Atomic Carbon in the Atmosphere of Venus

The densities of atomic carbon in the Venusian thermosphere are computed for a model which includes both chemistry and transport. The maximum density of C is 2.8×10 ⁷ cm ⁻³ near 150 km for an assumed O ₂ mixing ratio of 1×10 ⁻⁴ . Photoionization of atomic carbon is found to be the major source of C ⁺ above 200 km, and resonance scattering of sunlight by atomic carbon may be the major source of the C I emissions at 1561 Å, 1657 Å, and 1931 Å. The computed C ⁺ densities are found to be in substantial agreement with those measured by Pioneer Venus.