Iodine Chemistry and its Role in Halogen Activation and Ozone Loss in the Marine Boundary Layer: A Model Study   总被引：6，自引：0，他引：6  

Rainer Vogt  Rolf Sander  Roland von Glasow  Paul J. Crutzen 《Journal of Atmospheric Chemistry》1999,32(3):375-395

A detailed set of reactions treating the gas and aqueous phase chemistry of the most important iodine species in the marine boundary layer (MBL) has been added to a box model which describes Br and Cl chemistry in the MBL. While Br and Cl originate from seasalt, the I compounds are largely derived photochemically from several biogenic alkyl iodides, in particular CH2I2, CH2ClI, C2H5I, C3H7I, or CH3I which are released from the sea. Their photodissociation produces some inorganic iodine gases which can rapidly react in the gas and aqueous phase with other halogen compounds. Scavenging of the iodine species HI, HOI, INO2, and IONO2 by aerosol particles is not a permanent sink as assumed in previous modeling studies. Aqueous-phase chemical reactions can produce the compounds IBr, ICl, and I2, which will be released back into the gas phase due to their low solubility. Our study, although highly theoretical, suggests that almost all particulate iodine is in the chemical form of IO-3. Other aqueous-phase species are only temporary reservoirs and can be re-activated to yield gas phase iodine. Assuming release rates of the organic iodine compounds which yield atmospheric concentrations similar to some measurements, we calculate significant concentrations of reactive halogen gases. The addition of iodine chemistry to our reaction scheme has the effect of accelerating photochemical Br and Cl release from the seasalt. This causes an enhancement in ozone destruction rates in the MBL over that arising from the well established reactions O(1D) + H2O 2OH, HO2 + O3 OH + 2O2, and OH + O3 HO2 + O2. The given reaction scheme accounts for the formation of particulate iodine which is preferably accumulated in the smaller sulfate aerosol particles.  相似文献   

The atmospheric impact on fluxes of nitrogen, POPs and energy in the German Bight     

M. Schulz  J. van Beusekom  K. Bigalke  U. Brockmann  W. Dannecker  H. Gerwig  H. Grassl  C. -J. Lenz  K. Michaelsen  U. Niemeier  T. Nitz  E. Plate  T. Pohlmann  T. Raabe  A. Rebers  V. Reinhardt  M. Schatzmann  K. H. Schlünzen  R. Schmidt-Nia  T. Stahlschmidt  G. Steinhoff  K. von Salzen 《Ocean Dynamics》1999,51(2-3):133-154

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Probleme bei der Nutzung von Offshore-Wind-energie aus Sicht des Naturschutzes     

Merck  Thomas  von Nordheim  Henning 《Ocean Dynamics》1999,51(10):79-88

Ocean Dynamics - Allein für den Bereich der deutschen Ausschließlichen Wirtschaftszonen von Nord-und Ostsee sind Anfragen zur Genehmigungsfähigkeit von Windparken mit zusammen weit...  相似文献   

Elemental abundances for Nova LMC 1990#1     

Karen M. Vanlandingham  Sumner Starrfield  †  Steven N. Shore †  George Sonneborn † 《Monthly notices of the Royal Astronomical Society》1999,308(2):577-587

We present our analysis of the UV spectra of the fast ONeMg Nova LMC 1990#1. Observations with the IUE began on 1990 January 18 and continued through to 1990 March 15. We have analysed these spectra, and determined line fluxes and physical parameters as a function of time. Using both He  ii lines and the Balmer decrement, we find the reddening for the nova to be E ( B − V )≃0.22. Using the photoionization code cloudy 90.03b and the minimization routine minuit , we derive elemental abundances for the ejecta. We find the following abundances, relative to solar material: He=1, C=8, N=109, O=20, Ne=62, Mg=16, Al=257 and Si=41. These results are based on independent fits to different data sets acquired three weeks apart. These abundances are extremely similar to those found for V693 Corona Austrinae 1981. Given the position of V693 CrA in the Galaxy and the range of distances found for it, the similar abundances imply that the V693 CrA outburst took place on an older population white dwarf. The high N/O ratio implies an outburst on a massive white dwarf.  相似文献   

X-ray-luminous radio supernovae in the centre of M82?     

