Recent attempts1,2 to consolidate assessments of the effect of human activities on stratospheric ozone (O3) using one-dimensional models for 30° N have suggested that perturbations of total O3 will remain small for at least the next decade. Results from such models are often accepted by default as global estimates3. The inadequacy of this approach is here made evident by observations that the spring values of total O3 in Antarctica have now fallen considerably. The circulation in the lower stratosphere is apparently unchanged, and possible chemical causes must be considered. We suggest that the very low temperatures which prevail from midwinter until several weeks after the spring equinox make the Antarctic stratosphere uniquely sensitive to growth of inorganic chlorine, ClX, primarily by the effect of this growth on the NO2/NO ratio. This, with the height distribution of UV irradiation peculiar to the polar stratosphere, could account for the O3 losses observed.

Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction

A model for the photochemistry of the global troposphere constrained by observed concentrations of H2O, O3, CO, CH4, NO, NO2, and HNO3 is presented. Data for NO and NO2 are insufficient to define the global distribution of these gases but are nonetheless useful in limiting several of the more uncertain parameters of the model. Concentrations of OH, HO2, H2O2, NO, NO2, NO3, N2O5, HNO2, HO2NO2, CH3O2, CH3OOH, CH2O, and CH3CCl3 are calculated as functions of altitude, latitude, and season. Results imply that the source for nitrogen oxides in the remote troposphere is geographically dispersed and surprisingly small, less than 107 tons N yr−1. Global sources for CO and CH4 are 1.5 × 109 tons C yr−1 and 4.5 × 108 tons C yr−1, respectively. Carbon monoxide is derived from combustion of fossil fuel (15%) and oxidation of atmospheric CH4 (25%), with the balance from burning of vegetation and oxidation of biospheric hydrocarbons. Production of CO in the northern hemisphere exceeds that in the southern hemisphere by about a factor of 2. Industrial and agricultural activities provide approximately half the global source of CO. Oxidation of CO and CH4 provides sources of tropospheric O3 similar in magnitude to loss by in situ photochemistry. Observations of CH3CCl3 could offer an important check of the tropospheric model and results shown here suggest that computed concentrations of OH should be reliable within a factor of 2. A more definitive test requires better definition of release rates for CH3CCl3 and improved measurements for its distribution in the atmosphere.

/pdf/tropospheric-chemistry-a-global-perspective-29u7u1il4s.pdf

Tropospheric chemistry: A global perspective

Stratospheric ozone depletion through cat- alytic chemistry involving man-made chlorofluorocar- bons is an area of focus in the study of geophysics and one of the global environmental issues of the twentieth century. This review presents a brief history of the sci- ence of ozone depletion and describes a conceptual framework to explain the key processes involved, with a focus on chemistry. Observations that may be considered as evidence (fingerprints) of ozone depletion due to chlorofluorocarbons are explored, and the related gas phase and surface chemistry is described. Observations of ozone and of chlorine-related trace gases near 40 km provide evidence that gas phase chemistry has indeed currently depleted about 10% of the stratospheric ozone there as predicted, and the vertical and horizontal struc- tures of this depletion are fingerprints for that process. More striking changes are observed each austral spring in Antarctica, where about half of the total ozone col- umn is depleted each September, forming the Antarctic ozone hole. Measurements of large amounts of ClO, a key ozone destruction catalyst, are among the finger- prints showing that human releases of chlorofluorocar- bons are the primary cause of this change. Enhanced ozone depletion in the Antarctic and Arctic regions is linked to heterogeneous chlorine chemistry that oc- curs on the surfaces of polar stratospheric clouds at cold temperatures. Observations also show that some of the same heterogeneous chemistry occurs on the surfaces of particles present at midlatitudes as well, and the abundances of these particles are enhanced following explosive volcanic eruptions. The partition- ing of chlorine between active forms that destroy ozone and inert reservoirs that sequester it is a central part of the framework for our understanding of the 40-km ozone decline, the Antarctic ozone hole, the recent Arctic ozone losses in particularly cold years, and the observation of record midlatitude ozone de- pletion after the major eruption of Mount Pinatubo in the early 1990s. As human use of chlorofluorocarbons continues to decrease, these changes throughout the ozone layer are expected to gradually reverse during the twenty-first century.

