Possible existence and role of excited ozone precursors in the stratosphere

Laboratory kinetic experiments, quantum theoretical studies and certain recently discovered infrared emissions from the stratosphere together imply the possible existence of a metastable, energetic, and reactive form of ozone in the upper atmosphere. This species can potentially affect the upper atmospheric photochemistry and heat balance. For these reasons there is a need for further quantum theoretical and laboratory chemical kinetic studies addressing some of the relevant properties of the internally excited ozone precursors.     

Three-dimensional simulations of ozone in the stratosphere and comparison with UARS data

A 3-D Atmospheric Chemical Transport model has been developed and used to simulate the present-day ozone distributions in the troposphere and stratosphere. A 5-year-long steady-state model run using 1995 boundary conditions and circulation fields derived from the 24-layer University of Illinois at Urban a-Champaign (UIUC) Atmospheric General Circulation model has been carried out. The simulated distribution of ozone is compared with available observations made by the HALOE, CLAES and MLS instruments onboard the LIARS satellite. The comparison is carried out for the monthly zonal-mean climatology of the ozone distribution. The correlations between the monthly zonal-mean ozone derived from the simulated and measured data are calculated. The results of this comparison show reasonable agreement (within 30%) of the simulated and measured monthly zonal-mean ozone distributions, although the location of the simulated maximum in the ozone distribution is generally lower by about 2–3 km than shown by the satellite data. The model overestimates the ozone mixing ratio in the lower stratosphere and slightly underestimates it in the upper stratosphere. A better overall agreement was found between the simulated ozone and the ozone measured by HALOE than by CLAES and MLS.     

Satellite observed long-term averaged seasonal and spatial ozone variations in the stratosphere

Nine years of Nimbus-7 SBUV ozone mixing ratio data (October 1978–September 1987) have been used to analyze the distributions of the long-term average annual and semiannual ozone oscillations in the lower, middle, and upper stratosphere over the region 65°S to 65°N. It is shown that the derived harmonics are consistent with the results of earlier investigations based on limited sets of data. Year-to-year changes of amplitudes of the annual and semiannual variations are generally small except in the tropical midstratosphere (due to the effect of El Chichon) and the southern subpolar upper stratosphere.

Analyses are also presented to show the vertical and seasonal distribution of the zonal ozone variations. It is shown that, for the long-term averaged data, wave 1 is larger during winter than summer and in winter larger in the Northern than Southern Hemisphere. The importance of photochemical and thermal/dynamic processes in modifying the time and zonal variations is discussed.     

Interaction of photochemical and radiative processes in the stratosphere: An application on the retrieval of concentration profiles from satellite measurements

A new method is developed to determine the concentration profiles of chemical species from satellite measurements. The method takes into account the interaction of photochemical and radiative processes in the stratosphere and is applied for chemical species (nitric oxide and nitrogen dioxide) experiencing large diurnal changes. It is found that if the interaction of the photochemical and radiative processes is neglected, that is if the temporal and spatial variations of NO and NO₂ are not considered in the radiative transfer calculations, the resulting errors for the concentration profiles for altitudes less than 20 km reach 100 and 5% respectively, for both sunset and sunrise. A photochemical scheme is developed capable of providing the mixing ratio profiles of NO and NO₂ for different latitudes, altitudes and seasons and a retrieval code combining an iterative inversion algorithm, working from top of the atmosphere downwards, and a parameterization of the variability of NO and NO₂ is also constructed. The method is used to examine the accuracy of the retrieval of the vertical concentration profiles and the new results show that the recovered profiles are in good agreement (error 5–15%) with measured profiles (WMO, 1985) and reflect the trends of NO and NO₂ at sunset and sunrise.     

