Removal of Stratospheric O3 by Radicals: In Situ Measurements of OH, HO2, NO, NO2, ClO, and BrO

Simultaneous in situ measurements of the concentrations of OH, HO(2), ClO, BrO, NO, and NO(2) demonstrate the predominance of odd-hydrogen and halogen free-radical catalysis in determining the rate of removal of ozone in the lower stratosphere during May 1993. A single catalytic cycle, in which the rate-limiting step is the reaction of HO(2) with ozone, accounted for nearly one-half of the total O(3) removal in this region of the atmosphere. Halogen-radical chemistry was responsible for approximately one-third of the photochemical removal of O(3); reactions involving BrO account for one-half of this loss. Catalytic destruction by NO(2), which for two decades was considered to be the predominant loss process, accounted for less than 20 percent of the O(3) removal. The measurements demonstrate quantitatively the coupling that exists between the radical families. The concentrations of HO(2) and ClO are inversely correlated with those of NO and NO(2). The direct determination of the relative importance of the catalytic loss processes, combined with a demonstration of the reactions linking the hydrogen, halogen, and nitrogen radical concentrations, shows that in the air sampled the rate of O(3) removal was inversely correlated with total NOx, loading.     

Growth of continental-scale metro-agro-plexes, regional ozone pollution, and world food production

Three regions of the northern mid-latitudes, the continental-scale metro-agro-plexes, presently dominate global industrial and agricultural productivity. Although these regions cover only 23 percent of the Earth's continents, they account for most of the world's commercial energy consumption, fertilizer use, food-crop production, and food exports. They also account for more than half of the world's atmospheric nitrogen oxide (NOx,) emissions and, as a result, are prone to ground-level ozone (O(3)) pollution during the summer months. On the basis of a global simulation of atmospheric reactive nitrogen compounds, it is estimated that about 10 to 35 percent of the world's grain production may occur in parts of these regions where ozone pollution may reduce crop yields. Exposure to yield-reducing ozone pollution may triple by 2025 if rising anthropogenic NOx emissions are not abated.     

Increasing ozone over the Atlantic Ocean

Ship-borne ozone (O3) measurements over the Atlantic Ocean during the period from 1977 to 2002 show that O3 trends in the northern mid-latitudes are small. In contrast, remarkably large O3 trends occur at low latitudes and in the Southern Hemisphere, where near-surface O3 has increased by up to a factor of 2. The likely cause is the substantial increase of anthropogenic emissions of nitrogen oxides (NOx) associated with energy use in Africa, which has added to NOx from biomass burning and natural sources.     

Evidence for new sources of NOX in the lower atmosphere

Laboratory studies show that the reaction of short-lived O2(B3Sigmau) molecules (lifetime approximately 10 picoseconds) with N2 and the photodissociation of the N2:O2 dimer produce NOx in the stratosphere at a rate comparable to the oxidation of N2O by O(1D). This finding implies the existence of unidentified NOX sinks in the stratosphere. The NO2 observed in this experiment is isotopically heavy with a large 15N/14N enhancement. However, photodissociation of this NO2 unexpectedly produced NO molecules with a low 15N/14N ratio. The diurnal odd-nitrogen cycle in the stratosphere will be marked by a complex isotope signature that will be imprinted on the halogen and HOX catalytic cycles.     

Nitrogen dioxide in the stratosphere and troposphere measured by ground-based absorption spectroscopy

The NO(2) abundance in the stratosphere has been determined from ground-based spectra of the rising and setting sun and moon and of the twilight sky near 4500 angstroms. The spectra were taken at the Fritz Peak Observatory, at an altitude of 3 kilometers in the Colorado mountains. Separation of the stratospheric contribution requires observations at a relatively unpolluted site; direct measurement of the tropospheric absorption in the Colorado mountains often yields an upper limit on the tropospheric mixing ratio of 0.1 part per billion. The stratospheric NO(2) abundance is two to three times greater at night than during the day and increases significantly during the course of a sunlit day; these changes are related to photolytic decomposition of NO(2) and N(2)O(5) in the daytime stratosphere. Absorption by NO(3) was sought but not found; the results set an upper limit of 2 percent on the nighttime abundance ratio of NO(3) to NO(2) in the stratosphere.     

