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Impact of biomass burning on cloud properties in the Amazon Basin

Roberts, G. C. and Nenes, A. and Seinfeld, J. H. and Andreae, M. O. (2003) Impact of biomass burning on cloud properties in the Amazon Basin. Journal of Geophysical Research. Atmospheres, 108 (D2). Art. No. 4062. ISSN 2169-897X. doi:10.1029/2001jd000985.

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We used a one-dimensional (1-D) cloud parcel model to assess the impact of biomass-burning aerosol on cloud properties in the Amazon Basin and to identify the physical and chemical properties of the aerosol that influence droplet growth. Cloud condensation nuclei (CCN) measurements were performed between 0.15% and 1.5% supersaturation at ground-based sites in the states of Amazonas and Rondonia, Brazil during several field campaigns in 1998 and 1999 as part of the Large-Scale Biosphere - Atmosphere (LBA) Experiment in Amazonia. CCN concentrations measured during the wet season were low and resembled concentrations more typical of marine conditions than most continental sites. During the dry season, smoke aerosol from biomass burning dramatically increased CCN concentrations. The modification of cloud properties, such as cloud droplet effective radius and maximum supersaturation, is most sensitive at low CCN concentrations. Hence, we could expect larger interannual variation of cloud properties during the wet season that the dry season. We found that differences between CCN spectra from forested and deforested regions during the wet season are modest and result in modifications of cloud properties that are small compared to those between wet and dry seasons. Our study suggests that the differences in surface albedo, rather than cloud albedo, between forested and deforested regions may dominate the impact of deforestation on the hydrological cycle and convective activity during the wet season. During the dry season, on the other hand, cloud droplet concentrations may increase by up to 7 times, which leads to a model-predicted decrease in cloud effective radius by a factor of 2. This could imply a maximum indirect radiative forcing due to aerosol as high as ca. -27 W m(-2) for a nonabsorbing cloud. Light-absorbing substances in smoke darken the Amazonian clouds and reduce the net radiative forcing, and a comparison of the Advanced Very High Resolution Radiometer (AVHRR) analysis and our modeling studies suggests that absorption of sunlight due to smoke aerosol may compensate for about half of the maximum aerosol effect. Sensitivity tests show that complete characterization of the aerosol is necessary when kinetic growth limitations become important. Subtle differences in the chemical and physical makeup are shown to be particularly influential in the activation and growth behavior of the aerosol. Knowledge of the CCN spectrum alone is not sufficient to fully capture the climatic influence of biomass burning.

Item Type:Article
Related URLs:
URLURL TypeDescription
Roberts, G. C.0000-0002-3636-8590
Nenes, A.0000-0003-3873-9970
Seinfeld, J. H.0000-0003-1344-4068
Andreae, M. O.0000-0003-1968-7925
Additional Information:We thank G. Lala and P. Guyon for support with building the CCN instruments. These experiments would not be possible without support from the following Brazilian institutions: INPE, CPTEC, IBAMA, INCRA, and UNIR. This project was supported by the Max Planck Gesellschaft and by the European Commission (project EUSTACH-LBA). G.R. was funded by the Max Planck Institute for Chemistry and by Environment Now at the California Institute of Technology. This work was also supported by Office of Naval Research grant N00014-96-0119.
Funding AgencyGrant Number
Max Planck GesellschaftUNSPECIFIED
European CommissionUNSPECIFIED
Office of Naval Research (ONR)N00014-96-0119
Issue or Number:D2
Record Number:CaltechAUTHORS:20230221-772548500.1
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:119341
Deposited By: Tony Diaz
Deposited On:21 Feb 2023 23:40
Last Modified:21 Feb 2023 23:40

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