The Jovian stratosphere in the ultraviolet

The center-of-disk reflectivity of Jupiter in the wavelength range from 1450 to 3150A?has been computed from 30 low-dispersion IUE spectra taken during solar maximum in 1978–1980. A vertically inhomogeneous radiative transfer program is used to compute model reflectivities of various stratospheric compositions for comparison. Ammonia and acetylene are well determined because they show narrow absorption bands in the ultraviolet. Above 1800A?, these two gases provide a good fit to the data, but not below. At shorter wavelengths the fit would be much improved by a small amount (5–15 ppb) of propadiene/allene (C₃H₄). Voyager IRIS spectra show that the IR bands of allene are not strong enough to be detected in such a small amount. Additional absorption around 1600A?can be reproduced best with the presence of cyclopropane (C₃H₆, <15ppb), although other absorbers (e.g., hydrocarbon molecules with more than three carbon atoms, oxygen- or nitrogen-containing molecules, or a high-attitude haze) could also explain the spectrum in this region. The data are too noisy to detect possible CO Cameron band absorption near 2000A?.     

A steady state model of negative ions in the lower stratosphere

A chemical model of negative ions in the lower stratosphere is presented. Under the steady state condition at each height from 15 to 30 km, the fractional abundances of the individual negatively-charged constituents were calculated by simulating the chemical processes which start from electrons and reach the ion clusters having NO₃⁻and HSO₄⁻ cores. The computed result shows that while the NO₃⁻(HNO₃)₂ ions predominate at lower than 26 km in altitude, the HSO₄⁻(HNO₃)_m type of ions increase slowly with height and the HSO₄⁻(H₂SO₄)_n type of ions increase rapidly with height around 30 km. The result is compared with the experimental result which was obtained by the in situ balloon-borne mass spectrometric measurements (Viggiano et al., 1983). Both results have comparable height profile of respective ions with each other. As the “adjusted” reaction rates for the formation of cluster ions were assumed in the calculations, the result should be considered a preliminary one. Future works to be extended from the present one will be suggested.     

A photochemical model of the martian atmosphere

The factors governing the amounts of CO, O2, and O3 in the martian atmosphere are investigated using a minimally constrained, one-dimensional photochemical model. We find that the incorporation of temperature-dependent CO2 absorption cross sections leads to an enhancement in the water photolysis rate, increasing the abundance of OH radicals to the point where the model CO abundance is smaller than observed. Good agreement between models and observations of CO, O2, O3, and the escape flux of atomic hydrogen can be achieved, using only gas-phase chemistry, by varying the recommended rate constants for the reactions CO + OH and OH + HO2 within their specified uncertainties. Similar revisions have been suggested to resolve discrepancies between models and observations of the terrestrial mesosphere. The oxygen escape flux plays a key role in the oxygen budget on Mars; as inferred from the observed atomic hydrogen escape, it is much larger than recent calculations of the exospheric escape rate for oxygen. Weathering of the surface may account for the imbalance. Quantification of the escape rates of oxygen and hydrogen from Mars is a worthwhile objective for an upcoming martian upper atmospheric mission. We also consider the possibility that HOx radicals may be catalytically destroyed on dust grains suspended in the atmosphere. Good agreement with the observed CO mixing ratio can be achieved via this mechanism, but the resulting ozone column is much higher than the observed quantity. We feel that there is no need at this time to invoke heterogeneous processes to reconcile models and observations.     

The photodissociation of nitric oxide in the mesosphere and stratosphere

A detailed calculation of the nitric oxide photodissoeiation rate has been made for application to mesospheric and stratospheric photochemistry. It takes into account a new determination of the oscillator strengths of the NO bands and is based on a critical analysis of the solar flux. Moreover it entails a complete determination of the molecular oxygen attenuation allowing for the rotational fine structure including the Voight profile of the Schumann-Runge bands.     

Radiation chemistry in the Jovian stratosphere: laboratory simulations

Low-pressure continuous-flow laboratory simulations of plasma induced chemistry in H2/He/CH4/NH3 atmospheres show radiation yields of hydrocarbons and nitrogen-containing organic compounds that increase with decreasing pressure in the range 2-200 mbar. Major products of these experiments that have been observed in the Jovian atmosphere are acetylene (C2H2), ethylene (C2H4), ethane (C2H6), hydrogen cyanide (HCN), propane (C3H8), and propyne (C3H4). Major products that have not yet been observed on Jupiter include acetonitrile (CH3CN), methylamine (CH3NH2), propene (C3H6), butane (C4H10), and butene (C4H8). Various other saturated and unsaturated hydrocarbons, as well as other amines and nitriles, are present in these experiments as minor products. We place upper limits of 10(6)-10(9) molecules cm-2 sec-1 on production rates of the major species from auroral chemistry in the Jovian stratosphere, and calculate stratospheric mole fraction contributions. This work shows that auroral processes may account for 10-100% of the total abundances of most observed organic species in the polar regions. Our experiments are consistent with models of Jovian polar stratospheric aerosol haze formation from polymerization of acetylene by secondary ultraviolet processing.     