流动注射化学发光法检测卷烟主流烟气中的氮氧化物

[目的]探讨一种流动注射化学发光法间接测定卷烟主流烟气中氮氧化物（NOx）的方法。[方法]将NOx用氢氧化钠（NaOH）溶液吸收定量生成亚硝酸根（NO2-），在酸性条件下与过氧化氢（H2O2）反应，其产物与鲁米诺发生很强的化学发光反应，用流动注射化学发光分析仪根据化学发光强度测定卷烟主流烟气中的NO。含量。[结果]建立了一种新的卷烟主流烟气中的NOx鲁米诺一过氧化氢化学发光分析体系：H2O2浓度1．0×10^-3g/ml，硫酸浓度0．01mol／L，氢氧化钠浓度0．10mol／L溶液配制发光液，鲁米诺浓度为1．0×10^-3mol/L。方法的检出限为1．2×10^-5g/L，相对标准偏差〈3．00％。样品分析结果表明，烤烟型卷烟NOx含量普遍较混合型低，与烤烟型卷烟舍亚硝酸盐较低的规律比较吻合。[结论]流动注射化学发光法适用于卷烟主流烟气中的NOx的定量分析。     

An Explanation for Symmetry-Induced Isotopic Fractionation in Ozone

Application of a theory of nuclear symmetry-based reaction restrictions to the O2 + O --> O3 reaction provides a potential explanation for the symmetry-induced isotopic enrichment observed for laboratory and atmospherically produced O3. Within this theory, the rate of formation of O3 from collisions of O and isotopically homonuclear O2 depends on whether the O2 molecule is in an f (allowed) or an e (restricted) parity label state. The restriction can be relaxed by various potential energy surface coupling terms, and the assumption that approximately 78 percent of the restricted O2(e) levels produce O3 with the same efficiency as the allowed O2(f) levels can account for laboratory-observed isotopic fractionation. In particular, the theory explains the special enhanced formation of the completely asymmetric isotopomer 16O17O18O.     

光催化转化氮氧化物的研究进展

对光催化转化氮氧化物的研究进展进行了综述.首先介绍了氮氧化物的危害及传统处理方法的缺点以及光催化反应的机理;随后着重介绍了以TiO2为催化剂对NOx去除的研究进展,并对其他用于分解氮氧化物新型光催化进行了介绍;最后对应用前景作出展望.光催化转化氮氧化物的研究分为光催化氧化和光催化还原2种,反应器则主要为固定床反应器和流化床反应器.N原子的搀杂、氧空穴的产生以及表面负载Pt均能有效地利用可见光,炭(AC)、沸石、氧化钙、ZrO2、高岭土等载体也可明显地提高光催化转化氮氧化物的效率.此外,植入过渡金属离子沸石,也可有效地转化氮氧化物.     

Tracing the origin and fate of NOx in the Arctic atmosphere using stable isotopes in nitrate

Atmospheric nitrogen oxides (NOx =NO+ NO2) play a pivotal role in the cycling of reactive nitrogen (ultimately deposited as nitrate) and the oxidative capacity of the atmosphere. Combined measurements of nitrogen and oxygen stable isotope ratios of nitrate collected in the Arctic atmosphere were used to infer the origin and fate of NOx and nitrate on a seasonal basis. In spring, photochemically driven emissions of reactive nitrogen from the snowpack into the atmosphere make local oxidation of NOx by bromine oxide the major contributor to the nitrate budget. The comprehensive isotopic composition of nitrate provides strong constraints on the relative importance of the key atmospheric oxidants in the present atmosphere, with the potential for extension into the past using ice cores.     

Hydrogen radicals, nitrogen radicals, and the production of O3 in the upper troposphere

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.     

The silica balance in the world ocean: a reestimate

The net inputs of silicic acid (dissolved silica) to the world ocean have been revised to 6.1 +/- 2.0 teramoles of silicon per year (1 teramole = 10(12) moles). The major contribution (about 80 percent) comes from rivers, whose world average silicic acid concentration is 150 micromolar. These inputs are reasonably balanced by the net ouputs of biogenic silica of 7.1 +/- 1.8 teramoles of silicon per year in modern marine sediments. The gross production of biogenic silica (the transformation of dissolved silicate to particulate skeletal material) in surface waters was estimated to be 240 +/- 40 teramoles of silicon per year, and the preservation ratio (opal accumulation in sediment/gross production in surface waters) averages 3 percent. In the world ocean the residence time of silicon, relative to total biological uptake in surface waters, is about 400 years.     

