  The non-local thermodynaic equilibrium (non-LTE) line formation for the two
ions of zirconium is considered through a range of spectral types when the Zr
abundance varies from the solar value down to [Zr/H] = -3. The model atom was
built using 148 energy levels of Zr I, 772 levels of Zr II, and the ground
state of Zr III. It was shown that the main non-LTE mechnism for the minority
species Zr I is ultraviolet overionization. Non-LTE leads to systematically
depleted total absorption in the Zr I lines and positive abundance corrections,
reaching to 0.33 dex for the solar metallicity models. The excited levels of Zr
II are overpopulated relative to their thermodynamic equilibrium populations in
the line formation layers due to radiative pumping from the low-excitation
levels. As a result, the line source function exceeds the Planck function
leading to weakening the Zr II lines and positive non-LTE abundance
corrections. Such corrections grow towards lower metallicity and lower surface
gravity and reach to 0.34 dex for Teff = 5500 K, log g = 2.0, [M/H] = -2. As a
test and first application of the Zr I-Zr II model atom, Zr abundance was
determined for the Sun on the basis of 1D LTE model atmosphere. Lines of Zr I
and Zr II give consistent within the error bars non-LTE abundances, while the
difference in LTE abundances amounts to 0.28 dex. The solar abundance of
zirconium obtained with the MAFAGS solar model atmosphere is log eps(Zr) =
2.63+-0.07.
