Chemical characterization of water-soluble aerosols in different residential environments of semi aridregion of India

This paper deals with the atmospheric concentrations of PM₅ and PM_2.5 particulate matter and its water soluble constituents along with the size distribution of ions and spatial variation at three different residential environments in a semiarid region in India. Samples were collected from the indoors and outdoors of urban, rural and roadside sites of Agra during October 2007–March 2008. The mean concentrations of PM_2.5 indoors and outdoors were 178 μgm⁻³ and 195 μgm⁻³ while the mean concentrations of PM₅ indoors and outdoors were 231.8 μgm⁻³ and 265.2 μgm⁻³ respectively. Out of the total aerosol mass, water soluble constituents contributed an average of 80% (33% anions, 50% cations) in PM₅ and 70% (29% anions, 43% cations) in PM_2.5. The indoor–outdoor ratio of water soluble components suggested additional aerosol indoor sources at rural and roadside sites. Indoor–outdoor correlations were also determined which show poor relationships among concentrations of aerosol ions at all three sites. Univariate Pearson correlation coefficients among water soluble aerosols were determined to evaluate the relationship between aerosol ions in indoor and outdoor air.     

IMF BY dependence of the extent of substorm westward electrojet

In this paper the duskward extension of the westward auroral electrojet is investigated for substorm intervals on the basis of magnetograms recorded at the Indian Antarctic station, Maitri. The database comprises three years from 1998–2000. Based on an initial study of the magnetograms, an arbitrary local time of 2030 MLT is fixed to define the early manifestation of the substorm westward electrojet. Using this criterion 12 substorms are identified and the possible causes examined. Many of these events are observed to be associated with a moderate to intense ring current. The hourly average of the GSM B_Y-component of the interplanetary magnetic field (IMF) for the hour preceding the substorm onset at Maitri is negative for most of the events. It is suggested that the azimuthal shift of the auroral electrojets in the southern hemisphere resulting from a negative B_Y-component of the IMF influences the extent of the substorm westward electrojet. This finding implies that the IMF may have a role in controlling the longitudinal extent of substorm occurrence.     

Chronology and petrogenesis of a 1.8 g lunar granitic clast:14321,1062

A study was undertaken to determine the chronology of a pristine granite clast (1062) from Apollo 14 breccia 14321 using Rb-Sr, Sm-Nd and ³⁹Ar-⁴⁰Ar methods. The genesis of the granite as constrained by the isotopic results and trace element characteristics is discussed.Chronology: The Rb-Sr internal isochron is slightly disturbed and yields an age of 4.09 ± 0.11 AE ($\text{λ(}{}^{87}\text{Rb) = 0.0139}\text{AE}{}^{\mathrm{?1}}$) and an imprecise initial I(Sr) = 0.702 ? .008. If two data are excluded, the age becomes 4.13 ± 0.03 AE and I(Sr) = 0.698 ? .003. The whole rock and mineral separates are extremely radiogenic; they yield model ages which are relatively well-defined. The average model age is 4.12 ± 0.03 AE (relative to BABI = 0.69898). The Sm-Nd internal isochron is also slightly disturbed and gives an age of 4.11 ± 0.20 AE ($\text{λ(}{}^{147}\text{Sm) = 0.00654}\text{AE}$^?1). The ³⁹Ar-⁴⁰Ar average age of the non-magnetic fraction of the sample yields a slightly younger age of 3.88 ± 0.03 AE (K-Ar constants from Steiger and $\text{>a}\text{?}$, 1977). The concordancy of Rb-Sr and Sm-Nd internal isochrons with the Rb-Sr model age strongly suggests that the granitic clast formed at 4.1 AE ago in the shallow crust and was later excavated and brecciated about 3.88 AE ago.Petrogenesis: Isotopic and trace element data of the lunar granite show large K/La and Rb/Sr fractionations, small Sm/Nd fractionation and the distinct V-shaped REE distribution pattern at the time of crystallization. A two-stage model involving crystal fractionation followed by silicate liquid immiscibility (SLI) is proposed for lunar granite genesis. We propose that the granite can be the immiscible acidic liquid produced by SLI from a residual liquid which underwent fractionation of ca, 3% of phases with REE distribution coefficients similar to those of phosphate minerals from a highly evolved parental magma with REE contents about twice those of the 15405,85 quartz monzodiorite (QMD).The extreme scarcity of lunar granitic samples and their young formation ages suggest that they are probably not directly crystallized from the differentiation of the primordial magma ocean. Our isotopic results and trace elements data from other workers suggest that granites, QMD and probably Mggabbronorites may be genetically related and may have formed in a plutonic environment similar to gabbro-granophyre associations in terrestrial layered intrusions such as the Skaergaard Intrusions.     

Stereo Cartosat-1 satellite remote sensing data in assessing topographic potential of soil erosion

Stereo Cartosat-1 satellite data was processed to generate high spatial resolution digital elevation model (DEM) using ground control points (GCPs) collected through geodetic single frequency GPS in differential GPS mode. DEM was processed to generate bare earth DEM by removing heights of natural and man made features from DEM. The bare earth DEM was further analysed in GIS environment to generate terrain-topographic indices viz. wetness index (WI), stream power index (SPI) and sediment transport index (STI) to characterize topographic potential of soil erosion. Hillslopes in the studied watershed (part of Shiwalik hills of Dehradun district, Uttarakhand state) were characterized as low wetness index values indicating dry areas whereas high wetness index values at lower reaches of the watershed indicating as possible source areas for generation of saturated overland flow. Higher STI values were observed in hilly as well as upper part of the piedmont plain and at along sides of the streams in upper piedmont indicating areas susceptible to severe soil erosion. GIS based these topographic indices provided an easy and quick appraisal and scientific basis to identify spatial variability of soil erosion risk in a hilly watershed.     

