Preface Acknowledgements 1. Introduction 2. Atmospheric structure, composition and thermodynamics 3. The continuity and thermodynamic energy equations 4. The momentum equation in Cartesian and spherical coordinates 5. Vertical-coordinate conversions 6. Numerical solutions to partial differential equations 7. Finite-differencing the equations of atmospheric dynamics 8. Boundary-layer and surface processes 9. Radiative energy transfer 10. Gas-phase species, chemical reactions and reaction rates 11. Urban, free-tropospheric and stratospheric chemistry 12. Methods of solving chemical ordinary differential equations 13. Particle components, size distributions and size structures 14. Aerosol emission and nucleation 15. Coagulation 16. Condensation, evaporation, deposition and sublimation 17. Chemical equilibrium and dissolution processes 18. Cloud thermodynamics and dynamics 19. Irreversible aqueous chemistry 20. Sedimentation, dry deposition and air-sea exchange 21. Model design, application and testing Appendix A. Conversions and constants Appendix B. Tables References Index.

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Fundamentals of atmospheric modeling

The sun's total and spectral irradiance for solar energy applications and solar radiation models

The influence of breaking gravity waves on the dynamics and chemical composition of the 60- to 110-km region has been investigated with a two-dimensional dynamical/chemical model that includes a parameterization of gravity wave drag and diffusion. The momentum deposited by breaking waves at mesospheric altitudes reverses the zonal winds, drives a strong mean meridional circulation, and produces a very cold summer and warm winter mesopause, in general agreement with observations. The seasonal variations of the computed eddy diffusion coefficient are consistent with the behavior of mesospheric turbulence inferred from MST radar echoes. In particular, it is found that eddy diffusion is strong in summer and winter but much weaker at the equinoxes and that this seasonal behavior has important consequences for the distribution of chemical species. Comparison between computed atomic oxygen and ozone, and the abundances of these constituents inferred from the 557.7-nm and 1.27-μm airglow emissions, reveals excellent agreement. The consistency between model results and these diverse types of observations lends strong support to the hypothesis that gravity waves play a very important role in determining the zonally averaged structure of the mesosphere and lower thermosphere.

The effect of breaking gravity waves on the dynamics and chemical composition of the mesosphere and lower thermosphere

Pure cultures of the marine ammonium-oxidizing bacterium Nitrosomonas sp. were grown in the laboratory at oxygen partial pressures between 0.005 and 0.2 atm (0.18 to 7 mg/liter). Low oxygen conditions induced a marked decrease in the rate for production of NO2-, from 3.6 × 10−10 to 0.5 × 10−10 mmol of NO2- per cell per day. In contrast, evolution of N2O increased from 1 × 10−12 to 4.3 × 10−12 mmol of N per cell per day. The yield of N2O relative to NO2- increased from 0.3% to nearly 10% (moles of N in N2O per mole of NO2-) as the oxygen level was reduced, although bacterial growth rates changed by less than 30%. Nitrifying bacteria from the genera Nitrosomonas, Nitrosolobus, Nitrosospira, and Nitrosococcus exhibited similar yields of N2O at atmospheric oxygen levels. Nitrite-oxidizing bacteria (Nitrobacter sp.) and the dinoflagellate Exuviaella sp. did not produce detectable quantities of N2O during growth. The results support the view that nitrification is an important source of N2O in the environment.

Production of NO2- and N2O by Nitrifying Bacteria at Reduced Concentrations of Oxygen

Amongst the diversity of methods used by organisms to reduce damage caused by ultraviolet (UV) radiation, the synthesis of UV-screening compounds is almost ubiquitous. UV-screening compounds provide a passive method for the reduction of UV-induced damage and they are widely distributed across the microbial, plant and animal kingdoms. They share some common chemical features. It is likely that on early earth strong selection pressures existed for the evolution of UV-screening compounds. Many of these compounds probably had other physiological roles, later being selected for the efficacy of UV screening. The diversity in physiological functions is one of the complications in studying UV-screening compounds and determining the true ecological importance of their UV-screening role. As well as providing protection against ambient UV radiation, species with effective screening may also be at an advantage during natural ozone depletion events. In this review the characteristics of a wide diversity of UV-screening compounds are discussed and evolutionary questions are explored. As research into the range of UV-screening compounds represented in the biosphere continues, so it is likely that the properties of many more compounds will be elucidated. These compounds, as well as providing us with insights into natural responses to UV radiation, may also have implications for the development of artificial UV-screening methods to reduce human exposure to UV radiation.

Ultraviolet radiation screening compounds

On the molecular scattering in the terrestrial atmosphere : An empirical formula for its calculation in the homosphere

An analysis is made of the various reactions in which ozone and atomic oxygen are involved in the stratosphere. At the present time, hydrogen, nitrogen, and chlorine compounds in the ranges parts per million, parts per billion, and parts per trillion may have significant chemical effects. In the upper stratosphere, above the ozone peak, where there is no strong departure from photochemical equilibrium conditions, the action of hydroxyl and hydroperoxyl radicals of nitrogen dioxide and chlorine monoxide on atomic oxygen and of atomic chlorine on ozone can be introduced. A precise determination of their exact effects requires knowledge of (1) the vertical distribution of the H2O, CH4, and H2 dissociation by reaction of these molecules with electronically excited oxygen atom O(¹D); (2) the ratio of the OH and HO2 concentrations and their absolute values, which depend on insufficiently known rate coefficients; (3) the various origins of nitric oxide production, with their vertical distributions related to latitude and season; and (4) the various sources giving different chlorine compounds that may be dissociated in the stratosphere. In the lower stratosphere, below the ozone peak, there is no important photochemical production of O3, but there exist various possibilities of transport. The predictability of the action of chemical reactions depends strongly on important interactions between OH and HO2 radicals with CO and NO, respectively, which affect the ratio n(OH)/n(HO2) at the tropopause level; between OH and NO2, which lead to the formation of nitric acid with its downward transport toward the troposphere; between NO and HO2, which lead to NO2 and its subsequent photodissociation; between ClO and NO, which also lead to NO2 and become more important than the reaction of ClO with O; and between Cl and various molecules, such as CH4 and H2, which lead to HCl with its downward transport toward the troposphere. All these chemical processes are subject to many changes since they occur in the lower stratosphere where seasonal, latitudinal, and even day-to-day variations of the ozone concentrations are observed in association with advective and dynamic transports, which depend on meteorological conditions as indicated by variations of tropopause heights.

Marcel Nicolet

Papers

On the molecular scattering in the terrestrial atmosphere : An empirical formula for its calculation in the homosphere

Stratospheric Ozone: An Introduction to Its Study

Chemospheric processes of nitric oxide in the mesosphere and stratosphere

Solar spectral irradiances with their diversity between 120 and 900 nm

The aeronomic dissociation of nitric oxide