O aporte de poeira do Saara aos aerossóis na Amazônia Central determinada com medidas in situ e sensoriamento remoto

Abstract

The Amazon, during the wet season, receives dust supplies from the Sahara desert, which is the largest source of global dust. Sporadically, this dust arriving in the Amazon is accompanied by aerosol of biomass burning from the Sahel region. This transatlantic transport can act in the long term in providing essential nutrients to the forest, such as phosphorus. In this work we identify the events and quantify the aerosols transported to the Amazon from the north of Africa by the trade winds. The elemental compositions of the aerosols were investigated from continuous and long-term measurements at three sites in the Central Amazon, north of the city of Manaus, state of Amazonas. From an extensive and diverse database it was possible to determine the elemental concentration of dust aerosols of the Sahara desert and black carbon (Sahel) from Particle Induced X-ray Emission (PIXE) and fluorescence (EDXRF) applied to the filters obtained in a forest region (ZF2). We also used long-term measurements of aerosol optical thickness (AOD) using measurements of two solar photometers from the NASA / AERONET Network in central Amazonia. Aerosols were also analyzed by absorption and scattering measurements of visible radiation by the Matrix Ångström technique. It was also used remote sensing measurements obtained by the NASA-Giovanni system, as well as transport modeling with the HYSPLIT system. A strong seasonality was observed in the aerosol, and the presence of coarse particulate matter is predominant in the rainy season, with a mean volumetric radius ranging from 1.30 μm to 8.71 μm, and this contributes up to 78% of AOD at 500 nm. The highest prevalence of dust aerosols occurred during this same period, with a concentration of 204 ± 604 ng/m 3 , and from 141 pairs of filters, 60 dust-intensive events were identified between 2008 and 2015 represents 85% of traces elementes of dust identified. TheBC in the wet season has low concentrations, with an average of 265 ± 250 ng/m 3 , and has higher concentrations during the dust transport events. The Ångström parameter of scattering and absorption was obtained for the aerosol samples, obtaining during dust transport episodes scattering values ≤ 0.50 and absorption of ≥ 1,11. The analysis of back-trajetories and satellite products obtained with Terra's MODIS sensor confirm that the origin of the air masses are actually Sahara and Sahel. From these results it can be concluded that the highest frequency of dust deposition during the wet season occurs between mid-January and May and that soil dust has an average contribution of 14.6% of the measured total mass and its deposition has a strong impact on the absorption and scattering coefficients of the visible radiation.