ON THE AGE OF STRATOSPHERIC AIR AND INORGANIC CHLORINE AND BROMINE RELEASE

We estimate the average transport time from the tropical tropopause to various regions of the northern hemisphere lower stratosphere (strato spheric age) using simultaneous mixing ratio measurements of CFC-115 a nd CO2 measured by the Whole Air Sampler (WAS) during Airborne Arctic Stratospheric Expedition II (AASE II). Our inferred ages are consisten t with those presented in previous studies. We discuss sources of unce rtainties that affect age estimates in general, as well as specific un certainties arising from inferring ages using CO2 and CFC-115 abundanc es. We infer inorganic chlorine (Cl-y) and bromine (Br-y) at various l ower stratospheric locations using the WAS organic chlorine and bromin e measurements in combination with modeled tropospheric halocarbon tre nds and with our estimated ages. Inferred Cl-y and Br-y abundances gen erally increase with increasing latitude and altitude. For our analyze d locations inside the polar vortex, we estimate a maximum Cl-y abunda nce of about 2.7 parts per billion by volume (ppbv) and a maximum Br-y abundance of about 13.7 parts per trillion by volume (pptv). The loca tions of these maxima correspond to an average N2O mixing ratio of abo ut 100 ppbv, and to a fractional dissociation of organic chlorine and bromine of 0.85 and 0.90, respectively. Finally, we discuss the expect ed future limitations of using CFC-115 to estimate stratospheric age d ue to the production limitations prescribed by the amendments and adju stments to the Montreal Protocol.