Article

# N2O measurements of air extracted from antarctic ice cores: Implication on atmospheric N2O back to the last glacial-interglacial transition

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## Abstract

A method has been developed for determining the N2O concentrations of air bubbles trapped in ice cores. The air is removed by cutting ice samples of about 45 cm3 with a rotating knife, under pure nitrogen. About 2 cm3 of the gas extracted from the ice is analyzed. The N2O concentrations are measured by gas chromatography, using electron capture detection with a detection limit of approximately 1 ppbv. The accuracy of the analysis is lower than 6%. This method has been used to analyze 34 Antarctic ice samples. Twelve air samples are from the D57 core and date approximately from AD 1600 and 1900. Data indicate a concentration of about 270 ppbv approximately 400 years ago, and of about 293 ppbv for the beginning of the 20th Century. The other samples have been taken from the Dome C core and date back to the time period extending from the Holocene to the Last Glacial Maximum. The results obtained for the Holocene period are in very good agreement with the concentrations measured for the pre-industrial time from the D57 core and indicate that, during the Holocene period, atmospheric N2O mixing ratios may have remained fairly constant. The value observed during the last climatic transition suggest a slight increase in the N2O concentrations when the climate was warming up. The results obtained on samples formed during the Last Glacial Maximum show high scattering which is best explained by the bad quality of this part of the core.

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... It is believed that a real warming up of the globe of 0.3 0.6 K has taken place over the last century [1]. Analysis of air trapped in Antarctic ice cores at various depths made it possible to determine the evolution of atmospheric composition over more than 2000 years [10][11][12][13][14]. The results of such measurements are presented in Fig. 2, from which it is evident that prior to industrialisation, global concentrations of N20 were relatively constant at around 285 ppb. ...
... The results of such measurements are presented in Fig. 2, from which it is evident that prior to industrialisation, global concentrations of N20 were relatively constant at around 285 ppb. Following industrialisation, N20 levels have been increasing steadily at about 0.3% per year, to reach the Date of saml)le lyear AI)I Fig. 2. N20 measurements from ice-core samples (after IPCC, 1990 [1]; data by Khalil and Rasmussen [10], Etheridge et al. [13] and Zardini et al. [14]). current value of approximately 310 ppb (N20 is the most abundant atmospheric nitrogen species after molecular nitrogen). ...
Article
Coal combustion is examined as a source of nitrous oxide pollution and a review of relevant research is presented. The role N2O plays in global warming and in stratospheric ozone depletion is explained and comparisons are made between N2O and other greenhouse gases. A balance of known N2O sources and sinks is also reported. Nitrous oxide emerges as a powerful and long-lived greenhouse gas with atmospheric concentration increasing at an annual rate of 0.3%. Most anthropogenic sources of N2O are of comparable strength and all should be subject to control. The fate of fuel-bound nitrogen is discussed in detail starting with coal devolatilisation and pyrolysis, through gas-phase and heterogeneous N2O/NOx formation and destruction mechanisms, to conclude with the relevant side reactions. Kinetic data are provided where available and compiled in tables. The main nitrogenous products of coal pyrolysis are HCN and NH3, and both can act as gas-phase N2O/NO precursors. Nitrous oxide is preferentially formed from cyano species, whereas NH3-based compounds tend to react mainly to NO. Gas equilibrium calculations show that N2O concentrations in flue gas are several orders of magnitude above their equilibrium values. Gas-phase formation of N2O is competitive with respect to NO formation. As temperature decreases, more N2O is formed at the expense of NO. Heterogeneous N2O/NO formation probably involves a similar trade-off and underlying mechanisms are discussed. Only up to 10% of charbound nitrogen has been found to form N2O. Destruction mechanisms of N2O/NO on char surface are important under fluidised-bed combustion (FBC) conditions, especially in the presence of CO. NO reduction on char is believed to be a negligible source of N2O. Temperature has been identified as the most important parameter that controls N2O levels, high temperature leading to reduced N2O emissions. As a result, N2O emission is low (<20 ppm) in gas- and oil-fired boilers, pulverised-coal burners and most conventional combustors, whereas fluidised-bed combustion poses a threat of increased N2O emissions (20–250 ppm). Further augmentation of N2O presence in the atmosphere may result from the use of catalytic convertors in cars and from some NOx control technologies (e.g. selective non-catalytic reduction). Limestone addition tends to reduce N2O levels and to increase NO emission, whereas increased SO2 levels in the combustor have the opposite effect. The nature of these interactions is discussed. Due to different design, different N2O/NO formation and destruction pathways may be important in bubbling and circulating FBC's. In view of uncertainties surrounding the issue of global warming, cautious but prompt N2O control measures are advocated: (a) improvements in the existing plant (operating conditions, process control, etc.); (b) research directed to understand N2O/NO chemistry in an FBC which would lead to innovative design of new combustors and their operating régimes. Staged combustion, gas reburning and catalytic enhancement of N2O decomposition seem to be attractive options in N2O control. In view of the existing interactions among individual pollutants and pollution control measures, an integrated approach to SOx/NOx/N2O abatement is emphasised.
... Suitable extraction and analytical techniques are required. Dry extraction techniques, where ice is crushed to release the air, are required for CO, (Barnola et al. 1983) and preferred for other gases such as N,O (Zardini et al. 1989). For CH,, a simpler melt extraction technique is acceptable (Stauffer et al. 1985). ...
... A number of authors have measured N,O in ice cores from Antarctica (Pearman et al. 1986, Etheridge et al. 1988, Khalil & Rasmussen 1988, Zardini et al. 1989) and Greenland (Khalil & Rasmussen 1988). The data from the various papers vary in their estimate of the pre-industrial concentration from 270 to 285 ppbv. ...
Article
In their upper layers, the polar ice sheets contain a detailed record of changes in the atmosphere over the industrial period. Measurements from air bubbles in ice have shown that the CO2 content of the atmosphere has increased by 25% in the last 200 years, and that of CH4 has more than doubled. Ice core records have demonstrated a close correspondence between greenhouse gases and temperature during the last glacial cycle. Profiles of radioactive species in snow clearly document nuclear bomb tests in the atmosphere, and the recent Chernobyl accident has also left a signal in Northern Hemisphere ice. Nitrate has more than doubled in Greenland snow over the industrial period, while sulphate has more than trebled. No significant trend is seen in Antarctic snow for these anions. Pb increased 100-fold until the 1970s in Greenland snow, but concentrations appear now to be declining. A small increase is also recorded in Antarctic snow. Organochlorine compounds offer great potential for pollution studies in snow. The ability to study global scale pollution in polar ice could be hampered if there is significant local pollution. In Antarctica, impact on the atmosphere from local human activities is still mainly confined to small areas near stations.
... The interhemispheric gradient of atmospheric N20 concentration was estimated to be less than 1 ppbv [Khalil and Rasmussen, 1988], suggesting that the Antarctic ice core data would be representative of global atmospheric conditions. The Antarctic Byrd Station [Khalil and Rasmussen, 1988], Law Dome [Etheridge et al., 1988], and Adelie Land [Zardini et al., 1989] ice cores were all used to produce a high-resolution N20 record for the period 1500 to 1966; instrumental N20 data are available from 1984 [Prinn et al., 1994]; a polynomial was then fit through all four data series (Figure lc). The higher variability seen in the N20 record was attributed to differences in analytical techniques among the three sample sets and the and CH 4 trends are a cubic spline that was fit to both ice core data and instrumental data. ...
... use of different calibration gases [Zardini et al., 1989]. The current (1997) N20 concentration is 306.4 ppbv and has been increasing at a rate of .21 ...
Article
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A new compilation of annually resolved time series of atmospheric trace gas concentrations, solar irradiance, tropospheric aerosol optical depth, and stratospheric (volcanic) aerosol optical depth is presented for use in climate modeling studies of the period 1500 to 1999 A.D. Atmospheric CO2, CH4, and N2O concentrations over this period are well established on the basis of fossil air trapped in ice cores and instrumental measurements over the last few decades. Estimates of solar irradiance, ranging between 1364.2 and 1368.2 W/m2, are presented using calibrated historical observations of the Sun back to 1610, along with cosmogenic isotope variations extending back to 1500. Tropospheric aerosol distributions are calculated by scaling the modern distribution of sulfate and carbonaceous aerosol optical depths back to 1860 using reconstructed regional CO2 emissions; prior to 1860 the anthropogenic tropospheric aerosol optical depths are assumed to be zero. Finally, the first continuous, annually dated record of zonally averaged stratospheric (volcanic) optical depths back to 1500 is constructed using sulfate flux data from multiple ice cores from both Greenland and Antarctica, in conjunction with historical and instrumental (satellite and pyrheliometric) observations. The climate forcings generated here are currently being used as input to a suite of transient (time dependent) paleoclimate model simulations of the past 500 years. These forcings are also available for comparison with instrumental and proxy paleoclimate data of the same period.
... The Nitrous oxide is also one of the major components of the greenhouse effect. The pre-industrial concentration of N 2 O was 285 PPB (Zardini et al., 1989) but in the year 1990, its concentration was 310 PPB (Elkins and Rossen, 1989) and in recent times, the concentration is increased by 328 PPB. The major source of N 2 O are Oceans (McElroy and Wofsy, 1986), Aerobic Soil (Matson and Vitousek, 1987), and Fertilizers (Bremner et al., 1981). ...
... Between the LGM and the preindustrial period, a doubling or so of CH 4 has been documented (Stauffer et al., 1988). N 2 O also increases between these two periods (Zardini et al., 1989;Sowers et al., 2001) and shows variations during abrupt climate changes (Fluckiger et al., 1999). Obtained by Chappellaz et al. (1990), the CH 4 record covering the last glacial-interglacial cycle reveals a close correlation with temperature changes and appears also influenced by 15 monsoonal activity. ...
