Increased marine production of N2O due to intensifying anoxia on the Indian continental shelf

Eutrophication of surface waters and hypoxia in bottom waters has been increasing in many coastal areas, leading to very large depletions of marine life in the affected regions. These areas of high surface productivity and low bottom-water oxygen concentration are caused by increasing runoff of nutrients from land. Although the local ecological and socio-economic effects have received much attention, the potential contribution of increasing hypoxia to global-change phenomena is unknown. Here we report the intensification of one of the largest low-oxygen zones in the ocean, which develops naturally over the western Indian continental shelf during late summer and autumn. We also report the highest accumulations yet observed of hydrogen sulphide (H2S) and nitrous oxide (N2O) in open coastal waters. Increased N2O production is probably caused by the addition of anthropogenic nitrate and its subsequent denitrification, which is favoured by hypoxic conditions. We suggest that a global expansion of hypoxic zones may lead to an increase in marine production and emission of N2O, which, as a potent greenhouse gas, could contribute significantly to the accumulation of radiatively active trace gases in the atmosphere.     

Kinetics of Carbothermic Reduction of MnO2 and Catalytic Effect of La2O3

Kinetics of carbothermic reduction of manganese oxide and the catalytic effect of La2O3 on the reduction have been studied by the measurement of mass loss in N2 atmosphere at different temperatures and followed by SEM analysis. It is concluded that the kinetics of carbothermic reduction of manganese oxide is divided into three stages: gas diffusion controlling stage, carbon gasification controlling stage and solid state diffusion controlling stage. La2O3 has catalytic effect on the reduction. The catalytic effect of La2O3 increases with the added amount of La2O3. SEM analysis shows that the catalytic mechanism is that Laa2O3 promotes the transfer of oxygen ions so that carbon gasifying is catalyzed and thus carbothermic reduction of MnO3 is catalyzed.     

DO对短程反硝化过程中N2O产量的影响

利用SBR反应器,考察不同溶解氧(DO)条件下NO2-反硝化过程中N2O产生及释放过程。研究结果表明:控制曝气量为0.3 L/min,进水NO2--N质量浓度为40 mg/L,体系DO质量浓度分别为0,0.1,0.3,0.5和0.7 mg/L时,反硝化过程N2O释放量分别为0.41,0.60,2.62,4.98,6.83 mg/L;随DO质量浓度的增加,反硝化速率明显降低;当DO质量浓度由0 mg/L增至0.7 mg/L时,每克混合液悬浮固体(MLSS)的NO2-反硝化速率由14.9 mg/(L.h)降至10.2 mg/(L.h),每克MLSS的N2O产生速率由0.2 mg/(L.h)增至1.9 mg/(L.h)。其原因为:高DO质量浓度对氧化亚氮还原酶具有较强的毒性,抑制了N2O的进一步还原过程;高NO2-的存在导致抑制了氧化亚氮还原酶的活性。降低A/O和A2/O等生物脱氮过程中缺氧反应器内部DO质量浓度,保证严格缺氧条件,是减少短程生物反硝化过程中N2O产量的关键因素。     

Extreme deuterium enrichment in stratospheric hydrogen and the global atmospheric budget of H2

Molecular hydrogen (H2) is the second most abundant trace gas in the atmosphere after methane (CH4). In the troposphere, the D/H ratio of H2 is enriched by 120 per thousand relative to the world's oceans. This cannot be explained by the sources of H2 for which the D/H ratio has been measured to date (for example, fossil fuels and biomass burning). But the isotopic composition of H2 from its single largest source--the photochemical oxidation of methane--has yet to be determined. Here we show that the D/H ratio of stratospheric H2 develops enrichments greater than 440 per thousand, the most extreme D/H enrichment observed in a terrestrial material. We estimate the D/H ratio of H2 produced from CH4 in the stratosphere, where production is isolated from the influences of non-photochemical sources and sinks, showing that the chain of reactions producing H2 from CH4 concentrates D in the product H2. This enrichment, which we estimate is similar on a global average in the troposphere, contributes substantially to the D/H ratio of tropospheric H2.     

