Photochemistry of the Atmospheres of Mars and Venus

340 Pages·1986·11.267 MB·English

by  Professor Dr. Vladimir A. Krasnopolsky (auth.)

Physics and Chemistry in Space Vol. 13
Edited by L. J. Lanzerotti, Murray Hill
Vladimir A. Krasnopolsky
Photochemistry of
the Atmospheres
of Mars and Venus
Technical Editor
UlfvonZahn
With 209 Figures
Springer-Verlag
Berlin Heidelberg New York Tokyo
~----J
Professor Dr. VLADIMIR A. KRASNOPOLSKY
Space Research Institute
Academy of Sciences
Profsojusnaja, 84/32
117810 Moscow, USSR
Technical Editor:
Professor Dr. ULF VON ZAHN
Rheinische Friedrich-Wilhelms-Universitat Bonn
Physikalisches Institut
NuJ3allee 12
5300 Bonn, FRG
Title of the original Russian edition:
Fotokhimia atmosfer marsa i veneri
© by Nauka, Moscow 1982
ISBN-13 978-3-642-70403-1 e-ISBN-13: 978-3-642-70401-7
DOl: 10.1007/978-3-642-70401-7
Library of Congress Cataloging-in-Publication Data. Krasnopol'skiI, V. A. (Vla
dimir Anatol'evich), 1938- Photochemistry of the atmosphere of Mars and
Venus. (Physics and chemistry in space ; v. 13) Translation of: Fotokhimiia
atmosfer Marsa i Venery. Bibliography: p. Includes index. I. Mars (Planet) -
Atmosphere. 2. Venus (Planet) - Atmosphere. 3. Photochemistry. 4. Cosmo
chemistry. I. Title. II. Series. QC80l.P46 vol. 13 530'.0919 s 85-25008
[QB6411 [551.5'0999'231
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© by Springer-Verlag Berlin Heidelberg 1986
Softcover reprint of the hardcover I st edition 1986
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2131/3130-543210
Preface
Spacecraft study of the Solar system is one of humanity's most outstanding
achievements. Thanks to this study, our present knowledge of properties of
and conditions on the planets exceeds many-fold that of 20 years ago: planets
have been rediscovered. This is especially the case for planetary atmospheres,
whose properties were for the most part either not at all or only erroneously
known.
Much research has been invested in the study of the atmospheres of Mars
and Venus, and their chemical composition and photochemistry are basic
problems in these studies. In the present publication I have tried to summarize
all findings in this field.
The English version of the book includes new data in the field from the last
3 years since the book was published in Russian.
I wish to thank U. von Zahn, who initiated my talks with Springer-Verlag
and acted as technical editor.
December 2, 1985 V. A. KRASNOPOLSKY
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1 Chemical Composition and Structure of the Martian Atmosphere 4
1.1 Carbon Dioxide and Atmospheric Pressure . . . . . . . . . . . . . . . . . . . 4
1.2 CO and O2 Mixing Ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3 Ozone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.4 Water Vapor ............................................ 18
1.5 Composition of the Upper Atmosphere as Determined from
Airglow Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
1.6 Mass Spectrometric Measurements of the Atmospheric
Composition ............................................ 31
1.7 Ionospheric Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
1.8 Temperature Profile of the Lower Atmosphere. . . . . . . . . . . . . . . . 36
1.9 Temperature of the Upper Atmosphere ...................... 40
1.10 Eddy Diffusion Coefficient ................................ 42
2 Photochemistry of the Martian Atmosphere .................. 46
2.1 Ionosphere. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.2 Photochemistry of Nitrogen ............................... 53
