Role of spheroidal particles in closure studies for aerosol microphysical–optical properties

Sorribas, M.; Olmo, F.J.; Quirantes, A.; Lyamani, H.; Gil-Ojeda, Manuel; Alados-Arboledas, Lucas; Horváth, H.

doi:10.1002/qj.2557

Cited by 14 publications

(11 citation statements)

References 40 publications

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“…The paper is mainly focused on the city of Granada (Spain). Granada is located in the Western Mediterranean basin and it is frequently affected by long-range transport of Saharan dust (Lyamani et al, 2005;Fernández et al, 2019;Soupiona et al, 2019) and biomass burning, both from near sources (Alados-Arboledas et al, 2011) and those at large distances (e.g. Ortiz-Amezcua et al, 2017;Sicard et al, 2019).…”

Section: Andalusian Global Observatory Of the Atmospherementioning

confidence: 99%

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Different strategies to retrieve aerosol properties at night-time with the GRASP algorithm

et al. 2019

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Abstract. This study evaluates the potential of the GRASP algorithm (Generalized Retrieval of Aerosol and Surface Properties) to retrieve continuous day-to-night aerosol properties, both column-integrated and vertically resolved. The study is focused on the evaluation of GRASP retrievals during an intense Saharan dust event that occurred during the Sierra Nevada Lidar aerOsol Profiling Experiment I (SLOPE I) field campaign. For daytime aerosol retrievals, we combined the measurements of the ground-based lidar from EARLINET (European Aerosol Research Lidar Network) station and sun–sky photometer from AERONET (Aerosol Robotic Network), both instruments co-located in Granada (Spain). However, for night-time retrievals three different combinations of active and passive remote-sensing measurements are proposed. The first scheme (N0) uses lidar night-time measurements in combination with the interpolation of sun–sky daytime measurements. The other two schemes combine lidar night-time measurements with night-time aerosol optical depth obtained by lunar photometry either using intensive properties of the aerosol retrieved during sun–sky daytime measurements (N1) or using the Moon aureole radiance obtained by sky camera images (N2). Evaluations of the columnar aerosol properties retrieved by GRASP are done versus standard AERONET retrievals. The coherence of day-to-night evolutions of the different aerosol properties retrieved by GRASP is also studied. The extinction coefficient vertical profiles retrieved by GRASP are compared with the profiles calculated by the Raman technique at night-time with differences below 30 % for all schemes at 355, 532 and 1064 nm. Finally, the volume concentration and scattering coefficient retrieved by GRASP at 2500 m a.s.l. are evaluated by in situ measurements at this height at Sierra Nevada Station. The differences between GRASP and in situ measurements are similar for the different schemes, with differences below 30 % for both volume concentration and scattering coefficient. In general, for the scattering coefficient, the GRASP N0 and N1 show better results than the GRASP N2 schemes, while for volume concentration, GRASP N2 shows the lowest differences against in situ measurements (around 10 %) for high aerosol optical depth values.

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Section: Andalusian Global Observatory Of the Atmospherementioning

confidence: 99%

“…From these measurements, aerosol volume concentrations were obtained in the 0.05-10 µm radius range with the 5 min time resolution. For that, a Q value = 1 has been assumed for conversion from aerodynamic to mobility size distribution (Sorribas et al, 2015).…”

Section: In Situ Measurementsmentioning

confidence: 99%

Different strategies to retrieve aerosol properties at night-time with the GRASP algorithm

et al. 2019

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“…Differences in k or SSA caused by the spatial variability of the iron content may affect the sign of the dust radiative effect (heating vs. cooling) (Liao and Seinfeld, 1998;Claquin et al, 1999;Miller et al, 2014) and its global and regional implications (Myhre and Stordal, 2001;Colarco et al, 2014;Das et al, 2015;Jin et al, 2016;Bangalath and Stenchikov, 2016;Strong et al, 2018). The direct radiative effect of dust has a strong impact on the western African monsoon (Yoshioka et al, 2007;Konaré et al, 2008) and the Indian summer monsoon (Vinoj et al, 2014;Das et al, 2015;Jin et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…The direct radiative effect of dust has a strong impact on the western African monsoon (Yoshioka et al, 2007;Konaré et al, 2008) and the Indian summer monsoon (Vinoj et al, 2014;Das et al, 2015;Jin et al, 2016). However, there is no consensus on whether dust increases or decreases precipitation over these regions (Solmon et al, 2008;Jin et al, 2016;Strong et al, 2018). As an example, Solmon et al (2008) indicate that dust reduces precipitation over most of the Sahelian region but increases it over the northern Sahel-southern Sahara.…”