Article
Full-text available
For about 50 yr, ice cores have provided a wealth of information about past climatic and environmental changes. Ice cores from Greenland, Antarctica and other glaciers, now emcompass a variety of timescales. However, the longer time scales (e.g. at least back to the Last Glacial period) are covered by deep ice cores the number of which is still very limited, seven from Greenland, with only one providing an undisturbed record of a part of the Last Interglacial Period, and a dozen from Antarctica with the longest record covering the last 800 000 yr. This article aims to summarize this successful adventure initiated by a few pioneers and their teams and to review key scientific results in focusing on climate (in particular water isotopes) and climate related (e.g. greenhouse gases) reconstructions. Future research is well taken into account by the four projects defined by IPICS. However it remains a challenge to get an intact record of the Last Interglacial in Greenland and to extend the Antarctic record through the mid-Pleistocene transition, if possible back to 1.5 Myr.
... With the long term aim to extend the N20 record back in time, Zardini et al. (1989) initiated a program for measuring N20 in the air trapped in ice cores. A first set of measurements has been used to check the practicability of measurements with the existing experimental unit, but also provides preliminary measurements of glacial and interglacial levels of atmospheric N20. ...
Article
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Ice core analysis provides the most direct evidence of changes in some major greenhouse gases (CO2, CH4 and N2O) over the climatic cycle covering approximately the last 150,000 years. A remarkable overall correlation is observed between the CO2 or CH4 record and the climatic changes in the high latitudes of the Southern Hemisphere, with lowest greenhouse gas concentrations found under full glacial conditions. In terms of phase relationship, CO2 and CH4 are roughly in phase with the climatic signal during the deglaciation periods; when entering the glaciation, CH4 appears to decrease in phase with the Antarctic cooling but CO2 lags strikingly behind. The CH4 record exhibits a marked signal which is most likely associated with the abrupt cooling of the Younger Dryas. Existing differences between CO2 and CH4 records in comparison with climate reflect differences in sources which are mainly oceanic in the case of CO2 and continetal in the case of CH4. For N2O only few data are available suggesting that the N2O concentrations may also have been lower during the Last Glacial Maximum than during the Holocene. Greenhouse gases are likely to have played an important climatic role in amplifying, together with continental ice, the initial orbital forcing of the glacial-interglacial climatic changes.
... The only action between sowing and harvesting was watering the crop with tap water during long periods with no rain. Present day rain contains more N than rain in the past, but this could not be avoided (Vitousek et al. 1997;Zardini et al. 1989). ...
Article
Full-text available
Stable isotope analysis of charred Bronze Age emmer wheat and barley excavated in the northwest Netherlands reveals high values of δ15N. Cultivation of the same cereal species under controlled circumstances on the appropriate substrates provided baselines indicating that the prehistoric cereal fields must have been manured. Reconstruction of the size of the arable fields and livestock suggests that animal dung cannot have been the only source of fertilizer. Application of household waste and mud from ditches is considered as well as a possible effect from burning stubble. Growing of pulses was not practiced and therefore this method of ameliorating the soil has to be left out of the question. The outcome of the study presented here is that the Bronze Age farmers of the northwest Netherlands used several means to maintain the fertility of their arable land and that they may have adapted their strategy according to circumstances.
... Today reactive N from fossil fuel combustion, industrial fixation by the Haber–Bosch process and biological N fixation in leguminous plants dominate the global production of reactive N. Global increases in reactive N may be detected in a range of natural reservoirs throughout the world. For example, air trapped in ice cores in Antarctica and glaciers in Switzerland have demonstrated how the atmospheric N 2 O and NH 4 concentrations, respectively, have both increased, concomitant with the rise in N consumption during the last century (Zardini et al., 1989; Fagerli et al., 2007). The enhanced deposition of atmospheric N leads to a range of environmental effects including: (1) eutrophication of aquatic and terrestrial systems and in N sensitive ecosystems species loss (e.g. ...
Article
The NitroEurope project aims to improve understanding of the nitrogen (N) cycle at the continental scale and quantify the major fluxes of reactive N by a combination of reactive N measurements and modelling activities. As part of the overall measurement strategy, a network of 13 flux 'super sites' (Level-3) has been established, covering European forest, arable, grassland and wetland sites, with the objective of quantifying the N budget at a high spatial resolution and temporal frequency for 4.5 years, and to estimate greenhouse gas budgets (N 2 O, CH 4 and CO 2). These sites are supported by a network of low-cost flux measurements (Level-2, 9 sites) and a network to infer reactive N fluxes at 58 sites (Level-1), for comparison with carbon (C) flux measurements. Measurements at the Level-3 sites include high resolution N 2 O, NO (also CH 4 , CO 2) fluxes, wet and dry N deposition, leaching of N and C and N transformations in plant, litter and soil. Results for the first 11 months (1.8.2006 to 30.6.2007) suggest that the grasslands are the largest source of N 2 O, that forests are the largest source of NO and sink of CH 4 and that N deposition rates influence NO and N 2 O fluxes in non-agricultural ecosystems. The NO and N 2 O emission ratio is influenced by soil type and precipitation. First budgets of reactive N entering and leaving the ecosystem and of net greenhouse gas exchange are outlined. Further information on rates of denitrification to N 2 and biological N 2 fixation is required to
... Barnola et al., 1987;Zardini et al., 1989;Chappellaz et al., 1990; Barnola et al., 1991;Staffelbach et al., 1991;Jouzel et al., 1993;Chappellaz et al., 1993;, and its relationship with the changing climate or with anthropogenic activities has been investigated. Only recently, a change of CO mixing ratios during the last 200 years has been reported as well [Haan et al., 1996].The basis for these investigations is the assumption that the composition of the air extracted from ice core samples represents the air composition at the time of the closure of the bubbles. ...
Article
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A sublimation technique has been developed to extract air samples from polar ice cores for subsequent simultaneous measurement of several trace gases by frequency-modulated tunable diode laser absorption spectroscopy. This extraction and analysis technique is shown to be suitable as an extraction method for the determination of concentrations of the greenhouse gases CO2, CH4, and N2O in air samples of ~1-5 cm3 recovered from ice samples of 10-50 g. Air samples from the Siple ice core have been analyzed covering the period between 1772 and 1973. In addition, a few samples from two different ice cores from Vostok station have been analyzed. Our results are in a good agreement with results obtained by other researchers using melting and crushing extraction techniques. This agreement indicates that processes connected with the formation of clathrates in ice under high pressure at greater depths and their destruction after drilling are not affecting the CO2, CH4, and N2O measurements significantly.
... The records of CH 4 and CO 2 over this time period have provided interesting information about environmental changes in response to regional climate variations [Blunier et al., 1995;Chappellaz et al., 1997;Indermühle et al., 1999]. Little is known about the evolution of the N 2 O concentration during the Holocene apart from the last few hundred years [Khalil and Rasmussen, 1988;Zardini et al., 1989]. From the high-resolution N 2 O record presented in this paper we expect information about the global nitrogen cycle and changes of the main N 2 O sources and sinks. ...
Article
Nitrous oxide (N2O) concentration records exist for the last 1000 years and for time periods of rapid climatic changes like the transition from the last glacial to today's interglacial and for one of the fast climate variations during the last ice age. Little is known, however, about possible N2O variations during the more stable climate of the present interglacial (Holocene) spanning the last 11 thousand years. Here we fill this gap with a high-resolution N2O record measured along the European Project for Ice Coring in Antarctica (EPICA) Dome C Antarctic ice core. On the same ice we obtained high-resolution methane and carbon dioxide records. This provides the unique opportunity to compare variations of the three most important greenhouse gases (after water vapor) without any uncertainty in their relative timing. The CO2 and CH4 records are in good agreement with previous measurements on other ice cores. The N2O concentration started to decrease in the early Holocene and reached minimum values around 8 ka (
... Because of the long lifetime of N20, that value should also be applicable globally within a range of +-5 ppbv. On the other hand, the ice core data indicate that the preindustrial N20 mixing ratio in the troposphere averaged about 285 ppbv [Khalil and Rasmussen, 1989;Etheridge et al., 1988], with Zardini et al. [1989] reporting concentrations of about 270 ppbv approximately 400 years ago and Leuenberger and Siegenthaler [1992] quoting --•260 ppbv for preindustrial times. Moreover, the ice core data have been interpreted to show the increase in the atmospheric N20 mixing ratio to begin as early as 1700 [Houghton et al., 1990]. ...
Article
Full-text available
Infrared solar spectra recorded at the International Scientific Station of the Jungfraujoch (3580 m altitude), Switzerland, in 1950-1951 and from 1984 to 1992 have been analyzed to determine vertical column abundances of nitrous oxide (N2O) above the station. The best fit to the relatively dense set of measurements made between 1984 and 1992 indicates a mean exponential rate of increase equal to 0.36 +/- 0.06%/yr (1 sigma) and a seasonal modulation of 7.2% peak to peak, the minimum occurring at the end of the winter and the maximum in early September. The column abundances for April of the years 1951, 1984, and 1992 were found equal to 3.49 x 10(exp 18), 3.76 x 10(exp 18), and 3.87 x 10(exp 18) molecules/sq cm, respectively; they translate into N2O concentrations at the altitude of the Jungfraujoch equal to 275, 296, and 305 parts per billion by volume. These results indicate that the exponential rate of increase for 1951-1984 was equal to 0.23 +/- 0.04%/yr (1 sigma), thus substantially lower than for the 1984-1992 time interval and that the so-called preindustrial levels of N2O pertained until 1951 with most of the increase in atmospheric N2O occurring thereafter.
... Polynomial and linear fitting is performed by using the available ice core N 2 0 mixing ratio data (back only to 13,600 years BP) [Zardini et al., 1989]. The fitted curves are plotted in Figure 6-6 together with the calculated N 2 0 mixing ratios in Table 6 (236.5ppb). ...
