Carbon and the optical properties of atmospheric dust

Abstract

Atmospheric particulate matter was examined to estimate the significance of free carbon as an absorber of near-ultraviolet, visible, and near-infrared radiation. Bulk and size-fractionated samples have been disassembled into acetone-soluble, water-soluble, and insoluble fractions. The absorption coefficients for these fractions, and for the insoluble material after removal of the free carbon by burning, have been measured. The results show that in the visible and near infrared, free carbon, although not a major component by mass, is by far the dominant absorbing material. These measurements in relation to otherresearch suggest that geographic variations in and anthropogenic contributions to the free-carbon content cause much of the variation in the absorption coefficient of atmospheric particulate samples.

Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols

“…When absorption is stronger at shorter wavelengths, i.e., the particles appear brownish or yellow,Å will be significantly greater than unity. Values of 2.0 and more were found in aerosol collected near a lignite combustion plant (Bond et al, 1999b), in biomass smoke (Kirchstetter et al, 2004;Schmid et al, 2005;Schnaiter et al, 2005b), environmental tobacco smoke (Lawless et al, 2004), rural aerosol (Lindberg et al, 1993), and in particles produced by oxygen-deficient combustion of propane (Schnaiter et al, 2006). The highest values ofÅ are found for the yellowish to brownish products of pure smoldering combustion, e.g., tobacco smoke (3.5, Lawless et al, 2004) or water-soluble HULIS from biomass burning (6-7, Hoffer et al, 2005).…”

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

“…Black carbon (BC) aerosols are an important atmospheric component because of their potential deleterious impact on health and climate (Baumgardner et al, 2002), and dust, resulting from natural emissions, is involved in the biogeochemical cycling of iron, an essential micronutrient to marine phytoplankton (Arimoto, Balsam, & Schloesslin, 2002). Both BC (Bohren & Huffman, 1998;Lindberg, Douglass, & Garvey, 1993;Ackerman & Toon, 1981;Bodhaine, 1995) and dust (Gillespie & Lindberg, 1992, Caquineau, Gaudichet, Gomes, Magonthier, & Chatenet, 1998 particles absorb light at visible wavelengths, and therefore both, if present, contribute to measurements of aerosol absorption coefficient, aerosol ( , t) of the type reported here. It is therefore desirable to develop a method to estimate the contribution of each to such measurements.…”

Multi-angle absorption photometry—a new method for the measurement of aerosol light absorption and atmospheric black carbon

“…One reason for the remaining uncertainties is the unsolved problem of measuring aerosol light absorption (Horvath, 1993;Heintzenberg et al, 1997;Andreae, 2001). Black carbon (BC) is the most e cient light-absorbing aerosol species in the visible spectral range (Rosen, Hansen, Gundel, & Novakov, 1978;Lindberg, Douglass, & Garvey, 1993). Thus, the measurement of aerosol light absorption in the visible spectral range is strongly correlated to the measurement of black carbon.…”