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231.
A model study of ATMOS observations and the heterogeneous loss of N2O5 by the sulphate aerosol layer
The heterogeneous removal of N2O5 by sulphuric acid aerosols as been invoked to explain the decline of mid-latitude ozone in the last decade. We have used a photochemical model to study measurements of odd-nitrogen made by Spacelab 3. The gas-phase photochemical model overestimates the amount of N2O5 present. The loss of N2O5 by aerosols does reduce N2O5, but is likely to be slower than assumed in WMO (1992). The sunset measurements at 25.5 km cannot be explained by heterogeneous loss of N2O5 and is more likely to be due to a faster photolysis than assumed. New absorption cross-sections of HNO3 reduce the photolysis of HNO3 so that the model with gas-phase chemistry only gives better agreement at 19 km, than a model including heterogeneous chemistry. 相似文献
232.
First-arrival traveltimes from a multi-offset vertical seismic profile (VSP) were used to estimate velocity anisotropy in the presence of a vertical velocity gradient. A numerical model consisting of two layers with vertical velocity gradients of 3.1 and 1.2 s−1, respectively, and global anisotropy parameters of =0.12±0.02 and δ=0.30±0.06 yielded first-arrival traveltimes that matched the observed traveltimes well. Shallow receivers were found to be crucial for constraining the vertical velocity field and for determining the parameters of anisotropy at depth. 相似文献
233.
Rachel K. Gittman F. Joel Fodrie Christopher J. Baillie Michelle C. Brodeur Carolyn A. Currin Danielle A. Keller Matthew D. Kenworthy Joseph P. Morton Justin T. Ridge Y. Stacy Zhang 《Estuaries and Coasts》2018,41(3):884-895
Foundation species regulate communities by reducing environmental stress and providing habitat for other species. Successful restoration of biogenic habitats often depends on restoring foundation species at appropriate spatial scales within a suitable range of environmental conditions. An improved understanding of the relationship between restoration scale and environmental conditions has the potential to improve restoration outcomes for many biogenic habitats. Here, we identified and tested whether inundation/exposure stress and spatial scale (patch size) can interactively determine (1) survival and growth of a foundation species, Spartina alterniflora and (2) recruitment of supported fauna. We planted S. alterniflora and artificial mimics in large and small patches at elevations above and below local mean sea level (LMSL) and monitored plant survivorship and production, as well as faunal recruitment. In the first growing season, S. alterniflora plant survivorship and stem densities were greater above LMSL than below LMSL regardless of patch size, while stem height was greatest in small patches below LMSL. By the third growing season, S. alterniflora patch expansion was greater above LMSL than below LMSL, while stem densities were higher in large patches than small patches, regardless of location relative to LMSL. Unlike S. alterniflora, which was more productive above LMSL, sessile marine biota recruitment to mimic plants was higher in patches below LMSL than above LMSL. Our results highlight an ecological tradeoff at ~LMSL between foundation species restoration and faunal recruitment. Increasing patch size as inundation increases may offset this tradeoff and enhance resilience of restored marshes to sea-level rise. 相似文献
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236.
Hauser-Davis RA Bastos FF de Oliveira TF Ziolli RL de Campos RC 《Marine pollution bulletin》2012,64(8):1589-1595
Fish accumulate several trace elements in muscle, gills and liver, however studies also indicate that metals can be excreted through bile. Since metal contamination leads to modifications in bile composition, biliary excretion offers an alternative way to evaluate the presence of trace-elements. Bile is easier to obtain than other organs and presents a simpler matrix, making it easier for chemical pre-treatment. To verify if bile can be useful as a biomonitoring tool for metal contamination, liver and bile trace element concentrations were determined and correlated. The Artificial Neural Networks statistical technique was used to verify if liver trace-element quantification could be substituted by bile analysis. Results show that significant correlations were obtained between trace elements in bile and liver and the ANN validated the hypothesis that certain trace-elements in bile could be utilized instead of liver trace-elements. Further studies in this field are of interest to further validate this biomarker. 相似文献
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238.