... Today reactive N from fossil fuel combustion, industrial fixation by the Haber–Bosch process and biological N fixation in leguminous plants dominate the global production of reactive N. Global increases in reactive N may be detected in a range of natural reservoirs throughout the world. For example, air trapped in ice cores in Antarctica and glaciers in Switzerland have demonstrated how the atmospheric N 2 O and NH 4 concentrations, respectively, have both increased, concomitant with the rise in N consumption during the last century (Zardini et al., 1989; Fagerli et al., 2007). The enhanced deposition of atmospheric N leads to a range of environmental effects including: (1) eutrophication of aquatic and terrestrial systems and in N sensitive ecosystems species loss (e.g. ...
... Most of these values were obtained from uncharred material, but as mentioned above, charring does not have an important effect on the values. The fact that modern rain, which is the main source of water during the experiment, is held to have a higher N content than prehistoric rain seems not to have had a notable effect (Zardini et al. 1989;Vitousek et al. 1997). ...
Article
This paper describes an experiment to provide baselines for the δ¹⁵N values of prehistoric cereals. Emmer wheat and barley were grown in tubs filled with two different substrates and placed in a cage to protect them from birds and cats. The experiment lasted three years. Values obtained in this way may serve in cases where no experimental farms of long standing with unmanured fields can provide them. The results are in line with the values obtained at such farms, as well as with values presented for ethnographic cases in the literature.
... Between the LGM and the preindustrial period, a doubling or so of CH 4 has been documented (Stauffer et al., 1988). N 2 O also increases between these two periods (Zardini et al., 1989;Sowers, 2001) and shows variations during abrupt climate changes (Flückiger et al., 1999). Obtained by Chappellaz et al. (1990), the CH 4 record covering the last glacialinterglacial cycle reveals a close correlation with temperature changes and also appears influenced by monsoonal activity. ...
Article
Full-text available
For about 50 yr, ice cores have provided a wealth of information about past climatic and environmental changes. Ice cores from Greenland, Antarctica and other glacier-covered regions now encompass a variety of time scales. However, the longer time scales (e.g. at least back to the Last Glacial period) are covered by deep ice cores, the number of which is still very limited: seven from Greenland, with only one providing an undisturbed record of a part of the last interglacial period, and a dozen from Antarctica, with the longest record covering the last 800 000 yr. This article aims to summarize this successful adventure initiated by a few pioneers and their teams and to review key scientific results by focusing on climate (in particular water isotopes) and climate-related (e.g. greenhouse gases) reconstructions. Future research is well taken into account by the four projects defined by IPICS. However, it remains a challenge to get an intact record of the Last Interglacial in Greenland and to extend the Antarctic record through the mid-Pleistocene transition, if possible back to 1.5 Ma.
Article
Human activities have a serious impact on climate and on the natural composition of the atmosphere. Information recorded in polar ice cores over the last several hundred millennia is invaluable to studies aimed at understanding the preindustrial environmental system and anticipating the future evolution of the atmosphere. An excellent understanding of the mechanisms of the ice record formation as well as a good assessment of the present polar atmospheric composition (trace gases, aerosol) is a prerequisite to interpreting correctly the past variations of the measured parameters. This paper explains what and how atmospheric parameters are recorded. Ambient air samples are encapsulated and stored in the ice bubbled by relatively simple processes. The isotopic composition of the H2O (ice) lattice is a reliable paleothermometer. The interpretation of the chemical composition of deposited snow in terms of past atmospheric composition of deposited snow in terms of past atmospheric composition (trace gases, aerosol) is more intricate and necessitates detailed discussions. The data obtained from deep ice cores provide precise information on the ice age environmental conditions: when polar temperatures were some 10°C lower than now, atmospheric CO2 and CH4 contents were factors of 2 and 4 lower, respectively, than present conditions. At this time, sea salt and overall crustal dust depositions were significantly higher. The biogeochemical cycles of S and N were also disturbed according to modifications in source intensity and transport of gaseous precursors.
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A new extraction system has been constructed and tested which allows the extraction of gases from air bubbles in ice without melting it. An ice sample of up to 20 g is crushed in a sealed container by a milling cutter and the gas escaping from the opened bubbles is flushed with helium to a Porapak column where it is stored until its injection into the gas Chromatograph. To avoid any contamination with CH 4 produced by friction in the gear section, a helium-flushed rotary feed-through is used. CH 4 analyses on ice samples of about 10 g from the last 1000 years give precise and reproducible results. In the future, it is planned to measure also the CO 2 and N 2 O concentrations on the same sample.
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Humans seem to have doubled the global rate of terrestrial nitrogen fixation. Globally 50–70% (85 Tg, 1 Tg=1012 g) of the nitrogen supplied in fertilizer (80 Tg N/a) and leguminous crops (40–80 Tg N/a) are used to feed cattle. The aim of the present study was to derive some estimates of global N2O production from animal manure. As the parameter giving the most stable numerical basis for regional and global extrapolation we adopted the molar emission ratios of N2O to NH3. These ratios were measured in cattle, pig and chicken housings with different manure handling systems, in dung-heaps and in liquid manure storage tanks. Individual molar emission ratios from outside manure piles varied over two orders of magnitude, strongly dependent on the treatment of the manure. A median emission ratio of 1.6×10-2 (n=65) was obtained in cow-sheds with slatted floors and liquid manure stored underneath and a median ratio of 24×10-2 (n=31) was measured in a beef cattle housing with a solid manure handling system. We next extrapolated to global NH3 emissions from those estimated for Europe, using N uptake by the animals as a scaling factor. Multiplication with observed N2O to NH3 ratios next provided some estimates of regional and global N2O emissions. To account for the great variability of the emission ratios of N2O/NH3, we developed upper and lower case emission scenarios, based on lower and upper quartiles of measured emission ratios. The global emission from cattle and swine manure is in the range of 0.2–2.5 Tg N-N2O/a, representing 44+-39% of the annual atmospheric accumulation rate. This N2O emission arises from about 40 Tg N/a of cattle and pig manure stored in or at animal housings. We did not account for N2O emissions from another 50 Tg N/a excreted by grazing cattle, goats and sheep, and application of the manure to agricultural fields. Our study makes it clear that major anthropogenic N2O emissions may well arise from animal manure. The large uncertainty of emission ratios, which we encountered, show that much more intense research efforts are necessary to determine the factors that influence N2O emissions from domestic animal manure both in order to derive a more reliable global estimate of N2O release and to propose alternative waste treatment methods causing smaller N2O releases. In our studies we found large enhancements in N2O releases when straw was added to the manure, which is a rather common practice. In view of the ongoing discussion in Europe to re-install the traditional solid manure system (bed down cattle) for environmental and animal welfare reasons, it is noteworthy that our measurements indicate highest N2O release from this particulary system. In a similar manner, but based on a smaller data set, we also estimated the release of CH4 from cattle and swine manure and from liquid manure only to be about 9 Tg/year in good agreement with the estimate by the Environmental Protection Agency (1994) of 8.6+-2.6 Tg/year. A total annual methane release as high as 34 Tg/a was derived for solid and liquid cattle and pig manure from animals in housings.
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The rate of formation of N2O via the thermochemically favourable reaction of NO3(A2E) with N2, which would represent an additional source of stratospheric N2O and therefore NOx, has been investigated. Mixtures of NO2+O3 in synthetic air were photolysed at 662 nm. No evidence was found for the production of N2O via this pathway, the upper limit for the quantum yield of nitrous oxide formation being % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiiYdd9qrFfea0dXdf9vqai-hEir8Ve% ea0de9qq-hbrpepeea0db9q8as0-LqLs-Jirpepeea0-as0Fb9pgea% 0lrP0xe9Fve9Fve9qapdbaqaaeGacaGaaiaabeqaamaabaabcaGcba% GaeqOXdy2aaSbaaSqaamaaBaaameaadaWgaaqaamaaBaaabaGaamOt% amaaBaaabaGaaGOmaiaad+eaaeqaaaqabaaabeaaaeqaaaWcbeaatu% uDJXwAK1uy0HMmaeHbfv3ySLgzG0uy0HgiuD3BaGqbaOGae8hzIqOa% aGimaiaac6cacaaI2aGaaiyjaaaa!4E60!$\phi _{_{_{_{N_{2O} } } } } \le 0.6\%$. However, a dark conversion of NOx to N2O was observed and is attributed tentatively to a heterogeneous reaction on the wall of the reaction vessel. This process, although most likely to be insignificant in the atmosphere, needs to be taken into consideration in laboratory investigations or field studies of N2O emission or deposition.
Article
Tropospheric measurements show that nitrous oxide (N2O) concentrations are increasing over time. This demonstrates the existence of one or more significant anthropogenic sources, a fact that has generated considerable research interest for several years. The debate has principally focused on (1) the identity of the sources, and (2) the consequences of increased N2O concentrations. Both questions remain open, to at least some degree.The environmental concerns stem from the suggestion that diffusion of additional N2O into the stratosphere can result in increased ozone (O3) depletion. Within the stratosphere, N2O undergoes photolysis and reacts with oxygen atoms to yield some nitric oxide (NO). This enters into the well known O3 destruction cycle. N2O is also a potent absorber of infrared radiation and can contribute to global warming through the greenhouse effect.In combustion, the homogeneous reactions leading to N2O are principally NCO + NO → N2O + CO and NH + NO → N2O + H, with the first reaction being the more important in practical combustion systems. During high-temperature combustion, N2O forms early in the flame if fuel nitrogen is available. The high temperatures, however, ensure that little of this escapes, and emissions from most conventional combustion systems are quite low. The exception is combustion under moderate temperature conditions, where the N2O is formed from fuel nitrogen, but fails to be destroyed. The two principal examples are combustion in fluidized beds, and in applications of nitrogen oxide (NOx) control by the downstream injection of nitrogen-containing agents (e.g., selective non-catalytic reduction with urea). There remains considerable debate on the degree to which homogeneous vs. heterogeneous reactions contribute to N2O formation in fluidized bed combustion. What is clear is that the N2O yield is inversely correlated with bed temperature, and conversion of fuel nitrogen to N2O is favored for higher-rank fuels.Formation of N2O during NOx control processes has been confined primarily to selective non-catalytic reduction. Specifically, when the nitrogen-containing agents urea and cyanuric acid are injected, a significant portion (typically > 10%) of the NO that is reduced is converted into N2O. The use of promoters to reduce the optimum injection temperature appears to increase the fraction of NO converted into N2O. Other operations, such as air staging and reburning, do not appear to be significant N2O producers. In selective catalytic reduction, the yield of N2O depends on both catalyst type and operating condition, although most systems are not large emitters.Other systems considered include mobile sources, waste incineration, and industrial sources. In waste incineration, the combustion of sewage sludge yields very high N2O emissions. This appears to be due to the very high nitrogen content of the fuel and the low combustion temperatures. Many industrial systems are largely uncharacterized with respect to N2O emissions. Adipic acid manufacture is known to produce large amounts of N2O as a byproduct, and abatement procedures are under development within the industry.
