The role of inorganic bromine compounds in the chemistry of the midlatitude lowermost stratosphere is examined. Model studies are performed using a chemistry box model. Special emphasis is layed on investigating the implications of bromine chemistry on the atmospheric effects of subsonic aircraft NOx emissions. The simulations suggest that the presence of bromine constituents leads to an effective denoxification, an activation of HOx, and a significant ozone depletion in the background lowermost stratosphere. Bromine chemistry has the potential to induce large increases in the modeled ozone production caused by aircraft NOx emissions in the lowermost stratosphere. The modeled effect strongly depends on the availability of inorganic bromine compounds, on aerosol loading, and on the NOx background concentration. The hydrolysis reaction of BrONO2 on sulfate aerosols and the reaction of BrO with HO2 appear to be the key reactions driving the simulated impact of bromine chemistry on the aircraft-induced ozone changes. ¿ 2000 American Geophysical Union