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1.
A model is presented for the formation of HCN in the upper troposphere and lower stratosphere of Jupiter by ultraviolet photolysis of the C2H5N isomer aziridine, a product of the recombination of NH2 and C2H3 radicals, which originate, respectively, from ammonia photolysis and addition of H atoms to acetylene. An HCN column density of ～ 2 × 1017 cm?2 in the tropopause region, which is comparable to that observed by A. T. Tokunaga, S. C. Beck, T. R. Geballe, J. H. Lacy, and E. Serabyn (Icarus48, 283–289, 1981), is predicted when vertical mixing is slow above the ammonia cloudtops. Sensitivity of the HCN column density to the individual rate constants and the eddy diffusion coefficient profile is discussed, as is the possibility of the existence of additional HCN-yielding pathways. Ammonia, which is saturated in the upper troposphere, is strongly depleted by photolysis in the lower stratosphere. Phosphine is also strongly depleted by photolysis and its abundance in the upper troposphere is shown to depend strongly on vertical mixing in the tropopause region. The possibility of the formation of phosphirane, the P-containing analog of aziridine, is considered but found to be substantially less probable than aziridine. 相似文献
2.
Many of the key properties of Io’s atmosphere, such as its spatial distribution, temperature, column density and composition, are still not fully assessed despite decades of extensive observations. The contribution of the possible gas sources to the atmospheric replenishment are then still unclear.This paper presents disk-resolved observations performed with the Submillimeter Array (SMA) at 345 GHz of atmospheric rotational lines of the main atmospheric species SO2, and, for the first time, of the minor species SO and NaCl. All these species appear concentrated on the anti-jovian hemisphere, but do not share the same spatial distribution. The obtained maps and line-averaged fluxes are compared to realistic models simulating gas sources including volcanic plume outgassing, SO2 frost sublimation and photolysis. Arguments in favor of each sources are examined and compared to observations, putting constraints on their relative roles for each species.While sublimation clearly appears as the favored major source for SO2, SO2 photolysis may account for most of the production of SO. Using constraints on the volcanic plumes distribution from Galileo results, we find that direct volcanic input can only contribute for a minor fraction of atmospheric SO2, but represent a more significant source for SO atmosphere, and is likely to be the only source for NaCl. Temperature and column densities findings are also presented for SO2, and compare well to previously published observations and atmospheric models. 相似文献
3.
Vladimir A. Krasnopolsky 《Planetary and Space Science》2011,59(10):952-964
This paper deals with two common problems and then considers major aspects of chemistry in the atmospheres of Mars and Venus. (1) The atmospheres of the terrestrial planets have similar origins but different evolutionary pathways because of the different masses and distances to the Sun. Venus lost its water by hydrodynamic escape, Earth lost CO2 that formed carbonates and is strongly affected by life, Mars lost water in the reaction with iron and then most of the atmosphere by the intense meteorite impacts. (2) In spite of the higher solar radiation on Venus, its thermospheric temperatures are similar to those on Mars because of the greater gravity acceleration and the higher production of O by photolysis of CO2. O stimulates cooling by the emission at 15 μm in the collisions with CO2. (3) There is a great progress in the observations of photochemical tracers and minor constituents on Mars in the current decade. This progress is supported by progress in photochemical modeling, especially by photochemical GCMs. Main results in these areas are briefly discussed. The problem of methane presents the controversial aspects of its variations and origin. The reported variations of methane cannot be explained by the existing data on gas-phase and heterogeneous chemistry. The lack of current volcanism, SO2, and warm spots on Mars favor the biological origin of methane. (4) Venus’ chemistry is rich and covers a wide range of temperatures and pressures and many species. Photochemical models for the middle atmosphere (58-112 km), for the nighttime atmosphere and night airglow at 80-130 km, and the kinetic model for the lower atmosphere are briefly discussed. 相似文献
4.
