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1.
A variety of models are explored to study the photochemistry of CO2 in the Martian atmosphere with emphasis on reactions involving compounds of carbon, hydrogen, and oxygen. Acceptable models are constrained to account for measured concentrations of CO and O above 90 km, with an additional requirement that they should be in accord with observations of CO, O2, and O3 in the lower atmosphere. Dynamical mixing must be exceedingly rapid at altitudes above 90 km, with effective eddy diffusion coefficients in excess of 107 cm2 sec?1. If recombination of CO2 is to occur mainly by gas phase chemistry, catalyzed by trace quantities of H, OH, and HO2, mixing must be rapid over the altitude interval 30 to 40 km. The value implied for the diffusion coefficient in this region is a function of assumptions made regarding the rates for reaction of OH with HO2 to form H2O and of the rate for reaction of HO2 with itself to form H2O2. If rates for these reactions are taken to have values similar to rates used in current models for the Earth's stratosphere, the eddy diffusion coefficient at 40 km on Mars should be about 5 × 107 cm2 sec?1, consistent with Zurek's (1976) estimate for this parameter inferred from tidal theory. Surface chemistry could have an influence on the abundances of atmospheric CO and O2, but a major effect would imply sluggish mixing at all altitudes below 50 km and in addition would carry implications for the magnitude of the rates for reaction of OH with HO2 and HO2 with itself. 相似文献
2.
The rise of atmospheric O3 as a function of the evolution of O2 has been investigated using a one-dimensional steady-state photochemical model based on the chemistry and photochemistry of Ox(O3, O, O(1D)), N2O, NOx(NO, NO2, HNO3), H2O, and HOx(H, OH, HO2, H2O2) including the effect of vertical eddy transport on the species distribution. The total O3 column density was found to maximize for an O2 level of 10?1 present atmospheric level (PAL) and exceeded the present total O3 column by about 40%. For that level of O2, surface and tropospheric O3 densities exceeded those of the present atmosphere by about an order of magnitude. Surface and tropospheric OH densities of the paleoatmosphere exceeded those of the present atmosphere by orders of magnitude. We also found that in the O2-deficient paleoatmosphere, N2O (even at present atmospheric levels) produces much less NOx than it does in the present atmosphere. 相似文献
3.
G. M. Shved 《Solar System Research》2016,50(2):161-164
The isotopic composition of carbon dioxide in the Martian atmosphere from the measurements of Mars Science Laboratory have been used to estimate the relative abundances of CO2 isotopologues in the Martian atmosphere. Concurrently, this study has revealed long-standing errors in the amounts of some of low-abundance CO2 isotopologues in the Earth’s atmosphere in the databases of spectroscopic parameters of gases (HITRAN, etc.). 相似文献
4.
A theoretical reconstruction of the history of Martian volatiles indicates that Mars probably possessed a substantial reducing atmosphere at the outset of its history and that its present tenous and more oxidized atmosphere is the result of extensive chemical evolution. As a consequence, it is probable that Martian atmospheric chemical conditions, now hostile with respect to abiotic organic synthesis in the gas phase, were initially favorable. Evidence indicating the chronology and degradational history of Martian surface features, surface mineralogy, bulk volatile content, internal mass distribution, and thermal history suggests that Mars catastrophically developed a substantial reducing atmosphere as the result of rapid accretion. This atmosphere probably persisted—despite the direct and indirect effects of hydrogen escape—for a geologically short time interval during, and immediately following, Martian accretion. That was the only portion of Martian history when the atmospheric environment could have been chemically suited for organic synthesis in the gas phase. Subsequent gradual degrassing of the Martian interior throughout Martian history could not sustain a reducing atmosphere due to the low intensity of planet-wide orogenic activity and the short atmospheric mean residence time of hydrogen on Mars. During the post-accretion history of Mars, the combined effects of planetary hydrogen escape, solar-wind sweeping, and reincorporation of volatiles into the Martian surface produced and maintained the present atmosphere. 相似文献
5.
