Lower stratospheric organic and inorganic bromine budget for the Arctic winter 1998/99

In the Arctic winter 1998/99, two balloon payloads were launched in a co-ordinated study of stratospheric bromine. Vertical profiles (9-28 km) of all known major organic Br species (CH3Br, C2H5Br, CH2BrCl, CHBrCl2, CH2Br2, CHBr2Cl, CHBr3, H1301, H1211, H2402, and H1202) were measured, and total organic Br (henceforth called Br-y(org)) originating from these organic precursors was inferred as a function of altitude. This was compared with total inorganic reactive Br (henceforth called Br-y(in)) derived from spectroscopic BrO observations, after accounting for modeled stratospheric Br-y partitioning. Within the studied altitude range the two profiles differed by less than the estimated accumulated uncertainties. This good agreement suggests that the lower stratospheric budget and chemistry of Br is well understood for the specified conditions. For early 1999 our data suggest a Br-y(in) mixing ratio of 1.5 ppt in air just above the local Arctic tropopause (similar to 9.5 km), whilst at 25 km in air of 5.6 yr mean age it was estimated to be 18.4(+1.8/-1.5) ppt from organic pr cursor measurements, and (21.5+/-3.0) ppt from BrO measurements and photochemical modelling, respectively. This suggests a Br-y(in) influx of 3.1(-2.9/+3.5) ppt from the troposphere to the stratosphere.