This paper provides experimental evidence that each year after polar sunrise, the depleted gaseous elemental mercury is converted into particulate-bound mercury, which falls to the earth's surface much faster than gaseous elemental mercury and is much more easily taken up into the food chain. It links mercury to other species such as ozone and halogen species and provides experimental evidence for the ecological and biogeochemical relevance of the polar mercury transformation and deposition phenomenon. This paper presents an advanced and comprehensive research on atmospheric deposition of mercury into the Polar Regions. It brings new insights and solidifying perspectives to the domain of atmospheric chemistry in polar regions.

Yes, this paper describes a new and fascinating natural phenomenon and identifies a pathway of atmospheric mercury deposition to the Polar Regions. It provides experimental evidence about where the missed gaseous elemental mercury goes and in what chemical form(s) each year after polar sunrise. This information is important in understanding the mechanisms of polar mercury transformation phenomenon and predicting the reactivity, movement, and bioavailability of the mercury species. It is also important in assessing the impacts of the mercury transformation phenomenon on ecosystems and human health.

In 1996, I took on a postdoctoral research project at Environment Canada to develop a methodology for sampling and analysis of particulate mercury and also participated in an on-going project on monitoring gaseous elemental mercury in the Arctic. With our discovery of polar gaseous elemental mercury depletion phenomenon, I became very interested in finding out where the missed atmospheric gaseous elemental mercury went. The applications of our methodology at two sites in the Arctic and now in the Antarctic revealed that the missed gaseous elemental mercury is converted in to particulate oxidized mercury, which falls to the earth's surface much faster than gaseous mercury, in the chemical forms that are much more easily taken up into the food chain.

Mercury is of a concern because of its environmental persistence, toxicity, and ability to build up in humans and other species high on the food chain. Recent results show that mercury concentration is increasing in the Arctic. Our paper shows that each year in the polar regions after polar sunrise, mercury is converted from a gas into a solid by sun-induced reactions in the frigid polar atmosphere. This aerosol mercury falls to the earth's surface much faster than gaseous mercury, and accumulates in the ice, snow, and spring meltwater in an oxidized form that is much more easily taken up into the food chain. This newly revealed mercury behavior is scientifically significant and indicates a need to re-examine the traditional understanding of mercury's atmospheric characteristics. Furthermore, these "mercury showers" take place in the spring just as the ecosystem is coming to life; they expose the area's humans, plants, animals, and fish to yet another form of insidious toxic pollution.