A. Bar-nun 《Icarus》1980,42(3):338-342
The effects of the newly discovered thunderstorms on Venus upon the nitrogen and carbon species in its atmosphere were calculated. An Earth-like lightning frequency of 100 sec?1 was used for Venus, in accord with recent optical measurements by Pioneer-Venus (W. J. Borucki, J. W. Dyer, G. Z. Thomas, J. C. Jordon, and D. A. Comstock, submitted for publication). The rate of NO production by thunder shock waves, 2.5 × 1011 g year?1, is about an order of magnitude smaller than on the Earth. But on Venus, in the absence of precipitation, which is the major removal mechanism of odd nitrogen from the Earth's atmosphere, the mixing ratios of odd nitrogen species might be considerably higher. The global CO production is governed by CO2 photolysis rather than by CO2 pyrolysis by lightning. However, thunderstorms produce about 2.5 × 1011 g year?1 of CO in the cloud layer, far from the high altitude CO2 photolysis region. 相似文献
5.
Guido Visconti 《Icarus》1981,45(3):638-652
We present computations of the photodissociation coefficients for NH3, N2H4, PH3, and H2S in the Jupiter atmosphere. The calculations take into account multiple scattering and absorption using the radiative-transfer method known as δ-Eddington approximation. The atmospheric models include two cloud layers of variable thickness and haze layers above the upper cloud and between the clouds. One of the results of the radiative computations deal with the reflectivity of the Jovian atmosphere as a function of wavelength. A comparison with available data on the albedo of the planet gives some important indications about mixing ratios and distributions of gases and aerosols. The results for the photolysis rates are compared with similar rates obtained by considering either the direct flux or the flux determined by the molecular gas absorption alone. The latter is usually the approximation used in aeronomic models. The results of this comparison show that a considerable difference exists with direct flux photodissociation but significant differences with molecular absorption flux exist only in atmospheric regions where photodissociation is relatively small. 相似文献
6.
We explore the vertical convective flux Fc in a radiative-convective grey atmosphere. An expression of the form Fc=Fsτo/(C+Dτo) appears useful, where Fs is the shortwave flux absorbed at the base of an atmosphere with longwave optical depth τo and C and D are constants. We find excellent agreement with an idealized grey radiative-convective model with no shortwave absorption for D=1 and C=1∼2 depending on the surface-atmosphere temperature contrast and on the imposed critical lapse rate. Where shortwave absorption is correlated with longwave opacity, as in the atmospheres of Earth and Titan, C=2, D=2 provides an excellent fit, validated against the present terrestrial situation and the results of a nongrey model of Titan's strongly antigreenhouse atmosphere under a wide range of conditions. The expression may be useful for studying the energetics of planetary climates through time where there is insufficient data to constrain more elaborate models. 相似文献
7.
The photochemistry of the stratosphere of Venus was modeled using an updated and expanded chemical scheme, combined with the results of recent observations and laboratory studies. We examined three models, with H2 mixing ratio equal to 2 × 10?5, 5 × 10?7, and 1 × 10?13, respectively. All models satisfactorily account for the observations of CO, O2, O2(1Δ), and SO2 in the stratosphere, but only the last one may be able to account for the diurnal behavior of mesospheric CO and the uv albedo. Oxygen, derived from CO2 photolysis, is primarily consumed by CO2 recombination and oxidation of SO2 to H2SO4. Photolysis of HCl in the upper stratosphere provides a major source of odd hydrogen and free chlorine radicals, essential for the catalytic oxidation of CO. Oxidation of SO2 by O occurs in the lower stratosphere. In the high-H2 model (model A) the OO bond is broken mainly by S + O2 and SO + HO2. In the low-H2 models additional reactions for breaking the OO bond must be invoked: NO + HO2 in model B and ClCO + O2 in model C. It is shown that lightning in the lower atmosphere could provide as much as 30 ppb of NOx in the stratosphere. Our modeling reveals a number of intriguing similarities, previously unsuspected, between the chemistry of the stratosphere of Venus and that of the Earth. Photochemistry may have played a major role in the evolution of the atmosphere. The current atmosphere, as described by our preferred model, is characterized by an extreme deficiency of hydrogen species, having probably lost the equivalent of 102–103 times the present hydrogen content. 相似文献
8.
Cyanoacetylene (HC3N) and diacetylene (C4H2) play an important role in the photochemistry of Titan's atmosphere, in part because of their strong absorption between 110 and 180 nm. Accurate photoabsorption cross-sections at temperatures representative of Titan's atmosphere are required to interprete Cassini observations and to calculate photolysis rates used in photochemical models. Using synchrotron radiation as a tunable vacuum ultraviolet (VUV) light source, we have measured absolute photoabsorption cross-sections of C4H2 and HC3N with a spectral resolution of 0.05 nm in the region between 80 and 225 nm and at different temperatures between 173 and 295 K. The measured cross-sections are used to model transmission spectra of Titan atmosphere in the VUV. 相似文献
9.