Philipson Bani Clive Oppenheimer Vitchko I. Tsanev Simon A. Carn Shane J. Cronin Rachel Crimp Julie A. Calkins Douglas Charley Michel Lardy Tjarda R. Roberts 《Bulletin of Volcanology》2009,71(10):1159-1168
Volcanoes provide important contributions to atmospheric budgets of SO2 and reactive halogens, which play significant roles in atmospheric oxidative capacity and radiation. However, the global
source strengths of volcanic emissions remain poorly constrained. These uncertainties are highlighted here by the first measurements
of gas emission rates from Ambrym volcano, Vanuatu. Our initial airborne ultraviolet spectroscopic measurements made in January
2005 indicate fluxes of 18–270 kg s-1 of SO2, and 62–110 g s-1 of BrO, into the atmosphere, placing Ambrym amongst the largest known contemporary point sources of both these species on
Earth. We also estimate high Cl and F fluxes of ~8–14 and ~27–50 kg s-1, respectively, for this period. Further observations using both airborne and spaceborne remote sensing reveal a fluctuating
SO2 output between 2004 and 2008, with a surge in the first half of 2005, and underline the substantial contribution that a single
passively degassing volcano can make to the atmospheric budget of sulfur and halogens. 相似文献
239.
The 1998 eruption of Volcan Cerro Azul, Isla Isabela, Galápagos Islands, was observed in near real-time by the Geostationary
Operational Environmental Satellite-8 (GOES-8) weather satellite. Due to the remote location of the eruption site, 3.9-μm
radiance values derived from GOES band 2 provide the best timing of the start and termination of the eruption, which occurred
on 15 Sept. and 21 Oct., respectively. Throughout the 36-day long eruption, a total of 1335 thermal infrared images were collected,
of which 851 were cloud-free and permitted the thermal anomaly to be detected. A detailed chronology including 77 separate
events was assembled from the GOES data and field observations. Numerous attributes of the eruption were observed from the
GOES data, including the sizes and dispersal of seven eruption plumes and the occurrence and timing of intra-caldera effusive
activity. The growth of a lava flow on the SE flank, the formation of smoke and volcanic haze from the flank vent, and burning
of vegetation caused by lava flows entering vegetated areas were monitored both on the ground and with the satellite data.
In most cases GOES images were processed as they were received every 30 min and were then distributed over the Internet within
minutes of reception. These data provided timely high-temporal information to field parties as well as enabled the documentation
of the eruption. The GOES observations of Cerro Azul serve as a further example of the way in which the remote sensing community
and field volcanologists can collaborate during future eruptions, and permit the temporal and spatial resolution requirements
for future satellites systems to be better defined.
Received: 27 April 1999 / Accepted: 21 February 2000 相似文献
240.
Arya Udry Zoë E. Wilbur Rachel R. Rahib Francis M. McCubbin Kathleen E. Vander Kaaden Timothy J. McCoy Karen Ziegler Juliane Gross Christopher DeFelice Logan Combs Brent D. Turrin 《Meteoritics & planetary science》2019,54(4):785-810
We present petrologic and isotopic data on Northwest Africa (NWA) 4799, NWA 7809, NWA 7214, and NWA 11071 meteorites, which were previously classified as aubrites. These four meteorites contain between 31 and 56 vol% of equigranular, nearly endmember enstatite, Fe,Ni metal, plagioclase, terrestrial alteration products, and sulfides, such as troilite, niningerite, daubréelite, oldhamite, and caswellsilverite. The equigranular texture of the enstatite and the presence of the metal surrounding enstatite indicate that these rocks were not formed through igneous processes like the aubrites, but rather by impact processes. In addition, the presence of pre‐terrestrially weathered metal (7.1–14 vol%), undifferentiated modal abundances compared to enstatite chondrites, presence of graphite, absence of diopside and forsterite, low Ti in troilite, and high Si in Fe,Ni metals suggest that these rocks formed through impact melting on chondritic and not aubritic parent bodies. Formation of these meteorites on a parent body with similar properties to the EHa enstatite chondrite parent body is suggested by their mineralogy. These parent bodies have undergone impact events from at least 4.5 Ga (NWA 11071) until at least 4.2 Ga (NWA 4799) according to 39Ar‐40Ar ages, indicating that this region of the solar system was heavily bombarded early in its history. By comparing NWA enstatite chondrite impact melts to Mercury, we infer that they represent imperfect petrological analogs to this planet given their high metal abundances, but they could represent important geochemical analogs for the behavior and geochemical affinities of elements on Mercury. Furthermore, the enstatite chondrite impact melts represent an important petrological analog for understanding high‐temperature processes and impact processes on Mercury, due to their similar mineralogies, Fe‐metal‐rich and FeO‐poor silicate abundances, and low oxygen fugacity. 相似文献