The NO₃ measurement by the GOMOS instrument on board the ENVISAT platform is the first satellite measurements of this species. The simultaneous measurements of O₃ and NO₂ , which are strongly coupled chemically to NO₃ , allow us to test the self-consistency of the GOMOS measurements of the different species. In this paper, the self-consistency of the nighttime measurements by GOMOS of O₃ , NO₂ and NO₃ are tested using chemical data assimilation. Measurements obtained between 25 and 55 km during two distinct periods are assimilated. Analyzed NO₃ (i.e., NO₃ calculated by the model after assimilation of GOMOS O₃ and NO₂ data) are then compared to corresponding GOMOS NO₃ measurements in correlation plots (GOMOS NO₃ versus analyzed NO₃). Overall, the differences between the NO 3 measurements and corresponding analyzed NO 3 are found to be small, about 10% on average. The linear regressions for both periods are also found to be close to the 1-to-1 line with small standard errors. This agreement indicates that O₃ , NO₂ and NO₃ GOMOS measurements are self consistent chemically and that there is no substantial bias in GOMOS NO ₃ data. It also suggests that the nighttime NO₃ chemistry is well understood.