Dust in the Wind

Annual intrusion of Saharan dust has benefits, drawbacks

If you’ve been wondering what’s behind the unusually hazy skies we’ve seen lately, just look to the east. No, not Florida – keep going – all the way across the Atlantic.

The source is the Saharan Air Layer, or SAL – plumes of dust blown all the way from Africa’s Sahara Desert to the Americas, including Texas. It happens every year around this time, making it remarkable and also totally ordinary.

Among non-scientists, SAL is more commonly known as rain dust.

Wait – what? What in the world is that?

Remains of ancient life

About 6,000 years ago, much of North Africa was covered with lakes, home to microscopic creatures called diatoms. When the lakes dried up, the remnants of those creatures remained.

Fast forward to today’s Sahara – a windy, sand-swept desert roughly the size of the United States (including Alaska and Hawaii) – where each year, summer storms kick up some 180,000 tons of dust into the atmosphere.

Moving 10,000 to 15,000 feet above the ground, westward-bound waves of dusty air fall in a steady “rain” of particles.

Mystery solved!

Air quality concerns

As the dust makes its way across the Atlantic, most of the particles are smaller than what can be seen by the naked human eye. That can cause problems for people with asthma or other chronic lung conditions, says Weslee Copeland, TCEQ’s senior meteorologist.

While the Gulf Coast tends to bear the brunt of the sandy dust, Copeland says, it’s not uncommon for the plumes to carry all the way across Texas.

“The dust does degrade air quality when it’s here,” he says. “Most of the time it falls within the moderate range of EPA’s Air Quality Index, which means most healthy individuals will not be affected, but those who are more sensitive may experience some respiratory effects.”

If the symptoms sound familiar, it’s because you’ve lived in Central Texas long enough to associate them with allergies: itchy eyes, sneezing and coughing, increased nasal congestion, and, of course, that most annoying of conditions, the sniffles.

Copeland and other meteorologists at TCEQ keep a close on eye on air quality, including traces of Saharan dust, and issue a daily air quality forecast.

Hurricane vanquisher

While Saharan dust may mess with your marathon training schedule, the 2-mile-thick layer of bone-dry air, speeding across the ocean about a mile above the surface, also provides a surprising benefit by suppressing the formation and strengthening of tropical storms.

“Saharan dust and hurricanes typically do not occur at the same time or in the same place,” Copeland says, “because the dust, coming from a desert, is an extremely dry air mass, and hurricanes need warm, humid air to develop.”

That’s welcome news since this hurricane season is predicted to be more active than usual.

Ancient fertilizer

The dust has “an interesting relationship” with plants and marine ecosystems like coral reefs, Copeland notes.

On the one hand, the mineral particles that make up the dust plumes are rich in iron and phosphorus – nutrients that both plants on land and phytoplankton in the sea need to grow.

That said, the dust can also carry excess amounts of other compounds that can interfere with the healthy development and could harm crops.

A mixed bag, these ancient airborne critters from The Great Desert.

Photo NASA