The effect of the HO2+NO reaction rate constant on one-dimensional model calculations of stratospheric ozone perturbations

With the aid of a one-dimensional steady-state, stratospheric model we have calculated ozone changes coused by atmosphric injections of NO_x, N₂O and chlorofluoromethanes. Adopting the fast rate constant, for the reaction HO₂+NO»OH+NO₂ measured by Howard and Evenson, we calculate much smaller perturbations of the ozone layer by NO_x and N₂O additions than previously estimated, but about two times larger ozone reductions as a result of continued emissions of chlorofluoromethanes, CF₂Cl₂ and CFCl₃.The model results are sensitive to adopted values for the rate coefficients for the reactions HO₂+O₃»OH+2O₂ and OH+HO₂»H₂O+O₂ and the eddy diffusion profile near the tropopause. More accurate assessments of ozone perturbations require the development of photochemical models that incorporate meteorological processes in more than one dimension.     

A discussion of the chemistry of some minor constituents in the stratosphere and troposphere

A discussion is given of atmospheric reactions in the H₂O–CH₄–O₂–O₃–NO _x system. In the lower troposphere such reactions may lead to significant production of ozone. Their role in the odd hydrogen balance, especially of the troposphere and lower stratosphere, is discussed. CH₃OH may be an intermediate in the oxidation cycle of methane, especially in the cold stratosphere. Its photodissociation into H₂ and CH₂O may consequently provide an important source for stratospheric H₂. Catalytic photochemical chains of reactions involving NO _x and HO _x may also lead to tropospheric destruction of ozone. Due to lack of knowledge it is not possible at present to evaluate the importance of the before-mentioned reactions.With the aid of model calculations it is indicated that stratospheric ozone is most sensitive to changes in the adopted lower boundary values of N₂O and that an increase in water vapour concentrations in the lower stratosphere will indeed cause some increase in ozone as predicted.Fluctuations in the flux of solar radiation near 190 nm may cause significant variations in stratospheric ozone concentrations.     

A two-dimensional model of thermospheric nitric oxide sources and their contributions to the middle atmospheric chemical balance

The NASA/Goddard Space Flight Center two-dimensional (GSFC 2D) photochemical transport model has been used to study the influence of thermospheric NO on the chemical balance of the middle atmosphere. Lower thermospheric NO sources are included in the GSFC 2D model in addition to the sources that are relevant to the stratosphere. A time series of hemispheric auroral electron power has been used to modulate the auroral NO production in the auroral zone. A time series of the Ottawa 10.7-cm solar flux index has been used as a proxy to modulate NO production at middle and low latitudes by solar EUV and soft X-rays. An interhemispheric asymmetry is calculated for the amounts of odd nitrogen in the polar stratosphere. We compute a <∼3% enhancement in the odd nitrogen (NO_y=N, NO, NO₂, NO₃, N₂O₅, BrONO₂, ClONO₂, HO₂NO₂, and HNO₃) budget in the north polar stratosphere (latitude > 50°) due to thermospheric sources, whereas we compute a <∼8% enhancement in the NO_y budget in the south polar stratosphere (latitude > 50°).     

Impact of different energies of precipitating particles on NOx generation in the middle and upper atmosphere during geomagnetic storms

Energetic particle precipitation couples the solar wind to the Earth's atmosphere and indirectly to Earth's climate. Ionisation and dissociation increases, due to particle precipitation, create odd nitrogen (NO_x) and odd hydrogen (HO_X) in the upper atmosphere, which can affect ozone chemistry. The long-lived NO_x can be transported downwards into the stratosphere, particularly during the polar winter. Thus, the impact of NO_x is determined by both the initial ionisation production, which is a function of the particle flux and energy spectrum, as well as transport rates. In this paper, we use the Sodankylä Ion and Neurtal Chemistry (SIC) model to simulate the production of NO_x from examples of the most representative particle flux and energy spectra available today of solar proton events (SPE), auroral energy electrons, and relativistic electron precipitation (REP). Large SPEs are found to produce higher initial NO_x concentrations than long-lived REP events, which themselves produce higher initial NO_x levels than auroral electron precipitation. Only REP microburst events were found to be insignificant in terms of generating NO_x. We show that the Global Ozone Monitoring by Occultation of Stars (GOMOS) observations from the Arctic winter 2003–2004 are consistent with NO_x generation by a combination of SPE, auroral altitude precipitation, and long-lived REP events.     