Atmospheric nitrous oxide observations above the oceanic surface during CHINARE-18

The gas samples in the marine boundary layer were collected from the track for research ship Xuelong during the 18th Chinese Antarctic Research Expedition (CHINARE-18) and nitrous oxide measurements were made by HP5890ECD-GC in the laboratory. The results represent the shipboard N2O data set obtained within the lower troposphere with the average concentration of (313.5±2.6)nL*L-1 from 31°N to 69°S. The results showed a latitudinally weighted, mean interhemispheric difference of 0.61 nL*L-1. The latitudinal distribution of atmospheric N2O concentration was analyzed from northern midlatitudes to Southern Ocean around the Antarctic continent and it was showed that N2O concentration in the current confluences was higher than that in other oceanic areas. This indicated that strong N2O emissions occurred there. The longitudinal distribution of N2O concentrations in the Southern Ocean also showed similar situation. According to the interhemispheric difference of atmospheric N2O concentrations and the two-box model, we estimated that 2/5 of the global flux of N2O into the atmosphere is derived from the sources in the southern hemisphere.     

Mass exchange between stratosphere and trotosphere over the Tibetan Plateau and its surroundings

Using NCEP dataset we calculate the exchange of mass across the thermal tropopause by the Wei's method from 1978 to 1997 over the Tibetan Plateau and its surroundings. We also calculate the annual variation of aerosol and ozone of 100 hPa level with the monthly SAGE dataset from July 1988 to December 1993. Results indicate that ( i ) the mass from troposphere to stratosphere is magistral station in summer over the Tibetan Plateau and its surroundings. The air transport reaches the summit in midsummer with two large value centers, which lie in the north of Bengal Bay and southeastern Tibetan Plateau, respectively. A large value center, which lies over the Tibetan Plateau, is smaller than that aforementioned. In winter, the mass transport is from stratosphere to troposphere, and reaches the minimum in January. ( ii ) As far as the 19-year mean cross-tropopause mass exchange from June to September is concerned, the net mass transport is 14.84x1018 kg from troposphere to stratosphere. So the area from the Tibetan Plateau to the Bengal Bay is a channel through which the mass of lower atmosphere layer gets into upper troposphere and lower stratosphere. (iii) The cross-tropopause mass may take the lower level aerosol to the tropopause. Then, the concentration of aerosol near the tropopause becomes larger, which may cause the content of ozone to reduce.     

嫌气培养下砷酸盐和氮肥种类对土壤中微生物呼吸作用和反硝化作用的影响(英文)

在土壤生态系统中,砷污染和氮肥过量所引起的氮素污染越来越普遍．但至今仍很少了解砷污染对土壤中温室气体（Ｎ２Ｏ和ＣＯ２）产生和有关微生物过程的影响．本文通过土壤泥浆的嫌气培养试验,研究了添加砷酸盐和改变氮肥种类（氮素形态）对反硝化作用（Ｎ２Ｏ产生量）和呼吸过程（ＣＯ２产生量）的影响．试验结果表明,不同氮素形态对ＣＯ２产生量没有明显的影响．供应ＮＯ－３－Ｎ作为氮源时,无论是否添加砷酸盐,其Ｎ２Ｏ产生量没有明显的差异;但当供应ＮＨ＋４－Ｎ和尿素作为氮源时,其Ｎ２Ｏ产生量稍有增加．添加砷酸盐会使Ｎ２Ｏ量增加,但使ＣＯ２产生量降低．因此,砷污染可能会导致微生物呼吸作用和反硝化作用受到抑制．     

废水脱氮过程中N_2O的控逸理论及研究进展

N2O是大气中重要的温室气体之一,大量研究表明,污水生物处理的硝化反硝化过程是N2O的重要强源之一.通过对硝化反硝化全过程的机理分析,探讨了N2O的逸出机理.同时阐述了外界因素对N2O逸出量的影响规律.据此优化实际运行中的污水生物脱氮工艺,以达到有效控制N2O逸出的目的.     

