Long term measurements of aerosol optical properties at a primary forest site in Amazonia

Autor(es):Mostrar menos -

Rizzo, L. V. ^[1] ; Artaxo, P. ^[2] ; Mueller, T. ^[3] ; Wiedensohler, A. ^[3] ; Paixao, M. ^[3] ; Cirino, G. G. ^[4] ; Arana, A. ^[2] ; Swietlicki, E. ^[5] ; Roldin, P. ^[5] ; Fors, E. O. ^[5] ; Wiedemann, K. T. ^[6] ; Leal, L. S. M. ^[4] ; Kulmala, M. ^[7]

Afiliação do(s) autor(es)

^[1] Univ Fed Sao Paulo, Inst Environm Chem & Pharmaceut Sci, Dept Earth & Exact Sci, Sao Paulo - Brazil

^[2] Univ Sao Paulo, Inst Phys, Dept Appl Phys, Sao Paulo - Brazil

^[3] Leibniz Inst Tropospher Res, Leipzig - Germany

^[4] Natl Inst Amazonian Res INPA, Manaus, Amazonas - Brazil

^[5] Lund Univ, Inst Phys, Div Nucl Phys, Lund - Sweden

^[6] Harvard Univ, Dept Earth & Planetary Sci, Div Engn & Appl Sci, Cambridge, MA 02138 - USA

^[7] Univ Helsinki, Div Atmospher Sci, Dept Phys Sci, Helsinki - Finland

• Tipo de documento: Artigo Científico
• Fonte: Atmospheric Chemistry and Physics; v. 13, n. 5, p. 2391-2413, 2013.
• Citações Web of Science: 31

Resumo

A long term experiment was conducted in a primary forest area in Amazonia, with continuous in-situ measurements of aerosol optical properties between February 2008 and April 2011, comprising, to our knowledge, the longest database ever in the Amazon Basin. Two major classes of aerosol particles, with significantly different optical properties were identified: coarse mode predominant biogenic aerosols in the wet season (January-June), naturally released by the forest metabolism, and fine mode dominated biomass burning aerosols in the dry season (July-December), transported from regional fires. Dry particle median scattering coefficients at the wavelength of 550 nm increased from 6.3 Mm(-1) to 22 Mm(-1), whereas absorption at 637 nm increased from 0.5 Mm(-1) to 2.8 Mm(-1) from wet to dry season. Most of the scattering in the dry season was attributed to the predominance of fine mode (PM2) particles (40-80% of PM10 mass), while the enhanced absorption coefficients are attributed to the presence of light absorbing aerosols from biomass burning. As both scattering and absorption increased in the dry season, the single scattering albedo (SSA) did not show a significant seasonal variability, in average 0.86 +/- 0.08 at 637 nm for dry aerosols. Measured particle optical properties were used to estimate the aerosol forcing efficiency at the top of the atmosphere. Results indicate that in this primary forest site the radiative balance was dominated by the cloud cover, particularly in the wet season. Due to the high cloud fractions, the aerosol forcing efficiency absolute values were below -3.5 Wm(-2) in 70% of the wet season days and in 46% of the dry season days. Besides the seasonal variation, the influence of out-of-Basin aerosol sources was observed occasionally. Periods of influence of the Manaus urban plume were detected, characterized by a consistent increase on particle scattering (factor 2.5) and absorption coefficients (factor 5). Episodes of biomass burning and mineral dust particles advected from Africa were observed between January and April, characterized by enhanced concentrations of crustal elements (Al, Si, Ti, Fe) and potassium in the fine mode. During these episodes, median particle absorption coefficients increased by a factor of 2, whereas median SSA values decreased by 7 %, in comparison to wet season conditions. (AU)

• Processo FAPESP: 08/58100-2 - Aeroclima: efeitos diretos e indiretos de aerossóis no clima da Amazônia e Pantanal
• Beneficiário: Paulo Eduardo Artaxo Netto
• Linha de fomento: Auxílio à Pesquisa - Programa de Pesquisa sobre Mudanças Climáticas Globais - Temático