Amazon Basin ozone and aerosol Wet season ... - Wiley Online Library

10 downloads 0 Views 1MB Size Report
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-modeĀ ...
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