外源硝酸钙对盐胁迫黄瓜幼苗生长和光合作用的影响

以较耐盐黄瓜品种新泰密刺为试材,采用营养液栽培,研究了叶面喷施Ca(NO3)2对盐胁迫(65 mmol/L NaCl)下黄瓜幼苗生长、叶片叶绿素含量、光合及叶绿素荧光参数的影响。结果表明,外源Ca(NO3)2显著提高了盐胁迫下黄瓜幼苗的干鲜重和叶片叶绿素含量;Ca(NO3)2也提高了盐胁迫下黄瓜叶片净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、PSⅡ实际光化学效率(ФPSⅡ)、光条件下最大光化学效率(F'v/F'm)和光化学淬灭系数(qP),而对胞间CO2浓度(Ci)、暗条件下最大化学效率(Fv/Fm)和非光化学淬灭系数(qN)没有显著影响。这些结果说明外源Ca(NO3)2可能通过提高叶绿素含量和调节气孔限制,以缓解盐胁迫对黄瓜幼苗光化学效率的抑制,进而提高植株耐盐胁迫能力,促进其生长。     

A-Axis--Oriented YBa2Cu3O7/PrBa2Cu3O7 Superlattices

A modulated structure has been fabricated from high transition temperature superconductors where the individual CuO(2) planes are composed of alternating superconducting and insulating strips. This structure is made by growing a-axis-oriented YBa(2)Cu(3)O(7)/PrBa(2)Cu(3)O(7) superlattices by 90 degrees off-axis sputtering on (100)SrTiO(3) and (100)LaAlO(3) substrates. Superlattice modulation is observed to a modulation wavelength of 24 angstroms (12 angstroms-YBa(2)Cu(3)O(7)/12 angstroms-PrBa(2)Cu(3)O(7)), both by x-ray diffraction and by cross-sectional transmission electron microscopy. Rutherford backscattering spectroscopy indicates a high degree of crystalline perfection with a channeling minimum yield of 3 percent. Quasi-one-dimensional conductivity should be obtainable in these structures.     

光照对分蘖期水稻叶际及根系-培养液体系 N2O 和 NOX（NO，NO2）排放的影响

[目的]该研究探讨光照对分蘖期水稻根、叶界面N2O和NOX排放的作用及其机制。[方法]试验在水培控氮、小型光控培养箱控光和同步测定条件下,探讨了不同光质、光强及光控处理对分蘖期水稻叶际及根系-培养液体系 N2O和 NOX 排放的影响。[结果]①在相同氮源(NH4NO3-N,90 mg/L)、日间光照为6000、8000 lx条件下,分蘖期平均水稻叶际 N2O和NO排放速率分别为27.08、32.33μg/(pot·h)和0.114、0.057μg/(pot·h),分别占 N2O和 NO总排放的57.38%、58.65%和9.65%、4.52%,水稻叶际是N2O的重要排放源;②在光强(1600 lx)一致条件下,LED黄、绿、白、红、蓝光处理的平均水稻叶际N2O 排放速率分别为6.83、9.40、9.73、2.82和4.08μg/(pot·h),光 X强较高的红(3000 lx)、蓝光(2500 lx)处理能同步抑制分蘖期水稻根、叶界面N2O的挥发(P<0.01),LED红、白光有促进日间水稻叶际NO排放的作用,LED蓝光则有同步抑制水稻根、叶界面 NO挥发的作用效果,但不同光控处理下水稻根、叶界面均无明显的NO2净排放作用;③0~8000 lx 范围内随着光照增强,水稻根部NO及根、叶界面 N2O排放同步增加,但高光强(6000~8000 lx)下水稻叶际 NO排放显著大幅下降(P<0.01)。[结论]水稻根、叶界面均以N2O挥发为主;试验供氮水平下适度控制日间光强并同步增加红光、蓝光比例的技术,能同步抑制水稻根、叶界面氮氧化物的排放。     

Nitric oxide reduction coupled with carbon monoxide oxidation in the presence of soluble metal catalysts

Solutions of RhCl(3).xH(2)O in ethanol and Ru(NO)(2)[P(C(6)H(5))(3)](2) in benzene catalyze the reduction of nitric oxide to nitrous oxide concomitant with the oxidation of carbon monoxide to carbon dioxide at ambient temperature and atmospheric pressure. The reaction, which is followed by gas chromatography and by the decrease in pressure of the system, proceeds to 47 percent conversion of the reactants after 63 hours.     