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Nitrous oxide (N2O) is an important atmospheric trace gas. Changes in the concentration of N2O in the atmosphere have evoked considerable interest because of its role in (i) regulating stratospheric ozone levels, and (ii) contributing to the atmospheric greenhouse phenomenon. The global concentration of N2O in the atmosphere has been rising since the start of the Industrial Revolution, before which the concentration was almost constant at about 280–290 ppbv. In ad 1990, it reached about 310 ppbv and is rising at a rate of 0·5–1·1 ppbv (i.e. 0·2–0·3%) per year. In this paper, the history of N2O in the Earth's atmosphere, together with its latitudinal and altitudinal distributions, and seasonal oscillations, are described.
Article
We discuss the role of the concentration increase of atmospheric CH4 (currently ≈ 0.8% yr−1) in climate change, including effects through chemical feedbacks, notably through formation of O3 and stratospheric H2O, and reduction of OH levels, which increases the lifetime of CH4. We present results of simulations with a coupled 1-D radiative-convective model, which includes chemical and radiative processes in the troposphere and stratosphere, and which treats both hemispheres separately. Our results deviate appreciably from those reported in earlier studies; the reason for this is discussed in detail. The current climate forcing by CH4 (excluding indirect chemical effects) is 26 times that of CO2 (calculated on a basis). A recently introduced quantity to express the time integrated effect of CH4 relative to that of CO2 over a given time interval is the global warming potential (GW P). We assess that the GW P of CH4, including chemical feedbacks, over a 10 year integration period is 26.9 (), decreasing to 7.5 for a time horizon of 100 years. Considering that the use of fossil fuels is associated with emissions of both CO2 and CH4, we evaluated the climatic consequences of switching from coal or oil to natural gas. We conclude that, if the fractional gas leakage from production and distribution of natural gas is below 4.3 – 5.7%, a switch from coal to natural gas as energy source would reduce the rate of climate warming. The use of gas would be preferable over the use of oil (from a climate point of view), if the fractional gas leakage is less than 2.4 – 2.9%. The ranges express uncertainties in CH4 releases from coal and oil production.
Article
Concentrations of CH4 and N2O have been determined in bubbles extracted from the Mt. Logan (Yukon) and 20D (south Greenland) ice cores. The enclosure dates of the trapped gas samples range from 1802 to 1960; thus these data help to document the anthropogenic increases of these two greenhouse gases in the Northen Hemisphere atmosphere. In general, the new data are in accord with previous ice core studies showing accelerating increases in concentration of both gases since 1900. The Mt. Logan records appear to be the first for any trace gases from alpine glacial ice. The present data set is too sparse to be conclusive, but suggests generally higher CH4 concentrations over south Greenland than Mt. Logan, particularly for the 1850 - 1900 period.
Article
Tropospheric measurements show that nitrous oxide (N2O) concentrations are increasing over time. This demonstrates the existence of one or more significant anthropogenic sources, a fact that has generated considerable research interest over the last several years. The debate has principally focused on (1) the identity of the sources, and (2) the consequences of increased N2O concentrations. Both questions remain open, to at least some degree.The environmental concerns stem from the suggestion that diffusion of additional N2O into the stratosphere can result in increased ozone (O3) depletion. Within the stratosphere, N2O undergoes photolysis and reacts with oxygen atoms to yield some nitric oxide (NO). This enters into the well known O3 destruction cycle. N2O is also a potent absorber of infrared radiation and can contribute to global warming through the greenhouse effect.A major difficulty in research on N2O is measurement. Both electron capture gas chromatography and continuous infrared methods have seen considerable development, and both can be used reliably if their limitations are understood and appropriate precautions are taken. In particular, the ease with which N2O is formed from NO in stored combustion products must be recognized; this can occur even in the lines of continuous sampling systems.In combustion, the homogeneous reactions leading to N2O are principally NCO + NO → N2O + CO and NH + NO → N2O + H, with the first reaction being the most important in practical combustion systems. Recent measurements have resulted in a revised rate for this reaction, and the suggestion that only a portion of the products may branch into N2O + CO. Alternatively, recent measurements also suggest a reduced rate for the N2O + OH destruction reaction. Most modeling has been based on the earlier kinetic information, and the conclusions derived from these studies need to be revisited.In high-temperature combustion, N2O forms early in the flame if fuel-nitrogen is available. The high temperatures, however, ensure that little of this escapes, and emissions from most conventional combustion systems are quite low. The exception is combustion under moderate temperature conditions, where the N2O is formed from fuel-nitrogen, but fails to be destroyed. The two principal examples are combustion fluidized beds, and the downstream injection of nitrogen-containing agents for nitrogen oxide (NOx) control (e.g., selective noncatalytic reduction with urea).There remains considerable debate on the degree to which homogeneous vs heterogeneous reactions contribute to N2O formation in fluidized bed combustion. What is clear is that the N2O yield is inversely proportional to bed temperature, and conversion of fuel-nitrogen to N2O is favored for higher-rank fuels. Fixed-bed studies on highly devolatilized coal char do not indicate a significant role for heterogeneous reactions involving N2O destruction. The reduction of NO at a coal char surface appears to yield significant N2O only if oxygen (O2) is also present. Some studies show that the degree of char devolatilization has a profound influence on both the yield of N2O during char oxidation, and on the apparent mechanism. Since the char present in combustion fluidized beds will likely span a range of degrees of devolatilization, it becomes difficult to conclusively sort purely homogeneous behavior from potential heterogeneous contributions in practical systems.Formation of N2O during NOx control processes has primarily been confined to selective noncatalytic reduction. Specifically, when the nitrogen-containing agents urea and cyanuric acid are injected, a significant portion (typically > 10%) of the NO that is reduced is converted into N2O. The use of promoters to reduce the optimum injection temperature appears to increase the fraction of NO converted into N2O. Other operations, such as air staging and reburning, do not appear to be significant N2O producers. In selective catalytic reduction the yield of N2O depends on both catalyst type and operating condition, although most systems are not large emitters.Other systems considered include mobile sources, waste incineration, and industrial sources. In waste incineration, the combustion of sewage sludge yields very high N2O emissions. This appears to be due to the very high nitrogen content of the fuel and the low combustion temperatures. Many industrial systems are largely uncharacterized with respect to N2O emissions. Adipic acid manufacture is known to produce large amounts of N2O as a by-product, and abatement procedures are under development within the industry.
Article
A new extraction system has been constructed and tested which allows the extraction of gases from air bubbles in ice without melting it. An ice sample of up to 20 g is crushed in a sealed container by a milling cutter and the gas escaping from the opened bubbles is flushed with helium to a Porapak column where it is stored until its injection into the gas Chromatograph. To avoid any contamination with CH4 produced by friction in the gear section, a helium-flushed rotary feed-through is used. CH4 analyses on ice samples of about 10 g from the last 1000 years give precise and reproducible results. In the future, it is planned to measure also the CO2 and N2O concentrations on the same sample.
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Atmospheric carbon dioxide, which causes 50% of greenhouse warming, is increasing by 0.5% per year. Reducing and reversing deforestation would slow the increase, but plantations the size of Europe would sequester only 20–30% of the accumulation. Methane's concentration is increasing at a rate of 1% per year, and 70–90% comes from biotic sources. Even if drastic reductions in the world's cattle population, slash and bum agriculture and fuelwood burning could be achieved, CH4 would probably continue to increase. Atmospheric nitrous oxide, with almost exclusively biotic sources, contributes 5% to global warming and is increasing at 0.2–0.3% per year. The causes are poorly understood, but reductions in the use of N fertilizer and careful soil management may be effective.