Daniel Cariolle 《Planetary and Space Science》1983,31(9):1033-1052
The ozone concentration in the stratosphere results from the combined action of various catalytic cycles involving nitrogen oxides, HOx and Clx radicals, as well as from transport processes. The results of our one-dimensional model allow the relative efficiency o those cycles to be evaluated as a function of altitude. To take into account the chemical couplings between stratospheric species, a self-consistent scheme is used to determine the budget of Ox NOx Clx and HOx species. Furthermore, the concept of chemical relaxation time is developed for ozone and the other species. It leads to a better understanding of the role of “temporary reservoir” species in the stratospheric photochemistry.It is found that, in the upper stratosphere, the ozone budget can be established in a straightforward manner, whereas in the lower stratosphere, chemical couplings are more complex and transport processes increasingly important. Due to the oversimplified transport parametrization used in this model, results for this region of the atmosphere must be viewed with caution.The model evaluations of the impact of chlorofluorocarbon release and nitrous oxide and methane increase on the ozone layer are also presented. These results can be interpreted in terms of perturbation to the budget of Ox NOx Clx and HOx species. Nevertheless model predictions should be taken with caution because large uncertainties still remain in some key reaction rates and in the behaviour of most of the source gases. In addition, inadequacies in the model formulation are difficult to assess and contribute to the overall uncertainty. 相似文献
6.
Geologic evidence of the prior existence of liquid water on Mars suggests surface temperatures Ts were once considerably warmer than at present; and that such a condition may have arisen from a larger atmospheric greenhouse. Here we develop a simple climate model for a CO2/H2O Mars atmosphere including water vapor-longwave opacity feedback in the atmosphere and temperature-albedo feedback at surface icecaps, under the assumption that once the Martian surface pressure was ps ≥ 1 atm CO2. Longwave flux to space is computed as a function of Ts and ps using band-absorption models for the effect of the 15-μm fundamental, and the 10- and 15-μm hot bands, of the CO2 molecule; as well as the pure rotation bands and e continuum of H2O. The derived global radiative balance predicts a global mean surface temperature of 283°K at 1 atm CO2. When the emission model is coupled to a latitudinally resolved energy balance climate model, including the effect of poleward heat transfer by atmospheric baroclinic eddies, the solutions vary, depending on ps. We considered two cases: (1) the present Mars (ps ? 0.007 atm) with pressure-buffering by solid CO2 icecaps, and limited poleward heat flux by the atmosphere; and (2) a hypothetical “hot Mars” (ps ? 1.0 atm), whose much higher CO2 amount augmented by H2O evaporative feedback yields a theoretical Ts distribution with latitude admitting liquid water over 95% of the surface, water icecaps at the poles, and a diminished equator-to-pole temperature gradient relative to the present. 相似文献
7.
The 362.156 GHz absorption spectrum of H2O2 in the Mars atmosphere was observed on September 4 of 2003, employing the James Clerk Maxwell Telescope (JCMT) sub-millimeter facility on Mauna Kea, Hawaii. Radiative transfer analysis of this line absorption yields an average volume mixing ratio of 18±0.4 ppbv within the lower (0-30 km) Mars atmosphere, in general accordance with standard photochemical models (e.g., Nair et al., 1994, Icarus 111, 124-150). Our derived H2O2 abundance is roughly three times greater than the upper limit retrieved by Encrenaz et al. (2002, Astron. Astrophys. 396, 1037-1044) from infrared spectroscopy, although part of this discrepancy may result from the different solar longitudes (Ls) of observation. Aphelion-to-perihelion thermal forcing of the global Mars hygropause generates substantial (>200%) increases in HOx abundances above ∼10 km altitudes between the Ls=112° period of the Encrenaz et al. upper limit measurement and the current Ls=250° period of detection (Clancy and Nair, 1996, J. Geophys. Res. 101, 12785-12590). The observed H2O2 line absorption weakens arguments for non-standard homogeneous (Encrenaz et al., 2002, Astron. Astrophys. 396, 1037-1044) or heterogeneous (Krasnopolsky, 2003a, J. Geophys. Res. 108; 2003b, Icarus 165, 315-325) chemistry, which have been advocated partly on the basis of infrared (8 μm) non-detections for Mars H2O2. Observation of Mars H2O2 also represents the first measurement of a key catalytic specie in a planetary atmosphere other than our own. 相似文献
8.