2.3 H2 Dissociation and Escape of Atomic Hydrogen . . . . . . . . . . . . . . 58
2.4 Nonthermal Escape and Isotopic Composition of Oxygen and
Nitrogen ................................................ 61
2.5 Dissociation of CO2: Atomic Carbon in the Upper Atmosphere. . 65
2.6 Diffusion and Photolysis of Water Vapor .................... 69
2.7 Photochemistry of the Lower Atmosphere (Global Average
Conditions) ............................................. 74
2.8 Diurnal Variations of Minor Components in the Low Latitude
Atmosphere ............................................. 84
2.9 Latitudinal Distribution of Ozone in Different Seasons ......... 85
2.10 Seasonal Variations of Atmospheric Composition at a Latitude of
65°N ................................................... 91
VIII Contents
3 Chemical Composition and Structure of the Venusian
Atmosphere and Cloud Layer ............................. . 99
3.1 Properties of Aerosol in the Upper Part of the Cloud Layer
Deduced from Polarization Measurements .................. . 99
3.2 Interpretation of Spectroscopic Measurements of Escaping
Radiation ............................................. ,. 102
3.3 Spectroscopy in Visible and Infrared Ranges ................. . 105
3.4 Remote Sounding of Water Vapor and Carbon Monoxide in Far
Infrared and Microwave Regions. Radio Spectrum ........... . 110
3.5 Optical Measurements in the 0.45 -1.2 J.Lm Range from Venera
Landers ................................................ . 119
3.6 Mass Spectrometric and Gas Chromatographic Measurements
in the Lower Atmosphere .. , .............................. . 125
3.7 Physical Characteristics of the Cloud Layer ................. . 131
3.8 Ultraviolet Absorption in the Cloud Layer .................. . 143
3.9 Investigation of a Cloud Layer Elemental Composition by X-Ray
Fluorescent Spectroscopy in the Region of 1 to 20 A
(0.6-13 keY) ........................................... . 159
3.10 Summary of the Data on the Tropospheric and Cloud Layer
Composition ........................................... . 162
3.11 The Upper Atmosphere .................................. . 172
3.12 Ionosphere ............................................. . 189
3.13 Temperature, Eddy Mixing, Atmospheric Dynamics,
and Lightning .......................................... . 196
4 Photochemistry of the Venusian Atmosphere ................ . 205
4.1 Day Side Ionosphere ..................................... . 205
4.2 Nighttime Ionosphere .................................... . 209
4.3 Metastable Species in the Venusian Ionosphere. Nitric Oxide,
Atomic Nitrogen, and Atomic Carbon ...................... . 215
4.4 Light Components of the Upper Atmosphere (H, H2, He).
"Hot" Atoms and Nonthermal Escape of H, He, and 0 ....... . 220
4.5 Thermospheric Models ................................... . 229
4.6 Lightning and Lower Atmospheric Chemistry.
Nitric Oxide in the Lower Atmosphere ...................... . 232
4.7 Lower Atmospheric and Surface Rock Compositions (0 - 50 km) 236
4.8 Neutral Atmospheric Photochemistry Above 50 km. Main
Problems, Previous Results, Main Chemical Reactions ........ . 246
4.9 Radiative Transfer and Aerosol Transport in the Cloud Layer .. . 255
4.10 Boundary Conditions .................................... . 258
4.11 Atmospheric Composition at 50 to 200 km (Results of
Calculations) ........................................... . 260
4.12 0 1.27 J.Lm and OeD) 630 nm Airglow. Photolytic Rates ...... . 270
2
Contents IX
4.13 The Influence of Some Reaction Rate Coefficients on the Results
of Calculations .......................................... 274
4.14 Photochemistry of the Venusian Mesosphere as Considered by
Winick and Stewart (1980) ................................. 275
4.15 Analysis of Atmospheric Photochemistry on Venus by Yung and
DeMore (1982) . .. . . . . . . . . . ... .. . . . . . . . . . . . . . . . . . . . . . .. . . . 277
4.16 Loss of Water from Venus and Its Atmospheric Evolution ...... 295
4.17 Conclusions............................................. 310
References ................................................... 315
Subject Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
Introduction
The main aim of this book is to present experimental and theoretical results
achieved over the last decade on the chemical composition and structure of the
atmospheres of Mars and Venus, processes defining the properties of the at
mospheres, and other related phenomena.
Three basic aims for studies of an atmosphere exist: chemical composi
tion, thermal regime, and dynamics. The chemical composition of an atmo
sphere is determined by its origin and evolution, processes of gas exchange be
tween the atmosphere and the planetary body and space, and by chemical and
physical processes inside the atmosphere. The latter processes are defined in
the science of aeronomy, and this book is concerned primarily with findings in
this field. However, a planetary atmosphere is a single entity and all its com
ponents are interrelated, e.g., its chemical composition determines thermal
regime and the latter, in turn, affects its dynamics. Therefore, this book
provides a brief description of these problems as well.
Ample space is given to experimental results and their interpretation. For
theoretical findings, I will try to give an idea of a method or an interpretation,
followed by the results obtained. The advantages or speculative aspects of
some approaches are also considered. Unfortunately, in many cases I had no
possibility to discuss the papers described with their authors, thus, this may
have led sometimes to errors in my evaluations. Therefore, I would greatly
appreciate receiving some response from readers.
Of similar importance to experimental results are theoretical models which
describe the transformations of atmospheric constituents by photochemical
processes in the presence of transport. If these models are in accord with the
scope of experimental data, then they demonstrate the adequacy of our
knowledge of the intimate properties of the atmosphere. A photochemical ap
proach may be of use in the case of controversial experimental data. Besides,
model calculations yield the amounts and vertical profiles of components
which have been undetected or measured in a limited altitude range.
Important aspects of the space programs of the USSR and USA over the
last two decades include investigations of Mars and Venus. The structures of
these programs were different. The Soviet program from the beginning of the
1960's was directed toward the designing of space vehicles with descent
probes, while in the United States spacecraft with more and more complicated
functions were developed: flyby systems for short-term observations from a
distance of _104 km, orbiters, and descent probes.
