Condensation efficiency and average radius of newly formed carbon grains as a function of the isotropic mass of carbon M_C(4π/ΔΩ) (M_C is the carbon mass available for dust formation). The radius of carbon grains with 100 atoms is also shown (dotted). The vertical dashed line marks the amount of carbon gas which is required to produce the dust emission spectrum (M_{d, C} = 8 × 10⁻⁶ M_☉) in Figure 3 for ΔΩ = 4π.