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1.
Vegetable Crops for Biomonitoring Lead and Cadmium Deposition   总被引：5，自引：0，他引：5  
Leafy vegetables are of particular interest for the active biomonitoring of the heavy metal deposition in the environment. The leaves accumulate the deposited airborne trace elements, however, they are also influenced by soilborne metals. The level of root uptake and accumulation depends on the element concerned and specific plant characteristics that influence the sensitivity of the biomonitoring system to a large extend. Standardization of the soil substrate and a precise estimation of the root uptake are very important in order to improve the sensitivity of biomonitoring. Spinach (Spinacea oleracea), lettuce (Lactuca sativa), endive (Cichorium endivia) and lambs lettuce (Valerianella locusta), grown in containers filled with a common peat soil and supplied with a semi-automatic watering system, were successfully used as bioaccumulators for the Cd and Pb deposition in gardens of an industrial and a residential area. Comparisons were made between the Cd and Pb contents in the crops and the deposition flux measured with NILU particulate fallout collectors in order to determine the accumulation efficiency of each crop. The correlations found were very useful to estimate the tolerable dust deposition levels with reference to the EU Guideline for maximum levels of contaminants in leafy vegetables. Exposure of the crops in open-top chambers, which were supplied with filtered air, (provided with a roof), proved that the Pb dust deposition significantly increases the normal concentration in the vegetables from the reference area, whereas the cadmium deposition was too low to be measured biologically. Comparisons of exposure of the crops to ambient air with or without chamber enclosure, and in open-top chambers with filtered air allowed to determine the normal metal concentrations and to estimate the biological detection limits.  相似文献   

2.
Many lichens are very sensitive to air pollution due to their symbiotic nature. However, they are generally less sensitive to toxic effects of trace elements; therefore they can be used as accumulator organisms for estimating concentrations of these elements in the environment. Heavy metal accumulation in lichens is a commonly used bioindication method for assessing heavy metal ambient levels. An active biomonitoring method was used for the determination of short-term accumulation of zinc, lead, arsenic and cadmium by epiphytic lichens transplanted at different localities in Slovenia polluted by heavy metals. The atomic absorption spectrophotometry method was used for the determination of heavy metal content in lichen thalli. The content of heavy metals in lichens collected in the background area with clean air (Rogla, Pohorje Mountains) was used as the reference value. Lichens were transplanted from Rogla using the branch transplantation technique for a period of 6 months in the surroundings of Slovenian thermal power plants (Velenje, otanj, Zavodnje, Veliki Vrh, Vnajnarje, and Dobovec) and close to the lead and zinc ore smelter at erjav. The monthly accumulation of heavy metals was comparable within years at selected locations. Heavy metal pollution was the highest at erjav despite of remediation of lead and zinc ore smelter. The monthly accumulation of all four heavy metals was statistically significantly higher in lichens exposed at erjav than at other localities.  相似文献   

3.
Weekly bulk aerosol samples collected at Funafuti, Tuvalu (8°30S, 179°12E), American Samoa (14°15S, 170°35W), and Rarotonga (21°15S, 159°45W), from 1983 through most of 1987 have been analyzed for nitrate and other constituents. The mean nitrate concentration is about 0.11 g m–3 at each of these stations: 0.107±0.011 g m–3 at Funafuti; 0.116±0.008 at American Samoa; and 0.117±0.010 at Rarotonga. Previous measurements of mineral aerosol and trace metal concentrations at American Samoa are among the lowest ever recorded for the near-surface troposphere and indicate that this region is minimally affected by transport of soil material and pollutants from the continents. Consequently, the nitrate concentration of 0.11 g m–3 can be regarded as the natural level for the remote marine boundary layer of the tropical South Pacific Ocean. In contrast, over the tropical North Pacific which is significantly impacted by the transport of material from Asia and North America, the mean nitrate concentrations are about three times higher, 0.29 and 0.36 g m–3 at Midway and Oahu, respectively. The major sources of the nitrate over the tropical South Pacific are still very uncertain. A very significant correlation between the nitrate concentrations at American Samoa and the concentrations of 210Pb suggests that transport from continental sources might be important. This continental source could be lightning, which occurs most frequently over the tropical continents. A near-zero correlation with 7Be indicates that the stratosphere and upper troposphere are probably not the major sources. A significant biogenic source would be consistent with the higher mean nitrate concentrations, 0.16 to 0.17 g m–3, found over the equatorial Pacific at Fanning Island (3°55N, 159°20W) and Nauru (0°32S, 166°57E). The lack of correlation between nitrate and nss sulfate at American Samoa does not necessarily preclude an important role for marine biogenic sources.  相似文献   

