SMOCC

1. SMOCC Burning Transition Clean Diurnal and seasonal variations and the role of humidity in the scattering properties of aerosols over Amazon Basin. Duli Chand1, Meinrat O. Andreae1, Otmar Schmid1, Göran Frank1, Franz X. Meixner1, Paulo Artaxo2,Társis M. Germano2, Erik Swietlicki3 and Luciana V. Gatti4 (1) Max Planck Institute for Chemistry, Department of Biogeochemistry, PO Box 3060, D-55020 Mainz, Germany . (2) Universidade de Sao Paulo USP, Instituto de Fisica, CEP 05508-900, São Paulo, SP, Brazil. (3) Lund University, Division of Nuclear Physics, Sölvegatan 14, P.O. Box 118, S-22100 Lund, Sweden. (4) Instituto de Pesquisas Energéticas e Nucleares (IPEN), CEP 055508-900, São Paulo, SP, Brazil. Motivation ☼The direct effects of aerosols on the Earth’s radiative balance requires quantitative information on its optical properties. Light scattering by atmospheric aerosol contributes to cooling of the atmosphere, commonly described as negative radiative forcing. Accurate knowledge of scattering of light and their hygroscopic properties are crucial for determining the radiative forcing due to atmospheric aerosol. Objectives  Make field measurements of scattering of light by aerosols under biomass burning (smoky) and rainy (clean) seasons in the Amazon Basin.  To study the dependence of optical properties of aerosols on relative humidities by simultaneous measurements of scattering coefficient of light under humid and dry conditions.  Model the effect of biomass burning aerosol on cloud microphysics at the local and regional level and to investigate the effect of smoke aerosols on climate dynamics and the resulting large-scale climate effects. Experiment Light-scattering measurements were made with two single-wavelength (λ = 545 nm) nephelometers (model M903, Radiance Research, Seattle, USA) during the dry (burning) and wet (rainy) season of 2002. Dry and humid aerosols were sampled continuously by the nephlometers and the data were averaged and collected on a one-minute time resolution. The Instruments were calibrated using standard techniques [Anderson et al, 1996]. Figure 2 Inter-comparison for low values of scattering coefficients Figure 2 Inter-comparison for high values of scattering coefficients Figure 1 Comparison of the two nephelometers. Figure 5 (below) Humidification factor (ratio of wet to dry scattering coefficients) in burning, transition and relatively clean conditions 4a Figure 4a (left) Time series of scattering coefficients of dry and humid aerosol. Clean Burning Clean Transition Transition 4b Figure 4b (left) Time series of carbon monoxide used as a tracer for biomass burning (unprocessed raw data) Figure 6 (below) Humidification factor (σhumid/σdry) as a function of relative humidity. Conclusions (1) Large scale biomass burning significantly increases the particle induced light scattering In the atmosphere. (2) The preliminary results suggest that humidification factor of biomass burning aerosols is about 1.15 which is consistent during the earlier measurements [Kotchenruther and Hobbs, 1998]. Higher values are found during the transition period (~1.3) and highest (~1.4) during the relatively cleaner condition. This indicates increasing growth factor from dry to wet season. References Anderson, T. L., Covert, D. S., Marshall, S. F., Laucks, M. L., Charlson, R. J., Waggoner, A. P., Ogren, J. A., Caldow, R., Holm, R. L., Quant, F. R., Sem, G. J., Wiedensohler, A., Ahlquist, N. A., and Bates, T. S.: Performance characteristics of a high-sensitivity, three-wavelength, total scatter/backscatter nephelometer, J. Atmos. Ocean. Technol., 13, 967-986, 1996. Robert A. Kotchenruther and Peter V. Hobbs, Humidification factors of aerosols from biomass burning in Brazil, J. Geophys. Res.-Atmos., 103, 32081-32089, 1998. Acknowledgement We are gratefully acknowledge the support from the European Commission for providing the funds for the SMOCC project under contract No. EVK2-CT-2001-00110, SMOCC, and the Max Planck Society.