Implications of subsonic aircraft NOx emissions for the chemistry of the lowermost stratosphere: Model studies on the role of bromine

The role of inorganic bromine compounds in the chemistry of the midlatitude lowermost stratosphere is examined. Model studies are perfomed using a che mistry box model. Special emphasis is layed on investigating the implicatio ns of bromine chemistry on the atmospheric effects of subsonic aircraft NOx emissions. The simulations suggest that the presence of bromine constituen ts leads to an effective denoxification, an activation of HOx, and a signif icant ozone depletion in the background lowermost stratosphere. Bromine che mistry has the potential to induce large increases in the modeled ozone pro duction caused by aircraft NOx emissions in the lowermost stratosphere. The modeled effect strongly depends on the availability of inorganic bromine c ompounds, on aerosol loading, and on the NOx background concentration. The hydrolysis reaction of BrONO2 on sulfate aerosols and the reaction of BrO w ith HO2 appear to be the key reactions driving the simulated impact of brom ine chemistry on the aircraft-induced ozone changes.