Validation of the self‐consistency of GOMOS NO 3 , NO 2 and O 3 data using chemical data assimilation

The NO 3 measurement by the GOMOS instrument on board the ENVISAT platform is the first satellite measurements of this species. The simultaneous measurements of O 3 and NO 2 , which are strongly coupled chemically to NO 3 , 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 O 3 , NO 2 and NO 3 are tested using chemical data assimilation. Measurements obtained between 25 and 55 km during two distinct periods are assimilated. Analyzed NO 3 (i.e., NO 3 calculated by the model after assimilation of GOMOS O 3 and NO 2 data) are then compared to corresponding GOMOS NO 3 measurements in correlation plots (GOMOS NO 3 versus analyzed NO 3 ). 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 O 3 , NO 2 and NO 3 GOMOS measurements are self consistent chemically and that there is no substantial bias in GOMOS NO 3 data. It also suggests that the nighttime NO 3 chemistry is well understood.