A 5+ year record of satellite measurements of nitrogen dioxide columns from the Ozone Monitoring Instrument (OMI) is evaluated to establish the quality of the OMI retrievals and to test our understanding of stratospheric NO₂. The use of assimilation techniques to retrieve stratospheric vertical columns of NO₂ from OMI slant column observations is described in detail. Over remote areas the forecast model state is generally within 0.15 × 10¹⁵ molecules/cm² of the analysis. Dutch OMI NO₂ (DOMINO) and Standard Product (SP) stratospheric NO₂ columns agree within 0.3 × 10¹⁵ molecules/cm² (13%) with independent, ground-based measurements. This is comparable to the level of consistency (15-20%) among ground-based techniques. On average, DOMINO stratospheric NO₂ is higher than SP by 0.2 × 10¹⁵ molecules/cm², but larger differences occur on the synoptic scale. Overlapping OMI orbits poleward of 30° enabled us to extract information on the diurnal variation in stratospheric NO₂. We find that in the Arctic, the daytime increase of NO₂ has a distinct seasonal dependence that peaks in spring and fall. Daytime increase rates inside the denoxified Arctic polar vortex are low, but we find high rates (>0.4 × 10¹⁵ molecules/cm²/h) outside the vortex. A multilinear regression to the DOMINO record shows a distinct quasi-biennial oscillation (QBO) signal in stratospheric NO₂ columns over the tropics. The QBO's amplitude is comparable to the annual cycle and stronger over the Southern Hemisphere than over the Northern Hemisphere. We infer near-identical trends from DOMINO observations (+0.4%/decade) as from ground-based instrumentation over Lauder (+0.6%/decade) in the 2004-2010 period.