺点,但最终一定会实现替代转换。     

The effect of aircraft emissions on tropospheric ozone in the northern hemisphere

The effect of aircraft emissions on tropospheric ozone was studied using a two-dimensional zonal model, of longitude vs altitude, extending between 30°–60°N. An emission inventory for the 1987 civil aircraft fleet was constructed based on fuel usage and civil aviation statistics. The addition of the 1987 civil emissions to a modelled standard atmosphere caused increases in concentrations of O₃ (12%; 10 ppbv), NO_x (40%; 20 pptv) and OH (10%) between 8 and 12 km altitude. A doubling and tripling of the emissions corresponding to a present day inclusion of military aircraft and a future scenario, respectively, caused the increase in O₃ to double (19%) and almost triple (25%). The lightning source of NO_x was found to be an important parameter. When this source was ommitted the change in O₃ at the cruise flight altitude increased to 16%, with respect to a standard atmosphere not containing a lightning source of NO_x.     

Degradation of monofluorophenols in water irradiated with gaseous plasma

Decomposition of aqueous monofluorophenols (MFPs) was investigated by contact glow discharge electrolysis (CGDE). During CGDE, both MFPs and the corresponding total organic carbon (TOC) in water were consumed smoothly, suggesting that carbon atoms of benzene nucleus could be eventually mineralized to inorganic carbon (IC). And all the fluorine atoms in the MFPs were equally converted to fluoride ions. Based on the primary intermediates from each starting materials, it showed that aromatic hydroxylation preferentially occurred at the para- or ortho- position to the phenolic OH group of each MFPs. The disappearance of both MFPs and TOC followed the first-order rate law. The apparent rate constants for the decay of MFPs were independent from the pK_a values of MFPs.     

A numerical simulation of kinetic constraints upon achievement of the ammonium nitrate dissociation equilibrium in the troposphere

Various mechanisms and associated rate expressions for the reversible evaporation of volatile ammonium salts are presented, and experimental evidence for them discussed. The literature concerned with the existence of stable NH₄⁺ salt monomers in the gas phase in highlighted. Four kinetic mechanisms are presented: monomer formation; adsorption of one precursor species on the particle surface; biomolecular surface reaction; and transport-limited particle growth. No mechanism emerges as the rate-limiting process for all experimental studies. Rate constant ratios for the first two mechanisms are calculated from the literature and shown to differ greatly from the thermodynamic equilibrium constant.A simple box model is developed to determine the importance of kinetic constraints on aerosol growth and evaporation in the tropospheric boundary layer. No attempt is made to model actual tropospheric processes other than the daytime oxidation of NO₂ and the kinetics of aerosol growth itself, so that model output is representative rather than definitive.Substantial departures from equilibrium are seen, giving gas concentration products ranging from −200 to 5000% of the theoretical value, Ke. At low temperatures and high relative humidities (r.h.) a large proportion of the potential condensable NO₃⁻ remains in the gas phase. The behaviour is general over a range of initial aerosol loadings, temperatures, r.h. and model formulations. Both pure NH₄NO₃ aerosol and a hypothetical equimolar mixture with (NH₄)₂SO₄, conform to the general case.     

Evidence of the phase-out of CFC use in Europe over the period 1987–1990

European regulations exist to phase-out production of the ozone-depleting man-made CFCs. High frequency measurements of the principal CFCs and other radiatively active gases have been collected at Mace Head, Ireland from 1987–1990 as part of the Global Atmospheric Gases Experiment (GAGE). These measurements provide the first clear evidence that this phase-out is effective. Allocation of the time series beginning at the end of 1988, to a particular wind sector combined with simple modelling techniques indicates a significant reduction in European source strengths for CFC-11 and CFC-12 which is consistent with reliable emission estimates for CFC-11, but which seem to indicate a slightly smaller reduction for CFC-12, when likewise compared to emission figures. The study provides evidence that European CH₄, CCl₂F₂ and CCl₃F emission have already declined to about one-third of 1987 levels by the end of 1990. Over the same period, no evidence of any phase-out in the European usage of methyl chloroform and CFC-113 was detected.     

Methane reductions: Implications for global warming and atmospheric chemical change

Atmospheric methane (CH₄) concentrations have more than doubled over the last two centuries. These increases may contribute to global warming, enhance formation of tropospheric ozone, suppress OH and affect stratospheric ozone. Calculations show that stabilization of CH₄ could reduce projected temperature increases and possibly mitigate background tropospheric O₃ increases due to increasing levels of CH₄.     

