The only way into Alert, Nunavut Territory, is by air on an austere Hercules C-130 aircraft, a 10-hour flight flown once a week from Trenton, Ontario.

The local joke is there are no ways out.

Usually, the only people aboard the rattling transport are Canadian Forces personnel, dispatched to the hemisphere’s bleached, boreal rafters to electronically snoop on Russia, its rogue neighbor. A relic of the Cold War situated at 82.27 N and 62.31 W, Alert is actually closer to Moscow than Ottawa.

Lately, the military detail is frequently accompanied by a contingent of civilian scientists. Stationed in the Arctic basin 60 km from the northwestern reach of Greenland, far removed from the world’s acrid industrial regions, Alert has been found to be an ideal place to study atmospheric phenomena such as Arctic Haze, long range transport of air pollutants, and tropospheric ozone depletion.

Bill Schroeder is one of the civilians.

A Canadian meteorologist with over 30 years experience with the government research agency Environment Canada, Schroeder has been measuring concentrations of gaseous mercury in the air at Alert for nearly 10 years as part of an ongoing Canadian environmental research activity, called the Northern Contaminants Program (NCP), which is itself part of a multi-national effort called the Arctic Monitoring and Assessment Programme, established to monitor the levels of persistent, toxic and bio-accumulating substances transported into the Arctic environment by air from distant sources.

Until 1998, when atmospheric mercury measurements were started by American scientists at Point Barrow, AK and at Spitsbergen (Svalbard) by Norwegian investigators, Schroeder’s atmospheric mercury measurements at Alert were unique, providing the only continuous record of mercury concentrations in air and snow in the Arctic.

Schroeder’s work is financially supported by the Canadian Department of Indian Affairs and Northern Development, whose mandate extends to investigating environmental contamination in the Canadian Arctic and human health issues arising therefrom. His investigations at Alert focus on the long-range atmospheric transport pathway by which toxic chemicals such as mercury, other metallic substances, as well as persistent organic pollutants are introduced into the once-pristine Arctic environment.

"My interest in Arctic research was sparked during the early 1990s by Leonard Barrie, a former colleague," Schroeder says. "At that time, atmospheric monitoring of toxic and persistent organic pollutants - so-called POPs - had been initiated at several locations in the Canadian Arctic under the NCP. However, there existed little, if any, data on atmospheric concentrations of mercury or other heavy metals north of the Arctic Circle in any of the circumpolar nations, including Canada."

The importance of mercury measurement can be found in the amount of contamination reported in the food chain of aboriginal peoples living in the North, which has attracted widespread attention as a potentially serious environmental and human health issue.

Exposure to high levels of elemental mercury vapor can result in nervous system damage including tremors, mood and personality alterations. According to the U.S. Environmental Protection Agency, exposure to relatively high levels of inorganic mercury salts can cause kidney damage. Adult exposure to relatively high levels of methylmercury through fish consumption can result in numbness or tingling in the extremities, sensory losses and loss of coordination. Exposure of the developing fetus through maternal intake of contaminated fish can result in neurologic developmental abnormalities in cognitive and motor functions. Whether any of these symptoms actually occur, and the nature and severity of the symptoms, depend on the amount of exposure.

In August, 1992, challenged by the pressing need for information on atmospheric mercury concentrations in the Canadian Arctic, Schroeder initiated a one-year pilot project near Alert, at the site of a former global background monitoring laboratory. Due to logistical, technological and resource constraints, the methodology employed at that time consisted of manual sampling, achieved by concentrating mercury vapor present in ambient air in special collectors. Each week, the exposed collectors were carefully sealed and transported to Toronto by air, where they were analyzed in a trace analytical laboratory for their mercury content.

"This then state-of-the-art approach yielded the first annual time series of weekly-integrated total gaseous mercury concentrations anywhere in the Arctic," Schroeder says. "With this manual methodology, however, we could not observe any fluctuations in mercury concentrations occurring on a time-scale shorter than a week."

In January, 1995, buoyed by the success of the pilot study, Schroeder initiated continuous (30-minute) high-temporal resolution measurements using a new automated mercury vapor analyzer from Tekran, Inc., Toronto, an instrument he helped develop.

"This new technology represents a quantum leap forward in atmospheric mercury measurements," he says. "Thus, a task such as determining mercury concentrations in ambient outdoor air, that seven or eight years ago required a day or more to complete, is now automatically carried out in as little as five or 10 minutes. With this instrumentation we have successfully participated in three international field intercomparisons."

