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1.
Errors in the estimation of CO2 surface exchange by open-path eddy covariance, introduced during the removal of density terms [Webb et al. Quart J Roy Meteorol Soc 106:85–100, (1980) - WPL], can happen both because of errors in energy fluxes [Liu et al. Boundary-Layer Meteorol 120:65–85, (2006)] but also because of inaccuracies in other terms included in the density corrections, most notably due to measurements of absolute CO2 density (ρ c ). Equations are derived to examine the propagation of all errors through the WPL algorithm. For an open-path eddy covariance system operating in the Sierra de Gádor in south-east Spain, examples are presented of the inability of an unattended, open-path infrared gas analyzer (IRGA) to reliably report ρ c and the need for additional instrumentation to determine calibration corrections. A sensitivity analysis shows that relatively large and systematic errors in net ecosystem exchange (NEE) can result from uncertainties in ρ c in a semi-arid climate with large sensible heat fluxes (H s ) and (wet) mineral deposition. When ρc is underestimated by 5% due to lens contamination, this implies a 13% overestimation of monthly CO2 uptake.  相似文献   

2.
An instrument is developed for the measurement of peroxy radical using chemical amplification coupled with NO2-luminol chemiluminescence detection. The chain length of 147 ± 10 (1σ) is determined by an HO2 source that uses the photolysis of water vapor under 184.9 nm in air. A Nafion system equipped with a Nafion tube of ~2.2 mm external diameter and 350 mm length is employed in the PERCA instrument (Nafion-PERCA system). When flowing an air sample containing HO2 through the Nafion system, it is found that - 94.6 % of HO2 is removed. In contrast, only 17.8 % of RO2 radicals (a mixtures of CH3O2 and CH3C(O)O2 with a ratio of 1.1:0.9) are removed. The results indicate the Nafion system has a good selective removing performance of HO2 radical during the PERCA measurement. Therefore, the method could be applied to ambient and laboratory measurements of absolute concentrations of RO2 as well as the sum of HO2 and RO2.  相似文献   

3.
A box model is used to explore the detailed chemistry of C2 and C3 organic compounds in the marine troposphere by tracing the individual reaction paths resulting from the oxidation of ethane, ethene, acetylene, propane, propene and acetic acid. The mechanisms include chemical reactions in the gas phase and in the aqueous phase of clouds and aerosol particles at cloud level under conditions resembling those in the northern hemisphere. Organic hydroperoxides are found to be important intermediate products, with subsequent reactions leading partly to the formation of mixed hydroxy or carbonyl hydroperoxides that are readily absorbed into cloud water, where they contribute significantly to the formation of multifunctional organic compounds and organic acids. Organic hydroperoxides add little to the oxidation of sulfur dioxide dissolved in the aqueous phase, which is dominated by H2O2. Next to acetaldehyde and acetone, glycol aldehyde, glyoxal, methyl glyoxal and hydroxy propanone are prominent oxidation products in the gas and the aqueous phase. Acetaldehyde is not efficiently converted to acetic acid in clouds; the major local sources of acetic acid are gas-phase reactions. Other acids produced include hydroperoxy acetic, glycolic, glyoxylic, oxalic, pyruvic, and lactic acid. The mechanism of Schuchmann et al. (1985), which derives glycolic and glyoxylic acid from the oxidation of acetate, is found unimportant in the marine atmosphere. The principal precursors of glyoxylic acid are glyoxal and glycolic acid. The former derives mainly from acetylene and ethene, the latter from glycolaldehyde, also an oxidation product of ethene. The oxidation of glyoxylic acid leads to oxalic acid, which accumulates and is predicted to reach steady state concentrations in the range 30–90 ng m−3. This is greater, yet of the same magnitude, than the concentrations observed over the remote Pacific Ocean.  相似文献   

