精东传媒

October 10, 2017

Mercury from the northern hemisphere is ending up in Australia

Jenny Fisher, 精东传媒 of 精东传媒; Dean Howard, Macquarie 精东传媒; Grant C Edwards, Macquarie 精东传媒, and Peter Nelson, Macquarie 精东传媒

Mercury pollution has a long legacy in the environment. Once released into the air, it can cycle between the atmosphere and ecosystems for years or even decades before ending up deep in the oceans or land.

The amount of than it was before humans began to release it by mining. Even if we stopped all human mercury emissions now, .

To address the global and long-lasting mercury problem, a new United Nations treaty called the came into effect last month. The treaty commits participating countries to limit the release of mercury and monitor the impacts on the environment. Australia signed the Convention in 2013 and is now .

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Until now, we have only been able to guess how much mercury might be in the air over tropical Australia. Our new research, , shows that there is less mercury in the Australian tropics than in the northern hemisphere 鈥� but that polluted northern hemisphere air occasionally comes to us.

A global problem

While most of mercury鈥檚 come from its , its main entry point into the environment is through the atmosphere. Mercury in air comes from both natural sources and human activities, including mining and burning coal. One of the biggest mercury sources is 鈥� a trade that in developing countries but poses serious risks to human health and the environment.

Once released to the air, mercury can travel thousands of kilometres to end up in ecosystems far away from the original source.

Measuring mercury in the tropics

While the United Nations was gathering signatures for the Minamata Convention, we were busy measuring mercury at the Australian Tropical Atmospheric Research Station near Darwin. Our two years of measurements are the first in tropical Australia. They are also the only tropical mercury measurements anywhere in the region covering southeast Asia, Indonesia, and northern Australia.

We found that mercury concentrations in the air above northern Australia are 30-40% lower than . This makes sense; most of the world鈥檚 population lives north of the Equator, so most .

More surprising is the seasonal pattern in the data. There is more mercury in the air during the dry season than the wet season.

The Australian monsoon appears to be partly responsible for the seasonal change. The amount of mercury jumps up sharply at the start of the dry season when the winds shift from blowing over the ocean to blowing over the land.

But wind direction can鈥檛 explain the whole story. Mercury is likely being removed from the air by the intense rains that characterise the wet season. In other words, the lower mercury in the air during the wet season may mean more mercury is being deposited to the ocean and the land at this time of year. Unfortunately, there simply isn鈥檛 enough information from Australian ecosystems to know how this impacts local plants and wildlife.

Fires also play a role. Mercury previously absorbed by grasses and trees can be released back to the atmosphere when the vegetation burns. In our data, we see occasional large mercury spikes associated with dry season fires. As we move into a bushfire season , we may see even more of these spikes.

Air from the north

Although mercury levels were usually low in the wet season, on a few days each year the mercury jumped up dramatically.

To figure out where these spikes were coming from, we used two different models. These models combine our understanding of atmospheric physics with real observations of wind and other meteorological parameters.

Both models point to the same source: air transported from the north.

Australia is usually shielded from northern hemispheric air by a 鈥溾�� that stops air from mixing. This barrier isn鈥檛 static 鈥� it moves north and south throughout the year as the position of the sun changes.

A few times a year, the chemical equator moves so far south that the top end of Australia actually falls within the atmospheric northern hemisphere. When this happens, polluted northern hemisphere air can flow directly to tropical Australia.

We observed 13 days when our measurement site near Darwin sampled more northern hemisphere air than southern hemisphere air. On each of these days, the amount of mercury in the air was much higher than on the days before or after.

Tracing the air backwards in time showed that the high-mercury air travelled over the Indonesian archipelago before arriving in Australia. We don鈥檛 yet know whether that mercury came from pollution, fires, or a mix of the two.

A global solution

To effectively reduce mercury exposure in sensitive ecosystems and around the world, .

The cross-boundary influences on mercury that we have observed in northern Australia highlight the need for the type of multinational collaboration that the Minamata Convention will foster.

Our new data establish a baseline for monitoring the effectiveness of new actions taken under the Minamata Convention. With the first having taken place last week, hopefully it will only be a matter of time before we begin to see the benefit.

, Senior Lecturer in Atmospheric Chemistry, ; , , ; , Senior lecturer, , and , Pro Vice Chancellor (Research Performance and Innovation),

This article was originally published on . Read the .

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