The instrument, situated at a site called the Canadian baseline air chemistry observatory on an icy plateau 10 km inland from the Alert base camp, is now used by research groups investigating the environmental behavior, cycling and fate of mercury vapor released into the atmosphere from either natural or anthropogenic sources. Schroeder’s colleague Sandy Steffen makes regular trips North every three or four months to calibrate and perform preventive and corrective maintenance on the analyzer.

It’s not always easy going. Though the permafrost releases its chisel-cold grip on the Alert terrain during the quick, brisk summer, allowing a sparse carpet of ephemeral polar vegetation, for 10 months of the year Alert is snowbound.

Approaching the observatory from the main camp, this barren steppe on the northern fringe of the Hazen Plateau rises abruptly to an elevation of approximately 200 m with local folds pushing up 500 m. Beyond the observatory in the pristine distance, the Plateau itself continues to rise to the south, forming the frozen bosom of Ellesmere Island, reaching a typical elevation of 1,000 m, defined by a Canadian national park the size of West Virginia and the 7,500 km2 Agassiz Ice Cap - a permanent feature with a central elevation greater than 2,000 m. Southwest of Alert lie the rugged United States range, its bleak, sterile crags exceeding 2,500 m.

Tending to the measuring tasks and the instruments themselves in this forbidding environment is often perilous. Like road rage, storm conditions erupt suddenly in the Arctic, during which the hazard is so great no one is allowed outside the compound’s primitive dwellings. While temperatures during the brief July-August summer may climb to 10 degC, in October the long polar night begins, temperatures falling with the sable darkness, sometimes to -50 degC. Flesh freezes in seconds.

"It has happened that scientists left the base camp in the morning under good weather and visibility to go out to the Observatory (a 45 minute drive in special track-truck snow vehicles) for their weekly inspection and calibration visit and then, following completion of their tasks, found the visibility and weather conditions had deteriorated to such an extent that they couldn’t see to return to base camp and were forced to stay at the Observatory until the blizzard blew over," Schroeder says. After serving as an emergency shelter a few times, the scientists stocked the Observatory with emergency rations and a bunk bed for just such incidents.

In conditions this harsh, the vehicles must be left running, or their engines kept covered with engine blankets, to assure a getaway once the gale breaks. Nevertheless, vehicle breakdowns are common. The researchers, therefore, mainain radio communications with the base camp at all times.

In spite of the desperate weather, Schroeder’s research has produced some startling findings.

"We discovered a new phenomenon of atmospheric mercury chemistry: springtime depletion of mercury vapor in the lower troposphere resulting from the conversion of vapor-phase Hg to particulate-phase Hg species which are much more easily deposited from the atmosphere to the Earth's surface," Schroeder says. "To elucidate the photochemical mechanism responsible for oxidizing the normally long-lived elemental mercury vapor to the comparatively short-lived aerosol phase, we are continuing our environmental measurements at Alert while collaborating with atmospheric scientists at McGill University in Montreal."

The spring-time discovery came as a shock.

"It came as a total surprise to us, when, in April of 1995, we discovered for the very first time that periodically mercury vapor concentrations in surface-level Arctic air are much lower and more variable in the springtime (after polar sunrise) than at other times of the year," Schroeder says. "Curiously, the large oscillations, favoring lower mercury vapor concentrations, mimicked the well-known episodic depletions of surface-level ozone gas first observed at Alert in the spring of 1985 by scientists with the Atmospheric Environment Service (AES).

"However, from previous scientific studies, we knew that the relatively slow rate of the chemical reaction between mercury vapor and ozone - even in temperate climates, let alone under Arctic conditions - could not explain the rapid disappearance of gaseous mercury in Arctic air frequently observed during the three-month period from mid-March to mid-June."

This Arctic phenomenon of springtime depletion of mercury vapor has now also been observed at Point Barrow, Alaska and at Ny-Ålesund (Svalbard) in the Norwegian Arctic.

In an attempt to understand the phenomena, last summer [Ed note: summer 2000] Schroeder installed an atmospheric mercury monitor at Amderma in the northwestern part of Siberia near the Arctic Ocean, which should allow the scientists to determine the spatial extent and temporal variability in atmospheric mercury concentrations on the other side of the Arctic Ocean. The site is already being used, in a joint research project by Russia and Canada, to monitor the levels, sources, pathways and environmental fate of various persistent organic pollutants in the troposphere.

Even though the photochemical oxidation mechanism responsible for the Arctic spring vapor-phase mercury depletion episodes taking place is not yet known, Schroeder is confident of three points. One, that the transformation of mercury vapor produces one or more mercury species with much shorter atmospheric residence time(s) than the precursor; two, that this atmospheric process is environmentally significant since it provides a direct pathway for the introduction of bio-available Hg species into the polar environment; and three, that this large input of a toxic heavy metal into the Arctic food chain is occurring each year over a vast area of the Arctic and takes place at a time of year when biota are frenetically preparing for the all too short polar summer and the long polar night that inevitably follows.