4.
A field-based intercomparison study of a(DOAS) instrument (OPSIS AB, Sweden) andcommercial Differential Optical Absorption Spectroscopydifferent point-sample monitoring techniques (PM, basedon an air monitoring station, an air monitoring vehicle, and various chemical methods) was conducted inBeijing from October 1999 to January 2000. The mixing ratios of six trace gases including NO, NO2, SO2,03, benzene, and toluene were monitored continuously during the four months. A good agreement betweenthe DOAS and PM data was found for NO2 and SO2. However, the concentrations of benzene, toluene,and NO obtained by DOAS were significantly lower than those measured by the point monitors. Theozone levels monitored by the DOAS were generally higher than those measured by point monitors. Theseresults may be attributed to a strong vertical gradient of the NO-O3-NO2 system and of the aromatics atthe measurement site. Since the exact data evaluation algorithm is not revealed by the manufacturer ofthe DOAS system, the error in the DOAS analysis can also not be excluded.  相似文献   

5.
Ocean emissions of inorganic and organic iodine compounds drive the biogeochemical cycle of iodine and produce reactive ozone-destroying iodine radicals that influence the oxidizing capacity of the atmosphere. Di-iodomethane (CH2I2) and chloro-iodomethane (CH2ICl) are the two most important organic iodine precursors in the marine boundary layer. Ship-borne measurements made during the TORERO (Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOC) field campaign in the east tropical Pacific Ocean in January/February 2012 revealed strong diurnal cycles of CH2I2 and CH2ICl in air and of CH2I2 in seawater. Both compounds are known to undergo rapid photolysis during the day, but models assume no night-time atmospheric losses. Surprisingly, the diurnal cycle of CH2I2 was lower in amplitude than that of CH2ICl, despite its faster photolysis rate. We speculate that night-time loss of CH2I2 occurs due to reaction with NO3 radicals. Indirect results from a laboratory study under ambient atmospheric boundary layer conditions indicate a k CH2I2+NO3 of ≤4 × 10?13 cm3 molecule?1 s?1; a previous kinetic study carried out at ≤100 Torr found k CH2I2+NO3 of 4 × 10?13 cm3 molecule?1 s?1. Using the 1-dimensional atmospheric THAMO model driven by sea-air fluxes calculated from the seawater and air measurements (averaging 1.8 +/? 0.8 nmol m?2 d?1 for CH2I2 and 3.7 +/? 0.8 nmol m?2 d?1 for CH2ICl), we show that the model overestimates night-time CH2I2 by >60 % but reaches good agreement with the measurements when the CH2I2 + NO3 reaction is included at 2–4 × 10?13 cm3 molecule?1 s?1. We conclude that the reaction has a significant effect on CH2I2 and helps reconcile observed and modeled concentrations. We recommend further direct measurements of this reaction under atmospheric conditions, including of product branching ratios.  相似文献   

6.
A detailed photochemical box model was used to investigate the key reaction pathways between OH, HO2 and RO2 radicals during the summer and winter PUMA field campaigns in the urban city-centre of Birmingham in the UK. The model employed the most recent version of the Master Chemical Mechanism and was constrained to 15-minute average measurements of long-lived species determined in situ at the site. The results showed that in the summer, OH initiation was dominated by the reactions of ozone with alkenes, nitrous acid (HONO) photolysis and the reaction of excited oxygen atoms atoms with water. In the winter, ozone+alkene reactions were the primary initiation route, with a minor contribution from HONO photolysis. Photolysis of aldehydes was the main initiation route for HO2, in both summer and winter. RO2 initiation was dominated by the photolysis of aldehydes in the summer with a smaller contribution from ozone+alkenes, a situation that was reversed in the winter. At night, ozone+alkene reactions were the main radical source. Termination, under all conditions, primarily involved reactions with NO (OH) and NO2 (OH and RCO3). These results demonstrate the importance of ozone+alkene reactions in urban atmospheres, particularly when photolysis reactions were less important during winter and at nighttime. The implications for urban atmospheric chemistry are discussed.  相似文献   

7.
Climate is simulated for reference and mitigation emissions scenarios from Integrated Assessment Models using the Bern2.5CC carbon cycle–climate model. Mitigation options encompass all major radiative forcing agents. Temperature change is attributed to forcings using an impulse–response substitute of Bern2.5CC. The contribution of CO2 to global warming increases over the century in all scenarios. Non-CO2 mitigation measures add to the abatement of global warming. The share of mitigation carried by CO2, however, increases when radiative forcing targets are lowered, and increases after 2000 in all mitigation scenarios. Thus, non-CO2 mitigation is limited and net CO2 emissions must eventually subside. Mitigation rapidly reduces the sulfate aerosol loading and associated cooling, partly masking Greenhouse Gas mitigation over the coming decades. A profound effect of mitigation on CO2 concentration, radiative forcing, temperatures and the rate of climate change emerges in the second half of the century.  相似文献   