Section: Introductionmentioning

confidence: 99%

Complex refractive indices and single-scattering albedo of global dust aerosols in the shortwave spectrum and relationship to size and iron content

et al. 2019

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Abstract. The optical properties of airborne mineral dust depend on its mineralogy, size distribution, and shape, and they might vary between different source regions. To date, large differences in refractive index values found in the literature have not been fully explained. In this paper we present a new dataset of complex refractive indices (m=n-ik) and single-scattering albedos (SSAs) for 19 mineral dust aerosols over the 370–950 nm range in dry conditions. Dust aerosols were generated from natural parent soils from eight source regions (northern Africa, Sahel, Middle East, eastern Asia, North and South America, southern Africa, and Australia). They were selected to represent the global-scale variability of the dust mineralogy. Dust was resuspended into a 4.2 m3 smog chamber where its spectral shortwave scattering (βsca) and absorption (βabs) coefficients, number size distribution, and bulk composition were measured. The complex refractive index was estimated by Mie calculations combining optical and size data, while the spectral SSA was directly retrieved from βsca and βabs measurements. Dust is assumed to be spherical in the whole data treatment, which introduces a potential source of uncertainty. Our results show that the imaginary part of the refractive index (k) and the SSA vary widely from sample to sample, with values for k in the range 0.0011 to 0.0088 at 370 nm, 0.0006 to 0.0048 at 520 nm, and 0.0003 to 0.0021 at 950 nm, as well as values for SSA in the range 0.70 to 0.96 at 370 nm, 0.85 to 0.98 at 520 nm, and 0.95 to 0.99 at 950 nm. In contrast, the real part of the refractive index (n) is mostly source (and wavelength) independent, with an average value between 1.48 and 1.55. The sample-to-sample variability in our dataset of k and SSA is mostly related to differences in the dust iron content. In particular, a wavelength-dependent linear relationship is found between the magnitude of k and SSA and the mass concentrations of both iron oxide and total elemental iron, with iron oxide better correlated than total elemental iron with both k and SSA. The value of k was found to be independent of size. When the iron oxide content exceeds 3 %, the SSA linearly decreases with an increasing fraction of coarse particles at short wavelengths (< 600 nm). Compared to the literature, our values for the real part of the refractive index and SSA are in line with past results, while we found lower values of k compared to most of the literature values currently used in climate models. We recommend that source-dependent values of the SW spectral refractive index and SSA be used in models and remote sensing retrievals instead of generic values. In particular, the close relationships found between k or SSA and the iron content in dust enable the establishment of predictive rules for spectrally resolved SW absorption based on particle composition.

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“…From these 15 measurements, aerosol volume concentrations were obtained in the 0.05-10 μm radius range with the 5-min time resolution. For that, Q-value=1 has been assumed for conversion from aerodynamic to mobility size distribution (Sorribas et al, 2015).…”

Section: In-situ Measurementsmentioning

confidence: 99%

Different strategies to retrieve aerosol properties at night-time with GRASP algorithm

Benavent-Oltra¹,

Román²,

Casquero-Vera³

et al. 2019

Preprint

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Abstract. This study evaluates the potential of GRASP algorithm (Generalized Retrieval of Aerosol and Surface Properties) to retrieve continuous day-to-night aerosol properties, both column-integrated and vertically-resolved. The study is focused on the evaluation of GRASP retrievals during an intense Saharan dust event that occurred during the Sierra Nevada Lidar aerOsol Profiling Experiment I (SLOPE I) field campaign. For daytime aerosol retrievals, we combined the measurements of the lidar ground-based from EARLINET (European Aerosol Research Lidar Network) station and sun/sky photometer from AERONET (Aerosol Robotic Network), both instruments co-located in Granada (Spain). However, for night-time retrievals three different combinations of active and passive remote sensing measurements are proposed. The first scheme (N0) uses lidar night-time measurements in combination with the interpolation of sun/sky daytime measurements. The other two schemes combine lidar night-time measurements with night-time aerosol optical depth obtained by lunar photometry either using intensive properties of the aerosol retrieved during sun/sky daytime measurements (N1) or using the moon aureole radiance obtained by sky camera images (N2). Evaluations of the columnar aerosol properties retrieved by GRASP are done versus standard AERONET retrievals. The coherence of day-to-night evolutions of the different aerosol properties retrieved by GRASP is also studied. The extinction coefficient vertical profiles retrieved by GRASP are compared with the profiles calculated by Raman technique at night-time with differences below 30% for all schemes at 355, 532 and 1064&#8201;nm. Finally, the volume concentration and scattering coefficient retrieved by GRASP at 2500&#8201;m&#8201;a.s.l. are evaluated by in-situ measurements at this height at Sierra Nevada Station. The differences between GRASP and in-situ measurements are similar for the different schemes, with differences below 30&#8201;% for both volume concentration and scattering coefficient. In general, for the scattering coefficient, the GRASP N0 and N1 show better results than the GRASP N2 schemes, while for volume concentration, GRASP N2 shows the lowest differences against in-situ measurements, around 10&#8201;%, for high the aerosol optical depth values.

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Role of spheroidal particles in closure studies for aerosol microphysical–optical properties

Cited by 14 publications

References 40 publications

Different strategies to retrieve aerosol properties at night-time with the GRASP algorithm

Different strategies to retrieve aerosol properties at night-time with the GRASP algorithm

Complex refractive indices and single-scattering albedo of global dust aerosols in the shortwave spectrum and relationship to size and iron content

Different strategies to retrieve aerosol properties at night-time with GRASP algorithm

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