The free radicals OH, HO2, RO2, and NO3 are known to be the driving force for most chemical processes in the atmosphere. Since the low concentration of the above radicals makes measurements particularly difficult, only relatively few direct measurements of free radical concentrations have been reported to date.We present a comprehensive set of simultaneous radical measurements performed by Laser Induced Fluorescence (LIF), Matrix Isolation –Electron spin Resonance (MI-ESR), Peroxy Radical Chemical Amplification (PERCA), and Differential Optical Absorption Spectroscopy (DOAS) during the BERLIner OZonexperiment (BERLIOZ) during July and August of 1998 near Berlin, Germany. Most of the above radical species were measured by more than one technique and an intercomparison gave good agreement. This data set offered the possibility to study and quantify the role of each radical at a rural, semi-polluted site in the continental boundary layer and to investigate interconnections and dependencies among these free radicals.In general (box) modelled diurnal profiles of the different radicals reproduced the measurements quite well, however measured absolute levels are frequently lower than model predictions. These discrepancies point to disturbing deficiencies in our understanding of the chemical system in urban air masses.In addition considerable night-time peroxy radical production related to VOC reactions with NO3 and O3 could be quantified. 相似文献
Malignites from the Poohbah Lake complex of northwestern Ontario, Canada are melanocratic cumulates. Cumulus pyroxene and apatite are poikilitically enclosed in a groundmass of large plates of intercumulus orthoclase and nepheline. Nepheline-feldspar fingerprint-like intergrowths occur. Nephelines are commonly zeolitized and pyroxenes altered to aggregates of biotite and/or garnet by deuteric alteration. Pyroxenes are weakly zoned from Di71 Hd18Ac11 to Di63Hd22Ac15, and are similar to the least evolved pyroxenes of other alkaline rocks. Nephelines all have compositions within the Morozewicz-Buerger convergence field and feldspars have a limited compositional range from Or88 to Or95. Perthites are absent.Inconsistancies in the usage of the terms malignite and juvite are discussed and it is considered that a non-genetic petrographic classification of nepheline syenites leads to the obscuration of a group of potassic nepheline syenites, characterized by the presence of nepheline plus orthoclase which are typically associated with saturated to over-saturated alkaline rocks, contain pseudo-leucite or nepheline-orthoclase intergrowths, are emplaced in mobile belts and are not associated with rocks of the ijolite-carbonatite suite.A genetic classification of nepheline syenites is suggested and it is proposed that; (1) mafic-rich nepheline syenites be referred to as mela-nepheline syenites (sensu lato) rather than as malignites; (2) the term malignite be used for magmatic potassic nepheline syenites characterised by the presence of nepheline plus a single potassium-rich feldspar (orthoclase or microcline) and devoid of exsolution perthite under subsolvus conditions; (3) the metasomatic malignites and juvites of ijolite-carbonatite complexes be referred to as varieties of fenites. 相似文献
Rb/Sr geochronology on a folded greenstone-granitoid complex in the Agnew area, Western Australia, yields four distinct ages of igneous activity that conform with stratigraphic and intrusive relationships. They are (using , NBS 70A = 522 ppm Rb and 65.3 ppm Sr):
Ma
87Sr/86Sr initial (IR)
(1) Differentiated gabbro-granophyre from a stratigraphically old (Kathleen Valley) greenstone sequence
(2) Voluminous tonalite, the Lawlers Tonalite
(3) A less voluminous leucogranite, and a large complex pegmatite cutting the Perseverance nickel orebody
(4) Aplitic leucotonalite (very minor volumes but widespread)
Lakes of the Klutlan moraines originate by down-melting of stagnant ice under a mantle of rock debris and vegetation ranging from scattered herbs and shrubs on the younger moraines to multiple-generation closed spruce forest on the oldest moraines, which are 600–1200 yr old. Lakes on the youngest moraines are temporary, turbid with glacial silt, and marked by unstable ice-cored slopes. On older moraines most lakes have clear water and stable slopes. On the oldest moraines many lakes have brown water caused by dissolved humic materials derived from the thick forest floor, but even here some slopes are unstable because of continued melting of buried ice. Morainic lakes contain bicarbonate waters of moderate alkalinity and conductivity and low levels of nutrients. The highly diverse phytoplankton is dominated by chrysophytes and cryptomonads, with few diatoms. Extremely low values for phytoplankton biomass place most of the lakes in an “ultraoligotrophic” category. Zooplankton is dominated by copepods, which were found even in ice ponds only a few years old, and by the cladoceran Daphnia pulex. Surface-sediment samples contained a total of 16 species of chydorid Cladocera. Of these, Alonella excisa and Alona barbulata are apparently the pioneer species in the youngest lakes. Chydorus sphaericus only appears in lakes of the oldest moraines. A successional pattern is not conspicuous, however, partly because some of the lakes on the older moraines originated by recent collapse over buried ice. Lakes on the upland outside the dead-ice moraines yielded 39 species in the zooplankton. The distinctive assemblage on upland lakes may relate more to different water chemistry than to age. 相似文献
Diatom analysis of a varved sediment core from Elk Lake, Minnesotadocuments important natural and human-caused shifts in primary productivity atdecadal scales for the past 1500 years. Interpretations from a perspective ofplanktic diatom seasonal dynamics and from total phosphorus inferences based ona 111-lake training set of freshwater Canadian lakes reveal a major change tomore productive environments after 1000 years ago probably caused by earlierice-out and stronger, longer periods of lake circulation during the spring.European impacts in the region, principally logging in the Elk Lake drainage,during the past 100 years increased nutrient fluxes and turbulence during theopen water season to promote blooms of Aulacoseiraambigua. High resolution (semi-decadal) diatom analyses suggestsunspot cycle periodicities that may reflect short-term changes in thecharacter of irradiance and (or) sun-climate interactions. Total epilimneticphosphorus inferences from the Canadian training set applied to the Elk Lakediatom record document both long-term and short-term variations inproductivity and reconstruct past phosphorus values consistent with somepresent-day measured values at Elk Lake. The Elk Lake study underscores theneed for neolimnological monitoring of both training set and target lakes aswell as for the application of a multiple proxy protocol to documentpaleo-productivity that approaches neolimnological resolution. 相似文献
