TARFOX Abstracts
at AGU Special Sessions
Baltimore, MD, 5/29-30, 1997

A41C-11
"Transport of African Mineral Dust to the Southeast Coast of the United States: Impact on Regional Air Quality"

J M Prospero, D L Savoie
Div. of Marine and Atmospheric Chemistry, Univ. of Miami, Miami, FL
jprospero@rsmas.miami.edu

At a roof-top site on the seaward coast of Virginia Key, Miami, we have continuously collected daily high-volume filter samples during on-shore wind conditions since 1974. Our data show that large quantities of mineral dust are carried into the region during every summer, generally beginning in late June and early July. Daily trade-wind dust aerosol concentrations during the summer are often in the range of 10's ug/m3 and can exceed 100 ug/m3. Our studies in Miami and at other sites in the North Atlantic (e.g. Barbados and Bermuda) and those of other investigators, have clearly established that the dust is transported from sources in North Africa. Incursions of dust-laden African air are identifiable by their meteorological characteristics, in particular, by a relatively warm, dry isentropic layer that typically reaches to 3km. Atmospheric dust off the southeast coast of the US is often clearly detectable in satellite imagery (GOES, AVHRR and TOMS). Moreover, our aerosol data from Barbados, Bermuda and Miami show a large-scale temporal-spatial coherence in dust events. The regional character of these dust events is demonstrated by data from the State of Florida's air quality monitoring network; large dust events at our Miami site are usually accompanied by sharply increased concentrations of PM10 total suspended particulates throughout the State. In early August 1993, 40 monitoring sites ranging from the panhandle to the Florida Keys reported concentrations up to 113 ug/m3; the concurrent African dust concentration at our site was 99.5 ug/m3. The frequent advection of large dust events has implications regarding the enforcement of air quality standards. On the basis of our measurements over the past 25 years, we conclude that dust events would most likely place Florida in non-compliance with regard to the new standards proposed by the EPA for PM2.5 particulates. Because African dust incursions are synoptic-scale events, they could impact the air quality in a large region of the southeastern US and much of the east coast US as well.