4.
Six locations across mainland Portugal were selected for exposing Parmelia sulcata, for a one-year period (8 months for one site), with simultaneous measurement of total (dry + wet) deposition (one-month periods). The exposed lichens and the total (dry + wet) deposition were analysed for cobalt contents by INAA (instrumental neutron activation analysis) and ICP-MS (inductively coupled plasma mass spectroscopy), respectively. The designated wet deposition was evaluated through the collected water volume; the designated dry deposition was assessed after the (dried) residual mass of the wet deposition. An excellent agreement between Co contents in exposed lichens and the cumulative (1) Co contents in the dry deposition, (2) dry deposition, and (3) wet deposition has been found for the locations with alternate drought and precipitation months, high dry deposition, and high Co contents in the latter. Continuous rainfall was found to hinder the Co accumulation in the lichen due to its release from the lichen and/or lower Co contents in the dry deposition. At three locations, P. sulcata Co contents, after subtraction of the background (before exposure), equalled or exceeded the Co contents in the cumulative dry deposition at the end of the exposure time. The optimal exposure period for this species likely depends on the exposure conditions.  相似文献   

5.
Frequent fog severely restricts evaporation from blanket bogs in Newfoundland because it more than halves the radiant energy input, and it eliminates the vapor pressure deficit, resulting in evaporation at the equilibrium rate (average = 0.99 during fog). During these periods, there is no surface resistance to evaporation because the bog has been wetted by fog drip, and although the latent heat flux dominates over sensible heat (average = 0.8), both are small. In contrast, the surface dries during clear periods, increasing the surface resistance to evaporation so that sensible heat becomes more important ( = 1.05). When the mosses are dry, evaporation is below the equilibrium rate ( = 0.87), although the higher available energy ensures that actual evaporation is higher. During clear periods, daily evaporation averaged 2.5 mm, compared to 1.1 and 0.7 mm for fog and rain, respectively. The suppressed evaporation at this site is important in maintaining appropriate hydrological conditions for blanket bog development.  相似文献   

6.
Parameterization of evaporation from a non-plant-covered surface is very important in the hierarchy strategy of modelling land surface processes. One of the representations frequently used in its computation is the resistance formulation. The performance of the evaporation schemes using the , , and their combination resistance approaches to parameterize evaporation from bare soil surfaces is discussed. For that purpose, the nine schemes, based on a different dependence of and on volumetric soil moisture content and its saturated value, are used.The tests of performances of the considered schemes are based on time integrations by the land surface module (BARESOIL) using observed data. The 23 data sets at a bare surface experimental site in Rimski anevi, Yugoslavia on chernozem soil, were used for the resistance algorithm evaluation. The quality of the schemes was compared with the observed values of the latent heat flux using several statistical parameters.  相似文献   

