Saharan dust affects health, hurricanes
Particles present respiratory hazard, impact storm cells
Repeated weather advisories regarding Saharan dust have been issued this month.
Satellite models from NASA’s Earth Observatory showed plumes of dust blowing across the Atlantic in late June — most of it originating from the Bodele Depression, a dried Saharan lake bed in northeastern region of the central African country of Chad. Easterly trade winds blow the dust westward across the Atlantic to the Amazon, the Caribbean and states along the Gulf Coast, including Texas.
After traveling across the ocean, the dust visibly manifests in Houston as hazy beige or gray skies during the day and bright orange or yellow skies at sunrise and sunset.
“It’s not so much out of the ordinary,” meteorologist Matt Lanza, managing editor of Space City Weather, told the Chronicle earlier this month when the first Saharan dust blanketed the city. “It only happens a couple times per summer.”
Meteorologist Travis Herzog of KTRK-TV ABC13 says the dust clouds normally sweep through Houston in the summer months of May, June and July.
The dust brings with it a variety of implications for people and for the environment.
It is mainly a respiratory hazard, said Dr. David Engler, a Houston allergy and immunology specialist.
Engler said Tuesday that his practice has seen an increase in patients with respiratory trou-
ble over the past three to four weeks. Young and elderly patients, as well as patients with chronic lung conditions such as emphysema or severe asthma are most vulnerable.
“Go outside, get in your car, leave the air conditioning on, recirculate (your air),” Engler said. He said he tells patients with respiratory risks to minimize their time outside.
For those who have no choice but to go outside, Engler recommends wearing N95 masks as a preventative measure. The masks, which filter out 95 percent of particulate matter, can be bought at local hardware and home improvement stores. Online the N95 masks are sold in boxes of 10, 20 and more with prices ranging from about $7 to $25 per box depending on the features and sellers.
A hurricane deterrent
Engler also suggests taking an extra shower after coming back indoors.
“Take the clothes you’ve been wearing — either put them right in the washing machine or maybe put them in a covered hamper,” he said. “(The dust) really sticks in the hair, so make sure to not only shower but to shampoo also.”
From an environmental perspective, the Saharan dust and the winds that transport it act as a hurricane deterrent.
“We think a dust storm has three main components that can suppress a hurricane,” NOAA researcher Jason Dunion said in a NASA article.
“One, it’s got super-dry air. Hurricanes don’t like dry air in the middle parts of the atmosphere, and that’s exactly what the Saharan Air Layer has,” he said. “A Saharan dust storm also has a very strong surge of air embedded within it, called the midlevel easterly jet, that can rip a storm apart that’s trying to develop. We call that vertical wind shear. And then the third piece is all this dust.”
The dust particles are thought to suppress cloud formation, according to NASA, which prevents the intensification of ocean waves in tropical disturbances.
Can trigger red tide
The dust is also linked to algal blooms, though this issue is less relevant to Houston. According to NASA, the dust clouds deposit iron in the coastal waters of West Florida. A plant-like bacteria, called Trichodesmium, uses that iron to convert nitrogen in the water into a form that is usable by other marine organisms. Higher levels of iron mean more usable nitrogen, which encourages blooms of toxic algae, known as a red tide. However, this phenomenon tends to affect the coast of Florida more than that of Texas.
Wednesday’s forecast for Houston calls for a partly cloudy day with a high of 97 degrees and a low of 79, according to the Weather Channel. The chance of rain is slim, at just 10 percent. ABC13 predicts a Wednesday high of 98, and a low of 78. The haze from Saharan dust will, however, remain.
“African dust is expected to linger with at least light amounts covering the entire state,” the Texas Commission of Environmental Quality said in its Wednesday forecast. “The heaviest dust is forecast to remain over the northern half of the state” and “parts of Houston are predicted to fall under the lower to middle end of the ‘moderate’ range.”