One-decade trend analysis of stratospheric BrO over Harestua (60°N) and Lauder (45°S) reveals a decline

A trend analysis is performed of stratospheric BrO from ground-based UV-visible observations at Harestua (60 degrees N, 11 degrees E) and Lauder (45 degrees S, 170 degrees E) from 1995 through 2005. At both stations, a positive trend of about +2.5% per year is found for the 1995-2001 period, while a negative trend of about -1% per year is obtained between 2001 and 2005. Given a mean age of air of about 4 +/- 1 years, the decline in stratospheric bromine since 2002 follows the decline of tropospheric organic bromine observed since the second half of 1998, as a result of the Montreal Protocol. These findings confirm that the impact of the Montreal Protocol restrictions on brominated substances have now reached the stratosphere. From our study, we have also derived a contribution of 6 +/- 4 ppt of the brominated very short-lived substances and inorganic bromine tropospheric sources to the total bromine loading.