7.
Summary ¶In order to better understand land-atmosphere interactions and increase the predictability of climate models, it is important to investigate the role of forest representation in climate modeling. Corresponding to the big-leaf model commonly employed in land surface schemes to represent the effects of a forest, a so called big-tree model, which uses multi-layer vegetation to represent the vertical canopy heterogeneity, was introduced and incorporated into the National Center for Atmospheric Research (NCAR) regional climate model RegCM2, to make the vegetation model more physically based. Using this augmented RegCM2 and station data for China during 1991 Meiyu season, we performed 10 experiments to investigate the effects of the application of the big-tree model on the summer monsoon climate.With the big-tree model incorporated into the regional climate model, some climate characteristics, e.g. the 3-month-mean surface temperature, circulation, and precipitation, are significantly and systematically changed over the model domain, and the change of the characteristics differs depending on the area. Due to the better representation of the shading effect in the big-tree model, the temperature of the lower layer atmosphere above the plant canopy is increased, which further influences the 850hPa temperature. In addition, there are significant decreases in the mean latent heat fluxes (within 20–30W/m2) in the three areas of the model domain.The application of the big-tree model influences not only the simulated climate of the forested area, but also that of the whole model domain, and its impact is greater on the lower atmosphere than on the upper atmosphere. The simulated rainfall and surface temperature deviate from the originally simulated result and are (or seem to be) closer to the observations, which implies that an appropriate representation of the big-tree model may improve the simulation of the summer monsoon climate.We also find that the simulated climate is sensitive to some big-tree parameter values and schemes, such as the shape, height, zero-plane displacement height and mixing-length scheme. The simulated local/grid differences may be very large although the simulated areal-average differences may be much lower. The area-average differences in the monthly-mean surface temperature and heat fluxes can amount to 0.5°C and 4W/m2, respectively, which correspond to maximum local/grid differences of 3.0°C and 40W/m2 respectively. It seems that the simulated climate is most sensitive to the parameter of the zero-plane displacement among the parameters studied.  相似文献   

8.
Eighteen soil samples from central Sudan were fractionated by dry sieving ina size fraction from <45 m to >300 m while aerosols generatedfrom these soils were fractionated in the particle size range from 0.25 mto >16 m. The elemental concentrations of soil samples were determinedby energy-dispersive X-ray fluorescence, while the elemental concentrationsof generated aerosols were analysed by particle-induced X-ray emission. Theelements Al, K and Rb show a slight positive fractionation with decreasingparticle size throughout the particle size range studied. The concentrationsof Ca, Mn, Fe, Sr and Y are maximum in the small soil size fraction (<45m) and decrease for the coarse soil size fractions, while in the mineralaerosol particle sizes (0.25– > 16 m) the concentrations remainmore or less constant. The size distributions for Cr, Ti and Zr show a maximumin the particle size range 45–100 m and the concentrations of theseelements decrease sharply in the aerosol fraction down to 16 m to remainconstant in the smaller aerosol fractions.Enrichment factors for the elements were calculated relative to five referencematerials: average crustal rock, average soil, the investigated Sahara bulksoil, the finest fraction of this soil and the aerosol generated from thissoil, and using four reference elements: Al, Si, Ti and Fe. The enrichmentfactors were found to vary significantly depending on the choice of thereference material or the reference element. The enrichment factors for theSudan mineral aerosol were almost identical to those for Khartoum atmosphericaerosol but different from those for Namib mineral aerosol and Israelatmospheric aerosol following dust storms. Multivariate display methods(cluster analysis, principal component analysis and linear discriminantanalysis) were applied to the element ratios in the mineral aerosol from theSahara and Namib and this showed that these mineral aerosol can bedifferentiated into different groups. An attempt was also made to relate themineral aerosol to its parent soil through the use of these multivariatetechniques and the elemental ratios in both the mineral aerosols and the bulksoils (Namib and Sahara). It was also possible using the elemental ratios andthe multivariate display methods to associate the crustal component to themineral aerosol generated from the Sahara.  相似文献   

9.
Summary Mechanisms associated with Alpine lee cyclogenesis during the early phase of their generation are investigated using a variational quasigeostrophic filter technique. It was possible to extract the quasigeostrophic signal from the available analyzed real data set.The results presented here are for the 11–12 March 1982, an example of so-called orographically induced lee cyclogenesis. Non-quasigeostrophic fields, calculated as a difference between observations and the quasigeostrophic fields, show significant magnitudes indicating the possible importance of non-quasigeostrophic processes. A dipole structure in the residual geopotential field was observed, similar to the results of numerical model experiments. Also, a strong upper-level non-quasigeostrophic divergence was found in the Alpine region 24 hours prior to lee cyclogenesis, lasting for 6–12 hours. On the other hand, quasigeostrophic results indicate only a local effect of mountain slopes, suggesting possibly a dominant role of the low-level blocking. A hypothetical scenario of Alpine lee cyclogenesis is proposed, based on results obtained here.With 14 Figures  相似文献   