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A global inventory with 1°x1° resolution was compiled of emissions of nitrous oxide (N <sub>2</sub> O) to the atmosphere, including emissions from soils under natural vegetation, fertilized agricultural land, grasslands and animal excreta, biomass burning, forest clearing, oceans, fossil fuel and biofuel combustion, and industrial sources.A simple global model of the production potential of N <sub>2</sub> O in soils under natural vegetation was developed to analyze the relative importance of five major controls on N <sub>2</sub> O production: (i) input of organic matter, (ii) soil fertility, (iii) soil moisture status, (iv) temperature; and (v) soil oxygen status. Indices for the controls were derived from global gridded (1° x 1° resolution) data bases of soil type and texture, normalized difference vegetation index (NDVI) and climate. The model explains close to 60% of the variability found in measurements reported at about 30 sites in six different ecosystems throughout the world. The model results confirm conclusions from earlier studies that the major natural source regions of N <sub>2</sub> O are in the tropics.Literature data on N <sub>2</sub> O flux measurements from agricultural fields show that the fertilizerinduced N <sub>2</sub> O emission is higher for measurements covering longer periods than for measurements which represent short periods. A method to estimate the total annual direct N <sub>2</sub> O emission from fertilized fields was based on measurements covering periods of one year: N <sub>2</sub> O-N emission = I kg N ha <sup>-1</SUP>yr <sup>-1</SUP>plus 1.25 ± 1% of the amount of fertilizer N applied (kg N ha <sup>-1</SUP>yr <sup>-1</SUP>). This relationship was used to compile a global 1° x 1° resolution inventory of emissions of N <sub>2</sub> O from fertilized arable land.The inventory of N <sub>2</sub> O emission from animal excreta was based on estimates of nitrogen (N) excretion by various categories of domestic animals. The estimated global amount of N in animal excreta (-100 x 10 <sup>12</SUP>g N yr <sup>-1</SUP>) suggests that the associated N <sub>2</sub> O emission may be of the same order of magnitude as that caused by the use of synthetic N fertilizer (-80 x 10 <sup>12</SUP>g N yr <sup>-1</SUP>)To illustrate the difficulty to describe the cycling of N in ecosystems, N budgets were compiled for a deforestation sequence in the Atlantic Zone of Costa Rica. After forest clearing an important part of the soil organic N is mineralized. Part of the nitrate formed by nitrification of the mineralized N is lost via leaching, while most of the N loss occurs through denitrification. After a period of 3 to 5 years most of the easily decomposable material is lost, and denitrification and N <sub>2</sub> O fluxes decrease with time to levels lower than in the undisturbed forest. The global estimate of enhanced soil N <sub>2</sub> O emission from denitrification following tropical forest clearing, accounting for this decline of N <sub>2</sub> O fluxes along with ageing of the clearing, indicates that deforestation is an important global source.Global 10 x 1° resolution inventories were also compiled for N <sub>2</sub> O emissions from fossil fuel and fuelwood combustion, and industrial N2O sources. For N <sub>2</sub> O emissions from oceans and biomass burning, inventories from the literature were used. The complete inventory of annual N <sub>2</sub> O emissions including all sources, was compared with source estimates inferred from inversemodeling. The N <sub>2</sub> O inventories are in general agreement with inverse modeling results. However, there are major uncertainties, particularly in the tropics. The comparison between the emission inventory and the source estimates from inverse modelling, resulted in improved understanding of some sources:- The oceanic N <sub>2</sub> O emission may be higher than previous estimates; the 0°N-30°N latitudinal zone and the Antarctic ocean show much higher N <sub>2</sub> O fluxes than the mean global oceanic flux.- Most of the N <sub>2</sub> O from arable lands and grasslands including effects of synthetic fertilizers and animal excreta comes from the northern hemisphere. Inputs of N to soils from N deposition and from N fixation by leguminous crops are of the same order of magnitude as synthetic N fertilizer use. Their associated N <sub>2</sub> O release may also be similar in magnitude.- Fossil-fuel combustion and industrial N <sub>2</sub> O sources are dominant in the 30°N-90°N zone, while N <sub>2</sub> O from fuelwood combustion is mainly produced in the 0°N-30°N zone.- The major part of the N <sub>2</sub> O emitted from coastal marine and fresh water systems probably stems from the northern hemisphere.Global monthly estimates of N <sub>2</sub> O emissions were used to prescribe a three-dimensional atmospheric transport model. The simulated northern hemispheric N <sub>2</sub> O surface concentration was -1 ppb higher than in the southern hemisphere. This is in general agreement with atmospheric observations. The modeled N <sub>2</sub> O concentrations over strong source regions in continental interiors were up to 5 ppb higher than those over oceans. Predicted concentrations for the northern hemisphere were somewhat higher in summer than in winter, in agreement with the seasonality of N <sub>2</sub> O emissions. However, the atmospheric N <sub>2</sub> O concentration measurements show no seasonal variation in the northern hemisphere. The small seasonality in modeled atmospheric N <sub>2</sub> O concentrations for the southern hemisphere is more consistent with measurements. Inconsistencies between predicted and observed atmospheric N <sub>2</sub> O concentrations may be caused by overestimation of the seasonality in the northern hemisphere. The global N <sub>2</sub> O inventory used does not account for soil N <sub>2</sub> O consumption in temperate N-limited ecosystems and observed episodic emissions in temperate ecosystems during winter, early spring and autumn. These potential errors and possible underestimation of N <sub>2</sub> O emissions from combustion in winter may exaggerate the simulated seasonal trends.Another possible reason for the inconsistencies found between predicted and measured N <sub>2</sub> O concentrations is that seasonal trends in atmospheric N <sub>2</sub> O concentrations remain unobserved, because of the remote location of most monitoring stations. In addition, the precision of N <sub>2</sub> O measurements is not adequate for resolving seasonal trends.The major part of the atmospheric N <sub>2</sub> O increase stems from sources related to human food production. A growing world population will inevitably lead to more food demand. Moreover, an increasing portion of the synthetic fertilizers is used to increase animal production. At present, close to 40% of the global cereal production and 25% of the production of root and tuber crops is fed to animals. An important global reduction of N <sub>2</sub> O emission associated with food production could be achieved by a shift-away from animal production, by more efficient agricultural use of N, and by advanced fertilization techniques.Solutions to reduce N <sub>2</sub> O emission from fossil fuel combustion include technical options (e.g. development of new catalysts) and energy saving. Several industrial and chemical processes generate N <sub>2</sub> O, but so far only the N <sub>2</sub> O production from nitric and adipic acid production have been quantified. The global N <sub>2</sub> O emission from adipic acid production is currently decreasing as the major producers have agreed to reduce N <sub>2</sub> O emissions.
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The prediction of future greenhouse-gas-warming depends critically on the sensitivity of earth's climate to increasing atmospheric concentrations of these gases. Data from cores drilled in polar ice sheets show a remarkable correlation between past glacial-interglacial temperature changes and the inferred atmospheric concentration of gases such as carbon dioxide and methane. These and other palaeoclimate data are used to assess the role of greenhouse gases in explaining past global climate change, and the validity of models predicting the effect of increasing concentrations of such gases in the atmosphere.
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Nitrous oxide (N2O) is an important greenhouse gas that is presently increasing at a rate of 0.25 percent per year. Records measured along two ice cores from Summit in Central Greenland provide information about variations in atmospheric N2O concentration in the past. The record covering the past millennium reduces the uncertainty regarding the preindustrial concentration. Records covering the last glacial-interglacial transition and a fast climatic change during the last ice age show that the N2O concentration changed in parallel with fast temperature variations in the Northern Hemisphere. This provides important information about the response of the environment to global climatic changes.
Article
Data from weekly global measurements of nitrous oxide from 1981 to the end of 1996 are presented. The results show that there is more N2O in the northern hemisphere by about 0.7 +/- 0.04 ppbv, and the Arctic to Antarctic difference is about 1.2 +/- 0.1 ppbv. Concentrations at locations influenced by continental air are higher than at marine sites, showing the existence of large land-based emissions. For the period studied, N2O increased at an average rate of about 0.6 ppbv/year (approximately 0.2%/year) although there were periods when the rates were substantially different. Using ice core data, a record of N2O can be put together that goes back about 1000 years. It shows pre-industrial levels of about 287 +/- 1 ppbv and that concentrations have now risen by about 27 ppbv or 9.4% over the last century. The ice core data show that N2O started increasing only during the 20th century. The data presented here represent a comprehensive view of the present global distribution of N20 and its historical and recent trends.
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Sources and sinks of the atmospherically reactive gas nitrous oxide (N(2)O) were determined in the heavily nutrient loaded Childs River in Cape Cod, MA. Surface waters were supersaturated and bottom waters were depleted with N(2)O throughout the system. In apparent septic effluent plumes, N(2)O concentrations reached 3 orders of magnitude above atmospheric equilibrium. Because nitrate and N(2)O concentrations correlated in groundwater entering the estuary, septic tank effluent appeared responsible for the supersaturated concentrations of N(2)O in surface waters. A hyperbolic function fit nitrate and N(2)O concentrations in the water column of the estuary with a maximum supersaturation of approximately 60 nM. From surface water supersaturation we predicted a release of 480 nmol N(2)O m(-2) h(-1) to the atmosphere in the summer. Property plots of salinity vs. bottom-water N(2)O suggested a benthic sink of N(2)O. Consistent with this trend, sediments consumed rather than released N(2)O in most flux measurements. Nutrient loading did not directly alter benthic N(2)O flux, potentially because stratification limited exposure of sediments to nitrate-rich surface waters, but macroalgal cover increased benthic N(2)O consumption. Sediment N(2)O consumption averaged 111 nmol N(2)O m(-2) h(-1) and correlated with oxygen uptake. Losses from the system to the atmosphere and sediments exceeded inputs of N(2)O contaminated groundwater, which suggests missing N(2)O sources.
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A simple box model is developed which accounts for the natural and anthropo-genic sources and sinks of tropospheric nitrous oxide. Stable isotopic terms are included as well to investigate what additional insight they might provide concerning the overall picture of the global nitrous oxide budget. It is seen that fractionation associated with ultraviolet photolysis in the stratosphere plays a key role in balancing the isotopic budget. It is also noted that increased production due to human influence should have a unique isotopic sig-nature which should provide observable differences between preindustrial air trapped in polar tim or ice and modem air. This build-up of isotopically light, anthropogenic nitrous oxide can be thought of as an N20 "Suess effect" and should be observable in time series meas-urements of clean baseline atmospheric samples. High-precision records of such changes could lead to a better estimate of the preindustrial N20 isotopic signature as well as provide insight into the pathways of the anthropogenic sources.
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Gases trapped in polar ice provide our most direct record of the changes in greenhouse gas levels during the past 150,000 years. The best conducted trace-gas records are for CO2 and CH4. The measurements corresponding to the industrial period document the recent changes in growth rate. The variability observed over the last 1000 years constrains the possible feedbacks of a climate change on the trace gases under similar conditions as exist today. Changes in the levels of greenhouse gases during the glacial-interglacial cycle overall paralleled, at least at high southern latitudes, changes in temperature; this relation suggests that greenhouse gases play an important role as an amplifier of the initial orbital forcing of Earth's climate and also helps to assess the feedbacks on the biogeochemical cycles in a climate system in which the components are changing at different rates.
