Absorption coefficients by aerosols in remote areas: a new approach to decouple dust and black carbon absorption coefficients using seven-wavelength Aethalometer data

We present a new approach to decouple aerosol absorption coefficients due to iron oxide in Sahara dust from those due to black carbon (BC) particles. Absorption coefficients, sigma(aerosol)(lambda, t), were measured at the summit of Pico mountain (2225 m ASL) in the Azores Islands using a seven-wavelength Aethalometer. Measurements between 27th July and lst August, 2001, are analyzed here. Variations in aerosol absorption coefficients were uncorrelated to those of CO during the latter part of this period, suggesting the presence of non-combustion-derived aerosol, apparently African dust. To differentiate between BC and other absorbing particles, we analyzed the wavelength dependence Of sigma(aerosol)(lambda, t) and determined a best-fit exponent during the later period equal to -2.9 +/- 0.2, somewhat lower than previously reported for soil dust. Using this method, it is possible to estimate the aerosol absorption due to BC and that due to soil dust separately through the full period analyzed. (C) 2004 Elsevier Ltd. All rights reserved.