Sep 20, 1990 - Whitby, 1975]. The data show a two-mode structure for mixed layer aerosol (modes at about 0.1-0.2 txm and above 1 txm) and a three-mode ...
JOURNAL
OF GEOPHYSICAL
Amazon
RESEARCH,
Basin Ozone
VOL. 95, NO. D10, PAGES 16,903-16,912, SEPTEMBER
and Aerosol:
Wet
Season
20, 1990
Observations
GERALD L. GREGORY, EDWARD V. BROWELL, AND LINDA $. WARREN Atmospheric SciencesDivision, NASA Langley Research Center, Hampton, Virginia
CHARLES H. HUDGINS Operations Support Division, NASA Langley Research Center, Hampton, Virginia
The tropical environmentis recognizedas having a major impact on global troposphericchemistry. In particular, the Amazon Basin, with its emissionsand an abundance of moisture and sunlight, provides favorable conditions for the production of hydroxyl radical and subsequentchemical and photochemical reactions which generate or consume key atmospheric trace species. Wet season convection provides a mechanismfor efficient mixing between the surface and the free troposphere, and thus providesthe meansfor integratingAmazon Basin eventsinto the globalcirculation 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 ppbv at 3-km altitude. In addition, a negative ozone gradient (decreasingvalue to the surface)was observed within the mixed layer. The averaged wet seasonmixed layer ozone was about 7 ppbv lower than observed during the dry season.This is attributed to the enhancedconvective activity associatedwith the wet seasonand the changein mixed layer photochemistryfrom 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 troposphereof the Amazon Basin in that ozone (3- to 4-km altitude) is typically 15-25 ppbv as comparedto dry seasonvalues of 30-35 ppbv. In terms of the aerosol sourcecharacteristics of the Amazon Basin, mixed layer aerosols(0.1- to 0.4-/am diameter) are a factor of 5-10 higher than
observed in the troposphere with mixedlayervaluesof 100-200aerosols/cm 3. Analysesof both tropospheric and mixed layer aerosol samples show aerosolswhich are multisource. Tropospheric sampleshave size distributionswhich are trimodal and showmodesat aerosoldiameterswhich suggest the aerosols are (1) of lifetimes
