Large disagreements between measured and simulated NO2 have been observed several times in the Arctic polar vortex. Here we report on the comparison of two sets of nighttime balloonborne measurements of the couple (OClO, NO2) with Lagrangian model outputs in order to study the interactions between halogen and nitrogen species. Those measurements were characterized by the simultaneous presence of significant amounts of both species. Large disagreements are observed between modeled and measured NO2. Very surprisingly, good agreement can be achieved for OClO in spite of the supposed strong coupling between these two species. The only simultaneous agreement between model and measurements for both species occurs in the case of denoxified conditions, i.e., when there is no interaction between halogen and nitrogen compounds. Furthermore, agreement for OClO cannot be obtained if a source for NO2 is assumed to fit the measurements of this specie. This result shows that some uncertainties still exist in the interaction between nitrogen and halogen species.