Here we will present trends of the atmospheric mercury concentrations measured since February 1996 at the Mace Head Atmospheric Research Station on the Atlantic coast of Ireland.The data cover a nearly 18 year period until December 2013.Using meteorological analysis and a sophisticated Lagrangian dispersion model,the hourly averaged mercury concentrations were attributed to four different air mass types: baseline,local,European polluted,and sub-tropical maritime.Monthly median Hg concentrations of all types decreased over the analyzed period.With 0.0163 +/-0.0020 ng m?/yr the trend for sub-tropical maritime air masses was significantly smaller than the trends for all other three classes which varied between 0.0209 and-0.0227 ng m?/yr.The seasonal variation for sub-tropical maritime air masses is also shallower than for all other classes.The north-south gradient of the trend is qualitatively consistent with the GEOS-Chem model predictions based on decrease of mercury concentrations in surface waters of the North Atlantic but the trends are smaller than predicted.The period covered by the measurements is too short to detect changes in trends with certainty but some evidence shows that the trends might have slowed in the second half of the 18 year long period.