An isothermal reservoir of carbon dioxide in gaseous contact with the Martian atmosphere would reduce the amplitude and advance the phase of global atmospheric pressure fluctuations caused by seasonal growth and decline of polar CO2 frost caps. Adsorbed carbon dioxide in the upper ～10 m of Martian regolith is sufficient to buffer the present atmosphere on a seasonal basis. Available observations and related polar cap models do not confirm or refute the operation of such a mechanism. Implications for the amplitude and phase of seasonal pressure fluctuations are subject to direct test by the upcoming Viking mission to Mars. 相似文献
9.
In order to understand the complex multi-parameter system of destruction of organic material on the surface of Mars, step-by-step laboratory simulations of processes occurring on the surface of Mars are necessary. This paper describes the measured effects of two parameters, a CO2 atmosphere and low temperature, on the destruction rate of amino acids when irradiated with Mars-like ultraviolet light (UV). The results show that the presence of a 7 mbar CO2 atmosphere does not affect the destruction rate of glycine, and that cooling the sample to 210 K (average Mars temperature) lowers the destruction rate by a factor of 7. The decrease in the destruction rate of glycine by cooling the sample is thought to be predominantly caused by the slower reaction kinetics. When these results are scaled to Martian lighting conditions, cold thin films of glycine are assumed to have half-lives of 250 h under noontime peak illumination. It has been hypothesised that the absence of detectable native organic material in the Martian regolith points to the presence of oxidising agents. Some of these agents might form via the interaction of UV with compounds in the atmosphere. Water, although a trace component of Mars’ atmosphere, is suggested to be a significant source of oxidising species. However, gaseous CO2 or adsorbed H2O layers do not influence the photodestruction of amino acids significantly in the absence of reactive soil. Other mechanisms such as chemical processes in the Martian regolith need to be effective for rapid organic destruction. 相似文献
10.
Joel S. Levine 《Icarus》1976,28(2):165-169
The presence of 28% argon on Mars as calculated by Levine and Riegler and indirectly inferred from Soviet Mars-6 lander data has important implications for the outgassing history of H2O, CO2, and N2 on Mars. Even if the terrestrial volatile outgassing ratio is only approximately valid for Mars, then large quantities of H2O [of the order of 105 gcm?2 (about 108 more H2O than is currently present in the Martian atmosphere)] and about 104 gcm?2 of CO2 (about 103 times more CO2 than found at present in the Martian atmosphere) and some 450 gcm?2 of N2 may have outgassed over the history of Mars. 相似文献
11.
Thérèse Encrenaz 《Earth, Moon, and Planets》2009,105(2-4):127-134
Although Mars is a favored target for planetary exploration, there is still a need for complementary ground-based observing programs of the Martian atmosphere, and this need will remain in the future. Indeed, as the atmosphere is very tenuous (less than 0.01 bar at the surface), the lines are very narrow and a high spectral resolving power (above 104) is required over large spectral intervals. In addition, ground-based observations of Mars allow the instantaneous mapping of the whole planet, and thus the study of diurnal effects, which cannot be achieved from an orbiter. Recent ground-based achievements about the Martian atmospheric science include the first detection of H2O2 in the submillimeter range, the measurement of winds from CO millimetric transitions, the first detection of CH4 and the O3, H2O2, H2O, and CH4 mapping in the infrared. With an ELT, it will be possible to study at high spatial resolution transient atmospheric phenomena and to search for traces of minor constituents with unprecedented sensitivity. With ALMA, it will be also possible to search for minor species and to map the mesospheric winds for better constraining the climate models. 相似文献
12.