https://iri.columbia.edu/~goddard/EESC_W4400/CC/solomon_1999.pdf

Stratospheric ozone depletion: A review of concepts and history

Methane is the most abundant organic chemical in Earth's atmosphere, and its concentration is increasing with time, as a variety of independent measurements have shown. Photochemical reactions oxidize methane in the atmosphere; through these reactions, methane exerts strong influence over the chemistry of the troposphere and the stratosphere and many species including ozone, hydroxyl radicals, and carbon monoxide. Also, through its infrared absorption spectrum, methane is an important greenhouse gas in the climate system. We describe and enumerate key roles and reactions. Then we focus on two kinds of methane production: microbial and thermogenic. Microbial methanogenesis is described, and key organisms and substrates are identified along with their properties and habitats. Microbial methane oxidation limits the release of methane from certain methanogenic areas. Both aerobic and anaerobic oxidation are described here along with methods to measure rates of methane production and oxidation experimentally. Indicators of the origin of methane, including C and H isotopes, are reviewed. We identify and evaluate several constraints on the budget of atmospheric methane, its sources, sinks and residence time. From these constraints and other data on sources and sinks we construct a list of sources and sinks, identities, and sizes. The quasi-steady state (defined in the text) annual source (or sink) totals about 310(±60) × 1012 mol (500(±95) × 1012 g), but there are many remaining uncertainties in source and sink sizes and several types of data that could lead to stronger constraints and revised estimates in the future. It is particularly difficult to identify enough sources of radiocarbon-free methane.

/pdf/biogeochemical-aspects-of-atmospheric-methane-1j0pgr75la.pdf

Biogeochemical aspects of atmospheric methane

Preface. 1: The Middle Atmosphere and its Evolution. 1.1 Introduction. 1.2 Evolution of the Earth's Atmosphere. 1.3 Anthropogenic Perturbations. 2: Chemical Concepts in the Atmosphere. 2.1 Introduction. 2.2 Energy Levels of Molecules. 2.3 Thermodynamic Considerations. 2.4 Elementary Chemical Kinetics. 2.5 Heterogeneous and Multiphase Reactions. 2.6 Photolysis Processes. 2.7 Excited Species in the Middle Atmosphere. 3: Dynamics and Transport. 3.1 Introduction. 3.2 Structure of the Atmosphere and Some Observed Dynamical Characteristics. 3.3 Fundamental Description of Atmospheric Dynamics. 3.4 Atmospheric Waves. 3.5 Effects of Dynamics on Chemical Species: Transport. 3.6 Dynamics and Meridional Transport in Two Dimensions: A Conceptual View. 3.7 The Importance of Wave Transience and Dissipation. 3.8 Vertical Transport above the Mesopause. 3.9 Models of the Middle Atmosphere. 4: Radiation. 4.1 Introduction. 4.2 Definitions. 4.3 Extraterrestrial Solar Radiation. 4.4 The Attenuation of Solar radiation in the Atmosphere. 4.5. Radiative Transfer. 4.6 The Thermal Effects of Radiation. 4.7 Photochemical Effects of Radiation. 5: Composition and Chemistry. 5.1 General. 5.2 Oxygen Compounds. 5.3 Carbon Compounds. 5.4 Hydrogen Compounds. 5.5 Nitrogen Compounds. 5.6 Halogen Compounds. 5.7 Stratospheric Aerosols and Clouds. 5.8 Generalized ozone Balance. 6: Ozone Perturbations. 6.1 Introduction. 6.2 The Photochemically-Controlled Upper Stratosphere and mesosphere: 25-75 km. 6.3 Lower Stratospheric Ozone Depletion: Observations and Explanations. 6.4 Summary and Outlook. 7: The Ions. 7.1 Introduction. 7.2 Formation of Ions in the Middle Atmosphere. 7.3 Positive Ion Chemistry. 7.4 Negative Ion Chemistry. 7.5 Effect of Ionic Processes on Neutral Constituents. 7.6 Radio Waves in the Lower Ionosphere. Appendices. Appendix 1: Physical Constants and Other Data. Appendix 2: Conversion Factors and Multiplying Prefixes. Appendix 3: Rate Coefficients forSecond-Order Gas-Phase Reactions. Appendix 4: Rate Coefficients for Gas-Phase Associating Reactions. Appendix 5: Surface Reaction Probability. Appendix 6: Atmospheric Profiles. Figure acknowledgements. Index.

