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TG-02 Abstract

Influence of Amazonia Land-Use Change on Chemical Constituents in the Atmosphere

Luciana Vanni Gatti — IPEN - Instituto de Pesquisas Energeticas e Nucleares (USP) (SA-PI)
Alex B. Guenther — NCAR (US-PI)

We propose to investigate trace gas fluxes and aerosol concentrations and composition

in several Amazonian landscapes in order to improve our understanding of how land-use

change may alter the chemical composition of the atmosphere. Information to be obtained

will be relevant in two LBA-ECO theme areas: 1) trace gas fluxes and 2) carbon storage

and exchange.

We will employ a strategy that integrates field measurements of chemical fluxes,

satellite measurements and ground observations of landscape characteristics, and

atmospheric chemistry and transport modeling (Note that only field flux measurements are

funded through LBA-ECO). We propose to substantially improve estimates of trace gas

fluxes (CO, VOC, O3, NOx) and aerosol concentrations associated with major

Amazonian landscapes and to use a digital geographical information system (GIS) with

numerical models of atmospheric chemistry and transport to quantify the impact of land-use

change in Amazonia on the chemical composition of the atmosphere.

Trace Gas Fluxes

We propose to characterize trace gas fluxes and aerosol concentrations over a range of

landscapes and land-use types and improve our understanding of the surface and chemical

sources and sinks of these compounds. We will measure fluxes of CO, NOx and volatile

organic compounds (VOC) at four LBA flux towers for a period of 7-10 days each, using a

relaxed eddy accumulation (REA) system. Thirty minute integrated air samples associated

with up and down eddies will be collected into teflon bags or adsorbent cartridges and

analyzed for CO, CH4, isoprene, monoterpenes, methanol and other oxygenated

VOC, and NOx, all of which play a major role in tropospheric photochemistry. If isoprene

fluxes are sufficiently large to warrant further study, we have the capability of

continuously measuring isoprene flux using eddy covariance techniques with a

chemiluminescence fast isoprene analyzer.

In addition to tower REA studies, vertical profiles of chemical species (CO2,

CO, O3, NOx, VOC) will be measured at several heights between the surface and 2

km above ground level using a tethered balloon sampling system. Fluxes will be estimated

using mixed-layer gradient and mass balance techniques.

Organic aerosols play an important role in biogeochemical cycling of a variety of

elements, and influence the hydrological cycle and climate through their role as cloud

condensation nuclei. Atmospheric aerosol composition will be measured at three tower

sites. Fine (<2.0 mm diameter) and coarse (2.0 mm) aerosol fractions will be collected

using stacked filter units, and concentrations and size distributions of aerosols will be

determined. Trace elemental composition will be determined. Organic acids, nitrate and

sulfate, and major anions and cations will be measured in selected samples using ion


Trace gas flux estimates will be incorporated into a 3-D atmospheric chemistry and

transport model and used to predict the potential impact of land cover change on the

chemical composition of the atmosphere. Trace gas flux estimates will be coupled with a

3-D global atmospheric chemistry model, MOZART (Model of Ozone And Related Species in the

Troposphere), that will be used to examine the impact of changes in trace gas fluxes on

the chemical composition of the troposphere. MOZART is a fully diurnal model that

calculates the distribution and time evolution of approximately 50 chemical species from

the surface to the upper stratosphere. An explicit goal in the development of MOZART is to

provide a modeling tool for assessing how changes in trace gas fluxes, due to land-use

modifications, will impact global chemical budgets.

Carbon Storage and Exchange

The major flux of carbon between the atmosphere and the land surface is in the form of

CO2. However, there is a net efflux of carbon from forested ecosystems in the

form of trace gases and organic aerosols which is undetected using the proposed eddy

covariance CO2 flux techniques. The contribution of CO and VOC to the net

ecosystem exchange of carbon will be quantified at four tower CO2 flux sites,

using the REA system described above.

Research Team Responsibilities

  • Alex Guenther: Management and REA and tethered balloon flux measurements

  • Paulo Artaxo: Aerosol size distribution and composition

  • Brad Baker, University of Colorado: REA flux measurements and oxygenated VOC analysis

  • Bill Baugh, NCAR: Landscape characterization and tethered balloon flux measurements

  • Guy Brasseur: Atmospheric chemistry and transport modeling

  • Ken Davis, University of Minnesota: Mixed-layer gradient flux estimation

  • Jim Greenberg: Trace gas analyses and tethered balloon flux measurements

  • Peter Harley: REA flux measurements and VOC enclosure flux studies

  • Lee Klinger: Landscape characterization and NOx analysis

  • Pérola Vasconcellos, University of São Paulo: Ambient VOC and aerosol measurements

Preferred Sites

We hope to make REA trace gas flux measurements from four CO2 flux towers,

representing a range of land-use types, including primary and second-growth forest. Using

tethered balloon measurements, we will investigate trace gas fluxes and aerosol

concentrations from a minimum of nine landscapes, covering a range of successional stages,

and representing both undisturbed ecosystems and landscapes affected by forest conversion.

Site selection and the timing of our field deployments will be coordinated with the

LBA-ECO Science team and with other investigators measuring CO2 and trace

gas fluxes.

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