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Tiwari S.,Banaras Hindu University | Srivastava A.K.,Indian Institute of Tropical Meteorology | Singh A.K.,Banaras Hindu University | Singh S.,CSIRNational Physical Laboratory
Environmental Science and Pollution Research | Year: 2015

The aerosols in the Indo-Gangetic Basin (IGB) are a mixture of sulfate, dust, black carbon, and other soluble and insoluble components. It is a challenge not only to identify these various aerosol types, but also to assess the optical and radiative implications of these components. In the present study, appropriate thresholds for fine-mode fraction and single-scattering albedo have been used to first identify the aerosol types over IGB. Four major aerosol types may be identified as polluted dust (PD), polluted continental (PC), black carbon-enriched (BCE), and organic carbon-enriched (OCE). Further, the implications of these different types of aerosols on optical properties and radiative forcing have been studied. The aerosol products derived from CIMEL sun/sky radiometer measurements, deployed under Aerosol Robotic Network program of NASA, USA were used from four different sites Karachi, Lahore, Jaipur, and Kanpur, spread over Pakistan and Northern India. PD is the most dominant aerosol type at Karachi and Jaipur, contributing more than 50 % of all the aerosol types. OCE, on the other hand, contributes only about 12–15 % at all the stations except at Kanpur where its contribution is ∼38 %. The spectral dependence of AOD was relatively low for PD aerosol type, with the lowest AE values (<0.5); whereas, large spectral dependence in AOD was observed for the remaining aerosol types, with the highest AE values (>1.0). SSA was found to be the highest for OCE (>0.9) and the lowest for BCE (<0.9) type aerosols, with drastically different spectral variability. The direct aerosol radiative forcing at the surface and in the atmosphere was found to be the maximum at Lahore among all the four stations in the IGB. © 2015, Springer-Verlag Berlin Heidelberg.

Shankar A.,CSIRNational Physical Laboratory | Shankar A.,Netaji Subhas Institute of Technology | Chand M.,CSIRNational Physical Laboratory | Sonia,CSIRNational Physical Laboratory | And 2 more authors.
Advanced Science Letters | Year: 2014

A stable kerosene based ferrofluid having magnetite nanoparticles (∼10 nm) coated with oleic acid as primary was synthesized by coprecipitation route. The Rietveld refinement of XRD pattern of Fe3O4 nanoparticles was carried out using Fullprof. The Williamson-Hall method gives 10.2(3) m and 0.002(1) as average crystallite size and strain respectively. The HRTEM image shows that particles are nearly spherical in shape. The room temperature magnetic measurements shows the superparamagnetic nature of the fluid. Using modified Langevin function, the average particle size was found to be 9.8(2) nm with 0.5 as standard deviation. The low temperature ESR measurements were performed in the temperature range 4 K–300 K using zero-field cooled (ZFC) protocol. The deconvolutions of the spectra suggest coexistence of two different resonance modes; i.e., a broad resonance signal superimposed by a sharp signal. This observation is consistent for temperature range 200 K– 300 K. The behavior of resonance field, linewidth and intensity shows a characteristic spin-glass state near to 190 K. © 2014 American Scientific Publishers All rights reserved.

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