The atmospheric effects of October 2003 solar proton event simulated with the chemistry–climate model SOCOL using complete and parameterized ion chemistry

October 2003 solar proton events (SPE) is rather well covered by the observations; therefore its studies represent a good way for model validation and intercomparison. Here we apply chemistry–climate model (CCM) SOCOL with complete (SOCOLⁱ) and parameterized ion chemistry to evaluate the accuracy of a commonly used ion chemistry parameterization scheme. We performed ensemble experiments with and without SPE to characterize the effect of the October 2003 SPE on the NO_x, HO_x, ClO_x and O₃ in the middle atmosphere. Preliminary comparison of the simulated effects against MIPAS observations revealed rather good general agreement for most of the species. Comparison of the results obtained with complete and parameterized ion chemistry representation showed that the model with parameterized ion chemistry underestimates the effect of SPE on chemical composition of the middle atmosphere by up to 40% for NO_x and N₂O, up to 70% for HO_x and ClO_x and up to 600% for HNO₃. The parameterization is more accurate for ozone, however the model with parameterized ion chemistry underestimates ozone depletion by up to 15% during the SPE in the mesosphere and by 10% 2 weeks later in the stratosphere, which can be important for the long-term effects of SPE on the ozone layer.     

Nonlinear behavior on an ozone photochemical system in the stratosphere

A nonlinear box system describing ozone photochemistry in the stratosphere is presented. Influences of pollutants, such as odd chlorine (Cl_x) and odd nitrogen (NO_x) discharged by human activities, on photochemical states of the system are investigated in detail. The results show that the solutions of the box system constitute a ‘cusp’ catastrophe manifold in the state-parameter space. An increase of about 30% for Cl_x source strength or a decrease of about 30% for NO_x source strength from their current level may lead to catastrophic transition and results in a reduction of ozone concentration about 50 times. Project supported by the National Natural Science Foundation of China and Laboratory for Aeronomy and Global Environmental Observation of IAP.     

Influence of the Precipitating Energetic Particles on Atmospheric Chemistry and Climate

We evaluate the influence of the galactic cosmic rays (GCR), solar proton events (SPE), and energetic electron precipitation (EEP) on chemical composition of the atmosphere, dynamics, and climate using the chemistry-climate model SOCOL. We have carried out two 46-year long runs. The reference run is driven by a widely employed forcing set and, for the experiment run, we have included additional sources of NO _x and HO _x caused by all considered energetic particles. The results show that the effects of the GCR, SPE, and EEP fluxes on the chemical composition are most pronounced in the polar mesosphere and upper stratosphere; however, they are also detectable and statistically significant in the lower atmosphere consisting of an ozone increase up to 3?% in the troposphere and ozone depletion up to 8?% in the middle stratosphere. The thermal effect of the ozone depletion in the stratosphere propagates down, leading to a warming by up to 1?K averaged over 46?years over Europe during the winter season. Our results suggest that the energetic particles are able to affect atmospheric chemical composition, dynamics, and climate.     

Instantaneous global ozone balance including observed nitrogen dioxide

The catalytic destruction of stratospheric ozone by the oxides of nitrogen is believed to be an important part of the global ozone balance. The lack of sufficient measurements of NO _x concentrations has impeded efforts to quantify this process. Recent measurements of stratospheric nitrogen dioxide from ground-based stations as well as aircraft and balloons have provided a first approximation to a global distribution of NO₂ vertical columns at sunset. These observed vertical columns have been translated into time-dependent vertical NO₂ profiles by means of a one-dimensional atmospheric photochemical model. Using recent observations of air temperature and ozone along with this information, the independent instantaneous (one second) rates of ozone production from oxygen photolysis P(O₃), of ozone destruction from pure oxygen species (Chapman reactions) L(O _x ), and of ozone destruction by nitrogen oxides L(NO _x ) were estimated over the three-dimensional atmosphere. These quantities are displayed as zonal average contour maps, summed over various latitude zones, summed over various altitude bands, and integrated globally between 15 and 45 km. Although the global summation between 15 and 45 km by no means tells the complete story, these numbers are of some interest, and the relative values are: P(O₃), 100; L(O _x ), 15; L(NO _x ), 45±15. It is to be emphasized that this relative NO _x contribution to the integrated ozone balance is not a measure of the sensitivity of ozone to possible perturbations of stratospheric NO _x ; recent model results must be examined for current estimates of this sensitivity.     

Atmospheric ozone and the movement of the air in the stratosphere

Using over 2200 ozonesonde ascents, published byHering andBorden [1]–[5] and byDütsch et al. [6], [7], the average vertical distribution of the ozone mixing ratio is found for different latitudes and for different seasons up to a height of 30 km. The method by which the ozone formed at great heights in low latitudes becomes concentrated in the lower stratosphere of high latitudes is discussed, and the meridional circulation theory is strongly suggested.Oxford, May 1972.     

