Departure coefficients for selected levels of Al i as a function of log τ₅₀₀₀ in the model atmosphere 4710/1.65/−2.66 from the calculations with the standard DETAIL opacity package (top panel) and with no lines of Fe and Ca and no quasi-molecular hydrogen absorption (bottom panel). Ticks indicate the locations of line-centre optical depth unity for the Al i line 3961 Å (transition –).