The relative abundance of ethane to acetylene in the Jovian stratosphere

The observed ratio of C2H6 to C2H2 in the Jovian stratosphere increases from approximately 55 at 2 mbar to approximately 277 at 12 mbar. In current photochemical models this ratio typically increases between 2 and 12 mbar by a factor of < or = 3. Recent laboratory kinetics studies on the reaction between C2H3 and H2 to form C2H4 suggest an efficient chemical mechanism for hydrogenation of C2H2 to C2H6. Inclusion of this scheme as part of a comprehensive updated model for hydrocarbon photochemistry in the atmosphere of Jupiter provides an explanation of the altitude variation of the C2H6/C2H2 ratio. The sensitivity of these results to uncertainties in the key rate constants at low temperatures is illustrated, identifying needs for additional laboratory measurements. Since the key reaction rate constants decrease with decreasing temperature, the hydrogenation of C2H2 as proposed predicts a qualitatively decreasing trend in the C2H6/C2H2 value with decreasing distance from the Sun. The observed variation between Jupiter and Saturn is consistent with this prediction.     

Magnesium ion chemistry in the stratosphere

Laboratory measurements of reaction rate constants of magnesium ions and magnesium containing ions with O₃, NO, HNO₃, and H₂O₂ have been carried out in a flowing afterglow experiment. Mg⁺ ions react with O₃ to produce MgO⁺ ions, which in turn react with O₃ to produce Mg⁺ ions. Mg⁺ ions react with HNO₃ and H₂O₂ to produce MgOH⁺ ions. MgOH⁺ ions react rapidly with HNO₃ to produce NO⁺₂ ions and Mg(HO)₂. One can therefore conclude that Mg⁺, MgO⁺, or MgOH⁺ ions could not have significant concentrations in the stratosphere if gas phase magnesium compounds were present. The failure to observe these ions therefore cannot be used as evidence that the stratospheric magnesium, resulting from meteor ablation at higher altitudes, is in condensed phases. This is in contrast to the case for sodium where the ion chemistry is such that the failure to observe hydrated Na⁺ ions proves that gas phase sodium compounds are not present in the stratosphere.     

Chemical budgets of the stratosphere

A review is given of the stratospheric budgets of odd oxygen, odd nitrogen, nitrous oxide, methane and carbonyl sulfide. The stratospheric column production rate of NO by the reaction N₂O + O(¹D) → 2 NO is 1.1–1.9 × 10⁸ molecules cm^?2 s^?1. The stratospheric loss rates for N₂O, CH₄ and COS are equal to 0.9–1.4 × 10⁹, 1 × 10¹⁰ and 0.5 × 10⁷ molecules cm^?2 s^?1, respectively. From currently available information on the global distributions of N₂O and CH₄ there are some indications of about two times smaller OH concentrations below 35 km than those which are calculated based on the latest compilation of kinetic data.Most significantly, however, it is shown that photochemical models and available ozone observations cannot be reconciled and that there may be particularly severe problems in the 25–35 km region. This issue is thoroughly discussed.Volcanic emissions of SO₂ to the stratosphere may locally lead to much enhanced ozone concentrations and heating rates. These may influence the dynamic behaviour of volcanic plumes before their dispersion over large volumes of the stratosphere.     

