ATMOSPHERIC MERCURY DEPLETIONS IN THE CANADIAN HIGH ARCTIC:

PRELIMINARY RESULTS FROM ALERT 2000, AN INTERNATIONAL FIELD STUDY.

Alexandra Steffen*, Bill Schroeder and Julia Lu.

Atmospheric Environment Service, 4905 Dufferin St., Toronto, Ontario, M3H 5T4.

1995 marked the first year that episodic depletions of mercury after the polar sunrise were discovered by AES scientists in the Canadian high arctic. This unexpected phenomenon is strongly correlated to arctic surface ozone depletions. Since then many investigations into this phenomenon have been conducted and it has been shown that elemental mercury is being oxidized into a less volatile form and is being subsequently enriched on aerosols and in fresh snow during this time of the year. The mechanism for this reaction is not yet known.

ALERT 2000 is an international intensive field study that will take place at Alert, Nunavut, between February and May 2000. This study is intended to further understand post polar sunrise atmospheric chemistry occurring in the air, ice and snow. This program involves a highly qualified team of scientists from Canada, the US and Europe studying various aspects of chemistry relating to surface ozone depletions. A camp located on the frozen arctic ocean will be set up where a suite of questions related to mercury depletions will be addressed. These questions include: what role does the snow play, is it a sink or source for mercury? Where is the conversion initiated? What chemistry causes the conversion? Why is the missing vapour phase mercury only partially recovered in the aerosol phase?

The proposed work at an ice camp site will include vertical profiling of mercury; sample collection of aerosols and snow surface reaction chamber experiments. As well, total atmospheric mercury, total gaseous mercury and freshly fallen snow will be sampled at land-based sites. Preliminary results from this international scientific program will be presented.

*Alexandra Steffen

Phone: 416.739-4116 Fax: 416.739-4318

Alexandra.Steffen@ec.gc.ca