NO and N2O fluxes from agricultural soils in Beijing area

Chinese agriculture represents one of the most intensively managed agroecosystems in the world. Typical nitrogen fertilization rates are more than three times those of the world' s average, resulting in dramatically accelerated nitrogen cycling in China. In this study, we have examined NO and N2O exchange in the upland agricultural systems of Beijing area. Inorganic and organic fertilizer treatments were arranged in order to evaluate their impact on the magnitude and proportion of trace gas emissions. Increasing inorganic fertilization rates showed a highly significant impact upon emissions of both NO and N2O. Organic matter amendment did not have a statistically significant impact on the N-gas fluxes examined here. Overall losses of added nitrogen by NO and N2O emission averaged 1.24% and 0.22% respectively over the range of treatments in this study. Results from our field study indicate that compared with other studies done elsewhere, emissions of reactive nitrogen from agricultural systems in Beijing area are not so large as expected before.     

人工湿地污水脱氮中N2O的产生机理和影响因素

人工湿地技术具有良好的污水脱氮效果,但污水中脱除的氮有可能会以N2O的形式释放到大气中。由于N2O是一种重要的温室气体,随着人工湿地的不断推广应用,其向大气中释放N2O的研究引起国内外的关注。综述了目前关于人工湿地系统N2O的产生机理,从污水水质、环境条件、人工湿地系统以及微生物种群结构四个方面详细论述了国内外关于人工湿地系统释放N2O的影响因子的研究现状,并对该研究领域今后的研究重点进行了展望。     

燃煤烟气中喷氨脱硝对氧化亚氮(N_2O)生成的影响

实验研究发现,喷氨脱硝过程中是否会产生大量的N_2O,在很大程度上取决于喷氨处的烟气的成分,氧化性气氛有利于N_2O的产生.对喷氨脱硝的均相化学反应过程进行的动力学模拟表明,在混合良好的还原性烟气中喷入氨气不会导致N_2O排放量大幅度增加,但如果喷入的氨气与烟气和空气混合不良,或者烟气中存在由NH_3转化的氰基成分,那么N_2O的排放量会有所增加.     

O2/CO2气氛下燃煤过程中NOx排放特性实验研究

利用沉降炉在O2/CO2和O2/N2气氛下对煤粉燃烧过程中NOx排放特性进行实验,研究了不同停留时间、燃料/氧化学当量比、温度等因素对燃煤过程中NOx的排放特性的影响,并对2种燃烧方式下NOx的排放特性进行对比.结果表明:在O2/CO2气氛下NOx的生成量远远低于空气气氛下NOx的生成量,其主要原因是在O2/CO2气氛中高CO2质量浓度导致气氛中生成较高含量的CO,从而在未燃烧碳表面发生NO/CO/Char的反应,促进了NO还原为N2;O2/CO2气氛中没有N2,避免了热力型NOx和快速型NOx的生成;约80%的再循环烟气致使NOx的停留时间大为增加,即延长了NOx的还原反应时间,从而降低了NOx的排放.     

Removal of chlorofluorocarbons by increased mass exchange between the stratosphere and troposphere in a changing climate

Chlorofluorocarbons (CFCs), along with bromine compounds, have been unequivocally identified as being responsible for most of the anthropogenic destruction of stratospheric ozone. With curbs on emissions of these substances, the recovery of the ozone layer will depend on their removal from the atmosphere. As CFCs have no significant tropospheric removal process, but are rapidly photolysed above the lower stratosphere, the timescale for their removal is set mainly by the rate at which air is transported from the troposphere into the stratosphere. Using a global climate model we predict that, in response to the projected changes in greenhouse-gas concentrations during the first half of the twenty-first century, this rate of mass exchange will increase by 3% per decade. This increase is due to more vigorous extra-tropical planetary waves emanating from the troposphere. We estimate that this increase in mass exchange will accelerate the removal of CFCs to an extent that recovery to levels currently predicted for 2050 and 2080 will occur 5 and 10 years earlier, respectively.     

