Decreasing trends in total gaseous mercury observations in baseline air at Mace Head, Ireland from 1996 to 2009

In this study, the concentrations of total gaseous mercury in baseline air masses arriving at Mace Head, Ireland after having traversed the thousands of kilometres uninterrupted fetch of the North Atlantic Ocean, have been used for the assessment of possible trends in the atmospheric mercury background concentration over a 14-year period (i.e., 1996–2009), a statistically significant negative (downwards) trend of −0.028 ± 0.01 ng m−3 yr−1, representing a trend of 1.6–2.0% per year, has been detected in the total gaseous mercury levels in these baseline air masses. These findings are set in the context of the available literature studies of atmospheric Hg trends.