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741.
A. Bregman F. Arnold V. Bürger H. Fisher J. Lelieveld B. A. Scheeren J. Schneider P. C. Siegmund J. Ström A. Waibel W. M. F. Wauben 《Journal of Atmospheric Chemistry》1997,26(3):275-310
In situ aircraft measurements of O3, CO,HNO3, and aerosol particles are presented,performed over the North Sea region in the summerlower stratosphere during the STREAM II campaign(Stratosphere Troposphere Experiments by AircraftMeasurements) in July 1994. Occasionally, high COconcentrations of 200-300 pbbv were measured in thelowermost stratosphere, together with relatively highHNO3 concentrations up to 1.6 ppbv. The particlenumber concentration (at standard pressure andtemperature) between 0.018-1 mg src="/content/u1770n0262861812/xxlarge956.gif" alt="mgr" align="MIDDLE" BORDER="0">m decreased acrossthe tropopause, from >1000 cm-3 in the uppertroposphere to <500 cm-3 in the lowermoststratosphere. Since the CO sources are found in thetroposphere, the elevated CO mixing ratios areattributed to mixing of polluted tropospheric air intothe lowermost extratropical stratosphere. Further wehave used a chemical model to illustrate that nitrogenoxide reservoir species (mainly HNO3) determinethe availability of NOx (=NO + NO2) andtherefore largely control the total net O3production in the lower kilometers of thestratosphere. Model simulations, applying additionalNOx perturbations from aircraft, show that theO3 production efficiency of NOx is smallerthan previously assumed, under conditions withrelatively high HNO3 mixing ratios, as observedduring STREAM II. The model simulations furthersuggest a relatively high O3 productionefficiency from CO oxidation, as a result of therelatively high ambient HNO3 and NOxconcentrations, implying that upward transport of COrich air enhances O3 production in the lowermoststratosphere. Analysis of the measurements and themodel calculations suggest that the lowermoststratosphere is a transition region in which thechemistry deviates from both the upper troposphere andlower stratosphere. 相似文献
742.
Judit Bartholy Rita Pongrácz Margit Pattantyús-Ábrahám 《Theoretical and Applied Climatology》2009,96(1-2):133-144
Midlatitude cyclones are analyzed on a selected region covering most of southern Europe and the western part of the Mediterranean Sea (35–50°N, 10°W–25°E). On the basis of mean sea level pressure fields of the ECMWF (European Centre for Medium-range Weather Forecast) Reanalysis Dataset (ERA-40), detailed evaluation of Mediterranean cyclones is accomplished for the period between 1957 and 2002 on a 1° horizontal resolution grid. Cyclone centers are identified and their paths are tracked with a 6-h time step (using 00 UTC, 06 UTC, 12 UTC, and 18 UTC). Decadal, annual, and seasonal statistical analysis of cyclone tracks includes the study of the genesis, frequency, and activity of the Mediterranean cyclones as well as the variability of cyclone tracks. The results suggest that the cyclone frequency in the western Mediterranean region increased in summer and autumn, and decreased in winter and spring. A special belt-shaped area is identified, which plays a special role in cyclogenesis, and also, the cyclone tracks often remain within this belt. An overall decreasing trend is detected in winter and spring in the entire Mediterranean belt, while cyclone frequency increased in autumn. The largest positive and negative trend coefficients are identified in summer. 相似文献
743.
744.
Role of carbonates in mitigation of metal release from mining waste. Evidence from humidity cells tests 总被引:7,自引:0,他引:7
&#8194;Leaching of two contrasting types of sulphidic tailings in humidity cells has been performed. The release of heavy metals
and the oxidation rate have been studied. Tailings from the Laver mine contain a few percent sulphides and lack carbonates,
whereas tailings from the Stekenjokk mine are both sulphide- and carbonate-rich. The results showed that in the leachates
from the Laver samples, the metal concentrations increased and pH decreased with time, indicating an increased oxidation rate.
In the Stekenjokk samples, pH remained high during the experiment, thereby keeping the metal concentrations low in the leachates.
The oxidation rate also decreased with time, probably due to Fe-hydroxide coatings on sulphide surfaces. The results show
that addition of carbonates and the maintenance of a high pH not only reduce the solubility of heavy metals, but also decrease
the oxidation rate of sulphides.
Received: 20 January 1998 · Accepted: 2 April 1998 相似文献