Civil Engineering

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Shiv Nadar University

To investigate the potential role of ammonia in ion chemistry of PM2.5 aerosol, measurements of PM2.5 (particulate matter having aerodynamic diameter&lt;2.5μm) along with its ionic speciation and gaseous pollutants (sulfur dioxide (SO2), nitrogen oxides (NOx), ammonia (NH3) and nitric acid (HNO3)) were undertaken in two seasons (summer and winter) of 2007-2008 at four sampling sites in Kanpur, an urban-industrial city in the Ganga basin, India. Mean concentrations of water-soluble ions were observed in the following order (i) summer: SO42- (26.3μgm-3)&gt;NO3- (16.8)&gt;NH4+ (15.1)&gt;Ca2+ (4.1)&gt;Na+ (2.4)&gt;K+ (2.1μgm-3) and (ii) winter: SO42- (28.9μgm-3)&gt;NO3- (23.0)&gt;NH4+ (16.4)&gt;Ca2+(3.4)&gt;K+(3.3)&gt;Na+ (3.2μgm-3). The mean molar ratio of NH4+ to SO42- was 2.8±0.6 (mostly &gt;2), indicated abundance of NH3 to neutralize H2SO4. The excess of NH4+ was inferred to be associated with NO3- and Cl-. Higher sulfur conversion ratio (Fs: 58%) than nitrogen conversion ratio (Fn: 39%) indicated that SO42- was the preferred secondary species to NO3-. The charge balance for the ion chemistry of PM2.5 revealed that compounds formed from ammonia as precursor are (NH4)2SO4, NH4NO3 and NH4Cl. This study conclusively established that while there are higher contributions of NH4+, SO42- to PM2.5 in summer but for nitrates (in particulate phase), it is the winter season, which is critical because of low temperatures that drives the reaction between ammonia and HNO3 in forward direction for enhanced nitrate formation. In summary, inorganic secondary aerosol formation accounted for 30% mass of PM2.5 and any particulate control strategy should include optimal control of primary precursor gases including ammonia. © 2010 Elsevier B.V.

(SoE) School of Engineering

World University root node

Science of the Total Environment

Investigating the potential role of ammonia in ion chemistry of fine particulate matter formation for an urban environment

Total 360 samples (of 8 h each) of PM2.5 were collected from six sampling sites for summer and winter seasons in Kanpur city, India. The collected PM2.5 mass was subjected to chemical speciation for: (1) ionic species (NH+4, SO2-4, NO -3, and Cl-), (2) carbon contents (EC and OC), and (3) elemental contents (Ca, Mg, Na, K, Al, Si, Fe, Ti, Mn, V, Cr, Ni, Zn, Cd, Pb, Cu, As, and Se). Primary and secondary components of PM2.5 were assessed from speciation results. The influence of marine source to PM 2.5 was negligible, whereas the contribution of crustal dust was significant (10% in summer and 7% in winter). A mass reconstruction approach for PM2.5 could distinctly establish primary and secondary components of measured PM2.5 as: (1) Primary component (27% in summer and 24% in winter): crustal, elemental carbon, and organic mass, (2) Secondary component (45% in summer and 50% in winter): inorganic and organic mass, and (3) others: unidentified mass (27% in summer and 26% in winter). The secondary inorganic component was about 34% in summer (NH+4: 9%; SO 2-4: 16%; NO-3: 9%) and 32% in winter (NH+4: 8%; SO2+4: 13%; NO-3: 11%). The secondary organic component was 12% in summer and 18% in winter. In conclusion, secondary aerosol formation (inorganic and organic) accounted for significant mass of PM2.5 (about 50%) and any particulate control strategy should also include control of primary precursor gases. © 2010 American Association for Aerosol Research.

Fulltext

Aerosol Science and Technology

Reconstructing primary and secondary components of PM2.5 composition for an Urban Atmosphere

Natural soil deposits commonly exhibit cross-anisotropy about a vertical axis due to their depositional environment. This paper presents a study of the vertical stress distribution in a cross-anisotropic elastic soil deposit due to a point load. The study is based upon the exact solution derived by Liao and Wang (1998) that uses Fourier and Hankel transforms to solve the governing differential equations of the displacement functions. The solution has been first modified to consider a reduced parameter elastic model for cross-anisotropy as proposed by Graham and Houlsby (1983). The vertical stress distribution in the soil has been studied for a vertical point load with a varying degrees of anisotropy. © 2010 ASCE.

