News / Science & Technology

Africa Kicks-up A Lot of Dust

NASA satellite captures image of giant dust cloud from Western Sahara on Sept. 14, 2013. Winds carry the dust to the United States, South America and the Caribbean.  Credit: NASA
NASA satellite captures image of giant dust cloud from Western Sahara on Sept. 14, 2013. Winds carry the dust to the United States, South America and the Caribbean. Credit: NASA


Joe DeCapua
Bits and pieces of the African continent are falling on the United States and surrounding regions much of the year. Scientists say large amounts of African dust may be having major effects on the hurricane season, ocean organisms and human health.

African dust particles become airborne during storms and travel anywhere from 7,000 to 10,000 kilometers to reach the U.S.  Scientists can now distinguish between domestic dust particles and those from Africa.

Joseph Prospero studies dust. He’s professor emeritus at the University of Miami Rosenstiel School of Marine and Atmospheric Sciences. Prospero said dust is important for a number of reasons, including its effect on climate.

“The very fact that you can see dust in the atmosphere means that the dust is interacting with solar radiation, scatters and absorbs solar radiation. So, anything that affects the distribution of solar radiation on the Earth’s surface – whether it’s at the surface itself or in the atmosphere – will affect climate,” he said.

Dust will also reduce the amount of sunlight reaching the ocean. That’s a big deal, especially for those who live in the usual paths of hurricanes.

“The surface oceans will be somewhat cooler than they would be in the absence of dust. This is something of considerable interest because this region of the Atlantic is where we see tropical cyclones and hurricanes develop. And the fact that we have so much dust means you have cooler sea surface temperatures and the cooler sear surface temperatures mean less water vapor getting into the atmosphere. And water vapor is an essential component that drives tropical cyclones and hurricanes,” he said.

So, that’s a benefit of African dust for those who fear their houses will be damaged by such storms.

Prospero said, “Until recently – the last few weeks – this year has been unusually dusty and we’ve had remarkably few tropical cyclones and hurricanes.

Dust also affects climate by depositing in the ocean.

“Dust carries with it a lot of elements and one that’s [of] particular interest is iron, which in many regions, ocean regions, is a limiting nutrient. Phytoplankton – marine organisms – need iron in order to photosynthesize. It’s an essential micronutrient. Therefore, if there’s not enough iron, then you have less biological activity, which, of course, affects the carbon cycle. Anything that affects the carbon cycle will affect climate by modulating the amount of CO2 in the atmosphere,” he said.

Now, lest you think that African dust only has benefits, think again. It also ends up in people’s lungs – a problem for those with asthma, for example.

“[In] one of our studies we’ve shown that in the Caribbean region the concentrations of dust are so high that they often exceed the World Health Organization’s 24 hour standard for the concentration of particles,” said Prospero.

Recently, average concentrations of dust particles that could be inhaled more than doubled over Houston, Texas – all due to a major Saharan dust intrusion.

“With satellites we can see that that dust cloud extended from Central America – it was against the mountains of Central America – across all of Texas and up into northern Oklahoma. The satellite images lost the dust in a large area of cloud,” he said.

Prospero said there was a time when scientists did not pay much attention to atmospheric dust. That’s changed.

“When I first started this work in the mid-late 1960s, no one cared about dust and there were very few publications. And now, it’s phenomenal. Every year, there are literally hundreds and hundreds of publications about dust. I mean not only African dust, I mean there’s Asian dust. The other huge area of dust activity is in Asia.  Dust is ubiquitous and there hasn’t been much attention paid to it.”

Prospero -- and colleagues at the University of Houston and the Arizona State University -- published their findings in the journal of Environmental Science and Technology. But there’s much they don’t know because the interaction of dust with the atmosphere is very complex and not well understood.

For example, North Africa is expected to get drier and produce more dust. But computer models don’t agree on what that means in the long-term for climate and human health.

In case you’re wondering, Africa is not expected to blow away. Prospero says it’ll just keep producing more and more dust.

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