N2O4-O3硝化取代芳烃时取代基上的P轨道的邻位协助作用

对N2 O4 O3 硝化取代芳烃进行广泛的研究 ,发现其产物的异构体分布与传统的混酸硝化产物的异构体分布有很大差别 ,并对造成这种差别的原因进行了分析。分析表明 ,取代基上的P轨道的邻位协助作用是主要因素 ,电子密度分布计算及试验结果支持这种解释     

用^15N示踪标记法测定人工诱发黄瓜根瘤固氮酶活性

报道了用＾１５Ｎ示踪标记法对人工诱发黄大氮酶活性的测定结果，将长有人工诱发根瘤的黄瓜根系暴露在＾１５Ｎ２的气体中，部分根系浸在无氮培养液内，标记４８ｈ后，质谱分析测定结瘤黄瓜根＾１５Ｎ的丰度为０．４３１原子％＾１５Ｎ，样品为０３６９原子％＾１５Ｎ，对＾１５Ｎ示踪标记结果进行了统计学ｔ检验，ｔ＝３．１５〉６０．０１＝２．８１９，表明黄奶系根瘤内的细菌固氮作用所的氮与相比达９９．９％极显著性水平，同时     

Monitoring the concentration of N2O in the Fildes Peninsula, maritime Antarctica

Gases in the marine boundary layer in Fildes Peninsula, maritime Antarctica were sampled and analyzed for the first time. Sampling sites included areas covered by moss and lichen growth, penguin colonies and an area where scientific research stations are located. A total of 211 samples were analyzed for N2O concentrations, with an average of (321.33±3.07) nL/L. This is above the global average value of 314 nL/L. It is found that the N2O concentrations evidently increase during the summer months. Concentrations around the research stations are higher than at remote areas, indicating a potential source from human activities on the island. N2O concentrations at a large penguin colony on Barton Peninsula are the highest among the sampled areas. This may explain why N2O concentrations in Fildes Peninsula are higher than the global average. Our preliminary conclusions are that human activities and emissions from penguin dropping-amended soil and vegetation soil constitute the major sources of N2O in the maritime Antarctic atmosphere.     

Seasonal variation of global stratosphere-troposphere mass exchange

By Wei formula in pressure coordinate, the stratosphere-troposphere mass exchange (STME) is diagnosed globally for 44 years from 1958 to 2001 using the European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis datasets. Regions of mass flux into the stratosphere are found over Indonesia, bay of Bangladesh and the mid-west coast of South Africa. Compensating mass outflow from the stratosphere appears mainly over mid-latitudes near large-scale troughs. Upward and downward transport of mass at the middle and high latitudes accompany with each other. Mass flux into troposphere is stronger in autumn and winter than in spring and summer. Strong downward mass flux into the troposphere occurs in eastern Asia the whole year with nearly stable sites. Although the area of eastern Asia accounts for only 5.6% of that of the northern hemisphere (NH), its net mass exchange reaches 15.83% of that of the NH, which means that research on STME of eastern Asia is greatly important to that of the NH and even the global areas. Air across the tropopause enters more from stratosphere to troposphere than that from troposphere to stratosphere, which is possibly related with systematic bias of the assimilated datasets and with persistent rise of the tropopause height. Contributions of the mass exchange and the mass flux exchange in the NH and southern hemisphere (SH) on their latitudes increase from equator to pole, with larger contributions in the NH. Mass exchange and mass flux exchange per areas at high latitudes are larger than that at low latitudes, which means greater mass exchange efficiency at high latitudes.     

