A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Influence of Amazônia Land-use Change On Reactive Carbon Fluxes andthe Chemical Composition of the TroposphereAlex Guenther 1 , Paulo Artaxo 2 , Luciana Gatti 3 , Jim Greenberg 1 , Peter Harley 1 , ElisabethHolland 1 , James Sulzman 1 , Xuexi Tie 1 , Oscar Vega 3 , Christine Wiedinmyer 11 Atmospheric Chemistry Division, NCAR, 1850 Table Mesa Drive, Boulder CO, USA, guenther@ucar.edu2 Instituto de Fisica, U. São Paulo, Sao Paulo, SP, Brazil3 IPEN, Divisao de Quimica Ambiental, Sao Paulo, SP, BrazilLand-use and landcover change are expected to perturb the exchange of gases andaerosols between Amazônian landscapes and the atmosphere. The biosphere-atmosphereexchange of reactive carbon compounds, RCCs (e.g., isoprene, acetone, a-pinene, CO,carbonaceous aerosols) is particularly important because of their role in the processescontrolling oxidant, CO, aerosol, and organic acid evolution, as well as their contribution toglobal carbon cycles and budgets. Regional air quality policy decisions, which have largeenvironmental and socio-economic impacts, also rely on accurate RCC emission anddeposition estimates. The LBA research program has greatly expanded the Amazôniandatabase of leaf-scale (enclosure measurements), canopy-scale (eddy flux measurements), andregional-scale (vertical profiling measurements) biogenic VOC observations. We haveintegrated the LBA flux measurements into an emission modelling scheme that has a 1kmresolution and accounts for Amazonian vegetation distributions and land-use. The emissionspredicted by this model were input to both a global 3-D model (MOZART) with moderatelydetailed chemistry and a box model with very detailed chemistry (NCAR Master Mechanism)and used to investigate the impact of land-use change on the chemical composition of theatmosphere. Land-use change induced perturbations in both emission and deposition of RCCwere considered in these model simulations. LBA observations of volatile organic compoundand aerosol fluxes (from above canopy towers) and boundary layer concentrations (fromtethered balloon and aircraft sampling platforms) were used to evaluate the performance of themodels. Scenarios considered include conversion of forest to 1) pasture, 2) small family farms,and 3) large commercial plantations. The implications of other Amazonian emissions (e.g.biomass burning, the Manaus plume) were also considered. The model simulations indicate thatAmazônia land-use change will significantly perturb regional atmospheric chemistry includingoxidants, reactive nitrogen and carbon trace gases and aerosols. This presentation will describethe advances in biogenic emission and deposition modelling procedures and the predictedimpacts on atmospheric trace gas and aerosol distributions. The implications for regional airquality and climate will also be discussed.