Evidence of the impact of ENSO events on temporal trends of hexachlorobenzene air concentrations over the Great Lakes

Abstract

This study presents an evidence for association of the air concentrations of HCB measured in the Great Lakes region with the El Niño-Southern Oscillation (ENSO) during the 1990s. The measured HCB concentrations in the atmosphere collected by the Integrated Atmospheric Deposition Network (IADN) program in the Great Lakes during the 1990s show strong correlations with the Multivariate ENSO index (MEI) during winter (December-February) and spring (March-May) seasons. These correlations are stronger in the western upper Great Lakes than in the eastern portion of the Great Lakes ecosystem (lake Ontario), and correspond well to the spatial variability of the surface air temperature in North America during El Niño years. Departures of HCB air concentrations for each winter during 1992-1999 from that averaged over all winters of 1992-1999, i.e. the anomaly, also show the same temporal trend as that of the MEI during the same period. In the same time period, it has been reported that direct HCB emissions from application of HCB in agriculture, from industrial sources in North America and in the rest of the world have decreased substantially compared to those in the 1970s and could not by themselves account for observed HCB air concentrations around the Great Lakes since the 1990s. Interannual fluctuations of HCB concentrations are caused most likely by reemission due to volatilization of HCB from the soil contaminated from past use, followed by long-range transport associated with ENSO events. In addition to the high correlation (R2=0.61) between winter HCB air concentrations averaged over the Great Lakes region and the MEI the atmospheric circulation patterns associated with ENSO events are conducive to the long-range transport of HCB into the Great Lakes region. © 2003 Elsevier Science B.V. All rights reserved.