CHLORINATED ORGANIC-COMPOUNDS IN THE TROPOSPHERE OVER THE WESTERN NORTH-ATLANTIC OCEAN MEASURED BY AIRCRAFT

Results of 32 individual flights during 1985, 1986 and 1988 using a King Air research aircraft over the western North Atlantic Ocean and the Adirondack Mountains are presented. Measurements were made for selected trace organic compounds including alpha- and gamma-isomers of hexachlorocyclohexane (HCH), the summed isomers of alpha- and gamma-chlordane, dieldrin and polychlorinated biphenyls (PCBs). The concentrations of compounds at altitudes of 300-10,000 ft indicate that these compounds were well mixed in the atmosphere and that for the most part, ground-level and higher-altitude concentrations were similar in magnitude. There was a high degree of variability due to time, meteorological events and location. Concentrations over the Adirondack Mountains in 1985 were the highest measured with means of 0.198 ng m-3 for HCB, 0.388 ng m-3 for alpha-HCH, 0.509 ng m-3 for gamma-HCH, 0.340 ng m-3 for dieldrin, 0.480 ng m-3 for chlordane and 0.951 ng m-3 for total PCBs. Concentrations over the western North Atlantic south-east of Bermuda in summer 1988 were lower, with means of 0.093 ng m-3 for HCB, 0.142 ng m-3 for alpha-HCH, 0.012 ng m-3 for gamma-HCH, 0.016 ng m-3 for dieldrin 0.020 ng m-3 for chlordane and 0.600 ng m-3 for PCBs. During 1988 concentrations of most of the compounds were similar in the atmosphere of the coastal zone, 50-100 km off the U.S., to those measured near Bermuda. Chlordane, and to a lesser extent dieldrin, showed a decrease in concentration away from North America.