We show that photochemical models of Titan's atmosphere can give rise to bimodal distributions in the abundances of some major compounds, like C2H2 and C2H4. Sensitivity analysis enabled us to identify the causes and conditions of this bimodality. We propose several methods to control this behavior in photochemical models. In particular, we point out the importance of two key reactions and the needs for a critical evaluation of the kinetic data. We also show that the abundances of some compounds are hypersensitive to the ratio [CH4]/[H], suggesting that a time-dependent variation of this ratio might lead to a real bistability in the high atmosphere of Titan. 相似文献
10.
Systematic circulation systems within the thermosphere create major departures of composition of both major and minor species from diffusive equilibrium. For example, latitudinal gradients in the mixing ratios of major and minor species in recent empirical models of the Earth's thermosphere are inconsistent with changes of the thermal structure alone or with temporal or spatial changes of the turbopause altitude. A conservation equation describing the time rate of change of mean molecular weight is derived for a two-species gas, in the presence of molecular and turbulent diffusion and general global circulation. The equation is fully three-dimensional and time-dependent and is derived from a combination of the general diffusion equation and the time-dependent continuity equation. In the Earth's thermosphere, the two species are [O] the light species and [N2,O2] the heavy species and the approach is valid since the time constants of dissociation of [O2] and recombination of [O] are long compared with typical dynamical time constants. One of the major effects of allowing a wind-driven departure from diffusive equilibrium is that, at the solstice, the pole to pole exospheric temperature difference is increased by more than 50%, while the prevailing summer to winter meridional wind actually decreases. A conservation equation of this kind has general application to any planetary atmosphere which may be considered to be predominantly comprised of two species. Results for a three-dimensional, time-dependent thermospheric model for solstice conditions are presented for the conditions of solar heating only. The model results are compared with previous model results with composition fixed at pressure levels and with empirical temperature and composition models of MSIS. 相似文献
11.
To determine how active volcanism might affect the standard picture of sulfur dioxide photochemistry on Io, we have developed a one-dimensional atmospheric model in which a variety of sulfur-, oxygen-, sodium-, potassium-, and chlorine-bearing volatiles are volcanically outgassed at Io's surface and then evolve due to photolysis, chemical kinetics, and diffusion. Thermochemical equilibrium calculations in combination with recent observations of gases in the Pele plume are used to help constrain the composition and physical properties of the exsolved volcanic vapors. Both thermochemical equilibrium calculations (Zolotov and Fegley 1999, Icarus141, 40-52) and the Pele plume observations of Spencer et al. (2000; Science288, 1208-1210) suggest that S2 may be a common gas emitted in volcanic eruptions on Io. If so, our photochemical models indicate that the composition of Io's atmosphere could differ significantly from the case of an atmosphere in equilibrium with SO2 frost. The major differences as they relate to oxygen and sulfur species are an increased abundance of S, S2, S3, S4, SO, and S2O and a decreased abundance of O and O2 in the Pele-type volcanic models as compared with frost sublimation models. The high observed SO/SO2 ratio on Io might reflect the importance of a contribution from volcanic SO rather than indicate low eddy diffusion coefficients in Io's atmosphere or low SO “sticking” probabilities at Io's surface; in that case, the SO/SO2 ratio could be temporally and/or spatially variable as volcanic activity fluctuates. Many of the interesting volcanic species (e.g., S2, S3, S4, and S2O) are short lived and will be rapidly destroyed once the volcanic plumes shut off; condensation of these species near the source vent is also likely. The diffuse red deposits associated with active volcanic centers on Io may be caused by S4 radicals that are created and temporarily preserved when sulfur vapor (predominantly S2) condenses around the volcanic vent. Condensation of SO across the surface and, in particular, in the polar regions might also affect the surface spectral properties. We predict that the S/O ratio in the torus and neutral clouds might be correlated with volcanic activity—during periods when volcanic outgassing of S2 (or other molecular sulfur vapors) is prevalent, we would expect the escape of sulfur to be enhanced relative to that of oxygen, and the S/O ratio in the torus and neutral clouds could be correspondingly increased. 相似文献
12.
