Optical properties of accumulation mode, polluted mineral dust: effects of particle shape, hematite content and semi-external mixing with carbonaceous species

Abstract

A B S T R A C T The morphology, mixing state and hematite content of polluted mineral dust are not well accounted in the optical models and this leads to uncertainty in the radiative forcing estimation. In the present study, based on the morphological and mineralogical characterisation of polluted dust, the three-sphere, two-sphere and twospheroid model shapes are considered. The optical properties of the above model shapes are computed using Discrete Dipole Approximation code. The single scattering albedo, v 0 , was found to vary depending on hematite content (0Á6%) and model shape. For the two-sphere BC-mineral dust system, hematite was found to be a dominating absorber compared to that of black carbon as the R BC /R dust decreases. The v 0 of the polluted dust system is larger if polluted dust is considered as pure dust spheroid (with 4% hematite) while smaller value is observed for Q ext . Among all the systems, the v 0 of BCBCD (two BC spheres attached to one dust sphere) system showed the maximum departure (40 and 35% for polluted dust with 0 and 6% hematite, respectively) from that of pure dust spheroid with 0 and 6% hematite. For the Asian region (pollution-prone zone), the modelled polluted dust optics will help to trace the optical and radiative properties of dust.

Bulk Level to Individual Particle Level Chemical Composition of Atmospheric Dust Aerosols (PM5) over a Semi-Arid Urban Zone of Western India (Rajasthan)

“…With rapid development and urbanization of the state, mineral dust can get mixed with local pollution and that can significantly alter their optical properties (Mishra et al, 2012). State capital of Rajasthan, Jaipur (26.89°N, 75.81°E), also popularly known as Pink city is surrounded by several old forts situated on the medium scale barren mountains such as Amber, Jaigarh, Nahargarh of varying altitude ranging from 500-1000 m from ground level.…”

“…Subsequently, Mishra et al (2008b) also assessed the effect of mineral dust particle composition and shape on radiative forcing of dust aerosols. Recently Mishra et al (2012) further studied effects of particle shape, hematite content and semi-external mixing with carbonaceous species.…”

Chemical Characterization of Summertime Dust Events at Kanpur: Insight into the Sources and Level of Mixing with Anthropogenic Emissions

“…A large number of studies on mineral dust and dust storms have been carried out in different parts of India (Kumar and Sarin, 2009;Rastogi and Sarin, 2009) but most of these studies (Dey et al, 2004;Mishra et al, 2012) have only discussed the optical properties of mineral dust in the Indo-Gangetic Plain. Very little investigation has been carried out on the chemical properties of crustal/mineral dust in Kanpur region (Chinnam et al, 2006;Chakraborty and Gupta, 2010).…”

Perturbations of the optical properties of mineral dust particles by mixing with black carbon: a numerical simulation study

“…Different field studies show AR median values ranging between 1.4 and 1.9 (Chou et al, 2006;Clarke et al, 2004;Reid et al, 2003;Kandler et al, 2006;Dubovik et al, 2006;Mishra et al, 2012). In this study, we modeled dust aerosols as spheroids and rectangular prisms with an intermediate aspect ratio (compared to the refereed literature) of 1.75, which has also been found in CARES, PICO, MILA-GRO and the ClearfLo field campaigns (see Table 3).…”

“…Internal mixing of mineral dust and BC aggregates has a strong impact on the optical properties of originally externally mixed aerosol, on their radiative forcing (Mishra et al, 2012;Sokolik et al, 2001) and on spatial and temporal distribution of precipitations, for example during the monsoon in Asia (Lau and Kim, 2006) or the African jet streams (Reale et al, 2011). …”