Saharan dust absorption and refractive index from aircraft-based observations during SAMUM 2006

Petzold, A.; Rasp, Katharina; Weinzierl, Bernadett; Esselborn, Michael; Hamburger, T.; Dörnbrack, Andreas; Kandler, Konrad; Schütz, L.; Knippertz, Peter; Fiebig, Markus; Virkkula, Aki

doi:10.3402/tellusb.v61i1.16818

Cited by 49 publications

(85 citation statements)

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“…The lower boundaries correspond to the GK aggregate and the higher boundaries to the IH aggregate. These values are in good agreement with recent estimates of the complex refractive index for African mineral dust Kandler et al, 2008;Müller et al, 2009;Otto et al, 2009;Petzold et al, 2009;McConnell et al, 2010).…”

Section: Dependence On Representation Of the Mixing State Number Sizsupporting

confidence: 80%

Physico‐chemical and optical properties of Sahelian and Saharan mineral dust: in situ measurements during the GERBILS campaign

Klaver

Formenti

Caquineau

et al. 2011

Quart J Royal Meteoro Soc

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Regardless of origin, clays (illite, kaolinite) dominated the total volume (79-90%); the remainder was composed of quartz, calcium-rich minerals (calcite, dolomite, gypsum) and alkali feldspars. Iron oxides, measured using a selective chemical extraction method, accounted for 1-3% of the total dust mass. The dependence of particle number size and shape distribution on the origin of dust seems minor too, although our results might be slightly misleading due to the fact that those kinds of data have been gathered on flights when dust had comparable origins and residence time.Mineral dust is only weakly absorbing in the mid-visible wavelengths (single scattering albedo ω 0 > 0.95 at 550 nm), and ω 0 measured values can be reproduced by measuring the bulk fractions of the major minerals, i.e. clays, quartz, calcite and iron oxides. At this wavelength, knowledge of the nature of clays and iron oxides, or the state of mixing of the minerals, does not induce significant differences in the results. A more precise description of the nature of clays and iron oxides is necessary at lower wavelengths owing to larger differences in their spectral optical properties. In particular, knowledge of the nature of the dominant clay is important for determining light scattering in the backward hemisphere.

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Section: Dependence On Representation Of the Mixing State Number Sizsupporting

confidence: 80%

Physico‐chemical and optical properties of Sahelian and Saharan mineral dust: in situ measurements during the GERBILS campaign

Klaver

Formenti

Caquineau

et al. 2011

Quart J Royal Meteoro Soc

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“…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).…”

Section: Spectral and Size Variability Of The Mass Absorption Efficiencysupporting

confidence: 75%

“…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).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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Abstract. This paper presents new laboratory measurements of the mass absorption efficiency (MAE) between 375 and 850 nm for 12 individual samples of mineral dust from different source areas worldwide and in two size classes: PM 10.6 (mass fraction of particles of aerodynamic diameter lower than 10.6 µm) and PM 2.5 (mass fraction of particles of aerodynamic diameter lower than 2.5 µm). The experiments were performed in the CESAM simulation chamber using mineral dust generated from natural parent soils and included optical and gravimetric analyses.The results show that the MAE values are lower for the PM 10.6 mass fraction (range 37-135 × 10 −3 m 2 g −1 at 375 nm) than for the PM 2.5 (range 95-711 × 10 −3 m 2 g −1 at 375 nm) and decrease with increasing wavelength as λ −AAE , where the Ångström absorption exponent (AAE) averages between 3.3 and 3.5, regardless of size. The size independence of AAE suggests that, for a given size distribution, the dust composition did not vary with size for this set of samples. Because of its high atmospheric concentration, light absorption by mineral dust can be competitive with black and brown carbon even during atmospheric transport over heavy polluted regions, when dust concentrations are significantly lower than at emission. The AAE values of mineral dust are higher than for black carbon (∼ 1) but in the same range as light-absorbing organic (brown) carbon. As a result, depending on the environment, there can be some ambiguity in apportioning the aerosol absorption optical depth (AAOD) based on spectral dependence, which is relevant to the development of remote sensing of light-absorbing aerosols and their assimilation in climate models. We suggest that the sample-to-sample variability in our dataset of MAE values is related to regional differences in the mineralogical composition of the parent soils. Particularly in the PM 2.5 fraction, we found a strong linear correlation between the dust lightPublished by Copernicus Publications on behalf of the European Geosciences Union. 7176 L. Caponi et al.: Spectral-and size-resolved mass absorption efficiency of mineral dust aerosols absorption properties and elemental iron rather than the iron oxide fraction, which could ease the application and the validation of climate models that now start to include the representation of the dust composition, as well as for remote sensing of dust absorption in the UV-vis spectral region.

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“…These data have been incorporated into the Optical Properties of Aerosols and Clouds (OPAC) dataset (Hess et al, 1998), which has been widely used to calculate dust absorption in models (Kinne et al, 2006;Forster et al, 2007). However more recent observations conducted in the Saharan desert region indicate that dust is much less absorbing with the imaginary refractive index of 0.0001 to 0.0046 at 550 nm (Kaufman et al, 2001;Colarco et al, 2002;Haywood et al, 2005, Petzold et al, 2009McConnell et al, 2010). There is a pressing need to update dust absorption properties assumed in aerosol models with the most recent observations.…”

Section: Introductionmentioning

confidence: 99%

Dust optical properties over North Africa and Arabian Peninsula derived from the AERONET dataset

et al. 2011

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Abstract. Dust optical properties over North Africa and the Arabian Peninsula are extracted from the quality assured multi-year datasets obtained at 14 sites of the Aerosol Robotic Network (AERONET). We select the data with (a) large aerosol optical depth (AOD ≥ 0.4 at 440 nm) and (b) smallÅngström exponent (Å ext ≤ 0.2) for retaining high accuracy and reducing interference of non-dust aerosols. The result indicates that the major fraction of high aerosol optical depth days are dominated by dust over these sites even though it varies depending on location and time. We have found that the annual mean and standard deviation of single scattering albedo, asymmetry parameter, real refractive index, and imaginary refractive index for Saharan and Arabian desert dust is 0.944 ± 0.005, 0.752 ± 0.014, 1.498 ± 0.032, and 0.0024 ± 0.0034 at 550 nm wavelength, respectively. Dust aerosol selected by this method is less absorbing than the previously reported values over these sites. The weaker absorption of dust from this study is consistent with the studies using remote sensing techniques from satellite. These results can help to constrain uncertainties in estimating global dust shortwave radiative forcing.

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Saharan dust absorption and refractive index from aircraft-based observations during SAMUM 2006

Cited by 49 publications

References 0 publications

Physico‐chemical and optical properties of Sahelian and Saharan mineral dust: in situ measurements during the GERBILS campaign

Physico‐chemical and optical properties of Sahelian and Saharan mineral dust: in situ measurements during the GERBILS campaign

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

Dust optical properties over North Africa and Arabian Peninsula derived from the AERONET dataset

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