8.
The heterogeneous interaction of nitrogen dioxide with ammonium chloride was investigated in a molecular diffusion tube experiment at 295–335 K and interpreted using Monte Carlo trajectory calculations. The surface residence time (τsurf) of NO2 on NH4Cl is equal to 15 μs at 295 K, increases with temperature up to 323 K (τsurf = 45 μs) and probably decreases beyond 323 K. The same experiment also yields uptake coefficients, γ, which are derived from the absolute number of surviving molecules effusing out of the diffusion tube. The rate of uptake of NO2 on NH4Cl followed a rate law first order in [NO2] and the uptake coefficient γ is equal to 7 × 10−5 at 295 K, increases with temperature up to 323 K (γ = 2.1 × 10−4) and probably decreases beyond 323 K. Nitrous acid, water and nitrogen were detected as products. From these products, it is concluded that the reaction of NO2 with NH4Cl is a reverse disproportionation reaction where two moles of NO2 result in ammonium nitrite, NH4NO2, as an intermediate, and nitryl chloride, NO2Cl. NH4NO2 decomposes in two pathways, one to nitrous acid, HONO and NH3, the other to nitrogen and water. The branching ratio for the production of HONO + NH3 to that of N2 + H2O is approximately 20 at 298 K and increases with increasing temperature.  相似文献   

9.
The kinetics of heterogeneous reactions of NO2 with 17 polycyclic aromatic hydrocarbons (PAHs) adsorbed on laboratory generated kerosene soot surface was studied over the temperature range (255–330) K in a low pressure flow reactor combined with an electron-impact mass spectrometer. The kinetics of soot-bound PAH consumption due to their desorption and reaction with NO2 were monitored using off-line HPLC measurements of their concentrations in soot samples as a function of reaction time, NO2 concentrations in the gas phase being analyzed by mass spectrometer. No measurable decay of PAHs due to the reaction with NO2 was observed under experimental conditions of the study (maximum NO2 concentration of 5.5 × 1014 molecule cm−3 and reaction time of 45 min), which allowed to determine the upper limits of the first-order rate constants for the heterogeneous reactions of 17 soot-bound PAHs with NO2: k < 5.0 × 10−5 s−1 (for most PAHs studied). Comparison of these results to previous studies carried on different carbonaceous substrates, showed that heterogeneous reactivity of PAHs towards NO2 is, probably, dependent on the substrate nature even for resembling, although different carbonaceous materials. Results show that particulate PAHs degradation by NO2 alone is of minor importance in the atmosphere  相似文献   

10.
Carbon dioxide (CO2) is an important greenhouse gas that influences regional climate through disturbing the earth’s energy balance. The CO2 concentrations are usually prescribed homogenously in most climate models and the spatiotemporal variations of CO2 are neglected. To address this issue, a regional climate model (RegCM4) is modified to investigate the non-homogeneous distribution of CO2 and its effects on regional longwave radiation flux and temperature in East Asia. One-year simulation is performed with prescribed surface CO2 fluxes that include fossil fuel emission, biomass burning, air–sea exchange, and terrestrial biosphere flux. Two numerical experiments (one using constant prescribed CO2 concentrations in the radiation scheme and the other using the simulated CO2 concentrations that are spatially non-homogeneous) are conducted to assess the impact of non-homogeneous CO2 on the regional longwave radiation flux and temperature. Comparison of CO2 concentrations from the model with the observations from the GLOBALVIEW-CO2 network suggests that the model can well capture the spatiotemporal patterns of CO2 concentrations. Generally, high CO2 mixing ratios appear in the heavily industrialized eastern China in cold seasons, which probably relates to intensive human activities. The accommodation of non-homogeneous CO2 concentrations in the radiative transfer scheme leads to an annual mean change of–0.12 W m–2 in total sky surface upward longwave flux in East Asia. The experiment with non-homogeneous CO2 tends to yield a warmer lower troposphere. Surface temperature exhibits a maximum difference in summertime, ranging from–4.18 K to 3.88 K, when compared to its homogeneous counterpart. Our results indicate that the spatial and temporal distributions of CO2 have a considerable impact on regional longwave radiation flux and temperature, and should be taken into account in future climate modeling.  相似文献   