Influence of the vertical motion field on ozone concentration in the stratosphere

Computations of the mean meridional motion field in the stratosphere are applied to ozone distributions to evaluate the associated ozone concentration changes. These changes are compared with those produced by photochemical and quasi-horizontal eddy processes. For the period January–April 1964 there is a cooperative action between the mean and eddy motions with mean subsidence in middle latitudes supplying ozone to be carried polawards and equatorwards by quasi-horizontal eddy processes. At low latitudes mean horizontal motions offset the eddy transport while at high latitudes mean rising motion is the offsetting term. The mean ozone flux through 50 mb, 3.5×10²⁹ molecules sec^–1, is comparable with the fluxes evaluated by other techniques.The spring maximum is thought to be due to a modulation of the energy supply to the stratospheric eddies which, in turn, force the mean motions. Longer-term changes are to be expected; for example during Ice Ages when increased tropospheric eddy activity is anticipated there should be higher total ozone.     

Recent developments in photochemistry of atmospheric ozone

Summary A review is given of the increasingly rapid development of the photochemistry of odd oxygen particles which has taken place since the validity of the classical (oxygen only) theory was for the first time questioned by Hampson and Hunt less than 10 years ago. The relative importance of different reactions is discussed as a function of altitude and also the alterations of the H-system, introduced by NO_x, are investigated. It is shown that the fact that not only the observed ozone but also the HNO₃ distribution should be explained considerably limits the acceptable values of poorly known rate constants. The influence of stratospheric pollution on ozone concentration is also discussed under the assumption of photochemical equilibrium.List of symbols Õ Odd oxygen particles - active hydrogen particles - O^* excited (¹ D)-O-atom - NO_x nitrogen oxides (odd nitrogen) - n ₁ concentration of atomic oxygen [particles cm^–3] - n ₁ ^* concentration of excited [¹ D]-oxygen-atoms - n ₂ concentration of molecular oxygen - n _m concentration of air molecules - s =n _m /n ₂ - ñ n ₁+n ^*+n ₃, concentration of odd oxygen particles - x concentration of atomic hydrogen - y concentration of OH-radicals - z concentration of HO₂-radicals - [NO] concentration of nitric oxide - [NO₂] concentration of nitrogen dioxide - [NO₃] concentration of nitrogen trioxide - [NO_x] concentration of total odd nitrogen - [HNO₃] concentration of nitric acid - k _i reaction rates - f _i dissociation rates - a ₃ fraction off ₃ yielding excited O-atoms - [nomix] NO _x /air mixing ratio - relaxation time Part of the research reported in this article was done at the National Center for Atmospheric Research, Boulder, Colo. (sponsored by the National Science Foundation). The opportunity of using NCAR's computing facilities is especially acknowledged. This study has also been supported by the Swiss National Foundation.     

Trends in total ozone and the effect of the equatorial zonal wind QBO

Trends in total column ozone have been analyzed in terms of the equatorial zonal wind. We used zonal monthly mean total ozone from Total Ozone Mapping Spectrometer (TOMS) and monthly mean zonal wind in the equatorial stratosphere at 30 hPa to define the phases of the quasi-biennial oscillation (QBO). Total column ozone trends have been assessed during the period 1979–2004, for both Hemispheres, and for each month, under three conditions considering, all the ozone dataset, ozone values during easterly phase and ozone values during westerly phase of the QBO. When the whole dataset is considered, negative trends are observed. From low to midlatitudes a zonal pattern is noticed with increasing negative values toward higher latitudes. When the data is filtered according to the QBO phase, statistically significant positive trends appear in the westerly case during January to May at low latitudes .The trend pattern in the case of the easterly phase presents more negative values.     

The present-day and future impact of NOx emissions from subsonic aircraft on the atmosphere in relation to the impact of NOx surface sources

