Submitted to: Journal of Geophysical Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/1997
Publication Date: N/A
Interpretive Summary: It is well-known that dust from the Sahara in Africa can be transported in the atmosphere across the Atlantic to the Middle East, Europe, South America, and the Caribbean. New technology for air monitoring shows that Saharan dust can occasionally be tracked across much of the eastern United States and as far west as the Texas-New Mexico border. Saharan dust can be told apart from dust generated in North America by its unique physical and chemical properties, as well as by using new techniques for tracing the motion of air masses. Saharan dust entered the continental United States on the average of three times per year, for approximately ten days at a time, between 1992 and 1995. Saharan dust enters the United States during summer (especially July), at a time when blowing dust is at most a localized occurrence in the central United States; this research shows that the Plains states and the arid West are not always the primary source of fine, wind-eroded soil particles in the USA's atmosphere. This research also shows that the extremely fine Saharan dust particles may have some effect on the quality and chemistry of the air.
Technical Abstract: The long-range transport of Saharan dust to the Middle East, Europe, South America, and the Caribbean has been well documented during the past 25 years. With the advent of routine collection and analysis of fine (i.e., Dp<2.5µm) aerosols at national parks, monuments and wilderness areas in the continental United States, these Saharan dust incursions can now be tracked, characterized, and quantified across much of the eastern half of the U.S. Identification of the Saharan source of these dust episodes was confirmed by mass distribution measurements, a characteristic Al/Ca ration, isentropic backward airmass trajectories, and sequential plots of the spatial distribution of the dust plumes. Saharan dust incursions into the continental U.S. persisted for approximately 10 days and occurred, on average, three times per year from 1992 to 1995. Fine soil mass usually exceeded 10 µg m-3 during these dust episodes and dominated local fine soil dust by an order of magnitude or more, even in the so-called "dust bowl" states of the central U.S. Size-resolved measurements of elemental composition taken during July 1995 indicate that the mass mean diameter of the transported Saharan dust is < 1 µm. The high mass scattering efficiency and abundant particle surface area associated with these submicron soil aerosols could have important consequences for both the radiative balance of the region and the chemistry of the local aerosols during summer when the long-range transport of Saharan dust to the U.S. is most common.