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Is size distribution or chemical composition the key parameter to aerosols act as CCN?

Theotonio Pauliquevis, Instituto Nacional de Pesquisas da Amazônia, (Presenting)
Paulo Artaxo, Instituto de Física da USP,

Biomass burning is a subset of aerosols that have an important role on cloud particles. Smoke plumes typically have high particle concentration, small size (concentrated in fine mode, i.e. dp < 2.5 um) and rich in organic soluble compounds. Many papers deal with the ability of these particles to nucleate cloud drops, and if size distribution or chemical composition of particles is the critical feature of aerosols to act as CCN. In this work we discuss size distribution and hygroscopic properties of aerosols observed during the LBA/SMOCC 2002 campaign already published by Rissler et al. (2004). We purpose a new analysis of those data, and we conclude that size distribution was the key parameter for particles act as CCN, and not chemical composition. To conclude it we compared dry activation diameter of particles (as a function of supersaturation), which is calculated by its hygroscopic properties, and size distribution measurements for different aerosol loadings situations. For all aerosol loading condition analyzed (beginning and the mid of dry season, and the transition from dry to wet season, directly related to biomass burning emissions) size distribution was the more important parameter in determine the ability of particles to act as CCN. This conclusion is based on the fact that differences in aerosol loading were mainly related with particles bigger than the activation diameter. In other words, these particles are always activated because minimum activation diameter is always reached.

Science Theme:  TG (Trace Gases)

Session:  2C: Trace Gases and Aerosols

Presentation Type:  Oral

Abstract ID: 133

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