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African Dust Settles In Florida

Take a deep breath in Miami this summer and chances are you'll inhale a bit of Africa.

On some summer days, as much as half the dust in Miami's air has African origins, reports Joseph M. Prospero of the University of Miami's Rosenstiel School of Marine and Atmospheric Sciences.

Prospero reviewed 23 years of measurements of airborne particles at a coastal site in Miami. He believes the impact of African dust is comparable throughout the southeastern United States.

His findings will appear in the July 20 issue of Journal of Geophysical Research.

While there is nothing new about the transoceanic transport of African dust, which sometimes gives the Miami area a reddish haze, Prospero notes that little research has been done into the health effects of dust in the air, as contrasted with dust in coal mines and other contained industrial environments.

Prospero noted that African dust particles contain large amounts of iron as a coating, providing its characteristic red-brown color. Once dust is deposited in the lung, the iron coating would probably be released to the lung tissue.

On some days the African dust can push the total number of airborne particles above the limit set by the Environmental Protection Agency, he reports.

The EPA's standard is based on the total mass of particles measuring 2.5 microns or less that may be observed in a 24-hour period. Particles of this size can penetrate deep into the lung, where they are deposited and react with lung tissue. The standard does not distinguish among various types of particles, which include pollution and local dust along with African dust.

Prospero notes that manmade photochemical pollution in the eastern and southeastern United States is at its highest in summer, the same time that most of the African dust arrives.

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