In January of 1982 we measured a microwave spectrum of CO in the Martian atmosphere utilizing the rotational J = 1 → 2 transition of CO. We have analyzed data and reanalyzed the microwave spectra of R. K. Kakar, J. W. Waters, and W. J. Wilson, (Science196, 1090–1091, 1977, measured in 1975) and J. C. Good and F. P. Schloerb, (Icarus47, 166–172, 1981 measured in 1980) in order to constrain estimates of the temporal variability of CO abundance in the Martian atmosphere. Our values of CO column density from the data of Karar et al., Good and Schloerb, and our own are 1.7 ± 0.9 × 1020, 3.0 ± 1.0 × 1020, and 4.6 ± 2.0 × 1020cm?2, respectively. The most recent estimate of CO column density from the 1967 infrared spectra of J. Connes, P. Connes, and J.P. Maillard, (Atlas de Spectres Infarouges de Venus, Mars, Jupiter, et Saturne, Editions due Centre National de la Recherche Scientifique, Paris, 1969), is 2.0 ± 0.8 × 1020 cm?2 (L.D.G. Young and A.T. Young, Icarus30, 75–79, 1977). The large uncertainties given for the microwave measurements are due primarily to uncertainty in the difference between the continuum brightness temperature and atmospheric temperatures of Mars. We have accurately calculated the variation among the observations of the continuum (surface) brightness temperature of Mars, which is primaroly a function of the observed aspect of Mars. A more difficult problem to consider is variability of global atmospheric temperatures among the observations, particularly the effects of global dust storms and the ellipticity of the orbit of Mars. The large bars accompanying our estimates of CO column density from the three sets of microwave measurements are primarily caused by an assumed uncertainty of ±10°K in our atmospheric temperature model due to possible dust in the atmosphere. A qualitative consideration of seasonal variability of global atmospheric temperatures among the measurements suggests that there is not strong evidence for variability of the column abundance of CO on Mars, although variability of 0–100% over a time scale of several years is allowed by the data set. The implication for the variability of Mars O2 is, crudely, a factor of two less. We found that the altitude distribution of CO in the atmosphere of Mars was not well constrained by any of the spectra, although our spectrum was marginally better fitted by an altitude increasing profile of CO mixing ratios. 相似文献
13.
R.V. Gough J.J. Turley G.R. Ferrell K.E. Cordova S.E. Wood D.O. DeHaan C.P. McKay O.B. Toon M.A. Tolbert 《Planetary and Space Science》2011,59(2-3):238-246
It has been reported by several groups that methane in the Martian atmosphere is both spatially and temporally variable. Gough et al. (2010) suggested that temperature dependent, reversible physical adsorption of methane onto Martian soils could explain this variability. However, it is also useful to consider if there might be chemical destruction of methane (and compensating sources) operating on seasonal time scales. The lifetime of Martian methane due to known chemical loss processes is long (on the order of hundreds of years). However, observations constrain the lifetime to be 4 years or less, and general circulation models suggest methane destruction must occur even faster (<1 year) to cause the reported variability and rapid disappearance. The Martian surface is known to be highly oxidizing based on the Viking Labeled Release experiments in which organic compounds were quickly oxidized by samples of the regolith. Here we test if simulated Martian soil is also oxidizing towards methane to determine if this is a relevant loss pathway for Martian methane. We find that although two of the analog surfaces studied, TiO2·H2O2 and JSC-Mars-1 with H2O2, were able to oxidize the complex organic compounds (sugars and amino acids) used in the Viking Labeled Release experiments, these analogs were unable to oxidize methane to carbon dioxide within a 72 h experiment. Sodium and magnesium perchlorate, salts that were recently discovered at the Phoenix landing site and are potential strong oxidants, were not observed to directly oxidize either the organic solution or methane. The upper limit reaction coefficient, α, was found to be <4×10?17 for methane loss on TiO2·H2O2 and <2×10?17 for methane loss on JSC-Mars-1 with H2O2. Unless the depth of soil on Mars that contains H2O2 is very deep (thicker than 500 m), the lifetime of methane with respect to heterogeneous oxidation by H2O2 is probably greater than 4 years. Therefore, reaction of methane with H2O2 on Martian soils does not appear to be a significant methane sink, and would not destroy methane rapidly enough to cause the reported atmospheric methane variability. 相似文献
14.
