The troposphere acts as the source and sink for chemicals in the stratosphere. Tropospheric chemical changes can affect global environment hydrological processes, the cycling of nutrient compounds, the accumulation of infrared gases in the atmosphere, rain and snow acidity, and the rate of ozone depletion in the stratosphere and mesosphere by man-made chemicals introduced through the troposphere. It is at the surface that the biosphere-atmosphere interaction is strongest, and it is the entry of these gases into the free troposphere that begins the processes of truly global tropospheric chemical change.
The series of GTE field expeditions which have focused on studies of ecosystems that are known to exert a major influence on the "unperturbed" atmosphere have been designated as the Atmospheric Boundary Layer Experiments (ABLE). During the ABLE -campaigns the fluxes of gases between the surface and the atmospheric boundary layer, and the mixing of gases from the boundary layer into the "free troposphere" have been studied in great detail. (The tropospheric layer is typically 1 to 2 kilometers thick and is the layer of the atmosphere in direct contact with the surface. The free troposphere is that portion of the atmosphere directly above the boundary layer and extends to the stratosphere.)
Three ABLE campaigns have been conducted thus far. The ABLE-1, conducted in 1984 from Barbados, focused on the chemistry and transport processes occurring over the tropical Atlantic ocean and the rain forest of French Guyana. The ABLE-2, based in Manaus, Brazil, focused on the chemistry and transport over the Amazon Rain Forest during the dry season of 1985 ( ABLE-2A) and during the wet season of 1987 (ABLE-2B). The ABLE-3 mission, also conducted in 2-phases, focused on the chemistry in the northern latitude and the Arctic tundra as a source/sink of methane (CH4), ozone (O3), and CO. The first phase, ABLE-3A was conducted in 1988 from bases in Point Barrow and Bethel, Alaska. The second phase, ABLE-3B was conducted in 1990, from bases at North Bay and Goose Bay, Canada and a major ground site in Schefferville, Canada.