A. A. Berezhnoi 《Solar System Research》2010,44(6):498-506
Molecular nitrogen, the main component of the modern atmosphere of Titan, may have formed without significant changes in the
nitrogen and hydrogen isotopic composition from the clathrate hydrate of ammonia NH3 · H2OSLD, which is the main accreted form of nitrogen. The most preferable transformation mechanism of NH3 · H2OSLD into atmospheric N2 is its thermal decomposition in the interior of Titan rather than the photochemical decomposition of ammonia in the upper
atmosphere of early Titan. The photolysis of ammonia does not lead to a change in the isotopic composition of nitrogen, as
all the nitrogen remains in Titan’s atmosphere. The photolysis of NH does not lead to a change in the isotopic composition
of nitrogen in Titan’s atmosphere. Fractionation of hydrogen and nitrogen isotopes during the impacts of comets with Titan
does not seem to be significant either. It will be possible to determine the dissociative fractionation factor, the original
ratio 14N/15N, and the mass of Titan’s original atmosphere when fractionation of nitrogen isotopes in Titan’s atmosphere is examined in
additional theoretical and experimental studies that take into account processes occurring during the formation of a system
of Saturn’s satellites. 相似文献
13.
None of the Titan photochemical models currently available have been able to reproduce the full set of stratospheric molecular mixing ratios inferred from observations. In order to assess how well reaction sets describe hydrocarbon chemistry, theoretical modeling predictions were compared to the results of a laboratory experiment. A CH4-C2H2 mixture was irradiated at 185 nm in an atmospheric simulation chamber and the evolution of the gas mixture was followed in situ and in real time by infrared spectroscopy. In parallel, a 0D theoretical model of the laboratory experiment was developed. A new reaction set describing Titan's chemistry was built and incorporated in the model. Lebonnois et al. [Lebonnois, S., Toublanc, D., Hourdin, F., Rannou, P., 2001. Icarus 152, 384-406] reaction set was also used for comparison. The presence of small amounts of atmospheric O2 in the experiment was properly accounted for and led us to suggest that oxygenated chemistry might be a source of C2H4 in Titan's atmosphere. With Lebonnois et al. [Lebonnois, S., Toublanc, D., Hourdin, F., Rannou, P., 2001. Icarus 152, 384-406] reaction set, the model could not fit at all the experimental evolution of the compounds. This is explained by some of the choices made for crucial kinetic parameters such as the quantum yield of photolysis of C2H2. Also, the absence of some reactions led to the enhancement of pathways that would otherwise be negligible. For example, the lack of reactions between C4H4 and radicals induced an erroneously high photolysis rate for this species. With the reaction set built in this study, the model much better fits the experiment, especially when the “soot,” which includes C4H4, is recycled into C2H2. This shows that photochemistry of the larger species has a role in determining the lighter species concentrations and that considering that they are simply lost from the system is not a valid assumption. Including even an abridged set of C4 + hydrocarbon reactions will be required in future photochemical models. Especially, photolysis rates and yields for C2H2, C4H2, and C4H4, are important parameters in need of a better determination. 相似文献
14.
We present a detailed study of the distribution of key deuterated species (viz., atomic D and HD) and the associated deuterium Lyman-α airglow in the jovian thermosphere. The reactions that appear to govern the abundances of these deuterated species are used in conjunction with C2-chemistry in a 1-D photochemical-diffusion model. While the D abundance is mainly sensitive to H densities and the vibrational temperature profile, the D vertical distribution also depends on other parameters such as eddy mixing and the uncertain values of some of the reaction rate constants. We consider different scenarios by varying several parameters controlling the D distribution in the thermosphere. A radiative transfer model with coupling of the H and D Lyman-α lines is employed to obtain line profiles and total intensities at disk center for these scenarios. This allows a comparison of the impact of various parameters on the jovian D Lyman-α emission. A consequence of these chemical processes in the jovian thermosphere is the formation of CH2D, CH3D, and C2H5D, and other deuterated species. We also discuss the source of these deuterated hydrocarbons and their abundance. We find that HD vibrational chemistry impacts D in the thermosphere, CH3D and C2H5D are vibrationally enhanced in the thermosphere, and variations in abundance of CH3D and C2H5D in the thermosphere may reflect dynamical activity (i.e., Kh) in the jovian upper atmosphere. An observing program dedicated to providing such measurements of these testable phenomena would provide further insight into the synergistic coupling between chemistry, energetics and airglow in the jovian upper atmosphere. 相似文献
15.