It has been suggested that the residual polar caps of Mars contain a reservoir of permanently frozen carbon dioxide which is controlling the atmospheric pressure. However, observational data and models of the polar heat balance suggest that the temperatures of the Martian poles are too high for solid CO2 to survive permanently. On the other hand, the icelike compound carbon dioxide-water clathrate (CO2 · 6H2O) could function as a CO2 reservoir instead of solid CO2, because it is stable at higher temperatures. This paper shows that the permanent polar caps may contain several millibars of CO2 in the form of clathrate, and discusses the implications of this permanent clathrate reservoir for the present and past atmospheric pressure on Mars. 相似文献
15.
It is demonstrated that under conditions which approximate those of the Martian ionosphere traces of CO and O2 can be effectively incorporated in ion clusters via ion-molecule reaction schemes initiated by the CO2+ ion. For example, when 0.3 % CO is added to CO2, (CO)2+ and [(CO)2CO2]+ appear as the major cations (584 Å radiation, 300°K). In mixtures containing O2 in addition to CO2 (CO2. O2)+ and [(CO2)2O2]+ are important species. A recently proposed mechanism to account for the low abundance of CO and O2 in the Martian atmosphere is discussed in the light of these observations. 相似文献
16.
James L. Gooding 《Icarus》1978,33(3):483-513
Chemical weathering on Mars is examined theoretically from the standpoint of heterogeneous equilibrium between solid mineral phases and gaseous O2, H2O, and CO2 in the Martian atmosphere. Thermochemical calculations are performed in order to identify important gas-solid decomposition reactions involving the major mineral constituents of mafic igneous rocks. Where unavailable in the thermochemical literature, Gibbs free energy and enthalpy of formation are estimated for certain minerals and details of these estimation procedures are given. Partial pressure stability diagrams are presented to show pertinent mineral reaction boundaries at 298 and at 240°K. In the present Martian environment, the thermodynamically stable products of gas-solid weathering of individual minerals at 240°K should be Fe2O3, as hematite or maghemite (from fayalite, magnetite, and Fe-bearing pyroxenes), quartz (from all silicates), calcite (from Ca-bearing pyroxenes and plagioclase), magnesite (from forsterite and Mg-bearing pyroxenes), corundum (from all Al-bearing silicates), Ca-beidellite (from anorthite), and szomolnokite, FeSO4 or FeSO4·H2O (from iron sulfides). Albite, microcline, and apatite should be stable with respect to gas-solid decomposition, suggesting that gas-solid weathering products on Mars may be depleted in Na, K, and P (and, possibly, Cl and F). Certain montmorillonite-type clay minerals are thermodynamically favorable intermediate gas-solid decomposition products of Al-bearing pyroxenes and may be metastable intermediate products of special mineral surface reaction mechanisms. However, the predicted high thermodynamic susceptibility of these clay minerals to subsequent gas-solid decomposition implies that they should ultimately decompose in the present Martian surface environment. Kaolinite is apparently the only clay mineral which should be thermodynamically stable over all ranges of temperature and water vapor abundance in the present environment at the Martian surface. Considering thermodynamic criteria, including possible gas-solid decomposition reactions, it is doubtful that significant amounts of goethite and clay minerals can be currently forming on Mars by mechanisms known to operate to Earth. If major amounts of goethite and clay minerals occur on Mars, they probably owe their existence to formation in an environment characterized by the presence of liquid water or by mechanism possibly unique to Mars. In any case, any goethite or montmorillonite-type clay mineral on Mars must ultimately decompose. 相似文献
17.
