Cartoon of the observed emission and absorption regions in I Zw 1. The highly asymmetric profiles with nearly absent red wings can be explained with a rather vertically outflowing BLR. Inwards increasing (radial) velocity of the BLR clouds would result in the detected emission-peak blueshift that grows with ionisation. The outward acceleration of ionised absorption components A and B is directed along the line of sight, which allows N V line-locking to be seen in the spectrum. Additional transverse motion (e.g. Keplerian, perpendicular to the plane of the image) and a clumpy structure of the outflow B can produce the observed changes in the total column density of the otherwise persistent absorption, detected in the UV and X-ray spectra for over 20 years. If the line emission of unclear origin discussed in Sect. 4.4 belongs to blueshifted emission from outflow B, then this gas spans over a larger area and might have originated in the outflowing BLR.