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361.
Peter Bräuer Andreas Tilgner Ralf Wolke Hartmut Herrmann 《Journal of Atmospheric Chemistry》2013,70(1):19-52
A new detailed multiphase halogen mechanism, the CAPRAM Halogen Module 2.0 (HM2), has been developed and coupled to the multiphase chemistry mechanism RACM-MIM2ext/CAPRAM 3.0n. The overall mechanism comprises 1,705 reactions including 595 reactions of the HM2. Halogen chemistry box model studies have been, for the first time, performed with a non-permanent cloud scenario for pristine open ocean regions in mid-latitudes. Moreover, detailed time-resolved reaction flux analysis has been used to investigate the multiphase halogen reaction cycles in more detail. Clouds significantly change the multiphase halogen chemical system and new reaction cycles are proposed for in-cloud conditions. While most gas phase concentrations are decreased for chlorine and iodine species, they are increased for bromine. Flux analyses determined the relative contributions of the methylene dihalides CH2IX (X = Cl, Br, I) as the main I atom source with a contribution of about 80 % to the total iodocarbon sources. Furthermore, HOI was confirmed to be important for chlorine activation. It is shown that 25 % of the ozone loss can be attributed to halogens. VOC oxidation by halogens is important as halogens account for about 20 % of the methane oxidation and up to 80 % of the oxidation of other VOCs. In other cases, enhanced VOC and VOC oxidation product concentration levels were found. For example, 15 % of the methyl peroxyl radicals are formed after the reaction of chlorine atoms with methane or methyl hydroperoxide. In the aqueous phase, changes in the oxidation of organics do only occur for highly oxidised organics without a C-H bond. For example, over 80 % of oxalic acid are oxidised by electron transfer with Cl2 ? in deliquescent particles during non-cloud periods. 相似文献
362.
G. Spindler A. Grüner K. Müller S. Schlimper H. Herrmann 《Journal of Atmospheric Chemistry》2013,70(2):165-195
Size-segregated high-volume (HV) quartz filter samples were collected daily at the Melpitz rural site in Germany for PM10 (November 1992 until April 2012), and for PM2.5 and PM1 (January 2003 until April 2012, PM1 sampled every sixth day). The samples were analysed for mass concentration (gravimetrically), water-soluble ions (ion-chromatography) and since 2003 for organic carbon (OC) and elemental carbon (EC) (thermography). The long-term measurements first show a decreasing trend for PM10 (1993–2000) followed by a second period (2001–2011) with a mean mass concentration of about 22.4 μgm?3 and an inter-annual variation of about?±?2.9 μgm?3 (13% fluctuation margin). The absolute sulphate and calcium concentration (for the full period), as well as the EC concentration (time after 2003) decrease by about 50, 75 and 30% for PM10, respectively. The nitrate concentration remains constant all the time. For the daily objective weather type classification (OWTC, 1993–2002) the highest PM10 concentration was found for South-East (SE) and the lowest for North-West (NW) wind direction with 44 and 24 μgm?3, respectively. These concentrations decrease for 2003–2011 in comparison to 1993–2002 by about 21% and 26%, respectively. The highest PM10, PM2.5 and PM1 concentrations (2003–2011) were found for SE and the lowest for NW wind direction with about 34 and 17 μgm?3 (PM10), 28 and 19 μgm?3 (PM2.5) and 22 and 11 μgm?3 (PM1), respectively. The relative content of sulphate, OC and EC was the highest for SE wind direction. A differentiation into four categories for winter (Wi) and summer (Su) and air mass inflow from West (W) and East (E) was carried out. The highest PM concentrations were observed for WiE with the highest inter-annual fluctuation. In this category sulphate contents are largest. The lowest concentrations where found for SuW. The means for WiE show the strongest relative decreases, e.g. in PM10 sulphate (1993–2011) and EC (2003–2011) by about 60% and 40%, respectively. Nitrate is an indicator for NOx motor-car emissions. It shows a typical variation with maximum values in the middle of the week, especially for air mass inflow from West. In contrast, chloride mostly originating from sea spray doesn’t show such a concentration pattern. The PM2.5/PM10 as well the PM1/PM10-ratio have the highest median (0.878 and 0.654) during WiE and the lowest (0.718 and 0.578) during SuW, respectively. For the ratio PM2.5/PM10 a slightly increasing trend was found (about 0.71 and 0.83 for 1995 and 2011, respectively). The increase is stronger in summer than in winter. 相似文献
363.