11.
The choice of stabilization target for CO2 concentration depends on the following: what is considered to be dangerous anthropogenic interference with the climate system; the forcings that might arise from non-CO2 gases; and the climate sensitivity. These three factors are specified here probabilistically, as probability density functions (pdfs), and combined to produce a pdf for the CO2 concentration target. There is a probability of 17% that the stabilization target should be less than the present level, and the median target is 536 ppm. The effects of reducing the emissions of non-CO2 gases and/or implementing adaptation strategies are considered probabilistically and shown to alter these figures significantly.  相似文献   

12.
Products of the gas-phase reaction of the NO3 radical with thiophene have been investigated using different experimental systems. On the one hand, experiments have been conducted in our laboratory using two different methods, a Teflon static reactor coupled to a gas chromatograph combined with mass-spectrometry (GC-MS) and a discharge flow tube with direct MS spectroscopic detection. A qualitative analysis in these cases indicates that possible products for the reaction of thiophene+NO3 at room temperature include: sulphur dioxide, acetic and formic acids, a short-chain aldehyde, 2-nitrothiophene and 3-nitrothiophene. On the other hand, quantitative experiments have been performed in the European Photoreactor (EUPHORE) in Valencia, Spain. In this case, the major products were: HNO3 (≈80%), nitrothiophenes (≈30%), SO2 (≈20%), propanal (3%) and a fraction of particles (≈10%). The results obtained indicate that at least 70% of the reaction of NO3 with thiophene proceeds by an H-abstraction process at room temperature. The mechanism of the reaction studied is proposed on the basis of experimental results.  相似文献   

13.
The theoretical correction of CO2 fluxes for high frequency attenuation in closed-path systems was re-summarized and its applicability examined using both measurements obtained at an Asiaflux forest site and empirical transfer functions used in previous studies. For our measurement system, the theoretical transfer function was applicable to high frequency correction, even when condensation occurred in the sampling line. Further, in respect to some measurement systems described in previous studies, it was found that the theoretical function was potentially applicable along with the empirical functions used. Meanwhile, in some systems significant errors could not be resolved by re-estimation of the theories. In these systems, because of undefined buffering effects, the actual response lag time decided by the maximum covariance method or by measurement of the system response time using tracer gas was significantly different from the lag time calculated from the tube dimensions and the measured flow rate. If the average flow rate calculated by the actual lag time was used to determine the theoretical function, the theoretical function became closer to, and sometimes agreed with, the empirical function. Any remaining deviation from each function might be associated with pressure fluctuations, but this problem was unable to be examined here. The results suggested that an empirical formulation for each site is considered applicable rather than a theoretical approach, although the theories are being developed to practical application.  相似文献   

14.
Satellite measurements of tropospheric column O3 and NO2 in eastern and southeastern Asia are analyzed to study the spatial and seasonal characteristics of pollution in these regions. Tropospheric column O3 is derived from differential measurements of total column ozone from Total Ozone Mapping Spectrometer (TOMS), and stratospheric column ozone from the Microwave Limb Sounder (MLS) instrument on the Upper Atmosphere Research Satellite (UARS). The tropospheric column NO2 is measured by Global Ozone Monitoring Experiment (GOME). A global chemical and transport model (Model of Ozone and Related Chemical Tracers, version 2; MOZART-2) is applied to analyze and interpret the satellite measurements. The study, which is based on spring, summer, and fall months of 1997 shows generally good agreement between the model and satellite data with respect to seasonal and spatial characteristics of O3 and NO2 fields. The analysis of the model results show that the industrial emission of NOx (NO + NO2) contributes about 50%–80% to tropospheric column NO2 in eastern Asia and about 20%–50% in southeastern Asia. The contribution of industrial emission of NOx to tropospheric column O3 ranges from 10% to 30% in eastern Asia. Biomass burning and lightning NOx emissions have a small effect on tropospheric O3 in central and eastern Asia, but they have a significant impact in southeastern Asia. The varying effects of NOx on tropospheric column ozone are attributed to differences in relative abundance of volatile organic compounds (VOCs) with respect to total nitrogen in the two regions.  相似文献   

