Deposition of semi-volatile organochlorine compounds in the free troposphere of the eastern North Atlantic Ocean.

Deposition samples were taken at a height of 2367 m above sea level (m.a.s.l.) on the Island of Tenerife from May 1999 until July 2000 and analysed for 19 polychlorinated biphenyl (PCB) congeners, hexachlorobenzene (HCB), hexachlorocyclohexanes (HCH) and DDTs. This site is located above the inversion layer, so samples represent background concentrations of the free troposphere. The average deposition fluxes of HCB, total HCH, DDTs and PCBs were 86, 400, 110 and 780 ng m(-2) yr(-1), respectively, being lower than those reported at sea level in continental or marine areas. All compounds are generally found in higher abundance in the wet precipitation samples. However, these samples only represent a fraction, e.g. 33%, of the total deposition load. Annual mass balance calculations show that wet precipitation is essentially responsible for the deposition of the low molecular weight OC whereas dry deposition accounts for more than 50% of the higher molecular weight PCBs.