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Cloud condensation nuclei in the Amazon Basin : their role in a tropical rainforest


Roberts, Gregory Charles (2001) Cloud condensation nuclei in the Amazon Basin : their role in a tropical rainforest. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ebt1-np17.


Cloud condensation nuclei (CCN) are closely linked to cloud structure and precipitation; yet, their role in tropical climates remains largely unknown. CCN measurements were performed during several field campaigns during 1998 and 1999 as part of the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) in the states of Amazonas and Rondônia. An airborne experiment transected the Amazon Basin and allowed for sampling of different airmasses ranging from clean maritime aerosol along the eastern coast to the smoke plumes and regional haze of the biomass burning. CCN concentrations between 0.15% and 1.5% supersaturation were measured using static thermal-gradient CCN chambers. The wet-season CCN concentrations measured in the unpolluted Amazon Basin were surprisingly low and resembled conditions more typical of marine locations than of other continental sites. It is remarkable that very similar CCN concentrations prevail in pristine marine and continental regions, in spite of the different aerosol production mechanisms and particle compositions. Physical and chemical properties responsible for CCN activation were estimated using a number and mass size distribution closure. In spite of the large organic fraction in Amazonian aerosol, the results suggest that the soluble, inorganic component accounts for most of the CCN activity during the wet season. Biomass burning smoke aerosol dramatically increased CCN concentrations during the dry season, which likely increases colloidal stability and cloud lifetime, resulting in the observed non-precipitating clouds. Because of the low natural CCN abundance in Amazonia, climatic effects related to the enhanced aerosol emissions due to human activity may have a stronger impact on climate change than in other continental regions. An early part of my research also included measuring the air-to-sea flux of biogenic trace gases on the Black Sea and the characterization of aerosol composition and their sources in the central African rainforest.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Environmental Engineering
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Environmental Science and Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Hoffmann, Michael R. (advisor)
  • Andreae, Meinrat O. (advisor)
Thesis Committee:
  • Unknown, Unknown
Defense Date:12 December 2000
Record Number:CaltechTHESIS:10122010-122520361
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6136
Deposited By: Benjamin Perez
Deposited On:12 Oct 2010 20:17
Last Modified:16 Apr 2021 23:29

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