10.
Parameterizing turbulent diffusion through the joint probability density   总被引：3，自引：3，他引：0  
The convective mass flux parameterization often used in meteorological modeling expresses the vertical flux of a transported scalar as proportional to the product of the difference in mean values of the scalar in updrafts and downdrafts and their characteristic velocity. The proportionality factor is a constant to be specified. We show that this proportionality factor also appears in the relaxed eddy accumulation technique of Businger and Oncley. That associates the surface-layer flux of a scalar with the product of the standard deviation of vertical velocity and the mean concentration difference between updrafts and downdrafts.We show that this constant (b) is determined uniquely by the joint probability density (jpd) of vertical velocity and the scalar. Using large-eddy simulation, we generate this jpd for a conservative scalar diffusing through a convective boundary layer. It has quite different forms in top-down and bottom-up diffusion geometries. The bottom-up jpd is fairly well represented by a jointly Gaussian form and implies b ~ 0.6, in good agreement with the surface-layer value reported by Businger and Oncley. The top-down jpd is strikingly non-Gaussian and gives b ~ 0.47. Updrafts carry the bulk of the scalar flux - 70% in the bottom-up case, 60% in the top-down case.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

11.
Periodicity of annual precipitation in different climate regions of Croatia   总被引：1，自引：1，他引：0  
Summary The periodicity of a 100-year series of annual precipitation over Croatia has been studied by means of power spectrum analysis at 3 stations representing the different climatic regions of Croatia. The annual precipitation variance spectra in the continental lowland (Osijek) and at the north East Adriatic coast (Crikvenica) can be fitted by Markov white noise continuum, but in the transitional region between the Dinaric Alps and the Pannonian lowland (Zagreb-Gri) a non-white noise continuum is necessary. Quasi-periodic oscillations appear in two spectra ranges: short (2.2 and 4.7 years) and medium (25.0 and 33.3 years). These results are compared with those of other authors for other parts of the Europe.With 2 Figures  相似文献   

12.
Summary The first GCM climate change projections to include dynamic vegetation and an interactive carbon cycle produced a very significant amplification of global warming over the 21st century. Under the IS92a business as usual emissions scenario CO2 concentrations reached about 980ppmv by 2100, which is about 280ppmv higher than when these feedbacks were ignored. The major contribution to the increased CO2 arose from reductions in soil carbon because global warming is assumed to accelerate respiration. However, there was also a lesser contribution from an alarming loss of the Amazonian rainforest. This paper describes the phenomenon of Amazonian forest dieback under elevated CO2 in the Hadley Centre climate-carbon cycle model.  相似文献   

13.
This paper describes the similarity between atmospheric fluctuations of carbon dioxide, water vapor and temperature using data which cover a wide range of instability (0.02 < < 10). The is the Monin-Obukhov stability parameter including the humidity effect.The spectral analysis shows that the coherency between fluctuations of carbon dioxide and water vapor or temperature is very close to unity, and the phase difference is basically out of phase for whole frequency ranges analyzed. The stability dependence of the normalized standard deviation of carbon dioxide is very similar to those of water vapor and temperature. The normalized standard deviation is about 2.5 under near neutral conditions, and it decreases with increasing instability following the -1/3; power law as (-)-1/3. The skewness factors of carbon dioxide, water vapor and temperature show a systematic departure with increasing instabilities for 0.02 < s- < 1, and level off at high instabilities for 1 < -\s < 10. The stability dependence of the flatness factors is not so clear as that noted in the standrard deviation and skewness factors. Dissipation rates of carbon dioxide, water vapor and temperature variance are well related to the spectral peak wavelength. This seems to be real since the local production and local dissipation rates are the main terms, almost balancing one another in the variance budget equations for scalar entities.  相似文献   