Chemical kinetic model for the lower atmosphere of Venus 总被引：1，自引：0，他引：1
Vladimir A. Krasnopolsky 《Icarus》2007,191(1):25-37
A self-consistent chemical kinetic model of the Venus atmosphere at 0-47 km has been calculated for the first time. The model involves 82 reactions of 26 species. Chemical processes in the atmosphere below the clouds are initiated by photochemical products from the middle atmosphere (H2SO4, CO, Sx), thermochemistry in the lowest 10 km, and photolysis of S3. The sulfur bonds in OCS and Sx are weaker than the bonds of other elements in the basic atmospheric species on Venus; therefore the chemistry is mostly sulfur-driven. Sulfur chemistry activates some H and Cl atoms and radicals, though their effect on the chemical composition is weak. The lack of kinetic data for many reactions presents a problem that has been solved using some similar reactions and thermodynamic calculations of inverse processes. Column rates of some reactions in the lower atmosphere exceed the highest rates in the middle atmosphere by two orders of magnitude. However, many reactions are balanced by the inverse processes, and their net rates are comparable to those in the middle atmosphere. The calculated profile of CO is in excellent agreement with the Pioneer Venus and Venera 12 gas chromatographic measurements and slightly above the values from the nightside spectroscopy at 2.3 μm. The OCS profile also agrees with the nightside spectroscopy which is the only source of data for this species. The abundance and vertical profile of gaseous H2SO4 are similar to those observed by the Mariner 10 and Magellan radio occultations and ground-based microwave telescopes. While the calculated mean S3 abundance agrees with the Venera 11-14 observations, a steep decrease in S3 from the surface to 20 km is not expected from the observations. The ClSO2 and SO2Cl2 mixing ratios are ∼10−11 in the lowest scale height. The existing concept of the atmospheric sulfur cycles is incompatible with the observations of the OCS profile. A scheme suggested in the current work involves the basic photochemical cycle, that transforms CO2 and SO2 into SO3, CO, and Sx, and a minor photochemical cycle which forms CO and Sx from OCS. The net effect of thermochemistry in the lowest 10 km is formation of OCS from CO and Sx. Chemistry at 30-40 km removes the downward flux of SO3 and the upward flux of OCS and increases the downward fluxes of CO and Sx. The geological cycle of sulfur remains unchanged. 相似文献
18.
Exchange of CO2 and H2O between the Mars regolith and the atmosphere-cap system plays an important role in governing the evolution of the martian atmosphere and the martian climate. Most of the exchangeable CO2 (perhaps one or two orders of magnitude more than the atmospheric inventory) is currently adsorbed on the deep regolith, and can be “cryopumped” to a large quasipermanent CO2 cap (not now present) during lowest Mars obliquity (θ). During the obliquity driven regolith-cap CO2 exchange cycle, the atmospheric pressure varies harmonically between ~0.1 mb (lowest Θ) and ? 20 mb (highest Θ). The regolith buffer plays only a small or negligible role in the seasonal CO2 pressure variations caused by atmosphere-cap exchange because adsorption greatly inhibits diffusion of the seasonal “pressure wave” into the regolith. In contrast, thermally driven H2O seasonal exchange between the atmosphere and regolith appears to be in large part responsible for observed seasonal variations in the small atmospheric H2O inventory. Long term exchange of H2O may be dominated by transfer between the polar caps and ice in the regolith. Available and potential tests of regolith-atmospheric-cap volatile exchange models using ground-based and spacecraft-based techniques are discussed. 相似文献
19.
The abundances of molecular oxygen in the atmospheres of Venus and Mars are sensitive to fundamental photochemical processes. A new upper limit is reported for the molecular oxygen mixing ratio (O2/CO2 < × 10?7) in the integrated column above the visible cloud tops of Venus, based on spectroscopic observations carried out in early spring, 1982. During the same observing period, an O2 column abundance of 8.5 cm-am for the atmosphere of Mars was measured, slightly below the O2 abundances measured a decade earlier. 相似文献
20.
Spectrophotometric scans of Mars and the Moon in the region 4000–5000 Å were obtained and ratioed. No evidence of any absorption greater than 3% is visible in the Martian spectrum. Using our own laboratory spectra of NO2 as well as the published work of Hall and Blacet (1952) we confirm Marshall's (1964) upper limit of 8 μm atmospheres (0.0008 cm amagat) for the abundance of NO2 in the atmosphere of Mars. 相似文献