Comparison of 1D LOC results for cloud models presented in van Zadelhoff et al. (2002). The plots show the radial excitation temperature profiles of the HCO⁺J = 1 − 0 and J = 4 − 3 transitions for Model 2a and the optically thicker Model 2b. The LOC results are plotted with hashed red lines, the results of the Monte Carlo code Cppsimu are shown in blue and the other results (van Zadelhoff et al. 2002) in black (with different line types). In frame d, the cyan line shows LOC results for an alternative interpretation of the problem set-up.