Observations of the Io plasma torus and neutral clouds indicate that the extended ionian atmosphere must contain sodium, potassium, and chlorine in atomic and/or molecular form. Models that consider sublimation of pure sulfur dioxide frost as the sole mechanism for generating an atmosphere on Io cannot explain the presence of alkali and halogen species in the atmosphere—active volcanoes or surface sputtering must also be considered, or the alkali and halide species must be discharged along with the SO2 as the frost sublimates. To determine how volcanic outgassing can affect the chemistry of Io's atmosphere, we have developed a one-dimensional photochemical model in which active volcanoes release a rich suite of S-, O-, Na-, K-, and Cl-bearing vapor and in which photolysis, chemical reactions, condensation, and vertical eddy and molecular diffusion affect the subsequent evolution of the volcanic gases. Observations of Pele plume constituents, along with thermochemical equilibrium calculations of the composition of volcanic gases exsolved from high-temperature silicate magmas on Io, are used to constrain the composition of the volcanic vapor. We find that NaCl, Na, Cl, KCl, and K will be the dominant alkali and chlorine gases in atmospheres generated from Pele-like plume eruptions on Io. Although the relative abundances of these species will depend on uncertain model parameters and initial conditions, these five species remain dominant for a wide variety of realistic conditions. Other sodium and chlorine molecules such as NaS, NaO, Na2, NaS2, NaO2, NaOS, NaSO2, SCl, ClO, Cl2, S2Cl, and SO2Cl2 will be only minor constituents in the ionian atmosphere because of their low volcanic emission rates and their efficient photochemical destruction mechanisms. Our modeling has implications for the general appearance, properties, and variability of the neutral sodium clouds and jets observed near Io. The neutral NaCl molecules present at high altitudes in atmosph eres generated by active volcanoes might provide the NaX+ ion needed to help explain the morphology of the high-velocity sodium “stream” feature observed near Io. 相似文献
16.
Despite several spacecraft encounters and numerous groundbased investigations, we still do not know much about Jupiter's deep atmosphere; in fact, the Galileo probe results were so different than anyone had anticipated, that we understand even less about this planet's atmosphere now than before the Galileo mission. We formulate four basic questions in Section 1.3, which, if solved, would help to better understand the chemistry and dynamics in Jupiter's atmosphere. We believe that three out of the four questions (explanation of NH3 altitude profile, characterization of hot spots, altitude below which the atmosphere is uniformly mixed) may be solved from passive sounding of Jupiter's deep (∼ tens of bars) atmosphere via a radio telescope orbiting the planet. Question nr. 4 (the water abundance in Jupiter's deep atmosphere) has been singled out by the Solar System Exploration Decadal Survey as a key question, since the water abundance in Jupiter's deep atmosphere is tied in with planet formation models. In this paper we investigate the sensitivity of microwave retrievals to the composition of Jupiter's deep atmosphere, in particular the water abundance. Based upon present uncertainties in the ammonia abundance and other known and unknown absorbers, including uncertainties in clouds (density and index of refraction), and uncertainties in the thermal structure and lineshape profiles, we conclude that the retrieval of water at depth from microwave spectra (disk-averaged and locally) will be highly uncertain. We show that, if the H2O lineshape profile would be accurately known (laboratory data are needed!), an atmosphere with a near-solar H2O abundance can likely be distinguished from one with an abundance of 10-20×solar O based upon the difference in their microwave spectra at wavelengths ?50 cm. This would be sufficient to distinguish between some proposed scenarios by which Jupiter acquired its inventory of volatile elements heavier than helium. If, in addition, limb-darkening measurements are obtained (again, the H2O lineshape profile should be known), tighter constraints on the H2O abundance can be obtained (see also Janssen et al., 2004, this issue). 相似文献
17.