Ian R. Stevens  David K. Strickland  Karen A. Wills 《Monthly notices of the Royal Astronomical Society》1999,308(3):L23-L27

We investigate the X-ray emission from the central regions of the prototypical starburst galaxy M82. Previous observations have shown a bright central X-ray point source, with suggestions as to its nature including a low-luminosity active galactic nucleus or an X-ray binary. A new analysis of ROSAT HRI observations finds four X-ray point sources in the central kiloparsec of M82, and we identify radio counterparts for the two brightest X-ray sources. The counterparts are probably young radio supernovae (SNe) and are amongst the most luminous and youthful SNe in M82. We therefore suggest that we are seeing X-ray emission from young SNe in M82, and in particular that the brightest X-ray source is associated with the radio source 41.95+57.5. We discuss the implications of these observations for the evolution of X-ray-luminous SNe.  相似文献   

Dissolution of jarosite [KFe₃(SO₄)₂(OH)₆] at pH 2 and 8: Insights from batch experiments and computational modelling   总被引：1，自引：0，他引：1  

Adrian M.L. Smith  Karen A. Hudson-Edwards  William E. Dubbin 《Geochimica et cosmochimica acta》2006,70(3):608-621

Jarosite [KFe₃(SO₄)₂(OH)₆] is a mineral that is common in acidic, sulphate-rich environments, such as acid sulphate soils derived from pyrite-bearing sediments, weathering zones of sulphide ore deposits and acid mine or acid rock drainage (ARD/AMD) sites. The structure of jarosite is based on linear tetrahedral-octahedral-tetrahedral (T-O-T) sheets, made up from slightly distorted FeO₆ octahedra and SO₄ tetrahedra. Batch dissolution experiments carried out on synthetic jarosite at pH 2, to mimic environments affected by ARD/AMD, and at pH 8, to simulate ARD/AMD environments recently remediated with slaked lime (Ca(OH)₂), suggest first order dissolution kinetics. Both dissolution reactions are incongruent, as revealed by non-ideal dissolution of the parent solids and, in the case of the pH 8 dissolution, because a secondary goethite precipitate forms on the surface of the dissolving jarosite grains. The pH 2 dissolution yields only aqueous K, Fe, and SO₄. Aqueous, residual solid, and computational modelling of the jarosite structure and surfaces using the GULP and MARVIN codes, respectively, show for the first time that there is selective dissolution of the A- and T-sites, which contain K and SO₄, respectively, relative to Fe, which is located deep within the T-O-T jarosite structure. These results have implications for the chemistry of ARD/AMD waters, and for understanding reaction pathways of ARD/AMD mineral dissolution.  相似文献   

Macroalgal distribution patterns in a shallow, soft-bottom lagoon, with emphasis on the nonnativeGracilaria vermiculophylla andCodium fragile     

Mads Solgaard Thomsen  Karen J. McGlathery  Anna Christina Tyler 《Estuaries and Coasts》2006,29(3):465-473