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During the past decades, the investigation of various elements, species, and isotopes in the frozen atmospheric archives stored in the Greenland and Antarctic ice caps for several hundred thousand years has provided a wealth of fascinating information on past and recent changes in the atmospheric environment of our planet. After a brief description of the Antarctic and Greenland ice caps, we give an overview of the procedures that are used in the field for collecting snow and ice from the surface down to great depths. We discuss the techniques used to date and analyse the samples. The main results obtained to date are then presented, with special emphasis on the very recent. The analysis of the snow and ice layers deposited during the past few centuries, especially since the Industrial Revolution, has allowed us to assess clearly the impact human activity has had on the atmosphere, for important constituents such as heavy metals, sulfur and nitrogen compounds, greenhouse gases, carbon and organic compounds, and artificial radionuclides. The analysis of ancient ice up to several hundred thousand years old has provided unique insight on the past natural changes that affected our atmosphere during glacial–interglacial transitions, especially the temperature, greenhouse gases, soil- and sea-derived aerosols, and heavy metals.Key words: Greenland, Antarctica, ice, global pollution, climate change, heavy metals.
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We use atmospheric and ice core data on the concentrations of nitrous oxide to estimate that the present global anthropogenic emissions are 7+/-1 tg/yr. If the atmospheric lifetime of N2O is a hundred years or more, this estimate is virtually independent of the actual lifetime. The natural sources are estimated to be about 15 tg/yr. We also find that nitrous oxide started increasing rapidly only during the last century. The trends over the last decade are extremely variable; over 3-year periods the trends have ranged from 0.5+/-0.2 parts per billion by volume (ppbv/yr) to 1.2+/-0.1 ppbv/yr. The average rate of increase is about 0.80+/-0.02 ppbv/yr or 0.27+/-0.01%/yr (1977-1988). There is an indication that N2O may be increasing faster in recent years than during the middle 1970s by about 0.2+/-0.1 ppbv/yr. It is likely that several small anthropogenic sources may be causing the present trends, all emitting between 0.1 and 1.5 Tg/yr.
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In order to estimate the concentrations of atmospheric nitrous oxide (N2O) during the last 250 years, air samples were extracted from an Antarctic ice core, H15, using a dry extraction system and were then analyzed with a precision of ±2 ppbv. The results obtained were clearly less scattered and much tighter than those of the previous studies. Our data showed that the concentrations of atmospheric N2O in the 18th century were about 276 ppbv on average. It was also obvious that the N2O concentration began to increase in the mid-19th century and reached approximately 293 ppbv around 1965, the trend of the concentration increase correlating quite well with the direct atmospheric measurements at the South Pole. Such an increase in the atmospheric N2O concentration is thought to be of anthropogenic origin.
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The finding that catalytic converters enhance the N2O emissions from motor vehicles gave rise to the concern that they may represent a significant source of N2O. Measurements of N2O and CO2 emissions of a fleet of about 40,000 cars were conducted in two roadway tunnels in Stockholm, Sweden, and Hamburg, Germany, to estimate N2O emissions under normal driving conditions. To avoid any risk of artifact N2O formation, samples were analyzed within 1 min after collection. Median N2O to CO2 molar emission ratios of 1.4 × 10-4 and 0.6 × 10-4 were measured in Stockholm and Hamburg, respectively. The lower emission ratio in Hamburg may well reflect the smaller fraction of catalyst-equipped cars in Germany (22%) compared to the Swedish vehicle fleet (33%) as well as low N2O emissions from trucks which were not allowed in the Stockholm tunnel. From our measurements we derive a N2O to CO2 molar emission ratio from cars equipped with catalysts in the median to interquartile range of 3.8 ± 2.2 × 10-4, from which present worldwide N2O emissions from cars are estimated to be 0.38 ± 0.22 Tg N2O (0.24 ± 0.14 Tg N) per year, corresponding to 3-16% of the atmospheric growth of 4.7 ± 0.9 Tg N2O/yr (3.0 ± 0.6 Tg N/yr). From the worldwide emission of 0.38 Tg N2O we derived an emission of about 170 mg N2O/km for catalyst-equipped cars, significantly higher than those reported in earlier studies. If the entire present fleet of cars were to be equipped with current types of catalysts, the global N2O emission could double and reach 6-32% of the atmospheric growth rate.
Chapter
The most important soil borne and land use related greenhouse gases are carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). The present annual increase of atmospheric CO2 is 0.5%. The total emission of CO2 is 6.5 to 7.5 Gt C y-1. Fossil fuel combustion contributes 5.7 Gt C y-1. The present global rate of deforestation of 10 to 20 million ha y-1 causes an emission of 1 to 2 Gt C y-1 including the release of CO2 from soil organic matter oxidation. There is uncertainty about the sinks of CO2. The oceanic uptake is less than 1 Gt C y-1, while the atmospheric accumulation accounts for approximately 3.5 Gt C. Increasing net primary production and other terrestrial sinks balance the budget. The emissions from fossil fuel use will probably increase, and projections of efficiency and magnitude of future energy use are rather uncertain. Deforestation will continue in the coming decades to satisfy the growing demand for agricultural land. The atmospheric concentration of CH4 is rising at a rate of 1% y-1. The major part of this fast increment is caused by increasing emissions, while a minor part can be attributed to decreasing destruction in the atmosphere. The total annual emission from all sources is 400 to 640 Tg CH4. Biotic sources make up about 80% of the total annual emission, the rest is from fossil sources. The biotic sources of CH4 are: wetland rice cultivation (20% of the total source), natural wetlands (20%), ruminating animals (15%), landfills (10%), oceans and lakes (5%) and biomass burning (15%). The contribution by termites is very uncertain. Most sources are increasing at present. Nitrous oxide is increasing at a rate of 0.2 to 0.3% and its sources are almost exclusively biogenic. Nitrous oxide is inert in the troposphere, but it destroys stratospheric ozone (O3). The causes of the increase in atmospheric N2O are not well known. Fossil fuel combustion is a minor source of N2O. Increasing use of N-fertilizers in agriculture is a growing source of N2O. The emissions from natural ecosystems are not well known at present.
Chapter
There are many factors, both natural and human related, that are influencing the Earth’s climate. Of these factors, there is particular concern about the potential changes to climate that may be occurring due to growing atmospheric concentrations of gases that absorb terrestrial infrared radiation, termed greenhouse gases. Much of this concern has centeredaround carbon dioxide (CO2) because of its importance as — greenhouse gas and also because of the rapid rate at which its atmospheric concentration has been increasing. However, in the last decade, it has been shown that other greenhouse gases are contributing to about half of the overall increase in the greenhouse effect on climate. In addition to these direct effects, research studies have shown that chemical interactions in the atmosphere can lead to additional ‘indirect’ effects on climate. As an example, changes in stratospheric ozone have received much attention because of concerns about ultraviolet radiation, but ozone is also — greenhouse gas, and changes in its distribution can affect climate.
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Attempts to support the global warming thesis with analyses of the carbon dioxide content of air bubbles in glacial ice samples, are based on fudged data and ignorance of the physical processes of glacial ice formation.
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Valuable empirical data are provided by climate and greenhouse gases concentration records obtained from the Vostok ice core over the last climatic cycle. The temperature profile and CO2-CH4 concentrations are closely related with significant increases of CO2 (200 to 280 ppmv) and CH4 (doubled) associated with glacial-interglacial transitions. A statistical approach shows that temperature changes can be essentially explained by a Milankovich type forcing associated with a greenhouse gas forcing. This result is in agreement with GCM simulations of the Last Glacial Maximum, both on a local (Vostok) and global scale. -from Authors
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The N-enrichment of the biosphere due to human activities has potential global consequences in enhancing, cumulatively, the emission of N2O to the atmosphere. This aspect of nitrogen pollution demands a global analysis of the 'human nitrogen cycle'. We have used Norway as an example to analyze the nitrogen flows within a society and the dissipation of N to the environment. The present paper concentrates on the food producing sector, which was found to represent the largest N-flow and had the most complex interferences within the nitrogen cycle. The edible products that reach the consumers' mouths account for around 10% of the total N inputs at the primary (plant) production level. The largest N-dissipation occurs in plant production, but the performance of the society as a whole is largely determined by the human diet. The N-cost, defined as the ratio between fertilizer N-input (including animal manure) and the N in products, is around 3 for wheat, 14 for dairy products and 21 for meat. The analyses of different mitigation options also reveal the importance of recycling at the highest possible trophic level. Major reductions in the total consumption of N can be obtained by moderate changes towards a more vegetarian diet and better utilization of existing food. In contrast, recycling of waste at the lowest trophic level (compost) is very inefficient.
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Results from Antarctic ice cores are reported which show that the atmospheric N2O concentration was about 30 percent lower during the Last Glacial Maximum than during the Holocene epoch. The data also show that present-day N2O concentrations are unprecedented in the past 45 kyr and hence provide evidence that recent increases in atmospheric N2O are of anthropogenic origin.
Chapter
Ice cores have been revealed as a powerful indicator of global environmental conditions of the preindustrial time and the glacial-interglacial cycle (the last 150,000 years). Of special interest is the most direct evidence of past changes in radiatively active trace gases found in the ice record. We present here a review of the results concerning three of the main radiatively active gases: CO2, CH4, and N2O. The record indicates that the three gases had significantly lower concentrations during the preindustrial time and that we cannot disregard possible global fluctuations of the preindustrial background over the last millennium. The large increase (by up to a factor of 2 in the case of CH4) between preindustrial time and today is largely attributed to anthropogenic activities. The glacial-interglacial cycle has been documented for CO2 and CH4. Their variations are generally well-correlated with global climatic changes showing strongly depleted concentrations (by up to about a factor of 2 in the case of CH4) during the full glacial conditions relative to interglacial periods. The gas records obtained from ice cores can be interpreted, at least qualitatively, in terms of flux changes between ocean, continental biosphere, and atmosphere, and, in the case of CH4, of changes in tropospheric destruction rate. These changes are assumed to be induced by direct or indirect climatic forcings. In turn, the changes in CO2 and CH4 are participating on the paleoclimatic variability and information can be obtained from the record on the climate sensitivity of greenhouse gases.