V. I. Shematovich 《Solar System Research》2010,44(2):96-103
The ionization and dissociation of molecular hydrogen by the ultraviolet (UV) radiation of the parent star lead to the formation
of hydrogen atoms with an excess of kinetic energy and, thus, are an important source of suprathermal hydrogen atoms in the
upper atmosphere of exoplanet HD 209458b. Contemporary aeronomical models did not investigate these processes because they
assumed the fast local thermalization of the hot atoms of hydrogen by elastic collisions. However, the kinetics and transfer
of these atoms were not calculated in detail, because they require the solving of the Boltzmann equation for a nonthermal
atom population. This work estimates the effect of the UV radiation of the parent star and the accompanying photocleacton
flux on the production of the suprathermal fraction of atomic hydrogen in the H2 → H transition region. We also consider the formation of the escaping flux of Hatoms created by this effect in the upper
atmosphere of HD 209458b. We calculate the production rate and energy spectrum of the hydrogen atoms with excess kinetic energy
during the dissociation of H2. Using the numerical stochastic model created by Shematovich (2004) for a hot planetary corona, we investigate the molecular-scale
kinetics and transfer of suprathermal hydrogen atoms in the upper atmosphere and the emergent flux of atoms evaporating from
the atmosphere. The latter is estimated as 3.4 × 1012 cm−2 s−1 for a moderate stellar activity level of UV radiation, which leads to a planetary atmosphere evaporation rate of 3.4 × 109 g s−1 due to the process of the dissociation of H2. This estimate is close to the observational value of ∼1010 g s−1 for the rate of atmospheric loss of HD 209458b. 相似文献
18.
N. Fray Y. Bnilan H. Cottin M.‐C. Gazeau R. D. Minard F. Raulin 《Meteoritics & planetary science》2004,39(4):581-587
Abstract— This paper presents some preliminary results concerning the degradation of refractory nitrogenated polymers, which could be responsible for the CN extended source in comets. We are studying hexamethylenetetramine (HMT) and HCN polymers. Both compounds have been irradiated or heated to simulate the degradation processes they undergo in the cometary atmosphere. We show that, even if both compounds are quite stable under photolysis, the heating leads to a much more efficient degradation with the formation of HCN, NH3, and other heavier compounds. Moreover, the thermal degradation of HCN polymers appears to be more efficient than that of HMT. Thus, the HCN polymers seem to be better candidates for the CN extended source. We are now developing a new reactor to quantify the production of gaseous molecules and to detect in situ CN radicals. 相似文献
19.
Tetsuo Yamamoto 《Earth, Moon, and Planets》1981,24(4):453-463
The formation of cometary CN, C2 and C3 radicals is investigated in a photochemical reaction scheme. From an analysis of the observed brightness profiles of these radicals, it is shown that CN is formed as a primary product in the photolysis of its parent molecules, whereas C2 and C3 are formed via two-step photodissociation of their parents. We suggest that major parent of C2 is different species from those of CN and C3 on the basis of the difference of the variation with heliocentric distance of the sublimation rate of the parents of these radicals. Parent molecules and reaction schemes for the formation of these radicals are discussed. 相似文献
20.
This paper reports results obtained on ionosphere formation in the Jovian upper atmosphere with special reference to some of the recently available reaction rates, and to recent models of the Jovian neutral atmosphere based on the possibility of a warmer mesopause. We find that the role of the hypothetical radiative association of H+ to H2 to form H3+, as brought to light in our earlier study, is still important, even with a reaction rate as low as 10?15 cm3sec?1. In the lower regions of the ionosphere three-body processes leading to the formation of H3+ and H5+ ions, which have very fast dissociative recombination rates, produce a dramatic reduction in the electron density. When no radiative association takes place, and the H+ ions are lost by radiative recombination alone, we confirm that the photochemical equilibrium profile is also the diffusive equilibrium profile. However, with collisional-radiative recombination, whose rate becomes altitude-dependent, diffusion tends to bring about some redistribution of the ionization. Inclusion of radiative association enhances the role of diffusion. In this case, diffusion brings about all the expected changes. In particular, the differences in the electron density profile, originated in the lower-middle ionosphere by radiative association, are propagated up to all higher altitudes by diffusion. The rate constant of radiative association is, however, unknown. It is hoped that the critical importance of this reaction for the Jovian ionosphere will be an incentive towards a careful laboratory determination of its rate coefficient. In the older models of the Jovian ionosphere the major ions were H+ which were lost only by pure radiative recombination. This led to high electron densities and practically no diurnal change. In contrast, our new models have relatively much smaller electron densities, especially in lower regions, and may be susceptible to significant diurnal variation. 相似文献