The effect of present-day and future NO_x emissions from aircraft on the NO_x and ozone concentrations in the atmosphere and the corresponding radiative forcing were studied using a three-dimensional chemistry transport model (CTM) and a radiative model. The effects of the aircraft emissions were compared with the effects of the three most important anthropogenic NO_x surface sources: road traffic, electricity generation and industrial combustion. From the model results, NO_x emissions from aircraft are seen to cause an increase in the NO_x and ozone concentrations in the upper troposphere and lower stratosphere, and a positive radiative forcing. For the reference year 1990, the aircraft emissions result in an increase in the NO_x concentration at 250 hPa of about 20 ppt in January and 50 ppt in July over the eastern USA, the North Atlantic Flight Corridor and Western Europe, corresponding to a relative increase of about 50%. The maximum increase in the ozone concentrations due to the aircraft emissions is about 3-4 ppb in July over the northern mid-latitudes, corresponding to a relative increase of about 3-4%. The aircraft-induced ozone changes cause a global average radiative forcing of 0.025 W/m² in July. According to the ANCAT projection for the year 2015, the aircraft NO_x emissions in that year will be 90% higher than in the year 1990. As a consequence of this, the calculated NO_x perturbation by aircraft emissions increases by about 90% between 1990 and 2015, and the ozone perturbation by about 50-70%. The global average radiative forcing due to the aircraft-induced ozone changes increases by about 50% between 1990 and 2015. In the year 2015, the effects of the aircraft emissions on the ozone burden and radiative forcing are clearly larger than the individual effects of the NO_x surface sources. Taking chemical conversion in the aircraft plume into account in the CTM explicitly, by means of modified aircraft NO_x emissions, a significant reduction of the aircraft-induced NO_x and ozone perturbations is realised. The NO_x perturbation decreases by about 40% and the ozone perturbation by about 30% in July over Western Europe, the eastern USA and the North Atlantic Flight Corridor.     

Instantaneous photochemical rates in the global stratosphere

Starting with the average actual distribution of ozone (Dütsch [15]) and temperature in the stratosphere, we have calculated the solar intensity as a function of wavelength and the instantaneous rates (molecules cm^–3 sec^–1) for each Chapman reaction and for each of several reactions of the oxides of nitrogen. The calculation is similar to that ofBrewer andWilson [5]. These reaction rates were calculated independently in each volume element in spherical polar coordinates defined by R=1 km from zero to 50, =5° latitude, and ø=15° longitude (thus including day and night conditions). Calculations were made for two times: summer-winter (January 15) and spring-fall (March 22). As input data we take observed solar intensities (Ackerman [1]) and observed, critically evaluated. constants for elementary chemical and photochemical reactions; no adjustable parameters are employed. (These are not photochemical equilibrium calculations.) According to the Chapman model, the instantaneous, integrated, world-wide rate of formation of ozone from sunlight is about five times faster than the rate of ozone destruction, and locally (lower tropical stratosphere) the rate of ozone formation exceeds the rate of destruction by a factors as great as 1000. The global rates of increase of ozone are more than 50 times faster thanBrewer andWilson's [5] estimate of the average annual transfer rate of ozone to the troposphere. The rate constants of the Chapman reactions are believed to be well-enough known that it is highly improbable that these discrepancies are, due to erroneous rate constants. It is concluded that something else besides neutral oxygen species is very important in stratospheric ozone photochemistry. The inclusion of a uniform concentration of the oxides of nitrogen (NO_x as, NO and NO₂) averaging 6.6×10^–9 mole fraction gives a balance between global ozone formation and destruction rates. The inclusion of a uniform mole fraction of NO_x at 28×10^–9 also gives a global balance. These calculations support the hypethesis (Crutzen [10],Johnston [24]) that the oxides of nitrogen are the most important factor in the global, natural ozone balance. Several authors have recently evaluated the natural source strength of NO_x in the stratosphere; the projected fleets of supersonic transports would constitute an artificial source of NO_x about equal to the natural value, thus promising more or less to double an active natural stratospheric ingredient.     

The role of water-vapour photodissociation on the formation of a deep minimum in mesopause ozone

A one-dimensional atmospheric photochemical model with an altitude grid of about 1.5 km was used to examine the structure of the global mean vertical ozone profile and its night-time-to-daytime variation in the upper atmosphere. Two distinct ozone layers are predicted, separated by a sharp drop in the ozone concentration near the mesopause. This naturally occurring mesopause ozone deep minimum is primarily produced by the rapid increase in the destruction of water vapour, and hence increase in HO_x, at altitudes between 80 and 85 km, a region where water-vapour photodissociation by ultraviolet radiation of the solar Lyman-alpha line is significant, and where the supply of water vapour is maintained by methane oxidation even for very dry conditions at the tropospheric-stratospheric exchange region. The model indicates that the depth of the mesopause ozone minimum is limited by the efficiency with which inactive molecular hydrogen is produced, either by the conversion of atomic hydrogen to molecular hydrogen via one of the reaction channels of H with HO₂, or by Lyman-alpha photodissociation of water vapour via the channel that leads to the production of molecular hydrogen. The ozone concentration rapidly recovers above 85 km due to the rapid increase in O produced by the photodissociation of O₂ by absorption of ultraviolet solar radiation in the Schumann-Runge bands and continuum. Above 90 km, there is a decrease in ozone due to photolysis as the production of ozone through the three-body recombination of O₂ and O becomes slower with decreasing pressure. The model also predicts two peaks in the night-time/daytime ozone ratio, one near 75 km and the other near 110 km, plus a strong peak in the night-time/daytime ratio of OH near 110 km. Recent observational evidence supports the predictions of the model.     

