Optical depth calculated over the atmospheric column for CH₄ and C₂H₂. The transparent green and cyan bands represent the absorption spectral ranges used for the CR calculations. For CH₄ the absorption spectral range is considered between 125 nm and 130 nm and for C₂H₂ between 150 and 153 nm. The transparent magenta band is the non-absorbed (N.A.) spectral range over which hydrocarbon absorption was assumed to be negligible.