Changes in atmospheric lead and other pollution elements at Bermuda

Measurements of atmospheric lead at Bermuda during the Atmosphere-Ocean Chemistry Experiments (AEROCE) in 1993-1994 showed that annual-mean concentrations had decreased by an order of magnitude from the 1970s and by a factor of 4 since the 1980s. Seasonal patterns had changed as well, with lead no longer being highest during winter. Both changes are consistent with decreased use of leaded gasoline in North America, Pollution-derived zinc and antimony also decreased, probably because of reduced smelting in the United States or changed atmospheric transport to Bermuda. Lead/aluminum mass ratios depended on direction: 0.04 with western air-mass trajectories (pollution from North America) versus 0.0001 and 0.0003 with eastern trajectories. The eastern Pb/Al ratios were indistinguishable from typical crustal values of 0.0002. The lower eastern ratio probably represents pure Saharan dust, while the higher ratio may indicate minor amounts of superimposed pollution aerosol, possibly from Europe or the Mediterranean area. Crustal lead was not evident in the 1970s because more lead was emitted from gasoline and dust transport from the Sahara was weaker.