Abstract:
The ABLE missions have been designed specifically to study the rate of
exchange of material between the Earth's surface and its atmospheric
boundary layer, and the processes by which gases and aerosols are
moved between the boundary layer and the 'free' troposphere. These
expeditions are conducted in ecosystems of the world that are known to
exert a major influence
... on global atmospheric chemistry. In some
cases, these ecosystems are undergoing profound changes as a
consequence of natural processes and/or human impact.
The first GTE/ABLE expedition utilized the NASA Electra aircraft,
extensively arrayed with chemical and meteorological sensors, to
survey regions over the tropical Atlantic Ocean from a base in
Barbados (13N,60W) in June 1984. ABLE-1 flights above Barbados
observed a massive infusion of Saharan dust, confirming the long-range
Saharan dust hypothesis that wind-borne dust from arid African regions
is the principal source of mineral aerosols found in the global
troposphere. ABLE-1 flights through Guyana's wet tropical forest
boundary layer showed that this layer is a source of carbon monoxide,
isoprene, and dimethyl sulfide (DMS), as well as as a sink for ozone.
The Guyana forest was also revealed to be a major source of chemically
important aerosols. Measurements of tropospheric DMS concentrations
confirmed earlier conclusions that marine DMS production accounts for
fully half of natural sulfur emissions worldwide. Subsequent
oxidation of DMS contribute significantly to the levels of sulfur
dioxide (SO2) observed in the global free troposphere, and ultimately
to sulfuric acid. 
