Evolution of the dust properties per gas nucleon in intervals of molecular fraction in the gas column (left), of total gas column density N_{H mλ} (middle), and of dust colour temperature (right). The A_VQ/N_H ratios are in units of 10^-22 mag cm², τ₃₅₃/N_H in 10^-27 cm², and 4πR/N_H in 10^-31 W. To estimate the molecular fraction in N_H, we have assumed a DNM composition between half (stars) and fully (dots) molecular. The solid and dashed error bars respectively give the error on the means and the standard deviations in each sample. The thin lines mark the average values found in the (0.4−2) × 10²¹ cm^-2 range. The shaded area in the temperature plot shows the expectation for uniform radiated powers ranging between 3.4 and 5 × 10^-31 W H^-1, with the mean index β = 1.65 in the region. A power-law variation in opacity, σ₃₅₃ ∝N_H^{0.28 ± 0.03}, has been reported above 10²¹ cm^-2 in Orion. The shaded curve in the central plot shows this trend scaled at the value of the Chamaeleon complex opacity at N_{H mλ} = 10²¹ cm^-2.