The photochemical model of Titan’s atmosphere and ionosphere: A version without hydrodynamic escape

There are observational and theoretical evidences both in favor of and against hydrodynamic escape (HDE) on Titan, and the problem remains unsolved. A test presented here for a static thermosphere does not support HDE on Titan and Triton but favors HDE on Pluto. Cooling of the atmosphere by the HCN rotational lines is limited by rotational relaxation above 1100 km and self-absorption below 900 km on Titan. HDE can affect the structure and composition of the atmosphere and its evolution. Hydrocarbon, nitrile, and ion chemistries are strongly coupled on Titan, and attempts to calculate them separately may result in significant errors. Here we apply our photochemical model of Titan’s atmosphere and ionosphere to the case of no hydrodynamic escape. Our model is still the only after-Cassini self-consistent model of coupled neutral and ion chemistry. The lack of HDE is a distinct possibility, and comparing models with and without HDE is of practical interest. The mean difference between the models and the neutral and ion compositions observed by INMS are somewhat better for the model with HDE. A reaction of NH₂ with H₂CN suggested by Yelle et al. (2009) reduces but does not remove a significant difference between the ammonia abundances in the models and INMS observations. Losses of methane and nitrogen and production and deposition to the surface of hydrocarbons and nitriles are evaluated in the model, along with lifetimes and evolutionary aspects.     

The thermal history of interplanetary dust particles collected in the Earth's stratosphere

Abstract— Fragments of 24 individual interplanetary dust particles (IDPs) collected in the Earth's stratosphere were obtained from NASA's Johnson Space Center collection and subjected to pulse-heating sequences to extract He and Ne and to learn about the thermal history of the particles. A motivation for the investigation was to see if the procedure would help distinguish between IDPs of asteroidal and cometary origin. The use of a sequence of short-duration heat pulses to perform the extractions is an improvement over the employment of a step-heating sequence, as was used in a previous investigation. The particles studied were fragments of larger parent IDPs, other fragments of which, in coordinated experiments, are undergoing studies of elemental and mineralogical composition in other laboratories. While the present investigation will provide useful temperature history data for the particles, the relatively large size of the parent IDPs (～40 μm in diameter) resulted in high entry deceleration temperatures. This limited the usefulness of the study for distinguishing between particles of asteroidal and cometary origin.     

A photochemical model of Titan's atmosphere and ionosphere

A global-mean model of coupled neutral and ion chemistry on Titan has been developed. Unlike the previous coupled models, the model involves ambipolar diffusion and escape of ions, hydrodynamic escape of light species, and calculates the H₂ and CO densities near the surface that were assigned in some previous models. We tried to reduce the numbers of species and reactions in the model and remove all species and reactions that weakly affect the observed species. Hydrocarbon chemistry is extended to C₁₂H₁₀ for neutrals and C₁₀H⁺₁₁ for ions but does not include PAHs. The model involves 415 reactions of 83 neutrals and 33 ions, effects of magnetospheric electrons, protons, and cosmic rays. UV absorption by Titan's haze was calculated using the Huygens observations and a code for the aggregate particles. Hydrocarbon, nitrile, and ion chemistries are strongly coupled on Titan, and attempt to calculate them separately (e.g., in models of ionospheric composition) may result in significant error. The model densities of various species are typically in good agreement with the observations except vertical profiles in the stratosphere that are steeper than the CIRS limb data. (A model with eddy diffusion that facilitates fitting to the CIRS limb data is considered as well.) The CO densities are supported by the O⁺ flux from Saturn's magnetosphere. The ionosphere includes a peak at 80 km formed by the cosmic rays, steplike layers at 500-700 and 700-900 km and a peak at 1060 km (SZA = 60°). Nighttime densities of major ions agree with the INMS data. Ion chemistry dominates in the production of bicyclic aromatic hydrocarbons above 600 km. The model estimates of heavy positive and negative ions are in reasonable agreement with the Cassini results. The major haze production is in the reactions C₆H + C₄H₂, C₃N + C₄H₂, and condensation of hydrocarbons below 100 km. Overall, precipitation rate of the photochemical products is equal to 4-7 kg cm⁻² Byr⁻¹ (50-90 m Byr⁻¹ while the global-mean depth of the organic sediments is ∼3 m). Escape rates of methane and hydrogen are 2.9 and 1.4 kg cm⁻² Byr⁻¹, respectively. The model does not support the low C/N ratio observed by the Huygens ACP in Titan's haze.     