When not braced against the gellid Arctic winds, Schroeder is working on several other projects dealing with mercury in the Canadian environment.

"Steffen and I are providing input to the nation-wide Canadian Atmospheric Mercury Measurement Network, CAMNet. We’re also making field measurements of gaseous- and/or particulate-phase mercury fluxes releasing this heavy metal into the atmosphere from both natural sources and human activities."

Their other activities include developing improved sampling and analysis methodologies for mercury in the environment, including physical and chemical speciation of mercury and other toxic trace elements.

Regardless of the hardship and risk, Schroeder, Steffen and others have produced world-class environmental science using advanced technologies in the most remote of Earth’s far yards.

"Our scientific studies at Alert have revealed that, each spring the elemental mercury vapor in surface-level Arctic air is transformed (through an, as yet unknown, oxidation process) into one or more compound(s) which is/are much more readily removed from the troposphere than the original form," he says.

The implications of this annually occurring mercury vapor "depletion" phenomenon are wide-sweeping because the atmospheric photochemical oxidation reaction can provide a pathway for an environmentally significant input of mercury to Arctic biota, including those which are part of the human food chain in the North.

Alert is the site of another important field project. The Polar Sunrise Experiment 2000 took place last winter and spring, the goal of which was to study ozone depletion at the ground in the Arctic Atmosphere upon polar sunrise, and the potential role being played by chemical reactions in the snow pack and the ice surface.

According to Jan Bottenheim, an atmospheric photochemistry expert with AES, observations of unusually low O3 mixing ratios in the Arctic marine boundary layer at the time of polar sunrise were first reported in the mid 1980s. Linkage of the Alert O3 data with concurrent filterable bromine measurements soon thereafter led to the hypothesis that O3 is consumed via a chain reaction involving Br and BrO. Subsequent measurement campaigns at several locations in the Arctic (Alert, Barrow, Ny Alesund, Thule) have largely confirmed this mechanism. However, important details of the overall process remain poorly determined. Most prominent among these, he said, are the initialization of the apparent chain reaction, i.e. what is the origin of the active halogens involved in the process (aerosols, the snow/ice surface) and how its apparent high efficiency is maintained.

Some unexpected, and quite dramatic, phenomena have come to light in the last year, Bottenheim says. During Polar Sunrise Experiment 1998 strong evidence was obtained for the emission of formaldehyde (HCHO) from the snow pack at Alert after polar sunrise. Concurrently, a diel pattern was observed in NOx that could only be explained from an unknown source most likely in the snow pack as well. During the summer 1998 campaign at Summit, Greenland, direct evidence was obtained for a snow source of NOx and possibly HONO at that location.

"The reports of these observations at the American Geophysical Union annual meeting in December 1998 caused quite a stir, but work at the South Pole in January 1999 and Greenland in July 1999 has not only confirmed these observations but if anything has raised the level of excitement," Bottenheim says. "It now appears that the snowpack is a highly reactive medium under sunlight irradiation, which can promote the conversion of unreactive nitrate into reactive nitrogen oxides (NOx, HONO)."

While it is unclear what the details of the chemical mechanism are, it is clear that radical chemistry has to be involved, he says. "One would then postulate that this will also lead to the destruction of O3 in the interstitial air, as well as the formation of a variety of photochemical oxidation products, e.g. H2O2, PAN, RONO2 and carbonyl compounds."

All the observations then suggest that active photochemical or biological processes take place in the snow pack that will likely have a significant impact on the concentrations of gas phase species, he says. If confirmed, they may explain many of the missing details in the O3 depletion mechanism. Furthermore, these observations have implications for the interpretation of ice-core observations that are used to investigate climate variability, at least for the more photochemically reactive species.

They also raise new questions, foremost among those is the chemical mechanism of these reactions in the snow/ice. To a large extent this will also indicate whether this new chemistry can play a role in other snow covered regions of the globe than just the Arctic.

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Schroeder, W.H., et al, "Arctic springtime depletion of mercury," Nature 394: 331-332(1998).

Schroeder, W.H., et al, "Depletion of mercury vapor in the Arctic troposphere after polar sunrise," Proceedings of EUROTRAC Symposium '98, (Borrell PM & Borrell P, Eds.), WITPress, Southampton; Vol. 2, 358-362(1998).

Cheng, M.D., and Schroeder, W.H., "Potential atmospheric transport pathways for mercury measured in the Canadian High Arctic", Journal of Atmospheric Chemistry 35: 101-107(2000).