We determined the distribution of macroalgae in Hog Island Bay, a shallow coastal lagoon in Virginia, USA, seasonally at 12 sites from 1998 to 2000 and at 3 representative sites from 2000 to 2002. We analyzed macroalgal biomass, taxonomic richness, and abundance of two non-native species, the cryptic invaderGracilaria vermiculophylla and the conspicuousCodium fragile, with respect to season, location (mainland, mid lagoon, barrier island sites), and elevation (intertidal, subtidal). Taxonomic richness, total algal biomass, and nonnative biomass peaked in the summer months when temperature and light availability were highest. A few stress tolerant and ephemeral algae dominated the algal assemblage.G. vermiculophylla constituted 74% of the entire algal biomass, was the most abundant alga in all seasons, locations, and elevation levels, and was positively correlated with taxonomic richness and abundance of filamentous species.Ulva curvata, Bryopsis plumosa, andC. fragile accounted for an additional 16% of the algal biomass. There are distinct habitats in Hog Island Bay that can be classified into low diversity-low biomass regions near the mainland and barrier islands and high diversity-high biomass regions in the open mid lagoon, where abundant shells for attachment and intermediate levels of water column nutrients and turbidity likely create better growth conditions. Taxonomic richness and biomass were higher in subtidal than intertidal zones, presumably due to lower desiccation stress. This study provides an example of how a single invasive species can dominate an entire assemblage, both in terms of biomass (being most abundant in all seasons, locations, and tidal levels) and species richness (correlating positively with epiphytic filamentous taxa). By adding hard-substratum structural complexity to a relatively homogenous soft-substratum system,G. vermiculophylla increases substratum availability for attachment and entanglement of other algal species and enhances local diversity. Without widespread and abundantG. vermiculophylla, taxa likePolysiphonia, Ceramium, Bryopsis, Ectocarpus, andChampia would likely be much less common. This study also highlights the importance of using DNA analysis of voucher specimens in monitoring programs to accurately identify cryptic invaders.  相似文献   

Dissolution of lead- and lead-arsenic-jarosites at pH 2 and 8 and 20 °C: Insights from batch experiments     

Adrian M.L. Smith  William E. Dubbin  Karen A. Hudson-Edwards 《Chemical Geology》2006,229(4):344-361

Lead- and Pb-As-jarosites are minerals common to acidic, sulphate-rich environments, including weathering zones of sulphide ore deposits and acid rock or acid mine drainage (ARD/AMD) sites, and often form on or near galena. The structures of these jarosites are based on linear tetrahedral-octahedral-tetrahedral (T-O-T) sheets, comprised of slightly distorted FeO₆ octahedra and SO₄²⁻ (-AsO₄³⁻ in Pb-As-jarosites) tetrahedra. To better understand the dissolution mechanisms and products of the break down of Pb- and Pb-As-jarosite, preliminary batch dissolution experiments were conducted on synthetic Pb- and Pb-As-jarosite at pH 2 and 20 °C, to mimic environments affected by ARD/AMD, and at pH 8 and 20 °C, to simulate ARD/AMD environments recently remediated with slaked lime (Ca(OH)₂). All four dissolutions are incongruent. Dissolution of Pb-jarosite at pH 2 yields aqueous Pb, Fe and SO₄²⁻. The pH 8 Pb-jarosite dissolution yields aqueous Pb, SO₄²⁻ and poorly crystalline Fe(OH)₃, which does not appear to resorb Pb or SO₄²⁻, possibly due to the low solution pH (3.44-3.54) at the end of the experiment. The pH 2 and 8 dissolutions of Pb-As-jarosite result in the formation of secondary compounds (poorly crystalline PbSO₄ for pH 2 dissolution; poorly crystalline PbSO₄ and Fe(OH)₃ for pH 8 dissolution), which may act as dissolution inhibitors after 250 to 300 h of dissolution. In the pH 2 dissolution, aqueous Fe, SO₄²⁻ and AsO₄³⁻ also form, and in the pH 8 dissolution, Fe(OH)₃ precipitates then subsequently resorbs aqueous AsO₄³⁻. The dissolutions probably proceed by preferred dissolution of the A- and T-sites, which contain Pb, and SO₄²⁻ and AsO₄³⁻, respectively, rather than Fe, which is sterically remote, within the T-O-T Pb- and Pb-As-jarosite structures. These data provide the foundation necessary for further, more detailed investigations into the dissolution of Pb- and Pb-As-jarosites.  相似文献   

Permo-Carboniferous volcanism in late Variscan continental basins of the Bohemian Massif (Czech Republic): geochemical characteristic     

