Sahara’s dust may help sunsets, hurt air quality
AUSTIN, Texas – Each summer, wind carries millions of tons of dust from the Sahara Desert across the Atlantic Ocean to the Americas, sometimes leading to hazardous air quality. This year’s dust is already shrouding the Caribbean in an orange haze, but meteorologists think brewing storms in the tropics will prevent most of the dust from reaching Texas, at least for the time being.
“Looking at the satellites and all, there’s a good concentration of the dust coming off of Africa right now,” said Aaron Treadway, a meteorologist with the National Weather Service’s AustinSan Antonio office in New Braunfels, Texas.
Like a saloon for atmospheric cowboys, the Caribbean ain’t big enough for both dust and storms. That’s because Saharan dust can quash developing tropical storms.
The dust “can, at times, help suppress tropical storm and tropical cyclone formation because along with the dust it’s pulling that very warm and dry air off of Africa,” Treadway said.
Without enough moist air, tropical storms lose their strength.
Florida and some Caribbean islands began seeing the effects of the dust earlier this month. The dust would typically continue to creep westward, but ironically a different natural hazard, tropical storms, blocks it from reaching Texas.
“Dust season” extends from midJune through mid-August, so there’s still plenty of time for another round of dust to affect the state. Last June, an uncharacteristically large Saharan dust cloud – which some meteorologists nicknamed “Godzilla” – caused air quality problems across the Southeast. It also led to beautiful sunsets because the dust particles can scatter sunlight into vibrant shades of orange and red, like a prism.
Sascha Usenko, an environmental scientist at Baylor, remembered seeing the dust last year. Usenko said he walked to a bridge where he can typically see for 10 miles. During last year’s intrusion of dust, he could barely see the traffic a half-mile away.
“That was kind of my way of taking it in – like that is a lot of material being transferred across the Atlantic,” he said.
Usenko and another environmental scientist at Baylor, Rebecca Sheesley, help run an air quality monitoring network that takes real-time measurements of Saharan dust and other pollutants all across Texas.
“It’s possible that a lot of the dust can go above us,” Sheesley said.
If that happens, the dust might not actually lead to worse air quality, something satellites have a harder time picking up.
“You can look and see the satellites showing there’s this much dust between the surface and the upper troposphere, but then we can say this is how much it’s affecting the city of Houston right now,” she said.
Sheesley and Usenko have added new sensors to their network since last year and are now even better prepared to track the dust.
“The task at hand is for us to really understand some of these dust events in Texas and the millions of people that the dust can impact,” Usenko said.
Shankar Chellam, a professor of environmental engineering at Texas A&M University, has also studied the dust. He remembers when his instruments first picked up a massive spike in pollutants a few years ago that, at first, he couldn’t explain.
“We were totally confused. We were wondering what on earth is happening, no pun intended,” Chellam said.
After some research, he and his team figured out the culprit: Saharan dust.
“We were trying to establish industrial pollution, and we chanced upon a natural pollution source that literally crosses an ocean,” he said.
Chellam’s work focuses on identifying the specific sources of air pollution. While the stereotypical image of air pollution is dark clouds from a smokestack, Chellam stressed that “natural” pollutants such as dust and wildfire smoke can also affect our health.
“Snake venom is natural too,” he quipped.
He hopes that research will explore just how toxic the Saharan dust is compared with more conventional sources of air pollution.
Of course, the Saharan dust is not all bad. Besides intercepting hurricanes, the dust also provides nutrients for ocean life and even trees in the Amazon rainforest.
“It’s a much broader topic compared to just the health impacts of breathing in a little bit extra dust,” Chellam said.
Scientists disagree about whether the summer dust storms will get bigger or smaller over the coming years. One NASA study released this year concluded that climate change will cause weaker winds and more rain in parts of the Sahara, leading to damper dust that won’t travel as far.
A second study published this year – this one by researchers at the University of Kansas – found that the African jet stream will get stronger, leading to more dust getting deposited in the United States.