Impact of coupled perturbations of atmospheric trace gases on Earth's climate and ozone

We have studied the effects on the ozone concentration and surface temperature, of perturbations in the atmospheric content of nitrous oxide, methane, carbon dioxide and chlorofluorocarbons (CFC). The sensitivity study has been carried out with a radiative-convective-photochemical model. The doubling of carbon dioxide concentration has the effect of warming the troposphere and cooling the stratosphere. As a result of this cooling, the change of ozone columnar density produced by 10 ppb of chlorine amount to 9.3% as compared to –10.9% obtained without temperature feedback. Perturbation in nitrous oxide correspond to an increase in NO _x of the stratosphere with consequent ozone reduction while doubling the methane concentration correspond to a slight increase in columnar density. The effect of the increased methane concentration in the stratosphere contributes to reduce the effect of CFC due to the enhanced formation of HCl. The perturbation of these two minor constituents appreciably increase the greenhouse effect to 2.30 from 1.67°, obtained when carbon dioxide alone is considered.     

Stratospheric background aerosol and polar cloud observations by laser backscattersonde within the framework of the European project “Stratospheric Regular Sounding”

The Stratospheric Regular Sounding project was planned to measure regularly the vertical profiles of several tracers like ozone, water vapor, NO_x, ClO_x and BrO_x radicals, aerosol, pressure and temperature, at three latitudes, to discriminate between the transport and photochemical terms which control their distribution. As part of this project, the “Istituto di Fisica dell’Atmosfera” launched nine laser backscattersondes (LABS) on board stratospheric balloons to make observations of background aerosol and PSCs. LABS was launched with an optical particle counter operated by the University of Wyoming. Observations have been performed in the arctic, mid-latitudes and tropical regions in different seasons. Polar stratospheric clouds have been observed in areas inside and outside the polar vortex edge. A background aerosol was observed both in mid-latitudes and in arctic regions with a backscattering ratio of 1.2 at 692 nm. Very stratified aerosol layers, possibly transported into the lower stratosphere by deep convective systems, have been observed in the lower stratosphere between 20 and 29 km in the tropics in the Southern Hemisphere.     

Prediction of the trend of total column ozone over the Tibetan Plateau

By using 2-D chemical model, the trend of total column ozone over the Tibetan Plateau is simulated. The results show that from 1980 to 1993, the total column ozone over the Tibetan Plateau decreases; after 1995, it starts to recover. But until 2050, it will not still reach the level of 1980 total column ozone. Under Tibetan special circulation, its total column ozone recovers more rapidly than zonal mean. Therefore, the Tibetan special meridional circulation is not a main reason why the total column ozone over the Tibetan Plateau decreases more strongly than zonal mean.

     

Dynamical response of low-latitude middle atmosphere to major sudden stratospheric warming events

The zonally averaged UK Meteorological Office (UKMO) zonal mean temperature and zonal winds for the latitudes 8.75°N and 60°N are used to investigate the low-latitude dynamical response to the high latitude sudden stratospheric warming (SSW) events that occurred during winter of the years 1998–1999, 2003–2004 and 2005–2006. The UKMO zonal mean zonal winds at 60°N show a short-term reversal to westward winds in the entire upper stratosphere and lower mesosphere and the low-latitude winds (8.75°N) show enhanced eastward flow in the upper stratosphere and strong westward flow in the lower mesosphere during the major SSW events at high latitudes. The mesosphere and lower thermosphere (MLT) zonal winds acquired by medium frequency (MF) radar at Tirunelveli (8.7°N, 77.8°E) show a change of wind direction from eastward to westward several days before the onset of SSW events and these winds decelerate and weak positive (eastward) winds prevail during the SSW events. The time variation of zonal winds over Tirunelveli is nearly similar to the one reported from high latitudes, except that the latter shows intense eastward winds during the SSW events. Besides, the comparison of daily mean meridional winds over Tirunelveli with those over Collm (52°N, 15°E) show that large equatorial winds are observed over Tirunelveli during the 2005–2006 event and over Collm during the 1998–1999 events. The variable response of MLT dynamics to different SSW events may be explained by the variability of gravity waves.