14.
Surface-Layer Fluxes in Stable Conditions   总被引：2，自引：2，他引：0  
Micrometeorological tower data from the Microfronts experiment are analyzed. Scale-dependencies of the flux and flux sampling error are combined to automatically determine Reynolds turbulence cut-off time scales for computing fluxes from time series. The computed downward heat flux at the 3 m height averaged over nine nights with 7.3 hours each night is 20% greater than the downward heat flux computed at the 10 m height. In contrast, there is only a 1.2% difference between 3 m and 10 m heat fluxes averaged over daytime periods, and there is less than a 2% difference between 3 m and 10 m momentum fluxes whether averaged over nighttime or daytime periods.Stability functions, M(z/L) and H(z/L) are extended to z/L up to 10, where z is the observational height and L is the Obukhov length. For 0.01 < z/L < 1 the estimated functions generally agree with Businger-Dyer formulations, though the H estimates include more scatter compared to the M estimates. For 1 < z/L < 10, the flux intermittency increases, the flux Richardson number exceeds 0.2, and the number of flux samples decreases. Nonetheless the estimates of the stability function M based on 3-m fluxes are closer to the formula proposed by Beljaars and Holtslag in 1991 while the M functions based on 10-m fluxes appears to be closer to the formula proposed by Businger et al. in 1971. The stability function H levels off at z/L = 0.5.  相似文献   

15.
Summary The sign of the vector representing the atmospheric electric field has recently been subject of debate. For the sake of clarity, it is recommended to refer only to a normal or reversed clear-weather potential gradient.
Zusammenfassung Eine in letzter Zeit entstandene Diskussion darüber, welches Vorzeichen dem Vektor des atmosphärisch-elektrischen Feldes bzw. des Potentialgefälles zuerkannt werden soll, erscheint wenig sinnvoll. Zur Vermeidung künftiger Unklarheiten wird empfohlen, bei der atmosphärischen Elektrizität nur von normaler Schönwetterrichtung und umgekehrter Schönwetterrichtung des Feldes bzw. des Potentialgefälles zu sprechen.
Résumé Une récente discussion a porté sur le signe qui devait être attribué au vecteur du champ électrique atmosphérique respectivement de son gradient de potentiel. On recommande, pour éviter à l'avenir toute confusion, de ne parler en électricité atmosphérique et quand il s'agit du champ ou du gradient de potentiel, que de «direction normale de beau temps» et de «direction inversée de beau temps».

Dedicated to Dr.W. Mörikofer on the occasion of his 70th birthday.  相似文献   

16.
Experimental evidence indicates that the diurnal behaviour of the fluxes of heat into the ground and into the atmosphere versus the net flux of radiation can be modelled by closed curves, the hourly values folowing one another in either a clockwise or counter clockfashion. A general formulation to express the different heat fluxes as a function of net radiation is proposed. This relationship between the different heat fluxes and can be expressed as a sum of three terms: the first indicates a direct proportionality to , the second gives the deviation from linearity and depends on /t, and the third gives the value of the flux when = 0. The formulae are then expressed as a function of time and the ratios between the heat fluxes and are evaluated. A comparison with the approximations generally used shows that the latter may be considered as particular cases of the more general equations proposed here.  相似文献   

17.
Summary ¶Two cyclonic vortices close to each other, a binary cyclone or binary system, tend to rotate cyclonically relative to one another and to merge, i.e. the Fujiwhara effect. The point vortex model that represents barotropic binary cyclones predicts their rotation features as follows. The rotation rate is proportional linearly to the sum of the cyclones intensities and inversely to the square of their separation distance while the more intense cyclone rotates slower. Our earlier observational analysis of 1423 mid-latitude binary cyclones (Ziv and Alpert, 1995) showed a reasonable fit to theory, except for the absence of a correlation between individual speeds and intensities within the binary systems, and a reversal of the inverse rotation-separation relationship at the range of 1400–1800km.This study is the first attempt to describe the mid-latitude binary systems using potential vorticity concepts (PV thinking), which implies that a binary interaction takes place between the 3-D flow patterns induced by upper-PV or surface-thermal anomalies rather than by the surface cyclones alone. It is argued that the upper-anomalies dominate the rotation process, and hence the rotational speeds of the interacting surface cyclones are more closely correlated with the relative intensities of their corresponding upper-level anomalies rather than with their own intensities, as reflected in weather charts. Data analysis indicates that mid-latitude binary cyclones are normally associated with at least one upper-PV anomaly. This explains the absence of a correlation between the rotation speed and the intensity of the surface cyclones there.A unique type of a mid-latitude binary system is identified, in which one cyclone coincides with an upper major PV-anomaly and the other moves along the periphery of the former. Such a binary system is entitled here the Contact Binary System (CBS), in contrast with remote interacting systems implied by the point vortex theory.Analytical considerations yield an increase in the rotation rate with separation for CBSs of separation smaller than 1000–1500km, in contrast to the normal decrease with R 2. The contribution of CBSs is suggested here to explain the abnormal increase in rotation rate at 1400–1900km range.  相似文献   

