Various contributions (see legend) to the emission coefficients for the Stokes parameters I (top panel) and Q (bottom panel) as a function of height in the FAL-C model, in the absence of magnetic fields. The emission coefficients are evaluated at the wavelength λ = 4227.1 Å, corresponding to the maximum of the Q/I lobe in the red wing of the line, for a LOS with μ = 0.17. The shaded area in the panels highlights the atmospheric region where the optical depth at this wavelength and LOS is greater than 1. ε_X (where X= I or Q) is the total emissivity, , , and are the contributions from R^II, R^III, and R^III−CRD, respectively, while and are the contributions from the line thermal emissivity and continuum, respectively.