Geoscience Reference
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the Feautrier method generalized to arbitrary anisotropic scattering with
aerosol scattering properties based on Pioneer Venus measurements. Pho-
toabsorption and chemical kinetic data were drawn from critically reviewed
compilations 25 whenever possible. Temperature-dependent cross-sections
were used for CO 2 ,SO 2 ,O 3 , and OCS. The UV cross-sections for photolysis
of ClCO 3 from recent laboratory work 4 were included. Changes in kinetic
rate recommendations since 1997 are not expected to be significant. We
simultaneously solve the one-dimensional continuity equation for 47 species
using a finite difference iterative algorithm to converge to a steady-state
solution. Vertical transport via Eddy diffusion was set based on observa-
tions. The H 2 O profile was fixed to match the equilibrium vapor pressure
over 75 wt.% sulfuric acid. 26 Our model atmosphere, noon local solar time,
extends from 58 to 112 km altitude with 2-km thick layers. At the lower
boundary, the mixing ratio for CO 2 was set to 0.965, HCl to 0.4 ppm, OCS
to 1 ppb, and SO 2 to 1 ppm. The concentration gradient at the lower bound-
ary for all other species was set to zero. At the upper boundary, the upward
flux of molecules, such as CO 2 , was set equal to the downward flux of their
photodissociation products to simulate photodissociation occurring above
the upper boundary.
3. Model Results
Key results from the three alternative catalytic schemes for production of
CO 2 are compared with extant global-scale observations and the results
from a nominal chemistry model calculation in Table 1. The calculated
oxygen profiles are shown in Fig. 1.
The O 2 (c 1 Σ) model examined the effect of Reaction (1). O 2 (c 1 Σ) was
produced via 2O + M
O 2 (c 1 Σ) + M with an assumed branching ratio of
Table 1.
Comparison of global average observations and calculations.
Model calculation
Measured
O 2 (c 1 Σ)
Observation
Aerosol
P2004
Nominal
value
1 a
SO 2 scale height at 70 km (km)
3
±
3
3
4
4
20 430 a
f(SO 2 ) at 70 km (ppb)
50
40
40
90
SO peak near 65 km (10 10 cm 3 )
1 4 a
2
1
0.3
0.3
O 2 column (10 18 cm 2 )
< 1 . 5 b
2.6
2.1
16
20
O 2 ( 1 ∆) airglow (MR)
1 1 . 5 c , d
1.2
1.2
1.5
2.1
H 2 SO 4 production (10 11 cm 2 /s)
2 10 e , f
3
4
8
9
Sources for measured values : a Ref. 27; b Ref. 5; c Ref. 28; d Ref. 29; e Ref. 6; f Ref. 30.
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