关于大气臭氧问题的主要研究进展

大气臭氧是非常重要的温室气体,其在全球的分布具有不均匀性,受到人类活动的显著影响,近几十年来由于对流层臭氧增加造成正的辐射强迫会增加大气温室效应,而平流臭氧减少会使其吸收的紫外线辐射减少,为负的辐射强迫,使得平流层大气降温。因此关于大气臭氧浓度变化及其对气候的影响是非常复杂的,一直是科学界研究的热点和难点问题。自从20世纪50年代末到70年代就发现臭氧浓度有减少的趋势。1985年英国南极考察队在南纬60°地区观测发现存在大气臭氧层空洞;自此开始,大气臭氧问题引起了世界各国的极大关注,并给予很多研究。目前,平流层和对流层臭氧浓度的观测仍然是研究的重点。鉴于对流层臭氧浓度持续升高和平流层臭氧浓度的不断下降,以及他们在对流层和平流层大气温度中所起的不同作用,本文将主要针对近五年来大气臭氧相关的研究进展进行简要的综述,包括对流层和平流层臭氧浓度及其观测研究,和人类活动的影响等方面进行分述。最后给出目前研究工作的不足和未来工作展望。     

Seasonal variation of global stratosphere-troposphere mass exchange

By Wei formula in pressure coordinate, the stratosphere-troposphere mass exchange (STME) is diagnosed globally for 44 years from 1958 to 2001 using the European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis datasets. Regions of mass flux into the stratosphere are found over Indonesia, bay of Bangladesh and the mid-west coast of South Africa. Compensating mass outflow from the stratosphere appears mainly over mid-latitudes near large-scale troughs. Upward and downward transport of mass at the middle and high latitudes accompany with each other. Mass flux into troposphere is stronger in autumn and winter than in spring and summer. Strong downward mass flux into the troposphere occurs in eastern Asia the whole year with nearly stable sites. Although the area of eastern Asia accounts for only 5.6% of that of the northern hemisphere (NH), its net mass exchange reaches 15.83% of that of the NH, which means that research on STME of eastern Asia is greatly important to that of the NH and even the global areas. Air across the tropopause enters more from stratosphere to troposphere than that from troposphere to stratosphere, which is possibly related with systematic bias of the assimilated datasets and with persistent rise of the tropopause height. Contributions of the mass exchange and the mass flux exchange in the NH and southern hemisphere (SH) on their latitudes increase from equator to pole, with larger contributions in the NH. Mass exchange and mass flux exchange per areas at high latitudes are larger than that at low latitudes, which means greater mass exchange efficiency at high latitudes.     

N2O binding at a [4Cu:2S] copper-sulphur cluster in nitrous oxide reductase

Nitrous oxide (N(2)O) is generated by natural and anthropogenic processes and has a critical role in environmental chemistry. It has an ozone-depleting potential similar to that of hydrochlorofluorocarbons as well as a global warming potential exceeding that of CO(2) 300-fold. In bacterial denitrification, N(2)O is reduced to N(2) by the copper-dependent nitrous oxide reductase (N(2)OR). This enzyme carries the mixed-valent Cu(A) centre and the unique, tetranuclear Cu(Z) site. Previous structural data were obtained with enzyme isolated in the presence of air that is catalytically inactive without prior reduction. Its Cu(Z) site was described as a [4Cu:S] centre, and the substrate-binding mode and reduction mechanism remained elusive. Here we report the structure of purple N(2)OR from Pseudomonas stutzeri, handled under the exclusion of dioxygen, and locate the substrate in N(2)O-pressurized crystals. The active Cu(Z) cluster contains two sulphur atoms, yielding a [4Cu:2S] stoichiometry; and N(2)O bound side-on at Cu(Z), in close proximity to Cu(A). With the substrate located between the two clusters, electrons are transferred directly from Cu(A) to N(2)O, which is activated by side-on binding in a specific binding pocket on the face of the [4Cu:2S] centre. These results reconcile a multitude of available biochemical data on N(2)OR that could not be explained by earlier structures, and outline a mechanistic pathway in which both metal centres and the intervening protein act in concert to achieve catalysis. This structure represents the first direct observation, to our knowledge, of N(2)O bound to its reductase, and sheds light on the functionality of metalloenzymes that activate inert small-molecule substrates. The principle of using distinct clusters for substrate activation and for reduction may be relevant for similar systems, in particular nitrogen-fixing nitrogenase.