Spectral light absorption by ambient aerosols influenced by biomass burning in the Amazon Basin. I: Comparison and field calibration of absorption measurement techniquesReportar como inadecuado




Spectral light absorption by ambient aerosols influenced by biomass burning in the Amazon Basin. I: Comparison and field calibration of absorption measurement techniques - Descarga este documento en PDF. Documentación en PDF para descargar gratis. Disponible también para leer online.

1 MPIC - Max Planck Institute for Chemistry 2 USP - Universidade de São Paulo São Paulo 3 Desert Research Institute 4 Institute of Nuclear Energy Research 5 Research Center Karlsruhe

Abstract : Spectral aerosol light absorption is an important parameter for the assessment of the radiation budget of the atmosphere. Although on-line measurement techniques for aerosol light absorption, such as the Aethalometer and the Particle Soot Absorption Photometer PSAP, have been available for two decades, they are limited in accuracy and spectral resolution because of the need to deposit the aerosol on a filter substrate before measurement. Recently, a 7-wavelength ? Aethalometer became commercially available, which covers the visible VIS to near-infrared NIR spectral range ?=450?950 nm, and laboratory calibration studies improved the degree of confidence in these measurement techniques. However, the applicability of the laboratory calibration factors to ambient conditions has not been investigated thoroughly yet. As part of the LBA-SMOCC Large scale Biosphere atmosphere experiment in Amazonia ? SMOke aerosols, Clouds, rainfall and Climate campaign from September to November 2002 in the Amazon basin we performed an extensive field calibration of a 1-? PSAP and a 7-? Aethalometer utilizing a photoacoustic spectrometer PAS, 532 nm as reference device. Especially during the dry period of the campaign, the aerosol population was dominated by pyrogenic emissions. The most pronounced artifact of integrating-plate type attenuation techniques e.g. Aethalometer, PSAP is due to multiple scattering effects within the filter matrix. For the PSAP, we essentially confirmed the laboratory calibration factor by Bond et al. 1999. On the other hand, for the Aethalometer we found a multiple scattering enhancement of 5.23 or 4.55, if corrected for aerosol scattering, which is significantly larger than the factors previously reported ~2 for laboratory calibrations. While the exact reason for this discrepancy is unknown, the available data from the present and previous studies suggest aerosol mixing internal versus external as a likely cause. For Amazonian aerosol, we found no absorption enhancement due to hygroscopic particle growth in the relative humidity RH range between 40% and 80%. However, a substantial bias in PSAP sensitivity that correlated with both RH and temperature T was observed for 20%



Autor: O. Schmid - P. Artaxo - W. P. Arnott - D. Chand - L. V. Gatti - G. P. Frank - A. Hoffer - M. Schnaiter - M. O. Andreae -

Fuente: https://hal.archives-ouvertes.fr/



DESCARGAR PDF




Documentos relacionados