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

Modeling the influence of land use change on the concentration oforganic aerosol and oxidant species concentrations in Amazon.Luciana Varanda Rizzo (1), Paulo Artaxo (1), Ana Maria Cordova (2)and Luciana V.Gatti (2)(1) Instituto de Física, Universidade de São Paulo, Rua do Matão, Travessa R, 187,CEP 05508-900, Sao Paulo, S.P., Brazil. E-mail: lrizzo@if.usp.br(2) Laboratório de Química Atmosférica, IPEN, São Paulo, Brazil.Tropical forests are one of the most important sources of volatile organiccompounds (VOCs), which directly influence the atmospheric concentration of oxidativespecies, and also can act as gas phase precursors on the productions of new organicparticles. Biogenic VOC emission depends highly on the surface covering. Making use ofthe model MAPS – Model for Aerosol Processes Studies, an one-dimensional box modeldeveloped by NCAR – National Center for Atmospheric Research (USA), the influence ofland use change in Amazon over the secondary organic aerosol concentrations wassimulated. For forest, the program generated 2.1 µg/m 3 of new organic particles from gas toparticle conversion, in 24 hours of model simulation. The fine to coarse mode ratio oforganic aerosol obtained by the model fits the observed concentrations. Varying the landuse from forest to pasture, there is an alteration of monoterpene emissions, and, as a result,the secondary organic aerosol concentration changes. The variation of the organic aerosolconcentration can affect the population of cloud condensation nuclei (CCN). The modelalso indicates that land use changes affect significantly the hydroxyl radical concentration.This result could be an evidence that the VOCs concentrations greatly influence theoxidative capacity of the atmosphere in Amazonia.Financial support by FAPESP.