Non‐spherical aerosol retrieval method employing light scattering by spheroids

Dubovik, Оleg; Holben, B. N.; Lapyonok, Tatyana; Sinyuk, A.; Mishchenko, Michael I.; Yang, Ping; Slutsker, I.

doi:10.1029/2001gl014506

Cited by 431 publications

(440 citation statements)

References 23 publications

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“…The Wang-Gordon algorithm can thus serve as a valuable supplement to aerosol characterization studies, particularly during closure experiments for which success relies on obtaining an overdetermined set of aerosol properties [Ogren, 1995;Sokolik et al, 2001] within the allotted time period. The insensitivity of the algorithm to particle shape also promises to be useful in assessing the accuracy of nonspherical models used to deduce the optical properties of airborne mineral dust [Dubovik et al, 2002b].…”

Section: Discussionmentioning

confidence: 99%

Columnar aerosol single‐scattering albedo and phase function retrieved from sky radiance over the ocean: Measurements of Saharan dust

2003

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[1] The single-scattering albedo and phase function of African mineral dust are retrieved at 14 wavelengths across the visible spectrum from ground-based measurements of the aerosol optical thickness and the sky radiance taken in the solar principal plane. The retrieval algorithm employs the radiative transfer equation to solve by iteration for these properties that best reproduce the observed sky radiance, and is therefore independent of particle shape. The estimated error in the retrieved single-scattering albedo is less than 0.02 due to the precision of the solar-reflectance-based calibration of the radiometer. The phase function retrieved at 860 nm is robust under simulations of expected experimental errors and may be used to characterize aerosol scattering at the directly measured scattering angles (i.e., Â 155°). The phase function retrieved at 443 nm, however, is too sensitive to such errors to confidently describe the angular scattering at blue wavelengths. The single-scattering albedo displays a spectral shape expected of iron-bearing minerals but is much higher than climate models have assumed, indicating that wind-blown mineral dust cools Earth more than is generally believed. The method may be applied to any combination of airborne and ground-based measurements over the ocean and can complement more involved ground-based retrievals through its insensitivity to particle shape and ability to retrieve aerosol properties at relatively small aerosol optical depths.INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 1640 Global Change: Remote sensing; 1694 Global Change: Instruments and techniques; 4275 Oceanography: General: Remote sensing and electromagnetic processes (0689); KEYWORDS: aerosol, mineral dust, absorption, sky radiance, scattering, optical properties Citation: Cattrall, C., K. L. Carder, and H. R. Gordon, Columnar aerosol single-scattering albedo and phase function retrieved from sky radiance over the ocean: Measurements of Saharan dust,

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Section: Discussionmentioning

confidence: 99%

Columnar aerosol single‐scattering albedo and phase function retrieved from sky radiance over the ocean: Measurements of Saharan dust

2003

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“…Second, the instrument spins around, making sky diffuse radiation measurements at four spectral channels (440 nm, 675 nm, 870 nm and 1020 nm) to acquire aerosol microphysical and optical properties (Holben et al, 1998(Holben et al, , 2001). Parameters such as aerosol size distribution, single-scattering albedos, asymmetry factor and refractive index are obtained using inversion algorithms (Dubovik and King, 2000;Dubovik et al, 2002b). The uncertainty in AOD for Level 2 AERONET data is 0.01 to 0.02 (Eck et al, 1999).…”

Section: Aeronet Datamentioning

confidence: 99%

Similarities and differences of aerosol optical properties between southern and northern sides of the Himalayas

Panday

et al. 2014

Atmos. Chem. Phys.

