Sahara Desert Dust Storm Leaves "Fingerprint" in Houston

Houston, Texas, is nearly 5,000 miles away from the Sahara desert in Africa, but US researchers have distinguished between dust particles transported from the Sahara across the Atlantic Ocean with dust particles with local sources, effectively identifying a "fingerprint" of the African dust.

The researchers say that to their knowledge, theirs is the first study which isolates, differentiates and quantifies the air contaminants in the US during the incursion of African dust, which happens regularly.

Writing in the journal Environmental Science and Technology, Joseph Prospero, professor emeritus at the University of Miami Rosenstiel School of Marine and Atmospheric Science, and collaborators at the University of Houston and Arizona State University found that "the average air concentrations of inhalable particles more than doubled during a major Saharan dust intrusion in Houston, Texas."

Fine airborne dust particles are concerning because they could pose health problem for asthmatics and people with respiratory problems.

"Current EPA air quality standards are based on the total amount of particles that are in the air," Prospero said. "Our study will contribute to our ability to discriminate and identify the dominant components in the air during long-range transport events," he said. "Our hope is that our work is instrumental in assisting regulatory agencies respond to health and environmental issues linked to African dust."

The "fingerprint" could be used to address African dust intrusion in other affected regions of the world, the researchers said. The Caribbean Basin, for example, receives huge quantities of African dust every year. The dust intrusion impacts air quality. As the Caribbean is a hotbed of hurricane activity and the same forces that generate hurricanes are responsible for carrying dust across the ocean, there is a link between the two phenomena.

"African dust storms are associated with hurricane season because the meteorological situations that are involved with generating tropical cyclones are also associated with the generation and transport of dust," Prospero said. "The dust emerges from the coast of Africa in a hot, dry, elevated layer - the Saharan Air Layer (SAL) following behind Easterly Waves from which tropical cyclones sometimes develop," he said. "The SAL interacts with the waves in complex way, so that the relationship is not entirely clear. It is the subject of much ongoing research."

In addition, the dust suspended in the wind absorbs and scatters solar radiation, which inhibits sunlight from reaching the ocean surface, in turn causing lower surface temperatures. In the tropical Atlantic Ocean, which is the main region where hurricanes develop. Cooler ocean temperatures mean less energy for hurricanes to form and strengthen, the researchers said.

"Dust activity has been very intense this year and sea surface temperatures are unusually low," Prospero added. "These may have been contributing factors to the unusually weak hurricane season this year."

Prospero said scientists would be better able to predict future trends with better understanding of all the processes involved in Saharan air outbreaks.

"The question is what happens with climate change," Prospero said. "Although much of North Africa is expected to get drier, which would mean more dust, models can't agree on whether the climate in the current major dust sources will get drier or wetter in the future. We are still trying to understand what drives these differences and the possible impacts."