J. Ulrych  J. Pe&#x;ek  J. &#x;te pnkov-Svobodova&#x;  P. Bosk  F.E. Lloyd  V. von Seckendorff  M. Lang  J.K. Novk 《Chemie der Erde / Geochemistry》2006,66(1):37-56

Extensive Permo-Carboniferous volcanism has been documented from the Bohemian Massif. The late Carboniferous volcanic episode started at the Duckmantian–Bolsovian boundary and continued intermittently until Westphalian D to Stephanian B producing mainly felsic and more rarely mafic volcanics in the Central Bohemian and the Sudetic basins. During the early Permian volcanic episode, after the intra-Stephanian hiatus, additional large volumes of felsic and mafic volcanics were extruded in the Sudetic basins. The volcanics of both episodes range from entirely subalkaline (calc-alkaline to tholeiitic) of convergent plate margin-like type to transitional and alkaline of within-plate character. A possible common magma could not be identified among the Carboniferous and Permian primitive magmas, but a common geochemical signature (enrichment in Th, U, REE and depletion in Nb, Sr, P, Ti) in the volcanic series of both episodes was recognized. On the other hand, volcanics of both episodes differ in intensities of Nb, Sr and P depletion and also, in part, in their isotope signatures. High ⁸⁷Sr/⁸⁶Sr (0.707–0.710) and low ε_Nd (−6.0 to −6.1) are characteristic of the Carboniferous mafic volcanics, whereas low ⁸⁷Sr/⁸⁶Sr (0.705–0.708) and higher ε_Nd ranging from −2.7 to −3.4 are typical of the Permian volcanics. Felsic volcanics of both episodes vary substantially in ⁸⁷Sr/⁸⁶Sr (0.705–0.762) and ε_Nd (−0.9 to −5.1). Different depths of magma source or heterogeneity of the Carboniferous and Permian mantle can be inferred from variation in some characteristic elements of the geochemical signature for volcanics in some basins. The Sr–Nd isotopic data with negative ε_Nd values confirm a significant crustal component in the volcanic rocks that may have been inherited from the upper mantle source and/or from assimilation of older crust during magmatic underplating and ascending of primary basic magma. Two different types of primary magma development and formation of a bimodal volcanic series have been recognized: (i) creation of a unique magma by assimilation fractional crystallization processes within shallow-level reservoirs (type Intra-Sudetic Basin) and (ii) generation and mixing of independent mafic and felsic magmas, the latter by partial melting of upper crustal material in a high-level chamber (type Krkonoše Piedmont Basin). A similar origin for the Permo-Carboniferous volcanics of the Bohemian Massif is obvious, however, their geochemical peculiarities in individual basins indicate evolution in separate crustal magma chambers.  相似文献   

Time delayed control of structural systems     

Firdaus E. Udwadia  Hubertus F. von Bremen  Ravi Kumar  Mohammad Hosseini 《地震工程与结构动力学》2003,32(4):495-535

Time delays are ubiquitous in control systems. They usually enter because of the sensors and actuators used in them. Traditionally, time delays have been thought to have a deleterious effect on both the stability and the performance of controlled systems, and much research has been done in attempting to eliminate them, compensate for them, or nullify their presence. In this paper we take a different view. We investigate whether purposefully injected time delays can be used to improve both the system's stability and performance. Our analytical, numerical, and experimental investigation shows that this can indeed be done. Analytical results of the effects of time delays on collocated and non‐collocated control of classically damped and non‐classically damped systems are given. Experimental and numerical results confirm the theoretical expectations. Issues of system uncertainties and robustness of time delayed control are addressed. The results are of practical value in improving the performance and stability of controllers because these characteristics (performance and stability) improve dramatically with the intentional injection of small time delays in the control system. The introduction of such time delays constitutes a ‘minimal change’ to a controller already installed in a structural system for active control. Hence, from a practical standpoint, time delays can be implemented in a nearly costless and highly reliable manner to improve control performance and stability, an aspect that cannot be ignored when dealing with the economics and safety of large structural systems subjected to strong earthquake ground shaking. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献