UNIQUENESS OF A SOLUTION OF A STEADY-STATE PHOTOCHEMICAL PROBLEM - APPLICATIONS TO MARS

Authors
Citation
Va. Krasnopolsky, UNIQUENESS OF A SOLUTION OF A STEADY-STATE PHOTOCHEMICAL PROBLEM - APPLICATIONS TO MARS, J GEO R-PLA, 100(E2), 1995, pp. 3263-3276
Citations number
56
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geosciences, Interdisciplinary","Astronomy & Astrophysics
Journal title
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS
ISSN journal
2169-9097 → ACNP
Volume
100
Issue
E2
Year of publication
1995
Pages
3263 - 3276
Database
ISI
SICI code
2169-9097(1995)100:E2<3263:UOASOA>2.0.ZU;2-1
Abstract
Based on the conservation of chemical elements in chemical reactions, a rule is proved that the number of boundary conditions given by densi ties and/or nonzero velocities should not be less than the number of c hemical elements in the system, and the boundary conditions for specie s given by densities and velocities should include all elements in the system. Applications of this rule to Mars are considered. It is shown , that the problem of the CO2-H2O chemistry in the lower and middle at mosphere of Mars, say, in the range of 0-80 km does not have a unique solution, if only CO2 and H2O densities are given at the lower boundar y, and the remaining boundary conditions are fluxes. Two examples of m odels of this type are discussed. These models fit the same boundary c onditions; are balanced with a relative accuracy of 10(-4) for H-2 (an d much better for other species), and predict O-2, CO, and H-2 mixing ratios which differ by orders of magnitude. One more species density, e.g., that of O-2, should be specified at the boundary to obtain a uni que solution. The situation is better if the upper boundary is extende d to the exobase where thermal escape velocities of H and H-2 can be s pecified. In this case, however, either the oxygen nonthermal escape r ate (and hence the total hydrogen escape rate) or the O-2 (or other sp ecies) density at the surface should be given as a boundary condition. Two models of the photochemistry of the Martian atmosphere, with and without nitrogen chemistry, are considered. The oxygen nonthermal esca pe rate of 1.2x10(8) cm(-2)s(-1) is given at 240 km and is balanced wi th the total hydrogen escape rate within an uncertainty of 1% for both models. Both models fit the measured O-2 and CO mixing ratios, the O- 3 abundance, and the O-2 1.27-mu m dayglow almost within the uncertain ties of the measured values, though the model without nitrogen chemist ry fits better. The importance of nitrogen chemistry in the lower and middle atmosphere of Mars depends on a fine balance between production of NO and N in the upper atmosphere which is not known within the req uired accuracy.