/pdf/aeronomy-of-the-middle-atmosphere-chemistry-and-physics-of-4n65tw44ra.pdf

Aeronomy of the Middle Atmosphere: Chemistry and Physics of the Stratosphere and Mesosphere

This study proposes that the oxides of chlorine, ClOx, may constitute an important sink for stratospheric ozone. A photochemical scheme is devised which includes two catalytic cycles through which ...

Stratospheric Chlorine: a Possible Sink for Ozone

Calculations indicate that chlorofluoromethanes produced by man can greatly affect the concentrations of stratospheric ozone in future decades. This effect follows the release of chlorine from these compounds in the stratosphere. Present usage levels of chlorofluoromethanes can lead to chlorine-catalyzed ozone destruction rates that will exceed natural sinks of ozone by 1985 or 1990.

/pdf/stratospheric-ozone-destruction-by-man-made-ujzp4ho2wc.pdf

Stratospheric ozone destruction by man-made chlorofluoromethanes.

Radon 222 is an inert gas whose loss is due only to radioactive decay with a half life of 3. 83 days (5. 51-day 'exponential' lifetime). It is a very useful tracer of continental air because only ground level continental sources are significant. Previously published measured **2**2**2Rn profiles are analyzed here by averaging for the summer, winter, and spring-fall seasons. The analysis shows that in summer, about 55% of the **2**2**2Rn is transported above the planetary boundary layer, considerably more than during the other seasons. Similarly, in summer, about 20% rises to over 5. 5 km (500 mbar). The average profiles have been used to derive vertical eddy diffusion coefficients with maximum values of 5-7 multiplied by 10**5 cm**2 s** minus **1 in the midtroposphere and 8 multiplied by 10**3 to 5 multiplied by 10**4 cm**2 s** minus **1 near the surface.

/pdf/radon-222-and-tropospheric-vertical-transport-1egkzku01f.pdf

Radon 222 and tropospheric vertical transport.

The reaction of the hydroxyl radical (HO) with the stable carbon isotopes of methane has been studied as a function of temperature from 273 to 353 K. The measued ratio of the rate coefficients for reaction with (C-12)H4 relative to (C-13)H4 (k12/k13) was 1.0054 (+ or - 0.0009 at the 95 percent confidence interval), independent of temperature within the precision of the measurement, over the range studied. The precision of the present value is much improved over that of previous studies, and this result provides important constraints on the current understanding of the cycling of methane through the atmosphere through the use of carbon isotope measurements.

/pdf/carbon-kinetic-isotope-effect-in-the-oxidation-of-methane-by-36n7rny8f4.pdf

Carbon kinetic isotope effect in the oxidation of methane by the hydroxyl radical

We have measured gaseous methyl bromide (CH/sub 3/Br) and bromoform (CHBr/sub 3/) in air samples that were gathered approximately weekly from five ground-level sites: Point Barrow, Alaska; Mauna Loa Observatory and Cape Kumukahi, Hawaii; Matatula, Samoa; and Kaitorete Spit, New Zealand. Approximately 750 samples have been analyzed for CH/sub 3/Br between January 1985 and October 1987 and 990 samples have been analyzed for CHBr/sub 3/ between early 1984 and September 1987, all by gas chromatography/mass spectroscopy. Methyl bromide concentrations are typically 10--11 parts per trillion (ppt) by volume; there are no clear indications of temporal increases. Bromoform concentrations are typically 2--3 ppt, but large seasonal variations are seen at Point Barrow. copyright American Geophysical Union 1988

/pdf/measurements-of-atmospheric-methyl-bromide-and-bromoform-38cknkvtgj.pdf

Ralph J. Cicerone

Papers

Stratospheric Chlorine: a Possible Sink for Ozone

Stratospheric ozone destruction by man-made chlorofluoromethanes.

Radon 222 and tropospheric vertical transport.

Carbon kinetic isotope effect in the oxidation of methane by the hydroxyl radical

Measurements of atmospheric methyl bromide and bromoform