Long-term measurements of atmospheric mercury at Mace Head, Irish west coast, between 1995 and 2001

Monitoring of atmospheric mercury concentrations has been carried out at the Mace Head atmospheric research station on the west coast of Ireland between September 1995 and December 2001. Measurements were carried out with a time resolution of 15 min. No trend in the concentration levels has been detected during the measurement period, with the annual average concentrations remaining constant at 1.75 ng m−3. A slight increase in the concentration levels is derived, if only clean sector filtered air masses clearly of marine origin are used. The Mace Head data set shows a seasonal pattern with higher monthly mean concentrations in the winter months. Comparison with two continental sites in Sweden shows, that atmospheric mercury concentrations at the western inflow boundary are on an average higher than those at the two continental sites, expressing a west to east decreasing concentration gradient. At Mace Head, no indications for so-called Mercury Depletion Events (MDEs), recently reported for a number of sites in the Arctic and in the Antarctic, have been found between 1995 and 2001.