Single scattering albedo of fine mineral dust aerosols controlled by iron concentration

Abstract

[1] Sign and magnitude of solar aerosol direct radiative forcing are largely determined by the aerosol single scattering albedo (SSA) and the albedo of the underlying scene (e.g., surface albedo). On a global scale, mineral dust aerosol has the largest mass emission rate, average column mass burden, and average optical depth of all aerosol types. Therefore, better understanding of its optical properties with a focus on SSA is of great importance. Here, we entrain ten bulk soil samples from deserts and semi-arid regions in the Arabian Peninsula, from locations representative of the Sahara and Sahel in North Africa, and from Northeast Africa and South-Central Asia. We segregate the fine particle fraction (aerodynamic diameter < 2.5 mm) and measure its iron content with an x-ray fluorescence (XRF) spectrometer and its aerosol SSA and absorption, scattering, and extinction Ångström coefficients for two wavelengths (405 nm and 870 nm) with a photoacoustic instrument with integrating reciprocal nephelometer. Results show that SSA is much lower at 405 nm than at 870 nm and that SSA at both wavelengths is dominated by and linearly correlated with the iron content of the entrained mineral dust. The second result points toward potential use of SSA remote sensing to measure aerosol iron content and vice versa, measurements of iron content with simple filter sampling followed by XRF analysis, providing an assessment of SSA for aerosol radiative forcing calculations and modeling. Average Ångström coefficients were ≈3.2 for absorption, ≈À0.4 for scattering, and ≈À0.3 for extinction and showed little correlation with iron content.Citation: Moosmüller, H., J. P. Engelbrecht, M. Skiba, G. Frey, R. K. Chakrabarty, and W. P. Arnott (2012), Single scattering albedo of fine mineral dust aerosols controlled by iron concentration,

Iron oxide minerals in dust-source sediments from the Bodélé Depression, Chad: Implications for radiative properties and Fe bioavailability of dust plumes from the Sahara

“…Our results extend earlier research on the occurrences of iron-bearing minerals in Bodélé surface sediments and elsewhere in North Africa that aimed to establish linkages between dust mineralogy and potential environmental effects of dust (Lafon et al, , 2006Alfaro et al, 2004;Moreno et al, 2006;Mounkaila, 2006;Journet et al, 2008Journet et al, , 2104Chudnovsky et al, 2009;Lázaro et al, 2011;Maher, 2011;Shi et al, 2011;Moosmüller et al, 2012;Adetunji, 2014;Formenti et al 2014 a, b). These studies employed many methods for dust and soil mineralogy, including magnetic analyses, X-ray absorption analysis, X-ray diffraction, microscopy, elemental and isotopic chemistry combined with leaching experiments, as well spectroscopic techniques in the laboratory and applied to satellite retrievals.…”

Spectral- and size-resolved mass absorption efficiency of mineral dust aerosols in the shortwave spectrum: a simulation chamber study

“…Contrary to the MAE values, there is no statistically significant size dependence of the AAE values, ranging from 2.5 (±0.2) to 4.1 (±0.3), with an average of 3.3 (±0.7), for the PM 10.6 size fraction and between 2.6 (±0.2) and 5.1 (±0.4), with an average of 3.5 (±0.8), for the PM 2.5 fraction. Our values are in the range of those published in the literature (Fialho et al, 2005;Linke et al, 2006;Müller et al, 2009;Petzold et al, 2009;Yang et al, 2009;Weinzierl et al, 2011;Moosmüller et al, 2012;Denjean et al, 2016b), shown in Table 5. AAE values close to 1.0 are found for urban aerosols where fossil fuel combustion is dominant, while AAE values for brown carbon from incomplete combustion are in the range of 3.5-4.2 (Yang et al, 2009;Chen et al, 2015;Massabò et al, 2016).…”

“…Balkanski et al (2007) showed that lowering the dust absorption properties to an extent that reconciles them both with the remote-sensing observations and the state of knowledge of the mineralogical composition allowed calculating the clear-sky shortwave radiative effect of dust in agreement with satellite-based observations. A significant number of observations have quantified the shortwave lightabsorbing properties of mineral dust both by direct measurements Linke et al, 2006;Osborne et al, 2008;McConnell et al, 2008;Derimian et al, 2008;Yang et al, 2009;Müller et al, 2009;Petzold et al, 2009;Moosmüller et al, 2012;Wagner et al, 2012;Ryder al., 2013a;Utry et al, 2014;Denjean et al, 2016a, b) and indirectly by quantifying the amount and the speciation of the light-absorbing compounds in mineral dust, principally iron oxides (Lafon et al, , 2006Lazaro et al, 2008;Derimian et al, 2008;Zhang et al, 2008;Kandler et al, 2007Kandler et al, , 2009Kandler et al, , 2011Formenti et al, 2014a, b).…”

Optical Calibration and Equivalence of a Multiwavelength Thermal/Optical Carbon Analyzer

“…This is a good approximation for samples dominated by BC, where AAE = ~1. However, for many aerosols, such as those from smoldering combustion, this simple relationship is not followed and AAE varies with wavelength (Moosmüller et al, 2012). Interpolations between the seven wavelengths can be used to infer more complex functions of wavelength for different sources, a fraction of which can be verified by the more detailed spectrometric analyses outlined above.…”