Lake sediments from a closed basin in southern Patagonia (Argentina) provide a continental archive with which to reconstruct climate change and to test the interhemispheric synchroneity of abrupt events. High-resolution sub-bottom seismic profiles of Lago Cardiel indicate substantial lake-level changes since the late Pleistocene, which were identified and dated in a series of long piston cores. These data allow the reconstruction of the regional water balance at 49=" PSFT − BC "202S since the late glacial. The seismic stratigraphy reveals a dry late glacial climate with a desiccation of the basin around 11 220 yr BP (14C). Lake level rapidly increased by 135 m at the Holocene transition. Following the early Holocene highstand at + 55 m, lake level never dropped significantly below modern level. The palaeoclimate changes implied by the Lago Cardiel record are out-of-phase with those implied by records from tropical South America and demonstrate considerable latitudinal asynchroneity in the climate evolution of this continent. 相似文献
Three different techniques used tomeasure atmospheric formaldehyde were compared duringa field campaign carried out at a clean maritime siteon the West coast of Ireland. Two spectroscopictechniques Differential Optical AbsorptionSpectroscopy (DOAS) and Tunable Diode Laser AbsorptionSpectroscopy (TDLAS), together with a glass coil/Hantzschreaction/fluorescence technique, wereemployed for measurements of atmospheric formaldehydeof the order of a few hundred pptv. The betteragreement was observed between the fluorescence andDOAS instruments.Two DOAS instruments were compared to the glasscoil/Hantzsch reaction/fluorescence technique at asemi-polluted site on the North Norfolk coast, U.K.,where concentrations of formaldehyde were observed atlevels up to 4 ppbv. A very good agreement wasobserved between the two instruments.The glass coil/Hantzsch reaction/fluorescence and theTDLAS instruments were also deployed simultaneously inorder to measure indoor air inside a mobile laboratorylocated at the Imperial College Silwood Park site nearAscot, U.K. The doors of the mobile laboratory wereleft open in order to obtain the backgroundformaldehyde concentrations. Closing them afterwardsallowed us to observe the increase in concentrationsas a result of indoor emissions. The agreement betweenthe two instruments was outstanding (correlationcoefficient was 99%).The results from this study showed that of the fourinstruments included in this intercomparison the glasscoil/Hantzsch reaction/fluorescence technique provedthe most suitable for continuous measurements offormaldehyde in the background atmosphere. 相似文献
Fuel prices in 2006 continued at record levels, with uranium continuing upward unabated and coal, SO2 emission allowances, and natural gas all softening. This softening did not continue for natural gas, however, whose prices
rose, fell and rose again, first following weather influences and, by the second quarter of 2007, continuing at high levels
without any support from fundamentals. This article reviews these trends and describes the remarkable increases in fuel expenses
for power generation. By the end of 2005, natural gas claimed 55% of annual power sector fuel expenses, even though it was
used for only 19% of electric generation. Although natural gas is enormously important to the power sector, the sector also
is an important driver of the natural gas market—growing to over 28% of the market even as total use has declined. The article
proceeds to discuss globalization, natural gas price risk, and technology developments. Forces of globalization are poised
to affect the energy markets in new ways—new in not being only about oil. Of particular interest in the growth of intermodal
traffic and its a little-understood impacts on rail traffic patterns and transportation costs, and expected rapidly expanding
LNG imports toward the end of the decade. Two aspects of natural gas price risk are discussed: how understanding the use of
gas in the power sector helps define price ceilings and floors for natural gas, and how the recent increase in the natural
gas production after years of record drilling could alter the supply–demand balance for the better. The article cautions,
however, that escalation in natural gas finding and development costs is countering the more positive developments that emerged
during 2006. Regarding technology, the exploitation of unconventional natural gas was one highlight. So too was the queuing
up of coal-fired power plants for the post-2010 period, a phenomenon that has come under great pressure with many consequences
including increased pressures in the natural gas market. The most significant illustration of these forces was the early 2007
suspension of development plans by a large power company, well before the Supreme Court’s ruling on CO2 as a tailpipe pollutant and President Bush’s call for global goals on CO2 emissions.
This issue of the Journal of Atmospheric Chemistry contains a series of contributions describing recent developments in our understanding of the heterogeneous and homogeneous chemistry of reactive halogen compounds in the lower Troposphere. Twelve papers describe recent results in this very active area of research, were reported at the Annual Assembly of the European Geophysical Society 1998 in Nice, France, 20-24 April 1998. Considerable progress is documented on the elucidation of the various processes involved in the sources, transformation pathways and chemical consequences of the Reactive Halogen Species (RHS) in the troposphere. 相似文献