Apollo lunar module engine exhaust products

Organic combustion products generated by the lunar module descent engine, which burns a 1:1 mixture of unsymmetrical dimethylhydrazine fuel and nitrogen tetroxide oxidizer, have been analyzed. The major gaseous combustion products found were ammonia, water, carbon monoxide, nitrous oxide, oxygen, carbon dioxide, and nitric oxide. The minor products were acetylene, hydrogen cyanide, ethylene, formaldehyde, propadiene, ketene, cyanous acid, hydrazoic acid, various methylamines, acetaldehyde, methyl nitrite, formic acid, nitrous acid, butadiyne, nitrilohydrazines, nitromethane, and nitrosohydrazines with other oxidized derivatives of unsymmetrical dimethylhydrazine and hydrazine. The ion intensities of the various species in all mass spectra were estimated as the following concentrations: the gases (NH(3), H(2)O, CO, NO, O(2), CO(2), and NO(2)), 87.7 percent; compounds of C, H, and O, 6.0 percent; and compounds of C, H, and N (with traces of O), 5.8 percent.     

外源一氧化氮对铝胁迫下烟草叶片光能利用和光保护系统及活性氧代谢的影响

以云烟100(耐铝)和云烟105(铝敏感)为材料,采用水培法研究外源一氧化氮(NO)对铝胁迫下烟草植株生长、叶片活性氧含量、光合特性、叶绿素荧光参数、光呼吸和抗氧化酶活性的影响。结果表明,铝胁迫显著降低了烟草叶片叶绿素含量、净光合速率(Pn)、最大光化学效率(Fv/Fm)、PSII光合电子传递量子效率(FPSII)和光化学猝灭系数(q P),提高了反应中心PSII过剩激发能,从而导致叶片超氧阴离子(O_2·)和过氧化氢(H_2O_2)含量升高,植株生物量下降。外源NO可显著提高铝胁迫下烟草叶片叶绿素含量、Pn、Fv/Fm、FPSII、q P和植株生物量,降低反应中心PSII过剩激发能和叶片O_2·、H_2O_2含量,且云烟105变化幅度高于云烟100。此外,外源NO还显著提高了铝胁迫下烟草叶片非光化学猝灭系数、光呼吸速率、超氧化物歧化酶和抗坏血酸过氧化物酶活性,说明NO可通过提高烟草叶片光化学反应能力、热耗散、光呼吸以及抗氧化酶活性来降低反应中心PSII过剩激发能,防止或清除叶绿体内产生的活性氧,缓解铝对烟草的毒害,这种缓解效应在敏感基因型云烟105中表现更明显。     

Isotopic composition of the martian atmosphere

Results from the neutral mass spectrometer carried on the aeroshell of Viking 1 show evidence for NO in the upper atmosphere of Mars and indicate that the isotopic composition of carbon and oxygen is similar to that of Earth. Mars is enriched in (15)N relative to Earth by about 75 percent, a consequence of escape that implies an initial abundance of nitrogen equivalent to a partial pressure of at least 2 millibars. The initial abundance of oxygen present either as CO(2) or H(2)O must be equivalent to an exchangeable atmospheric pressure of at least 2 bars in order to inhibit escape-related enrichment of (18)O.     

Mechanism of the selective catalytic reduction of nitric oxide by ammonia elucidated by in situ on-line fourier transform infrared spectroscopy

The selective catalytic reduction reaction of nitric oxide bv ammonia over vanadia-titania catalysts is one of the methods of removing NOx pollution. In the present study, it has been possible to identify the reaction mechanism and the nature of the active sites in these catalysts by combining transient or steady-state in situ (Fourier transform infrared spectroscopy) experiments directly with on-line activity studies. The results suggest a catalytic cycle that consists of both acid and redox reactions and involves both surface V-OH (Br?nsted acid sites) and V=O species. A fundamental microkinetic model is proposed, which accounts for the observed industrial kinetics performance.     

A functional model for O-O bond formation by the O2-evolving complex in photosystem II

The formation of molecular oxygen from water in photosynthesis is catalyzed by photosystem II at an active site containing four manganese ions that are arranged in di-mu-oxo dimanganese units (where mu is a bridging mode). The complex [H2O(terpy)Mn(O)2Mn(terpy)OH2](NO3)3 (terpy is 2,2':6', 2"-terpyridine), which was synthesized and structurally characterized, contains a di-mu-oxo manganese dimer and catalyzes the conversion of sodium hypochlorite to molecular oxygen. Oxygen-18 isotope labeling showed that water is the source of the oxygen atoms in the molecular oxygen evolved, and so this system is a functional model for photosynthetic water oxidation.