Emission, evolution, and radiative properties of particles from biomass burning in Brazil

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Emission, evolution, and radiative properties of particles from biomass burning in Brazil

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Title: Emission, evolution, and radiative properties of particles from biomass burning in Brazil
Author: Reid, Jeffrey Spencer
Abstract: In this dissertation measurements of the physical, chemical, and radiative properties of biomass-burning particles, obtained by the Cloud and Aerosol Research Group (CARG), Department of Atmospheric Science, are described and discussed. Data on aging smoke particles were collected by the CARG from the University of Washington C-131A aircraft as part of the Smoke, Clouds, and Radiation (SCAR) studies on the US West Coast (SCAR-C, September, 1994), and in Brazil (SCAR-B, August and September, 1995).The physical and optical characteristics of smoke particles were measured from three prescribed forest fires on the U.S. West Coast, and from nineteen forest, cerrado, and grass fires in Brazil. The sizes of the particles from tropical forest fires were related to fuel type, fire intensity, and combustion efficiency. An analysis of smoke particles in regional hazes in Brazil suggests that as smoke aerosols age, their particle sizes increase by $\sim$30-50% by coagulation and gas-to-particle conversion. Furthermore, condensation and gas-to-particle conversion of organic vapors increase the aerosol mass by $\sim$20-40%. One-third to one-half of this mass growth likely occurs in the first few hours of aging due to the condensation of large primary organic molecules. The remaining mass growth probably is probably produced by photochemical and cloud processing over time periods of several days.Changes in particle sizes and compositions during the aging of smoke in Brazil have a large impact on the optical properties of the aerosol. Over a two to four day period, the fine particle mass scattering efficiency increased by more than 30%, and the single-scattering albedo increased by $\sim$0.04-0.1. Conversely, the Angstrom coefficient, backscatter ratio, and mass absorption efficiency decreased significantly with age, due no doubt to particle growth.Smoke particles are also shown to affect some cloud properties, Although in the presence of heavy smoke (CN concentrations $>$2,500 cm$\sp{-3}$), perturbations in smoke particle concentration do not affect the cloud droplet effective radius of convective cumuliform clouds. However, in stratiform clouds, smoke particles may affect the cloud droplet effective radius and hence cloud reflectivity.
Description: Thesis (Ph. D.)--University of Washington, 1998
URI: http://hdl.handle.net/1773/10099

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