15.
Expedition data obtained in the coastal-shelf zone of the East Siberian Sea in September 2003, 2004, and 2008 are generalized. Studies of carbonate system in water and CO2 fluxes between ocean and atmosphere in this region confirmed that it was reasonable to divide the water area studied into two biogeochemical provinces and that the ecosystem of its coastal part is mainly of a heterotrophic nature. In different years, the extent of water supersaturation in carbon dioxide in the East Siberian Sea and the area of the CO2 release significantly changed. Geographic localization of the atmosphere action centers over the Arctic and their intensity were main determining factors; that told both on the formation of a basic character of the atmospheric and hydrological processes and on the dynamics of the CO2 exchange between water and air.  相似文献   

16.
A new complex earth system model consisting of an atmospheric general circulation model, an ocean general circulation model, a three-dimensional ice sheet model, a marine biogeochemistry model, and a dynamic vegetation model was used to study the long-term response to anthropogenic carbon emissions. The prescribed emissions follow estimates of past emissions for the period 1751–2000 and standard IPCC emission scenarios up to the year 2100. After 2100, an exponential decrease of the emissions was assumed. For each of the scenarios, a small ensemble of simulations was carried out. The North Atlantic overturning collapsed in the high emission scenario (A2) simulations. In the low emission scenario (B1), only a temporary weakening of the deep water formation in the North Atlantic is predicted. The moderate emission scenario (A1B) brings the system close to its bifurcation point, with three out of five runs leading to a collapsed North Atlantic overturning circulation. The atmospheric moisture transport predominantly contributes to the collapse of the deep water formation. In the simulations with collapsed deep water formation in the North Atlantic a substantial cooling over parts of the North Atlantic is simulated. Anthropogenic climate change substantially reduces the ability of land and ocean to sequester anthropogenic carbon. The simulated effect of a collapse of the deep water formation in the North Atlantic on the atmospheric CO2 concentration turned out to be relatively small. The volume of the Greenland ice sheet is reduced, but its contribution to global mean sea level is almost counterbalanced by the growth of the Antarctic ice sheet due to enhanced snowfall. The modifications of the high latitude freshwater input due to the simulated changes in mass balance of the ice sheet are one order of magnitude smaller than the changes due to atmospheric moisture transport. After the year 3000, the global mean surface temperature is predicted to be almost constant due to the compensating effects of decreasing atmospheric CO2 concentrations due to oceanic uptake and delayed response to increasing atmospheric CO2 concentrations before.  相似文献   

17.
Observational data from sonic anemometers are commonly rotated from sonic to streamline coordinates, a procedure that is called tilt correction. Tilt corrections are often used to post-process air velocity data collected from sonic anemometers to allow objective interpretation of air flow data relative to the Earth. Since streamline coordinates depend on dynamical characteristics of the flow, the tilt correction depends not only on temporal and spatial variations of the flow, but also on local circulations. We found that ensemble- averaged slope flows are approximately parallel to the terrain slope close to the ground within the canopy layer, but not above, due to the influence of the diurnal variation of local vertical circulations. As a result, the diurnal variation of the observed vertical velocity in streamline coordinates at 21.5 m above the ground over 11-m tall forest canopies can be opposite to that calculated from the continuity equation. To estimate CO2 transport over sloping terrain, a workable reference coordinate system is needed such that multiple sonic anemometers have a common reference relative to the Earth. Streamline coordinate systems can be the choice of the common reference coordinate system only if flow, at least ensemble-averaged flow, is parallel to terrain slopes. The choice of the reference coordinate system and its implication in investigation of CO2 transport are discussed. The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

