The tropical environment is recognized as having a major impact on global tropospheric chemistry. In particular, the Amazon Basin, with its emissions and an abundance of moisture and sunlight, provides favorable conditions for the production of hydroxyl radical and subsequent chemical and photochemical reactions which generate or consume key atmospheric trace species. Wet season convection provides a mechanism for efficient mixing between the surface and the free troposphere, and thus provides the means for integrating Amazon Basin events into the global circulation processes. The data show that the wet season Amazon Basin is an effective sink for ozone and a net source for aerosols. Mixed layer ozone at 150-m altitude averaged 8.5 ppbv compared to about 18 ppvb at 3-km altitude. In addition, a negative ozone gradient (decreasing value to the surface) was observed within the mixed layer. The averaged wet season mixed layer ozone was about 7 ppbv lower than observed during the dry season. This is attributed to the enhanced convective activity associated with the wet season and the change in mixed layer photochemistry from net ozone production (dry season) to a net destruction (wet season).

The net sink characteristics of the wet season mixed layer are seen throughout the troposphere of the Amazon Basin in that ozone (3- to 4-km altitude) is typically 15--25 ppbv as compared to dry season values of 30--35 ppbv. In terms of the aerosol source charactertistics of the Amazon Basin, mixed layer aersols (0.1- to 0.4-μm diameter) are a factor of 5--10 higher than observed in the troposphere with mixed layer values of 100--200 aerosols/cm3. Analyses of both tropospheric and mixed layer aerosol samples show aerosols which are multisource. Tropospheric sample have six distributions which are trimodal and show modes at aerosol diameters which suggest the aerosols are (1) of lifetimes <1 hour, (2) of lifetimes of days, and (3) mechanically generated elements (e.g., wind-blown dust). Mixed layer data show two of the three modes with no mode which respresent aeosols with lifetimes of days. ¿American Geophysical Union 1990