Article
Investigations of the relationship between changes in climate and the variation of composition of the atmosphere can be performed most directly and with the highest resolution possible by analyzing the air sampled and preserved in the polar ice sheets for hundreds of thousands of years by nature itself. For the determination of CO2, CH4, N2O, and CO in air samples of 1–3 cm3 extracted from ice cores, a high-frequency modulated tunable diode laser absorption spectrometer has been developed. The instrument can measure CO2, CH4, N2O, and CO at ambient mixing ratios of 300 ppmv (1 ppmv=10−6 volume mixing ratio), 1700, 300, and 100 ppbv (1 ppbv=10−9 volume mixing ratio), respectively, with a precision of 1%–2%. The measurement of high CO2 mixing ratios is not constrained by the detection limit. For other gases mixing ratios of 20 ppbv of CH4, 0.9 ppbv of N2O, and 1.6 ppbv of CO are detectable with the instrument in 2 cm3 standard temperature and pressure. These detection limits and the measurement precision are sufficient for the determination of past changes in atmospheric composition. The technique is also suitable for other applications in which several infrared active trace gases have to be determined in the low ppbv and possibly even in the upper pptv range in air samples of a few cm3 or small samples of other matrices. The sensitivity or the reproducibility of the instrument can be improved by another order of magnitude by using more powerful lasers and by averaging over longer periods. Such improvement could result in a capability to detect sub-ppbv mixing ratios in samples of the present size or ppbv measurements in even smaller air samples. The higher reproducibility would also make the technique interesting for measurements of isotope ratios. © 1997 American Institute of Physics.
Article
In this paper we first summarise major findings of recent atmospheric studies of nitrogen and sulphur species present in the boundary layer of coastal Antarctic regions. We then discuss the implications of such atmospheric data for the interpretation of nitrate, ammonium, methanesulphonate and sulphate records in deep ice cores extracted from central Antarctica in terms of past atmospheric chemistry changes.
Article
Analysis This review article summarizes the results of Soviet‐French investigations into the ice core from a deep drillhole at Vostok Station in Antarctica. Changes in air temperature, snow accumulation, greenhouse gases, aerosols and other chemical components in the environment are traced over 160,000 years, i.e., over a full climatic cycle. Orbital and atmospheric impacts on the climate and on the role of greenhouse gases in these processes are analyzed. On the basis of these analyses, it is predicted that with a doubling of atmospheric CO2 (which many scientists believe to be highly probable) temperatures may rise by 3–4° C; this in turn could lead to a massive collapse of the world's marine ice sheets and to a sea‐level rise of 5–7 m; mountain glaciers in temperate and subtropical latitudes would almost entirely disappear.
Article
The extraction and analysis of air from the snowpack (firn) at the South Pole provides atmospheric concentration histories of biogenic greenhouse gases since the beginning of the present century which confirm and expand on those derived from studies of air trapped in ice cores. Furthermore, calculations based on the inferred atmospheric concentrations of oxygen and carbon dioxide indicate that–in contrast to the past few years—the terrestrial biosphere was neither a source nor sink of C02 between ˜1977 and 1985.
Article
Analysis of air trapped in ice cores shows that the atmospheric contents of the greenhouse gases CO2, CH4 and N2O have increased from the glacial to the preindustrial holocene. Further increases have been occurring during the industrial era, which may have contributed to the observed global warming. In addition, CH4 and N2O play large roles in ozone and hydroxyl chemistry. Here we present a model analysis of the changes in atmospheric temperatures and the concentration of O3, OH and related gases between the three epochs. Despite large changes in the atmospheric contents of CO2, CH4 and N2O, total ozone and tropospheric OH hardly changed between the glacial and preindustrial holocene. The global annual atmospheric CH4 sink increased from 90 to 210 Tg between the glacial and preindustrial, and since then to 510 Tg, largely following the changes in atmospheric concentrations. Our results indicate less than half as much CH4 production from tropical wetlands during the ice age than during the holocene.
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We analyzed ice cores from both northern and southern polar regions to determine the concentrations of nitrous oxide in the pre-industrial and ancient atmospheres from about 150 years to 3000 years B.P. We found that the pre-industrial concentration of nitrous oxide remained constant over the period we studied and that the average atmospheric concentration was 285 ± 1 ppb volume (90% confidence limits), representing about 2100 Tg (2100 × 10 ¹² g) of N 2 0 in the atmosphere, whereas the average concentration in 1984 was about 307 ppb volume or 2260 Tg. This is a change of 22 ppb volume (160 Tg), or about 8%, between pre-industrial and present times. Now the rate of change is between 0.7 and 0.9 ppb volume/year or 5 and 6.5 Tg/year, which is a slow increase of about 0.3% per year. The changes observed are probably caused by increasing use of fossil fuels, particularly coal and oil, and perhaps to a lesser extent by the use of nitrogen fertilizers in recent years. The atmospheric lifetime of N 2 O is probably between 100 and 150 years. The pre-industrial concentrations, present levels, and a lifetime of 100 years are consistent with natural sources, mostly soils and oceans, of about 22 Tg/year and the present anthropogenic sources of about 8.7 Tg/year. In the next 50 years we expect nitrous oxide levels to reach 360–390 ppb volume, or about 16–25% more than present.
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The atmospheric CH4 increase from ∼0.7 to 1.68 p.p.m.v. over about the past 300 years which has been documented from analysis of air trapped in ice cores1-4 and from tropospheric measurements (see ref. 5 for example) is attributed to anthropogenic modifications of the CH4 cycle. The concern about this increase is due to the radiatively and chemically active nature of CH4. Here we present strong evidence from analysis of the Vostok ice core, that CH4 concentrations increased from 0.34 to 0.62 p.p.m.v. between the end of the penultimate ice age and the following interglacial, about 160-120 kyr BP. This CH4 change may be explained by considering the effect of the climatic change on the CH4 cycle. Its contribution (including chemical feedback) to the global climatic warming is estimated to be about 25% of that due to CO2.
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Recent measurements1,2 on ice samples from Camp Century (Greenland, 77°10'N, 61°08'W), Byrd Station (Antarctica, 80°01'S, 110°31'W) and Dome C (74°40'S, 125°10'E) suggest that during the late part of the last glaciation the atmospheric CO2 concentration was significantly lower than during the Holocene. Further investigation of this natural increase of the atmospheric CO2 concentration in the past should aid our understanding of the climatic implications of the man-made CO2 increase since the beginning of industrialization3. Here we report new and precise measurements of the CO2 concentration of the air occluded in bubbles of ice samples from Camp Century and Byrd Station, using a new dry extraction technique. The extracted gases were analysed with an IR-laser spectrometer (IRLS). Samples from 22 different depths were analysed from each core. The samples are distributed over a depth interval corresponding approximately to the past 40,000 yr. In addition results for ice samples from selected depth horizons from a colder region (North Central, Greenland 74°37'N, 39°36'W) and from a warmer region (Dye-3, Greenland 65°11'N, 43°50'W) are given. Based on these results we estimate the trend of the atmospheric CO2 concentration during the past 40,000 yr.
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In photosynthesis, O2 is continuously formed from H2O and released to the atmosphere. Coupled with respiration, photosynthesis forms a loop in which oxygen isotopes are exchanged between O2 and H2O. During the ice ages, sea water was enriched in delta18O by ~1.30/00 relative to the present value1. Continental waters in the areas of high primary productivity exchange rapidly with the oceans. They probably presented a similar isotopic enrichment. Since the delta18O of glacial water was greater than at present, we would expect that the delta18O of atmospheric O2 was also greater than at present. Fireman and Norris2 and Horibe et al.3 have measured the delta18O of O2 from the glacial atmosphere by analysing trapped gases in ice cores. However, their data are either too few or too imprecise to demonstrate whether delta18O of atmospheric O2 has, in fact, varied. Here we present data on the changes, during the past 22 kyr approximately, in the delta18O of atmospheric O2 trapped in the ice core Dome C (East Antarctica, 74° S, 124° E). The results show that the isotopic composition of atmospheric O2 has indeed varied along with that of sea water, and that the delta18O (O2) record offers a tool for studying several important aspects of the global cycles of O2 and H2O in relation to the climate.
Chapter
Ice cores provide the most direct tool for reconstructing the evolution of the atmospheric CO2 during the last 40,000 years. The results obtained on antarctic cores indicate that the atmospheric C02 was increasing by a factor of about 1.3 at the end of the last Ice Age. They suggest a close C02-climate relation, with the C02 change starting almost simultaneously or even slightly before the temperature change at high latitudes. For the recent period (the last 500 years) the antarctic ice suggest that the “pre-industrial” C02 level was not constant and was in the 260–280 ppmv range. If so, it was significantly lower than the 290 ppmv adopted previously in modelling the evolution of the atmospheric C02 during the present period and the corresponding climatic response.
Article
The gas content in polar ice samples was extracted and analysed. The composition of the gas content is close to the present atmospheric composition except for C02. Nevertheless, the 02-content of ice is systematically less than the atmospheric content whereas the Ar-content is higher. C02-contents of a few tenths of per cent are obtained. Various processes which could explain the observed effects are discussed.