18.
In this study, CarbonTracker, an inverse modeling system based on the ensemble Kalman filter, was used to evaluate the effects of data assimilation parameters (assimilation window length and ensemble size) on the estimation of surface CO2 fluxes in Asia. Several experiments with different parameters were conducted, and the results were verified using CO2 concentration observations. The assimilation window lengths tested were 3, 5, 7, and 10 weeks, and the ensemble sizes were 100, 150, and 300. Therefore, a total of 12 experiments using combinations of these parameters were conducted. The experimental period was from January 2006 to December 2009. Differences between the optimized surface CO2 fluxes of the experiments were largest in the Eurasian Boreal (EB) area, followed by Eurasian Temperate (ET) and Tropical Asia (TA), and were larger in boreal summer than in boreal winter. The effect of ensemble size on the optimized biosphere flux is larger than the effect of the assimilation window length in Asia, but the importance of them varies in specific regions in Asia. The optimized biosphere flux was more sensitive to the assimilation window length in EB, whereas it was sensitive to the ensemble size as well as the assimilation window length in ET. The larger the ensemble size and the shorter the assimilation window length, the larger the uncertainty (i.e., spread of ensemble) of optimized surface CO2 fluxes. The 10-week assimilation window and 300 ensemble size were the optimal configuration for CarbonTracker in the Asian region based on several verifications using CO2 concentration measurements.  相似文献   

19.
A mesoscale meteorological model (FOOT3DK) is coupled with a gas exchange model to simulate surface fluxes of CO2 and H2O under field conditions. The gas exchange model consists of a C3 single leaf photosynthesis sub-model and an extended big leaf (sun/shade) sub-model that divides the canopy into sunlit and shaded fractions. Simulated CO2 fluxes of the stand-alone version of the gas exchange model correspond well to eddy-covariance measurements at a test site in a rural area in the west of Germany. The coupled FOOT3DK/gas exchange model is validated for the diurnal cycle at singular grid points, and delivers realistic fluxes with respect to their order of magnitude and to the general daily course. Compared to the Jarvis-based big leaf scheme, simulations of latent heat fluxes with a photosynthesis-based scheme for stomatal conductance are more realistic. As expected, flux averages are strongly influenced by the underlying land cover. While the simulated net ecosystem exchange is highly correlated with leaf area index, this correlation is much weaker for the latent heat flux. Photosynthetic CO2 uptake is associated with transpirational water loss via the stomata, and the resulting opposing surface fluxes of CO2 and H2O are reproduced with the model approach. Over vegetated surfaces it is shown that the coupling of a photosynthesis-based gas exchange model with the land-surface scheme of a mesoscale model results in more realistic simulated latent heat fluxes.  相似文献   

20.
A global ocean general circulation model (L30T63) is employed to study the uptake and distribution of anthropogenic CO2 in the ocean. A subgrid-scale mixing scheme called GM90 is used in the model. There are two main GM90 parameters including isopycnal diffusivity and skew (thickness) diffusivity. Sensitivities of the ocean circulation and the redistribution of dissolved anthropogenic CO2 to these two parameters are examined. Two runs estimate the global oceanic anthropogenic CO2 uptake to be 1.64 and 1.73 Pg C yr-1 for the 1990s, and that the global ocean contained 86.8 and 92.7 Pg C of anthropogenic CO2 at the end of 1994, respectively. Both the total inventory and uptake from our model are smaller than the data-based estimates. In this presentation, the vertical distributions of anthropogenic CO2 at three meridional sections are discussed and compared with the available data-based estimates. The inventory in the individual basins is also calculated. Use of large isopycnal diffusivity can generally improve the simulated results, including the exchange flux, the vertical distribution patterns, inventory, storage, etc. In terms of comparison of the vertical distributions and column inventory, we find that the total inventory in the Pacific Ocean obtained from our model is in good agreement with the data-based estimate, but a large difference exists in the Atlantic Ocean, particularly in the South Atlantic. The main reasons are weak vertical mixing and that our model generates small exchange fluxes of anthropogenic CO2 in the Southern Ocean. Improvement in the simulation of the vertical transport and sea ice in the Southern Ocean is important in future work.  相似文献   

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