NOAA/WDS Paleoclimatology - Col du Dome, France 70 Year Ice Core Bromine Data

Total bromine (Br) was investigated in seasonally-resolved alpine ice cores covering the 20th century. Results revealed increased Br concentrations in summer (from 0.7 ng g-1 in the late 1940s to 1.6 ng g-1 in the mid 1970s), followed by a slight decrease to 1.25 ng g-1 during the last decade of the 20th century. In winter, a more moderate increase was observed from prior to 1950 (0.35 ng g-1) to the 1970-2000 period (~0.50 ng g-1). Measurements of lead suggest that ~75% of the bromine increase in summer alpine ice between 1930-1950 and 1965-1985 was from bromine-containing aerosol (PbBrCl) emitted during combustion of leaded gasoline. This contribution decreased to ~27% in 2000 following the large decrease of lead additive content in gasoline used in western Europe. Summer ice bromine concentrations, not related to PbBrCl aerosol (denoted Bry*), increased by 40% from the late 1940s to the 1990-2000 decade. In winter, the contribution of leaded-gasoline aerosol to total bromine levels was weaker than in summer, with the winter bromine trend mainly caused by enhanced Bry* levels (~40%) after 1950. These Bry* variations in glacial ice are discussed in terms of past atmospheric reactive bromine (Bry) changes in the European troposphere including anthropogenic CH3Br emissions and transport from the stratosphere.