Modelling the role of nitrogen oxides,hydrocarbons and carbon monoxide in the global formation of tropospheric oxidants

A new zonally averaged two-dimensional chemical and transport model of the lower atmosphere has been used to study the budgets of photochemical oxidants on a global scale in the troposphere. The sensitivities of these budgets to controls on the emissions of NO_x, CO and hydrocarbons from a variety of sources have also been considered. The species studied include O₃, PAN, H₂O₂ and organic peroxides, as well as the global budget of the hydroxyl radical. The results show the relative impacts of emissions from natural and from man-made sources. Overall, some 75% of the turnover of tropospheric ozone results from in situ chemical production, with only 25% having its origins in the stratosphere. The respective fractions for chemical loss and dry deposition are similar. Of the ozone formed in situ, approximately one-third is formed from natural emissions, and two-thirds from man-made emissions. Over half of this man-made contribution is due to industrial society, with much of the rest being caused by biomass burning and methane emitted from paddy fields. Although reducing emissions of NO_x is the most effective way of controlling tropospheric O₃, this also increases the inventories of peroxides and the rate of increase in the concentration of methane, due to a reduction in the inventory of the OH radical. It is, therefore, necessary to control the emissions of a wide range of species in order to reduce the budget of all photochemical oxidants without adversely perturbing the budget of CH₄.     

Anthropogenic land use substantially increases riverine CO2 emissions

Carbon dioxide (CO₂) emissions from inland waters to the atmosphere are a pivotal component of the global carbon budget. Anthropogenic land use can influence riverine CO₂ emissions, but empirical data exploring cause-effect relationships remain limited. Here, we investigated CO₂ partial pressures (pCO₂) and degassing in a monsoonal river (Yue River) within the Han River draining to the Yangtze in China. Almost 90% of river samples were supersaturated in CO₂ with a mean ± standard deviation of 1474 ± 1614 µatm, leading to emissions of 557 - 971 mmol/m²/day from river water to the atmosphere. Annual CO₂ emissions were 1.6 - 2.8 times greater than the longitudinal exports of riverine dissolved inorganic and organic carbon. pCO₂ was positively correlated to anthropogenic land use (urban and farmland), and negatively correlated to forest cover. pCO₂ also had significant and positive relationships with total dissolved nitrogen and total dissolved phosphorus. Stepwise multiple regression models were developed to predict pCO₂. Farmland and urban land released nutrients and organic matter to the river system, driving riverine pCO₂ enrichment due to enhanced respiration in these heterotrophic rivers. Overall, we show the crucial role of land use driving riverine pCO₂, which should be considered in future large-scale estimates of CO₂ emissions from streams. Land use change can thus modify the carbon balance of urban-river systems by enhancing river emissions, and reforestation helps carbon neutral in rivers.     

中国超大城市不透水面扩张对对流层NO2柱浓度的影响

基于Aura卫星的臭氧检测仪(OMI)数据及Landsat卫星影像,分别分析了中国7座超大城市2005—2017年的对流层NO_2柱浓度(TroNO_2浓度)时空变化规律和不透水面扩张模式,并探讨了二者之间的联系,结果表明:①7座城市总体表现为TroNO_2浓度先升高后降低、高值区域先扩大后收缩甚至消失的趋势.变化存在显著的周期性,冬季浓度远高于夏季.②各城市不透水面面积分别扩张至120%～200%,扩张模式多表现为由中心向四周辐射式扩张,不透水面的空间分布和扩张趋势与TroNO_2浓度高度相关.③各城市市辖区TroNO_2浓度与不透水面覆盖率(ISC)呈高度正相关,二者冷热点空间分布规律一致,松散型、紧凑型、密集型、高度密集型市辖区的TroNO_2浓度均值依次增加,发生不透水面扩张的区域标准化TroNO_2指数呈上升趋势.④自然条件、经济产业结构、机动车尾气排放、重大赛会的举办及相关政策等因素均与TroNO_2浓度密切相关.     

Formation of HNO2 on aerosol surfaces during foggy periods in the presence of NO and NO2

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 NO_x into HNO₂.     

Atmospheric residence times for soluble species: Differences in numerical and analytical model results

We have compared numerically calculated soluble species residence times with several analytic residence time models. The numerical results are dependent on whether randomly or periodically distributed precipitation events are assumed. A preferred time of occurrence for rain, such as morning or afternoon, influences the computed HNO₃ residence time for precipitation cycle times (wet plus dry period) of about a day, but exerts less influence as the cycle time increases. An analytic residence time model developed by Rodhe and Grandell (1972, Tellus24, 442–454) is found to agree well with residence times computed for randomly distributed precipitation events while a model developed by Giorgi and Chameides (1985, J. geophys. Res.90, 7872–7880 is more suitable for periodic rain. The present numerical calculations resolve an apparent ambiguity in HNO₃ residence times computed in earlier numerical studies.Using mean precipitation periods and rainfall amounts characteristic of the northeastern U.S. as a guide, we find that residence times computed under the assumption of randomly distributed wet and dry events agree better with observed aerosol lifetimes than do those computed assuming periodic rain.     