A one-dimensional gasdynamical model of magnetospheric convection

The plasma flow in the equatorial plane of the magnetosphere is examined within the framework of a one-dimensional model in which all quantities are supposed to depend only on the distance along the Sun-Earth axis. The following models are considered: (1) the gasdynamical model in which the Ampère force is ignored, (2) the magnetohydrodynamical model in which the normal component of the Ampère force on the magnetopause is taken into account. The flow regime is calculated in the region including two regions: (1) the layer of the return flow where flow velocity is directed from the Sun, (2) the region of convection where the velocity is directed toward the Sun - on the assumption that the form of the magnetopause and the distribution of the solar wind pressure on the magnetopause are known.The following physical mechanisms are taken into account: (1) the appearance of a centrifugal force owing to the magnetopause curvature, the centrifugal force partly compensating for the solar wind pressure; (2) the existence of the critical point which is analogous to the point of transition through the local sound velocity in the Laval nozzle or in the Parker model of the solar corona. The thickness of the layer of the return flow and the velocity of convection in the magnetosphere are calculated; and the following peculiarities are found: (1) in the gasdynamical model the convection regime is only possible with high velocities corresponding to the substorm, (2) in the magnetohydrodynamic model the convection velocity and the thickness of the layer of the return flow are reduced; the reduction being connected to the fact that the pressure of the solar wind is partially compensated for by the jump of the magnetic pressure on the magnetopause.     

The first height measurements of the negative ion composition of the stratosphere

For the first time, height profiles of the stratospheric negative ion composition are presented. The results are from two nights of balloon borne mass spectrometers and cover an altitude range from 23.8 to 38.9 km. Below approx. 30km, NO^?₃ · mHNO₃ ions are dominant. These are replaced by HSO₄^? · nH₂SO₄ · oHNO₃ ions above this height. There are indications that the most abundant ions above 32 km have masses greater than 280 atomic mass units (amu), the instruments' mass range. The fractional ion count rates as a function of altitude are presented and their significance for neutral trace gas analysis and ion sampling is discussed.     

A model of temporal variations in ozone density in the Martian atmosphere

Temporal variations of the Martian ozone density profile at high latitudes have been calculated for an entire Martian year, taking into account the seasonal and diurnal variations in temperature, water vapor and solar radiation. A new technique facilitates the long-term model calculations, including diurnal variations. The result is in better agreement with MARINER 9 observations of the time and magnitude of the seasonal maximum than is the result of the previous seasonal model calculated for the diurnally averaged temperature, water vapor and solar radiation. The large scatter of the MARINER 9 data may be partly experimental, but the effect of surface condition, including the water vapor variability and the surface chemistry, may explain some of the dispersion of the observed data. The predicted diurnal variation is substantial except near solstices, and the nighttime total column density is generally larger than the daytime value. The magnitude of the day-and-night difference and the shape of the diurnal variation change markedly with season. The opposite temporal variation is predicted for ozone density between the upper and lower regions. The model predicts the production of a ozone layer at 35–50 km, which is consistent with observations at low latitudes by MARS-5. The observed ozone density may be explained, if the atmospheric temperature is as low as ～ 140 K or if the atmosphere is subsaturated. Effects of the simultaneous existence of an aerosol layer, also observed by MARS-5, are briefly discussed.     

A theoretical model of atmospheric ozone depletion

A critical study on different ozone depletion and formation processes has been made and following important results are obtained:(i) From analysis it is shown that O₃ concentration will decrease very minutely with time for normal atmosphere when [O], [O₂] and UV-radiation remain constant. (ii) An empirical equation is established theoretically between the variation of ozone concentration and time. (iii) Special ozone depletion processes are responsible for the dramatic decrease of O₃-concentration at Antarctica.     

The relaxation time of a one-dimensional self-gravitating system

A computer experiment on a one-dimensional self-gravitating system is described. We attempt to observe the dynamic time required for this system to thermalize by comparing the position and velocity densities with those predicted by the microcanonical ensemble. Hohl and Broaddus (1967) have previously reported an estimate of the thermalization time which is inferred from studies of the kinetic energy covariance. We ran the system for the time which they report and find that the system has not thermalized. Furthermore, there is no evidence that the system is even proceeding towards equilibrium in the time-scale considered here. Significant changes in the distribution do occur in a short time, after which the system remains in a stationary state which is not characteristic of equilibrium.