The Effect of Aerosol Particle Burning of the Amazon in radiative balance of the atmosphere

Author(s)

Jose Vanderlei Martins

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 1999-08-30

Examining board members

Paulo Eduardo Artaxo Netto; Juan Carlos Ceballos; Pedro Leite da Silva Dias; Ricardo Magnus Osorio Galvao; Mikiya Muramatsu

• Advisor: Paulo Eduardo Artaxo Netto

Abstract

In situ measurements in the Amazon Basin showed a large variety of aerosol particles in the atmosphere due mainly to biogenic and biomass burning sources. Particles from biomass burning are generally composed of a mixture of spherical and non-spherical particles, and chain aggregates of thousands of tiny black carbon (BC) spherules. The morphology and structure of smoke particles from biomass burning are determined by the type of fuel, the phase of combustion, and the age of the smoke. This structure changes due to interactions with water vapor, cloud droplets and due to condensation of gases on its surface (eg. sulfates and organic gases). Non-spherical and large (tens of micrometers) fluffy aggregates become more compacted and increasingly spherical with age. They are generally found only near the source of flaming-phase combustion, which suggests that particle compaction occurs in a relatively short time (likely, few hours) after release from a biomass fire. This change in morphology produces a significant change in the optical properties of these particles, enhancing its absorption and scattering cross sections. Scanning electron microscope photographs of aerosol particles from biomass burning taken in parallel with other physical measurements show correlation between morphology and the absorption coefficients suggesting the effect of the particle shape on optical properties. Intensive microphysical properties of the particles were measured and modeled in this work for biomass burning and biogenic aerosols. Despite of completely distinct sources, biogenic and biomass burning aerosols show some important similarities in chemical composition and particle sizes. Angström coefficients and backscattering ratios of biogenic aerosols were also found in the same range as biomass burning particles, but the scattering and absorption efficiencies, as well as single scattering albedo showed significantly different values. A new methodology was developed to obtain the spectral direct radiative forcing (DRF) by aerosol particles using remote sensing images and new parameters were defined in this work to access the radiative impact of the aerosols. Spectral measurements with the AVIRIS spectrometer (224 wavelengths between 0.38 and 2.5 µm) onboard the NASA-ER2 aircraft during the SCAR-B experiment (Smoke Clouds and Radiation -Brazil) have been used in this work to derive the spectral single scattering albedo of the aerosol particles, the aerosol optical thickness, and .the DRF.Significant values of spectral direct radiative forcing were found between 0,25 and 1.6 µm with a peak about -200 W m-2 µm-1 for a wavelength around 0.5 µm, per unity of optical depth (optical depth values at 0.66 µm). The integral over the whole solar spectrum averaged over heterogeneous surfaces (urban areas and vegetation) is about -60 W m-2 for the studied region (Cuiabá). The DRF over urban areas is smaller than over vegetation due to its brighter surface reflectance. (AU)

• FAPESP's process: 93/05017-3 - The effect of aerosol particles from ground fires on the radioactive balance of the atmosphere
• Grantee: José Vanderlei Martins
• Support Opportunities: Scholarships in Brazil - Doctorate