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Ultraviolet over-ionisation of iron atoms in the solar atmosphere leads todeviations in their level populations from the Saha-Boltzmann statistics. Thiscauses their line profiles to form in Non-Local Thermodynamic Equilibrium(NLTE) conditions. While inverting such profiles to determine atmosphericparameters, the NLTE effects are often neglected and deviations from LTE arecompensated for by tweaking other quantities. We investigate how the routinelyemployed LTE inversion of iron lines formed in NLTE under- or over-estimatesatmospheric quantities such as temperature (T), line-of-sight velocity (v_LOS),magnetic field strength (B) and inclination (gamma) while the previous papershave focused mainly on T. We synthesize the Stokes profiles of Fe I 6301.5 Aand 6302.5 A lines in both LTE and NLTE using a snapshot of a 3D MHDsimulation. The profiles are then inverted in LTE. By considering theatmosphere inferred from inversion of LTE profiles to be the fiducial model, wecompare atmosphere from the inversion of NLTE profiles with it. Any differencesobserved are attributed to NLTE effects. Neglecting the NLTE effects introduceserrors in the inverted atmosphere. While the errors in T can go up to 13%, inv_LOS and B the errors can be as high as 50% or more. We find these errors tobe present at all three inversion nodes. Importantly, they survive degradationfrom spatial averaging of the profiles. We give an overview of how the neglectof NLTE effects influences the values of T, v_LOS, B and gamma determined byinverting Fe I 6300 A line pair, as observed, e.g., by Hinode. Errors are foundat the sites of granules, intergranular lanes, magnetic elements, basically inevery region susceptible to NLTE effects. For an accurate determination ofatmospheric quantities and their stratification, it is therefore important totake account of NLTE effects.

The influence of NLTE effects in Fe I lines on an inverted atmosphere I. 6301 A and 6302 A lines formed in 1D NLTE