New York - Each summer, microscopic dust particles kicked up by African sandstorms blow thousands of kilometres across the Atlantic to arrive in the Caribbean, limiting aeroplane pilots’ visibility to just a few kilometres and contributing to the suffering of asthmatics.
The phenomenon has been around as long as there’s been sand in the Sahara. But it’s attracting ever more attention from regional scientists who say the clouds have grown, even if there’s no global consensus on the issue.
In recent days and weeks a particularly large cloud dusted eastern Caribbean islands, made for hazy skies and intense, tangerine-tinted sunsets off Havana, drifted over Mexico’s Yucatan Peninsula and was detected as far away as Wyoming. In satellite images provided by Nasa, the enormous, smoky clouds can be seen wafting westward from Africa covering hundreds of square kilometres.
While the clouds have mostly been treated as a meteorological curiosity, scientists say periodic masses of dust may have important climactic consequences, even hindering hurricane formation to some degree. Nasa has been sending unmanned drones into storms this year to study the phenomenon.
Experts say particulate matter found in the clouds may also be cause for health concerns, and are calling for more study to understand their potential impact.
“It is a matter of great magnitude, interest and importance for health,” said Braulio Jiménez-Velez, a specialist in molecular and environmental toxicology at the University of Puerto Rico at Mayaguez, who is researching the issue.
African dust has prompted two health alerts this year in Puerto Rico for asthma sufferers and people with allergies, and the Dominican Republic also issued a lower-level warning.
Airborne particulate matter is connected to respiratory disease worldwide, usually among people with existing problems such as asthma. Parts of the Caribbean, such as Puerto Rico, have high asthma rates. However, no direct link between African dust and higher rates of asthma or lung cancer has been established.
A 2011 study in Atmospheric Chemistry and Physics estimated that north Africa is behind more than 70 percent of global dust emissions.
Charles Darwin may have suspected as much back in 1832, when he collected the grime that caked the HMS Beagle at the Cape Verde islands.
“The dust falls in such quantities as to dirty everything on board,” Darwin wrote. Analysis showed micro organisms and plant silica in his sample.
Since then, increasing human activity has changed the composition of the clouds.
Scientists say they contain trace amounts of things like metals, micro organisms, bacteria, spores, pesticides and faecal matter, though there’s no evidence that the quantities are enough to pose a threat.
Joseph M Prospero, professor emeritus of marine and atmospheric chemistry at the University of Miami, said: “The specific impact on health is not known here or anywhere else. It has been extremely difficult to link specific particle composition to health effects.”
Eugenio Mojena of Cuba’s Institute of Meteorology said the particles were believed to originate in the semi-arid Sahel region south of the Sahara, where farmers raise livestock and employ chemical fertilisers and pesticides.
“Today’s dust is not the same as what Darwin studied,” Mojena said. Before, “it didn’t have pesticides or herbicides”.
Some experts worry that iron in the clouds may pose a threat to coral by feeding populations of algae and spores that damage it.
On the flip side, the clouds may inhibit the formation of tropical cyclones in the Caribbean.
Prospero said lower rainfall in West Africa caused more dust, which reduced sunlight, lowered water temperatures and cut evaporation, all factors in cyclonic formation. – Sapa-AP