氯氟烃替代物与OH自由基光化学反应

保护生物多样性生物多样性是人类社会赖以生存和发展的物质基础，保护生物多样性，保证生物资源的持续利用是一项全球性任务，也是全球环境保护行动计划的重要组成部分。按照生物多样性国际公约的定义，生物多样性“是指所有来源和形形色色的生物体，这些来源包括陆地、海...     

活性炭催化过氧化氢去除荧光增白剂

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.     

臭氧浓度升高对植物源挥发性有机化合物(BVOCs)影响的研究进展

伴随地表臭氧(O_3)浓度在全球范围内的普遍上升,针对植物源挥发性有机化合物(biogenic volatile organic compounds,BVOCs)与地表O_3之间复杂的交互作用,本文综述了O_3浓度升高对BVOCs影响方面取得的研究进展,并对未来研究提出了展望.研究进展主要包括BVOCs应对单因子O_3胁迫的影响因素(如BVOCs种类,植物功能类型,植物O_3敏感性及O_3胁迫程度),以及O_3分别与升温/二氧化碳(CO_2)/干旱/氮(N)沉降等因子复合对BVOCs释放的影响.虽然O_3胁迫不影响BVOCs释放的研究最多,但O_3胁迫的降低作用在异戊二烯和落叶树种的研究中更突出,增加的结果更多地出现在单萜(MTs)、常绿植物和急性熏蒸的实验里. O_3与升温/N沉降复合处理增加MTs释放,O_3与CO_2复合处理降低了异戊二烯释放.鉴于研究样本的稀缺,建议加强该领域研究,同时要考虑短期和长期处理、个体和生态系统水平研究的差异;加强以O_3为主的多因子复合及生物与非生物多重胁迫对BVOCs影响的研究,以便更好评估陆地生态系统BVOCs对当前及未来O_3污染情景的响应,为今后大气污染防治提供有价值的理论支撑.     

麦草及其烟尘中正构烷烃的组成

在明火和闷烧条件下对6种麦草进行焚烧试验,用GC/MS测定了秸秆和烟尘中正构烷烃的组成.结果表明,从麦秆和烟尘中检出的正构烷烃主要是C16~C33.麦秸中正构烷烃的总含量变化范围是19.6~62.3 mg·kg-1,平均值为36.0mg·kg-1.低碳数(碳数相似文献   

Predicting the night-time NO3 radical reactivity in the troposphere

A statistically significant linear correlation between the reaction, k_NO3, for the NO₃ free radical reaction with 69 organic compounds in the gas phase at 298 K and the corresponding vertical ionization energies, E_i,v, allows an a priori prediction to be made of hitherto not measured compounds. With these reaction rate constants and a mean concentration of NO₃ during the night, the upper limit of the tropospheric half-life of organic compounds and their persistence in the troposphere can be estimated. From the fairly good linear correlation between k_NO3 and k_OH it can be deduced that in the gas phase both free radicals react in a very analogous manner with organic compounds.     