2 Introduction
The first successful experiments for the study of Mars were carried out by
the American flybys Mariner 4 (1965) and Mariner 6, 7 (1969). The first
orbiters were in 1971: Soviet Mars 2 and 3 and U.S. Mariner 9. That year, the
first descent probe, Mars 3, was launched into the Martian atmosphere to
measure its properties. Though the descent and landing proceeded normally,
information transmission ceased soon after it started, probably as a result of
extremely strong winds of a global dust storm on the planet which could have
led to the disturbance of the antenna's operation. In 1974, four Soviet probes,
i.e., two flybys (Mars 4 and 7), one orbiter (Mars 5), and one descent probe
(Mars 6), investigated the planet. The most extensive research program of
Mars was carried out by Viking 1 and 2 (1976 until 1981), which incorporated
long-lived landers and orbiters.
The first space studies of Venus were made by the American flybys
Mariner 2 (1962) and Mariner 5 (1967). The latter was accompanied by the
successful descent of the Soviet Venera 4. Then, a series of first generation
Soviet descent probes followed (Veneras 5 to 8, 1969-1972). In 1974,
Mariner 10 flew by Venus and Mercury. The second generation of Soviet
spacecraft to study Venus was started in 1975 by Veneras 9 and 10, each in
cluding a descent probe and an orbiter. At the end of 1978 the U.S. Pioneer
Venus spacecraft arrived at Venus, which incorporated four descent probes
intended to operate at different locations (low and high latitudes, day and
night sides), an entry probe (bus) for measurements down to 130 km, and an
orbiter with a pericenter at 150 km. At the same time, Soviet Veneras 11 and
12 operated. Since then, studies of Venus were continued by Veneras 13, 14
lander probes (1982) and Veneras 15, 16 orbiters (1983 -1984).
Results obtained by the spacecraft, supplemented by some ground-based
observations, especially high resolution spectroscopy in infrared and micro
wave regions, form the foundation of our modern knowledge of both planets.
Studies of the solar system, which may seem at first glance to be far
removed from the needs and concerns of humanity, are of great cognitive and
philosophical value, especially the problem of the origin and evolution of the
solar system. However, it is our deep belief that atmospheric photochemistry
will find ever increasing use. Human activity influences the environment
negatively, in particular, leads to air pollution. Effective methods to maintain
the existing properties of the atmosphere might be developed in the future.
One significant problem is to study the atmospheric resilience to influences
which might result in some irreversible consequences in definite conditions.
For example, the atmospheric temperature depends on abundances of water
vapor and carbon dioxide and the area of clouds reflecting solar radiation.
The situation when high atmospheric temperature could be maintained by the
amount of increased atmospheric water vapor does not seem totally im
probable. Another apt example widely discussed in the last decade is the nega
tive consequences of reduced amounts of ozone in the atmosphere as a result
of enhanced delivery of chlorfluormethanes and nitrogen oxides, which act as
catalysts in the process of destroying the ozone layer.
Introduction 3
The mathematical background of photochemical modeling is a system of
continuity equations for every component under consideration:
onj -
--+ V¢Jj= Pj-njLj
ot
where nj is the number density, V = i ~ + j ~ + k ~ is the differential op-
oX oy oz
fPj
erator, P and L are the production and loss rates by chemical reactions, is
j j
the flux of the component which can be given by
-(K OT] (K
¢Jj = +Dj) [onj +~(1 + aj) -nj + Dj)
oz oz
T H H
j
for one-dimensional models and in the approximation of the minor
component nj ~ L nj. Here, K is the eddy mixing coefficient, Dj is the
j
molecular diffusion coefficient, Hand H are the mean atmospheric scale
j
heights and that of the i component, T is the temperature, and aj is the ther
mal diffusion factor. In a physical sense, the continuity equation implies that
changes in the density of a component number are due to chemical reactions
or transport from or to other atmospheric regions.
Since altitude variations of atmospheric composition as a rule greatly ex
ceed horizontal variations, derivatives with respect to horizontal coordinates
are much less than those with respect to height and may be neglected. This ap
proximation gives one-dimensional models. When diurnal and other temporal
variations are not taken into consideration, time independent models are used
which simplify the system of partial differential equations to that of ordinary
differential equations. In some cases, e.g., for ionospheric calculations, when
photochemical lifetimes, Tc = L -1, are much less than transport time con
stants, Tm = H2/(K + D), transport effects can be neglected, and one gets a
system of algebraic equations, Pj = njLj.
In most cases these systems of equations need a special computation tech
nique, the description of which is beyond the scope of our book.
Boundary and (in the case of time-dependent problems) initial conditions
should be introduced. The usual form of boundary conditions is number den
sities or fluxes at both (upper and lower) boundaries. Below, some widespread
cases are given: ¢Jj = 0 at the upper boundary implies diffusive equilibrium of
the component nj, its altitude distribution having a scale height H = ~
j
mjg
above the upper boundary. The same at the lower boundary implies that inter
actions with the low lying atmosphere or surface are negligible (chemically
passive surface). A condition of photochemical equilibrium at the boundary,
nj = P;lL is a partial case of the boundary condition for a component
j,
number density.
This book is based on data published up to the beginning of 1984.