Mercury cycling in the Environment - Effects of Climate Change
Two simple models have been used to evaluate the possible effect of climate change in respect to changed atmospheric oxidation potential of mercury and re-emission from the oceans. In both cases only the effect of temperature increase was considered. This is an obviously limitation considering the complexity of mercury cycling as a whole. However, the result suggests that in a warmer climate gas phase oxidation of GEM in the marine troposphere may be less efficient causing the mercury concentration in the atmosphere to increase. Simultaneously the mercury re-emission flux from the ocean to the atmosphere tends to increase. If this really is the case it means that part of the oceanic mercury pool will be moved to the atmosphere. The environmental effect of that not obvious. A somewhat higher GEM concentration is not harmful as such, but means that mercury distribution via the atmosphere could be even more important in the future. Another conceivable consequence of mercury being moved from the sea to the atmosphere is that the oceanic sink of mercury may be slightly less important. Simulations with a complex atmospheric chemistry model have shown results pointing in the same direction. In the lower troposphere the effect of increased temperature on slow-down of Hg oxidation was, comparing to the effect of the reaction rate only, magnified by the fact that Br concentrations decreased significantly in the +5K case. Thus, in a 5K warmer marine boundary layer the Hg0 oxidation rate was reduced by 40% resulting in c.a. 15% increase in concentrations of RGM. In higher altitudes the bromine concentrations were much lower, the dominating source was photolysis of halocarbons and there was only small temperature effect on concentrations. The effect of temperature on slow-down of oxidation of Hg0 was accordingly less pronounced.