Organic peroxy radicals: Kinetics,spectroscopy and tropospheric chemistry

The present state of knowledge of organic, or carbon-based, peroxy radicals (RO₂) is reviewed. Data on the chemical and physical properties of peroxy radicals in the gas-phase is considered, as well as the role of peroxy radicals in tropospheric chemistry and measurements of their concentrations in the atmosphere. Where appropriate, peroxy radicals are grouped together by type (alkyl, acyl, oxygen-substituted, halogen-substituted and aromatic radicals) to facilitate comparison. Data on the hydroperoxy radical (HO₂) is included where it is directly relevant to measurements on organic peroxy radicals, eg. absorption cross-sections used in measurements of RO₂ + HO₂ rate constants. The literature data is critically reviewed and recommendations for absorption cross-sections, rate constants and branching ratios are made where considered appropriate.The laboratory experimental techniques which have been used for the generation and detection of peroxy radicals and the products of their reactions are discussed. The structure, spectroscopy and thermochemistry of the radicals are examined. Although the majority of spectroscopic data concerns the u.v. spectra much used for kinetic studies, near-infrared, infrared and electron spin resonance spectra are also considered. In many cases, peroxy radical u.v. spectra are well-fitted by a Gaussian distribution function, enabling the cross-sections to be easily calculated at any wavelength.For the purpose of this review, the chemical reactions of peroxy radicals are divided into reactions with organic peroxy radicals with HO₂, with NO and NO₂, and finally with other species. Peroxy radical abstraction and addition reactions with closed-shell species are sufficiently slow to be of negligible importance at temperatures pertinent to the atmosphere and are consequently not covered. Data on both the kinetics and mechanisms of peroxy radical reactions are considered.The role of peroxy radicals as intermediates in the atmospheric degradation of volatile organic compounds and in the production of ozone in the troposphere under both low and high [NO_x] conditions is discussed. The involvement of peroxy radicals in night-time oxidation chemistry and the oxidation of halocarbons is also indicated. The techniques used for the difficult measurement of peroxy radical concentrations in the atmosphere are described, together with the results to date.Finally, some tentative suggestions as to further avenues of research are made, based on the data reviewed here and with particular reference to the solution of outstanding problems in atmospheric chemistry. Although a great deal of progress has been made in recent years, it is clear that additional work is needed in most areas covered by this review. New, sensitive and selective laboratory techniques are required for studies of peroxy radical kinetics and high level ab initio calculations would help design laser-based detection techniques. Further product studies of photooxidation systems are needed, particularly as a function of temperature. Recent work has shown that the rate constants for RO₂ + HO₂ reactions used in modelling studies may be too low; if so, these reactions will be correspondingly more important than previously believed in tropospheric oxidation. Recent kinetic studies of the potentially important reactions of methylperoxy radicals with ClO and NO₃ need to be confirmed and mechanistic work is necessary. Although substantial progress has been made towards the monitoring of peroxy radical concentrations in the atmosphere, more work is needed, both on measurements and the development of new techniques.     

不同温度下的土壤微生物呼吸及其与水溶性有机碳和转化酶的关系

为研究不同温度下的土壤微生物呼吸及其与水溶性有机碳(DOC)和转化酶的关系,设置了室内培养实验.采集南京市周边老山、紫金山、宝华山的土壤,研究不同土壤的微生物呼吸对温度升高的响应规律,并分析土壤DOC含量及转化酶活性.结果表明,不同土壤的累积微生物呼吸与土壤温度之间的关系均可用指数方程描述,其P值均达到极显著水平(P0.001),不同地点土壤的微生物呼吸温度敏感系数(Q10值)在1.762~1.895之间变异.累积土壤微生物呼吸的Q10值随着土壤温度升高表现出降低的趋势.培养后27 d土壤微生物呼吸的Q10值与培养后1 d的Q10值无显著差异(P0.05),这表明难分解有机质的温度敏感性与易分解有机质的温度敏感性一致.对于所有土壤而言,累积土壤微生物呼吸与DOC含量之间存在极显著(P=0.003)的线性回归关系,DOC可以解释累积土壤微生物呼吸31.6%的变异性.无论是单独分析不同土壤还是综合所有土壤的测定结果,累积微生物呼吸与土壤转化酶活性均存在极显著(P0.01)的一元线性回归关系,由此说明转化酶活性是衡量土壤微生物呼吸大小的一个较好的指标.     

龙川江楚雄站碳侵蚀通量的动态分析

选取龙川江楚雄水文站进行了为期3年的采样,分析了水体中各形式碳的含量,并估算各碳的输送通量.结果表明:楚雄站3年的碳通量(FTC)分别为27.12×106g·km-2·a-1、24.87×106g·km-2·a-1和10.34×106g·km-2·a-1,分析流域在对碳输送过程中,以输送无机碳为主,分别占输送总量的89.7%、90.3%及91.9%;而汛期碳输送量分别占全年总量的90.9%、84.9%和83.8%,表现出流域汛期对碳的搬运量远远高于非汛期;溶解性有机碳通量(FDOC)与颗粒有机碳通量(FPO C)平均比为0.82,不同季节表现情况不一,非汛期溶解性有机碳(DOC)与颗粒有机碳(POC)含量相当,汛期机械侵蚀作用增强,导致FPO C远远大于FDOC,反映汛期对流域侵蚀作用以机械剥蚀为主,化学侵蚀为辅.研究期内恰遇2008年一场洪水,11月碳的侵蚀通量为8.53×106g·km-2·a-1,其中溶解性无机碳(DIC)、溶解性有机碳(DOC)和颗粒有机碳(POC)的输送量分别为7.37×106、0.36×106、0.80×106g·km-2·a-1,分别占2008年全年相应形式碳总量的33.3%、34.4%和59.9%,为当年非汛期碳侵蚀总量的2.3倍,反映洪水期的碳输出量对流域碳输出总量及构成存在不可忽略的贡献.