Article
A technique for extracting and analysing large air samples from bubbles occluded in an Antarctic ice core is discussed. Core samples of up to 1400 g were milled to release approximately 120 cm ³ of air, which was dried, collected in a cold finger and then analysed by gas chromatography. The concentrations of atmospheric carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) over the past 450 years have thus been revealed. Measurements of a chlorofluorocarbon (CCl 2 F 2 ) in the ice-core air were used to check core quality and the air-occlusion process. The ice core, designated BHD, was thermally drilled from the summit of Law Dome, Antarctica, where the average accumulation rate is 0.65 m a ⁻¹ water equivalent and the annual average temperature is –22°C. Ice dating was achieved by counting annual cycles of oxygen-isotope ratio and d.c. conductivity, and air dating was deduced from the density profile. The results show the pre-industrial concentrations of the gases to be 288 ± 5 ppm volume for CO 2 , 800 ± 50 ppb volume for CH 4 and 285 ± 10 ppb volume for N 2 0.
Article
The concentration of nitrous oxide has been measured in air samples collected from monitoring stations and aboard oceanographic vessels in the major world oceans. These measurements demonstrate that the tropospheric nitrous oxide concentration is increasing at approx.0.2% per year, thus confirming earlier observations of the increase based on stored samples. The measurements also show that the concentration of nitrous oxide in the northern hemisphere is higher than in the southern hemisphere, the average difference during the sampling interval having been about 0.8 parts per billion (ppb), compared to a January 1, 1978 northern hemisphere dry air mole fraction of 300.2 ppb. The data are well represented by a simple box model which relates the tropospheric rate of increase to an exponentially increasing source function. The observed increase may be explained by combustion of fossil fuels and agricultural activity, with a total source strength of approx.11 x 10Â¹Â° mol/yr as of January 1, 1978. A substantial fraction of this production is explained by combustion, and agricultural production is therefore considerably less than has been previously estimated. The concentration of nitrous oxide in the preindustrial unperturbed troposphere is estimated to have been between 281 and 291 ppb, depending upon the rate of increase of the mean anthropogenic source function, and the preindustrial latitudinal distribution is estimated to have been nearly uniform. According to the model projections, the concentration of tropospheric nitrous oxide in the year 2000 will be 5 to 7% above present values. The observed rate of tropospheric increase directly affects the production of stratospheric nitric oxide, and plays a significant role in the earth's radiation balance, conservatively estimated as 10--15% of the effect due to increasing carbon dioxide.
Article
D 57 station in Terre Adélie lies between the coast and the central Antarctic plateau. A 200 m ice core was recovered in summer 1980–81 at this location and analyzed by an electroconductometric method to detect exceptional acid levels linked to fallout from major volcanic eruptions. Several signals were indeed found. The corresponding ice-core sections were then analyzed for mineral acids (H 2 SO 4 and HNO 3 ). We detected several large volcanic events, in particular two eruptions identified as Tarabora (1815) and Galunggung (1822). The background concentration of sulphate was found to be relatively low (about 0.5 μeq 1 ⁻¹ ). On the other hand nitrate values were higher than at coastal or central Antarctic locations (except for the Sauth Pole). Two spikes were found in the nitrate profile at depths of 140 and 148 m. It is thought that they could be either linked to the 1604 and 1572 supernovae Kepler and Tycho or correspond to epochs of particularly high solar activities. With the aid of these sulphate and nitrate exceptional events, a dating of the D 57 ice core can now be proposed which corresponds to a mean snow accumulation rate of 22 cm of ice equivalent per year over the last four centuries.
Article
The measurement of gases enclosed in polar ice cores provides valuable Information concerning the history of the ice sheets and their environment. The extraction of gases from ice is a critical step in the experimental procedure. We found that the most efficient methods of gas extraction for 20 to 50 g samples were ice melting and controlled refreezing of the melt water for the total gas content and ice crushing far the CO 2 content. These two experimental methods are described in detail. It is shown, in particular, that ice is easily contaminated by carbonate dust during sample preparation. This contamination introduces an excess of CO 2 when gases are extracted using a procedure involving ice melting.
Article
Atmospheric carbon dioxide (CO2) levels before the industrial revolution were ~ 260–280 p.p.m.v. (parts per 106 by volume) as determined from studies of air trapped in ice1,2. We report here similar results, using Antarctic ice, for the CO2 levels during the seventeenth and eighteenth centuries, which suggest an average concentration of 281 (standard deviation σ = 7) p.p.m.v. The data constrain the net release of biospheric carbon to the atmosphere over the past 200 yr, to ~5 × 1010 tonnes of carbon, mostly during 1850–1900. Measurements of two other ‘greenhouse’ gases, methane (CH4) and nitrous oxide (N2O), show increases of about 90 and 8% respectively since 1600. This CH4 increase is similar to the recently reported3–6 doubling over the same period, and the N2O increase, the first direct evidence of historical changes in N2O, is consistent with releases due to expanding anthropogenic combustion processes7.
Article
Air entrapped in bubbles formed in cold ice has essentially the same composition as that of the atmosphere at the time of bubble formation. The analysis of dated ice samples therefore enables the history of atmospheric composition to be investigated.1–3 The age of the entrapped air is, however, not the same as that of the surrounding ice because air bubbles only become isolated from the atmosphere during the transition from firn to ice. Typically the age of the ice at this transition is between 100 and 3,000 yr, depending mainly on firn temperature and snow accumulation rate. The mean age difference between ice and enclosed air, as well as the age distribution width for a given sample, are especially important for the investigation of the anthropogenic increase of CO2 and trace gases in the atmosphere over the last centuries, and for the comparison of climatic parameters recorded in the ice with parameters recorded in the bubbles. For Siple Station (Antarctica), this age difference and age distribution width were deduced from the bubble volume measured as a function of depth. The values are 95 yr and 22 yr respectively.
Article
Simple glaciological conditions at Dome C in east Antarctica have made possible a more detailed and accurate interpretation of an ice core to 950 m depth spanning some 32,000 yr than that obtained from earlier ice cores. Dated events in comparable marine core has enabled the reduction of accumulation rate during the last ice age to be estimated. Climatic events recorded in the ice core indicate that the warmest Holocene period in the Southern Hemisphere occurred at an earlier date than in the Northern Hemisphere.
Article
Direct evidence of past atmospheric CO2 changes has been extended to the past 160,000 years from the Vostok ice core. These changes are most notably an inherent phenomenon of change between glacial and interglacial periods. Besides this major 100,000-year cycle, the CO2 record seems to exhibit a cyclic change with a period of some 21,000 years.
Article
Air entrapped in bubbles of cold ice has essentially the same composition as that of the atmosphere at the time of bubble formation. Measurements on ice core samples from Byrd Station (Antarctica) and Dye 3 (Greenland) show that the atmospheric methane concentration was only about 350 parts per 109 by volume (p.p.b.v.) during the last glaciation, compared with a mean preindustrial level of about 650 p.p.b.v. and a present value of 1,650 p.p.b.v.
Article
Human activity this century has increased the concentrations of atmospheric trace gases, which in turn has elevated global surface temperatures by blocking the escape of thermal infrared radiation. Natural climate variations are masking this temperature increase, but further additions of trace gases during the next 65 years could double or even quadruple the present effects, causing the global average temperature to rise by at least 1 °C and possibly by more than 5 °C. If the rise continues into the twenty-second century, the global average temperature may reach higher values than have occurred in the past 10 million years.
Article
Rasmussen and Khalil (1981) have shown that the concentration of methane is increasing in the earth's atmosphere. A continuing increase of methane may perturb the global environment in the future by warming the earth and leading to more ozone and carbon monoxide in the atmosphere. It appears that the present concentration of methane may be more than twice as high as the natural levels of 150 years ago. An analysis of air bubbles buried long ago in polar ice makes it possible to deduce the concentrations of methane in the old and ancient atmospheres. The present investigation is concerned with the results of an analysis of more than 80 ice core samples, taking into account both polar regions of the earth. The samples range in age from about 100 to nearly 3000 years old. It is found that the concentration of methane started changing significantly about 150 years ago. These findings suggest that the increase of methane is probably indirectly caused by the rapid increase of human population.
Article
Emissions of nitrous oxide (N2O) have been analyzed from industrial boilers and from a large experimental combustor burning natural gas, oil, or coal. Production of N2O and production of NO(x) were observed to be correlated, with an average molar ratio of 0.58:1 (N2O-N:NO). In conventional single-stage combustors, about 14 percent of fuel nitrogen is converted to N2O and 24 percent is converted to NO(x). Conversion of fuel nitrogen to N2O was much less efficient in a two-stage experimental combustor and in wood fires. A model is presented describing emissions of N2O globally, from the beginning of the industrial revolution to the present. It is expected that concentrations of N2O should rise more than 20 percent to about 367 ppb by the year 2050, based on conservative projections of world energy consumption.
Article
Concentrations of the halocrbons CCl3F (F-11), CCl2F2 (F-12), CCl4, and CH3CCl3, methane (CH4), and nitrous oxide (N2O) over the decade between 1975 and 1985 are reported, based on measurements taken every January at the South Pole and in the Pacific Northwest. The concentrations of F-11, F-12, and CH3CCl3 in both hemispheres are now more than twice their concentrations 10 years ago. However, the annual rates of increase of F-11, F-12, and CH3CC13 are now considerably slower than earlier in the decade, reflecting in part the effects of a ban on their nonessential uses. Continued increases in these trace gas concentrations may warm the earth and deplete the stratospheric ozone layer, which may cause widespread climatic changes and affect global habitability.
Article
The ozone layer in the upper atmosphere is a natural feature of the earth's environment. It performs several important functions, including shielding the earth from damaging solar ultraviolet radiation. Far from being static, ozone concentrations rise and fall under the forces of photochemical production, catalytic chemical destruction, and fluid dynamical transport. Human activities are projected to deplete substantially stratospheric ozone through anthropogenic increases in the global concentrations of key atmospheric chemicals. Human-induced perturbations may be occurring already.
The Greenhouse Effect
• H J Bolle
• W Seiler
• B Bolin
• H. J. Bolle
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Composition des gas contenus dans la glace polaire
• D Raynaud
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Etude des variations passées du CO2 atmosphérique à partir de l'analyse de l'air piégé dans la glace
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