18.
Summary The Balkan Peninsula is situated in the impact zone of Saharan dust storms. The case of Saharan dust transport to Belgrade in the period of 14–17 April 1994 is analyzed using the Eta model for synoptic and meso scale processes. Air back trajectories are calculated at six model levels from 434 up to 5129m with horizontal grid resolutions of 1°×1° and 10×10. Following cyclonic circulation the dust was picked up from North Africa, and transported over Mediterranean. Simultaneously, according to the analysis of the three lowest trajectories, transport of trace metals from Macedonia and southern Serbia by the Koshava wind might be dominant in the observed episode. Turbulent flow enhanced the coagulation process of initially clean dust particles with particles containing Pb and Cd. The coagulation and scavenging processes below and in clouds increased deposition rates of Pb and Cd in Belgrade in the course of wet removal, and consequently trough resuspension processes. Dry deposition samples contained characteristic particles up to 30µm in diameter with Fe content of 11 to 15 atomic% and significant ratio Si/Fe of 3 to 5, determined for selected single particles by the SEM/EDX method. Following dry and wet deposition of Cd and Pb, a residual effect of dustfall is noticed throughout the vegetational period.  相似文献   

19.
Cloud water and interstitial aerosol samples collected at Mt. Sonnblick (SBO) were analyzed for sulfate and aerosol carbon to calculate in-cloud scavenging efficiencies. Scavenging efficiencies for sulfate (SO) ranged from 0.52 to 0.99 with an average of 0.80. Aerosol carbon was scavenged less efficiently with an average value (AC) of 0.45 and minimum and maximum values of 0.14 and 0.81, respectively. Both SO and AC showed a marked, but slightly different, dependence on the liquid water content (LWC) of the cloud. At low LWC, SO increased with rising LWC until it reached a relatively constant value of 0.83 above an LWC of 0.3 g/m3. In the case of aerosol carbon, we obtained a more gradual increase of AC up to an LWC of 0.5 g/m3. At higher LWCs, _ remained relatively constant at 0.60. As the differences between SO and A varied across the LWC range observed at SBO, we assume that part of the aerosol carbon was incorporated into the cloud droplets independently from sulfate. This hypothesis is supported by size classified aerosol measurements. The differences in the size distributions of sulfate and total carbon point to a partially external mixture. Thus, the different chemical nature and the differences in the size and mixing state of the aerosol particles are the most likely candidates for the differences in the scavenging behavior.  相似文献   

20.
Flux densities of carbon dioxide were measured over an arid, vegetation-free surface by eddy covariance techniques and by a heat budget-profile method, in which CO2 concentration gradients were specified in terms of mixing ratios. This method showed negligible fluxes of CO2, consistent with the bareness of the experimental site, whereas the eddy covariance measurements indicated large downward fluxes of CO2. These apparently conflicting observations are in quantitative agreement with the results of a recent theory which predicts that whenever there are vertical fluxes of sensible or latent heat, a mean vertical velocity is developed. This velocity causes a mean vertical convective mass flux (= cw for CO2, in standard notation). The eddy covariance technique neglects this mean convective flux and measures only the turbulent flux c w. Thus, when the net flux of CO2 is zero, the eddy covariance method indicates an apparent flux which is equal and opposite to the mean convective flux, i.e., c w = – c w. Corrections for the mean convective flux are particularly significant for CO2 because cw and c w are often of similar magnitude. The correct measurement of the net CO2 flux by eddy covariance techniques requires that the fluxes of sensible and latent heat be measured as well.  相似文献   

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