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Abstract. The Himalaya mountains along the southern edge of the Tibetan Plateau act as a natural barrier for the transport of atmospheric aerosols from the polluted regions of South Asia to the main body of the Tibetan Plateau. In this study, we investigate the seasonal and diurnal variations of aerosol optical properties measured at two Aerosol Robotic Network (AERONET) sites on the southern side of the Himalaya (Pokhara, 812 m above sea level (a.s.l.) and EVK2-CNR, 5079 m a.s.l. in Nepal) and one on the northern side (Qomolangma (Mt. Everest) station for Atmospheric and Environmental Observation and Research, Chinese Academy of Sciences (QOMS_CAS) in Tibet, 4076 m a.s.l. in China). While observations at QOMS_CAS and EVK2-CNR can generally be representative of a remote background atmosphere, Pokhara is a lower-elevation suburban site with much higher aerosol load due to both the influence of local anthropogenic activities and to its proximity to the Indo-Gangetic Plains. The annual mean aerosol optical depth (AOD) during the investigated period was 0.05 at QOMS_CAS, 0.04 at EVK2-CNR and 0.51 at Pokhara, respectively. Seasonal variations of aerosols are profoundly affected by large-scale atmospheric circulation. Vegetation fires, peaking during April in the Himalayan region and northern India, contribute to a growing fine mode AOD at the three stations. Dust transported to these sites, wind erosion and hydrated/cloudprocessed aerosols lead to an increase in coarse mode AOD during the monsoon season at QOMS_CAS and EVK2-CNR. Meanwhile, coarse mode AOD at EVK2-CNR is higher than at QOMS_CAS in August and September, indicating that the transport of coarse mode aerosols from the southern to the northern side may be effectively reduced. The effect of precipitation scavenging is clearly seen at Pokhara, which sees significantly reduced aerosol loads during the monsoon season. Unlike the seasonal variations, diurnal variations are mainly influenced by meso-scale systems and local topography. The diurnal pattern in precipitation appears to contribute to diurnal changes in AOD through the effect of precipitation scavenging. AOD exhibits diurnal patterns related to emissions in Pokhara, while it does not at the other two high-altitude sites. At EVK2-CNR, the daytime airflow carries aerosols up from lower-altitude polluted regions, leading to increasing AOD, while the other two stations are less influenced by valley winds. Surface heating influences the local convection, which further controls the vertical aerosol exchange and the diffusion rate of pollution to the surrounding areas. Fine and coarse mode particles Published by Copernicus Publications on behalf of the European Geosciences Union. C. Xu et al.: Similarities and differences of aerosol optical propertiesare mixed together on the southern side of the Himalaya in spring, which may lead to the greater inter-annual difference in diurnal cycles of Ångström exponent (AE) at EVK2-CNR than that at QOMS_CAS.

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“…We adopted a similar approach to calculate additionally the DRE of BC and total aerosol. Size distributions and refractive indices were then used for calculating the aerosol optical properties for the non-BrC mixture, which was done by utilizing the spheroid aerosol model by Dubovik et al (2002). The model is consistent with the one used for the retrieval of AERONET products, assuming a portion of the aerosols to be spheroids, as described by Dubovik et al (2006).…”

Section: Calculation Of the Radiative Effectmentioning

confidence: 99%

Direct radiative effect by brown carbon over the Indo-Gangetic Plain

et al. 2015

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Abstract. The importance of light-absorbing organic aerosols, often called brown carbon (BrC), has become evident in recent years. However, there have been relatively few measurement-based estimates for the direct radiative effect of BrC so far. In earlier studies, the AErosol RObotic NETwork (AERONET)-measured aerosol absorption optical depth (AAOD) and absorption Angstrom exponent (AAE) were exploited. However, these two pieces of information are clearly not sufficient to separate properly carbonaceous aerosols from dust, while imaginary indices of refraction would contain more and better justified information for this purpose. This is first time that the direct radiative effect (DRE) of BrC is estimated by exploiting the AERONETretrieved imaginary indices. We estimated it for four sites in the Indo-Gangetic Plain (IGP), Karachi, Lahore, Kanpur and Gandhi College. We found a distinct seasonality, which was generally similar among all the sites, but with slightly different strengths. The monthly warming effect up to 0.5 W m −2 takes place during the spring season. On the other hand, BrC results in an overall cooling effect in the winter season, which can reach levels close to −1 W m −2 . We then estimated similarly also the DRE of black carbon and total aerosol, in order to assess the relative significance of the BrC radiative effect in the radiative effects of other components. Even though BrC impact seems minor in this context, we demonstrated that it is not insignificant. Moreover, we demonstrated that it is crucial to perform spectrally resolved radiative transfer calculations to obtain good estimates for the DRE of BrC.

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Non‐spherical aerosol retrieval method employing light scattering by spheroids

Cited by 431 publications

References 23 publications

Columnar aerosol single‐scattering albedo and phase function retrieved from sky radiance over the ocean: Measurements of Saharan dust

Columnar aerosol single‐scattering albedo and phase function retrieved from sky radiance over the ocean: Measurements of Saharan dust

Similarities and differences of aerosol optical properties between southern and northern sides of the Himalayas

Direct radiative effect by brown carbon over the Indo-Gangetic Plain

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