Interação entre a radiação solar direta e os aerossóis atmosféricos na Amazônia

Abstract

In this work an evaluation of the effects of aerosols on direct radiation in Amazonia was carried out. Different approaches were used to evaluate scattering and absorption properties, which included long-term measurements by remote sensing (AERONET) and in situ measurements. Basing on the spectral properties of the aerosols, a separation of the contributions of organic carbon (OC) and elemental carbon (EC) on the radiation flux, as well as the quantification of the optical absorption depth fractions into black carbon (AAOD-BC) and brown carbon (AAOD-BrC) was carried out. The analysis of the scattering and absorption properties in the atmospheric column evidenced that the scattering is the majority in the extinction process of the radiation, moreover it was verified that the land cover strongly influences the absorption processes. The analysis of the biogenic aerosols in central Amazonia found that the absorption and the scattering has a linear relationship and that these effects are the majority for angstrom values of absorption ranging from 1 to 2.5, characterizing an absorption range for organic fraction of the aerosol in that region, the brown carbon. It was found that AAOD-BrC values represent 18% of the AAOD-BC values for central Amazonia and approximately 15% for regions with high rates of deforestation or for Cerrado. It was observed that in the central Amazon, in the dry season, the fraction of OC produces instantaneous effects reaching a values of -100 Wm-2 in the radiative surface forcing (FR-Surface), while in the Cerrado region (Cuiabá) the values reached -350 Wm-2 . The relation between the biogenic fraction of aerosols in central Amazonia and the values of radiative forcing at surface (FR-Surface) showed an equal competition between the absorption and scattering fractions (R2 0.69 and 0.71 for scattering and absorption, respectively), however, it was verified through the efficiency of radiative forcing that the absorption is the most impacting effect on the radiative flux. By averaging the seasonal FR at the surface and at the top of the atmosphere, an effects of biogenic aerosols was quantify, as well as the effects of aerosols originated from biomass burning. The FR average values in central Amazonia passed from -9.17 to -17.10 Wm-2 at the top of the atmosphere and from -21.27 to - 41.05 Wm-2 on the surface from wet season to dry season. In general, the background effects on radiation (causing by biogenic particles) accounted for approximately 45% of the whole observed effect on the influence of burnings on the radiative flux.