Geotechnical Special Publication

Vertical stress under point load on cross-anisotropic elastic half-space with reduced parameter material model

Design of many geotechnical problems, such as the stability of slopes and excavations, are strongly governed by the shear strength of soil represented in three dimensions. In literature, a number of failure criteria have been proposed using isotropic invariant of stress tensor in three dimensional stress spaces. For a linearly pressure-dependent material, there are four basic failure criteria which have been commonly used to describe the behavior; Mohr-coulomb, Drucker - Prager (1952), Lade and Duncan (1975), and Matsuoka and Nakai (1985). Mohr-Coulomb criterion is defined in a 2-D stress space and it follows plane strain condition. The other three which are 3-D failure criteria have been considered during this study for analysis. Calibration of such a model is relatively easy when the tests are performed in axisymmetric conditions and principal stresses are applied on the specimen, e.g. triaxial tests. This paper will present the solutions for calibrating such failure criteria assuming associative flow rule and using the shear strength parameter (ps) obtained from the laboratory tests performed under plane strain conditions e.g. Direct Shear and Simple Shear Test. © 2010 ASCE.

Calibration of 3-D failure criteria for soils using plane strain shear strength data

This manuscript presents a new multiscale framework for the analysis of failure of thin heterogeneous structures. The new framework is based on the asymptotic homogenization method with multiple spatial scales, which provides a rigorous mathematical basis for bridging the microscopic scales associated with the periodic microstructure and thickness and the macroscopic scale associated with the in-plane dimensions of the macrostructure. The proposed approach generalizes the Caillerie-Kohn-Vogelius elastostatic heterogeneous plate theory for failure analysis when subjected to static and dynamic loads. Inelastic fields are represented using the eigendeformation concept. A computationally efficient n-partition computational homogenization model is developed for simulation of large scale structural systems without significantly compromising on the solution accuracy. The proposed model is verified against direct 3D finite element simulations and experimental observations under static and dynamic loads. {\textcopyright} 2010 The Author(s).

A multiscale failure model for analysis of thin heterogeneous plates

The experimental findings on the mechanical behavior of clays with dispersed microfabric are indicative of the need for comprehensive evaluation of the constitutive theories being widely used in practice. The clay deposits can be found having all the stages of microfabrics in their natural state and the dispersed microfabric is one of those. Despite the fact that the effects of microfabric can be radical sometimes, those are seldom given due consideration during the design process. Since the success of numerical modelling of a geotechnical structure is strongly dependent on the accuracy of the constitutive equations, the results produced by commonly used constitutive models can be highly misleading. The present paper is focused on identifying such issues which make the study of dispersed clays important and show the need for incorporating the influence of microfabric into constitutive formulations. Two of the most widely known models, Modified Cam-Clay (MCC) model (Roscoe and Burland, 1968) and the single hardening (SH) model (Lade, 1990), have been calibrated for the Kaolin clay with dispersed microfabric and the predicted response has been compared with the experimental observations. This comparative study has been used to provide an insight into the important issues which still need attention.

12th International Conference on Computer Methods and Advances in Geomechanics 2008

Issues in modeling the stress-strain behavior of Kaolin clay with dispersed microfabric

We present a new multiscale model for failure analysis of thin composite structures. The present model is based on the asymptotic homogenization method with multiple spatial scales. The proposed approach is a generalization of the elastostatic Caillerie-Kohn-Vogelius theory to study the failure mechanics of thin composite plates under static and dynamic loads. We employ a model reduction methodology based on the eigendeformation concept to minimize the computational burden. An efficient n-partition computational homogenization model is developed for simulation of large scale structural systems without significantly compromising on the solution accuracy. The proposed model is verified against direct 3-D finite element simulations.

American Society for Composites - 23rd Technical Conference of the American Society for Composites 2008

A multiscale failure model for thin heterogeneous plates

Free-flow spillways are simpler and safer than gated ones, but the low specific flow of their traditional shapes requires high spilling nappe depths and thus huge losses of storage (100 × 109m3 worldwide). A newly evolved shape of free-flow spillway (the "Piano Key weir") has the potential to increase the specific flow as high as fourfold at lower discharges. It could substantially increase, at low cost, the safety and the storage and/or the flood control efficiency of many existing as well as new dams. It is thus very advantageous to increase the specific flow as much as possible. Some tens of existing spillways have been designed accordingly as vertical walls on a flat bottom, with a trapezoidal labyrinth layout which is much longer than the spillway length (often four times). They usually double the specific flow of an Ogee Spillway. Piano-Key Weir derives its name from its plan-form shape which looks like a 'piano-key'. It is configured as polygonal walls such as to provide a much longer crest length than the conventional ogee spillways. This paper presents experimental data analysis on this new (not patented) solution in order that: Increasing the storage of many irrigation dams is justified by the increased needs or due to the sedimentation of reservoirs. Increasing the spillage capacity is often justified by a better knowledge of hydrology. Improving flood mitigation by existing dams may be very cost effective. Positive outcome of this study will be very much relevant for dam safety concerns worldwide in the context of adverse hydrological consequences due to ongoing global warming phenomenon.