Risk characterization and surface water quality assessment of Manas River,Assam (India) with an emphasis on the TOPSIS method of multi-objective decision making

The present study centers on the investigation of surface water quality with the aid of quality indices and explores the application of a multi-objective decision-making method (TOPSIS) in arranging decisions for policy makers on the basis of overall ranking of the sampling locations. A case study has been performed on the Manas River, Assam (India). Water Quality Index (WQI) involving physico-chemical parameters, and heavy metal pollution index (HPI) and contamination index (CI) involving heavy metal influences were employed for water quality assessment. WQI graded two sampling locations “very poor” and all other locations “poor”. HPIs of all the locations were below the critical value of 100, but the CI depicted that two locations were “moderately contaminated”. Risk assessment to human health was done using hazard quotient and hazard index. Cluster analysis (CA) demonstrated site similarity by grouping the relatively more polluted and less polluted (LP) sites into two major clusters. However, there surfaced difficulty in discerning the overall water quality, as all the three quality indices included different parameters and contradicted each other. A multi-objective decision-making tool, TOPSIS was therefore employed for ranking the locations on the basis of their relative pollution levels. The novelty of the study reflects in the identification of the relatively more or relatively less polluted sites within the same cluster in CA by the application of TOPSIS. The study justifies the effectiveness of TOPSIS method in prioritizing decisions in complex scenarios for policy makers.     

Finite-difference modelling of S-wave splitting in anisotropic media

We have implemented a 3D finite‐difference scheme to simulate wave propagation in arbitrary anisotropic media. The anisotropic media up to orthorhombic symmetry were modelled using a standard staggered grid scheme and beyond (monoclinic and triclinic) using a rotated staggered grid scheme. The rationale of not using rotated staggered grid for all types of anisotropic media is that the rotated staggered grid schemes are more expensive than standard staggered grid schemes. For a 1D azimuthally anistropic medium, we show a comparison between the seismic data generated by our finite‐difference code and by the reflectivity algorithm; they are in excellent agreement. We conducted a study on zero‐offset shear‐wave splitting using the finite‐difference modelling algorithm using the rotated staggered grid scheme. Our S‐wave splitting study is mainly focused on fractured media. On the scale of seismic wavelenghts, small aligned fractures behave as an equivalent anisotropic medium. We computed the equivalent elastic properties of the fractures and the background in which the fractures were embedded, using low‐frequency equivalent media theories. Wave propagation was simulated for both rotationally invariant and corrugated fractures embedded in an isotropic background for one, or more than one, set of fluid‐filled and dry fractures. S‐wave splitting was studied for dipping fractures, two vertical non‐orthogonal fractures and corrugated fractures. Our modelling results confirm that S‐wave splitting can reveal the fracture infill in the case of dipping fractures. S‐wave splitting has the potential to reveal the angle between the two vertical fractures. We also notice that in the case of vertical corrugated fractures, S‐wave splitting is sensitive to the fracture infill.     

Modelling of magnetic data for scaling geology

Interpretation of magnetic data can be carried out either in the space or frequency domain. The interpretation in the frequency domain is computationally convenient because convolution becomes multiplication. The frequency domain approach assumes that the magnetic sources distribution has a random and uncorrelated distribution. This approach is modified to include random and fractal distribution of sources on the basis of borehole data. The physical properties of the rocks exhibit scaling behaviour which can be defined as P(k) = Ak^?β, where P(k) is the power spectrum as a function of wave number (k), and A and β are the constant and scaling exponent, respectively. A white noise distribution corresponds to β = 0. The high resolution methods of power spectral estimation e.g. maximum entropy method and multi‐taper method produce smooth spectra. Therefore, estimation of scaling exponents is more reliable. The values of β are found to be related to the lithology and heterogeneities in the crust. The modelling of magnetic data for scaling distribution of sources leads to an improved method of interpreting the magnetic data known as the scaling spectral method. The method has found applicability in estimating the basement depth, Curie depth and filtering of magnetic data.     

Mapping of magnetic basement in Central India from aeromagnetic data for scaling geology

The Central Indian region has a complex geology covering the Godavari Graben, the Bastar Craton (including the Chhattisgarh Basin), the Eastern Ghat Mobile Belt, the Mahanadi Graben and some part of the Deccan Trap, the northern Singhbhum Orogen and the eastern Dharwar Craton. The region is well covered by reconnaissance‐scale aeromagnetic data, analysed for the estimation of basement and shallow anomalous magnetic sources depth using scaling spectral method. The shallow magnetic anomalies are found to vary from 1 to 3 km, whereas magnetic basement depth values are found to vary from 2 to 7 km. The shallowest basement depth of 2 km corresponds to the Kanker granites, a part of the Bastar Craton, whereas the deepest basement depth of 7 km is for the Godavari Basin and the southeastern part of the Eastern Ghat Mobile Belt near the Parvatipuram Bobbili fault. The estimated basement depth values correlate well with the values found from earlier geophysical studies. The earlier geophysical studies are limited to few tectonic units, whereas our estimation provides detailed magnetic basement mapping in the region. The magnetic basement and shallow depth values in the region indicate complex tectonic, heterogeneity, and intrusive bodies at different depths, which can be attributed to different thermo‐tectonic processes since Precambrian.