Influence of Amazonia Land-use Change on Chemical Constituents in the Atmosphere
Alex Guenther -- National Center for Atmospheric Research (NCAR)
Luciana Vanni Gatti -- Instituto de Pesquisas Energeticas e Nucleares (IPEN)
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
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 chromatography.
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
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.