Hydrothermal precipitates associated with bimodal volcanism in the Central Bransfield Strait,Antarctica 总被引:1,自引:0,他引:1
Sven?PetersenEmail author Peter?M.?Herzig Ulrich?Schwarz-Schampera Mark?D.?Hannington Ian?R.?Jonasson 《Mineralium Deposita》2004,39(3):358-379
Polymetallic sulfide-sulfate mineralization enriched in Pb-Ag-As-Sb-Hg occurs in the Bransfield Strait, a late Tertiary-Quaternary marginal basin close to the Antarctic Peninsula. The mineralization is associated with bimodal volcanism and pelagic and volcaniclastic sediment in rifted continental crust. Hydrothermal precipitates have been recovered from two shallow (1,050–1,000 m water depth) submarine volcanoes (Hook Ridge and Three Sisters) in the Central Bransfield Strait. Mineralization at Hook Ridge consists of polymetallic sulfides, massive barite, and pyrite and marcasite crusts in semilithified pelagic and volcaniclastic sediment. Native sulfur commonly infills void space and cements the volcaniclastic sediment. The polymetallic sulfides are dominated by sphalerite with minor galena, enargite, tetrahedrite-tennantite, pyrite, chalcopyrite, and traces of orpiment cemented by barite and opal-A. The presence of enargite at Hook Ridge, the abundance of native sulfur, and the low Fe content of sphalerite indicate a high sulfur activity of the hydrothermal fluids responsible for mineralization. The sulfur isotopic composition of Hook Ridge precipitates documents the complexity of the sulfur sources in this hydrothermal system with variable influence of biological activity and possibly magmatic contributions. Homogenization temperatures and salinities of fluid inclusions in barite and opal-A suggest that boiling may have affected the hydrothermal fluids during their ascent. The discovery of massive barite-silica precipitates at another shallow marine volcano (Three Sisters volcano) attests to the potential for hydrothermal mineralization at other volcanic edifices in the area. The characteristics of the mineralization in the Bransfield Strait with rifting of continental crust, the presence of bimodal volcanism, including highly evolved felsic volcanic rocks, the association with sediments, and the Pb-Ag-As-Sb-Hg enrichment are similar to the setting of massive sulfide deposits in the Okinawa Trough, and distinct from those of sediment-dominated hydrothermal systems such as Escanaba Trough, Middle Valley, and Guaymas Basin. The geological setting of the Bransfield Strait is also broadly similar to that of some of the largest volcanogenic massive sulfide deposits in the ancient record, such as the Iberian Pyrite Belt.Editorial handling: B. Lehmann 相似文献
364.
Darcy F. Morey George M. Crothers Julie K. Stein James P. Fenton Nicholas P. Herrmann 《Geoarchaeology》2002,17(6):521-553
Indian Knoll is the largest Archaic shell midden excavated by WPA archaeologists in Kentucky. Situated in a large alluvial valley, the site is not associated with a known river shoal as might be expected, making its fluvial and geomorphic setting of interest. Based on sediment cores and auger samples, undisturbed portions of the site remain despite extensive excavations. In undisturbed portions, a shell‐bearing layer is overlain by a shell‐free midden layer. Profiles of organic matter and calcium carbonate content for both layers are similar to those of other Green River shell middens. New radiocarbon determinations date the shell deposit at 5590–4530 cal yr B.P. Analysis of mussel species collected from the Indian Knoll indicates that shell fishing took place in a swiftly flowing, shallow to moderately deep setting of the main river channel. Overall, the prehistoric river setting adjacent to Indian Knoll was characterized by deeper water on average with variable but finer‐grained substrate compared to other Green River shell midden sites. © 2002 Wiley Periodicals, Inc. 相似文献
365.
We consider the COMPTON scattering of a distribution of photons and relativistic electrons in a constant magnetic field. The influence of the magnetic field upon the energy spectrum of the photons scattered by the electrons has been calculated. 相似文献