Our directory of things of interest

University Directory

Storm riders: how mercury is transported by bad weather

Storm riders: how mercury is transported by bad weather Mihai Simonia
17 Nov
Thunderstorms in the US could be transporting harmful mercury from the atmosphere to the ground

Southeastern states in the US, such as Florida and Louisiana, receive higher deposits of mercury from the atmosphere compared to the rest of the North American continent. They also have the stormiest weather. Scientists at the University of Florida do not think this is a coincidence.

‘Tall thunderstorms are bringing mercury down to Earth,’ says atmospheric scientist Christopher Holmes. In a recent study, Holmes found thunderheads (the cumulonimbus clouds seen during a storm) to be carrying 50 per cent higher levels of the harmful pollutant than other cloud types, even when the rainfall itself was of equal amounts. ‘The highest concentrations of mercury occurred during thunderstorms,’ he says, ‘and the lowest during a regular rainstorm.’

It seems the storms scour the mercury from the higher atmosphere and deposit it on the ground

The link could be the thunderclouds’ height. Most mercury in the atmosphere sits at high altitudes, in the upper troposphere. While normal rain clouds are just a few kilometres thick, storms can form towering clouds that plume 15 kilometres in the air. ‘It seems the storms scour the mercury from the higher atmosphere and deposit it on the ground,’ says Holmes. The pollutant’s affinity for rough weather would explain why mercury levels are high in the southeast – often double those of northern states – despite the fact that Florida and Louisiana emit less mercury than many northern regions.

Mercury is a rogue element. Often emitted as an unwanted by-product of fossil burning and small-scale gold mining, it can remain in the upper atmosphere for decades, drifting thousands of miles from its original source. When it comes back down, it can accumulate in the food chain as methylmercury, which is highly toxic to animals and humans. In fact, the consumption of many fish species in southeastern states are banned due to excessive contamination.

This was published in the November 2016 edition of Geographical magazine.

Related items

NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in NATURE...


Xavi Bou's artistic visions of flight beguile the eye


Hydropower is considered essential if the world is to reach…


An overlap between populations of grizzly bears and Indigenous groups…


Climate change is having a huge impact on the oceans,…


The first COP26 draft agreement has been released


Marco Magrini explores the complex issue of carbon markets –…


The youth found marching outside the COP26 conference in Glasgow…


Energy day at COP26 was all about coal. Marco Magrini…


The world is reliant on the climate models that forecast…


Geographical editor, Katie Burton, spends the day at COP26: finance…


Lawyers are using the power of the courts to challenge…


Mike Robinson, chief executive of the Royal Scottish Geographical Society…


Will China's climate pledges be enough to achieve Xi Jinping's…