Department of Civil & Infrastructure Engineering

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This study examines the light absorption characteristics of fine atmospheric particulates using the co-located real-time measurements of chemical and optical aerosol characteristics at a site located in Delhi during winter. The contribution of absorption by black carbon and brown carbon (BC and BrC) to the total absorption (babs) is computed using the absorption Ångström exponent (AAE) method. The period average contribution of BrC absorption (babs_BrC) to babs is found to be highest at 370 nm (23%) that decreased exponentially with increasing wavelengths, i.e.,18, 12, 10, and 4% at 470, 520, 590, and 660 nm, respectively. The absorption spectrum of BrC is used to study the bulk composition of BrC, which indicates that primary BrC was dominant during morning and night time, whereas secondary BrC was significant during the rest of the time. Further, organic aerosols (OA) were divided into different factors using positive-matrix factorization (PMF) analysis, and the mass absorption efficiency (Eabs) of each factor was assessed through multivariate linear regression of babs_BrC with OA factors. The biomass burning OA (BBOA) exhibited the highest Eabs at 370 nm (0.86 m2 g−1), followed by semi-volatile oxygenated OA (SVOOA; 0.67 m2 g−1) and hydrocarbon-like OA (HOA; 0.42 m2 g−1). Further, although the composition of OA was dominated by LVOOA (32%) and BBOA (32%), followed by SVOOA (22%), and HOA (14%), their contribution to bBrC followed different order due to differences in their mass absorption efficiencies. The BBOA contributed almost half (48%) of babs_BrC followed by SVOOA (26%), and HOA (10%). This study provides quantitative information on the sources of BrC and their relative contribution to BrC absorption over a heavily polluted region, which is still lacking in the literature. These results have implications in understanding the source-specific BrC absorption. © 2021 Elsevier Ltd

World University root node

Atmospheric Environment

Sources and characteristics of light-absorbing fine particulates over Delhi through the synergy of real-time optical and chemical measurements

This paper proposes a continuum model based on a three-dimensional flow-concentration surface for multi-class traffic. The model assumes that the flow of any vehicle class is a function of the class density as well as the fraction of road area occupied by other vehicle classes. By considering occupancy of road area instead of lane occupancy, the model effectively describes traffic flow that does not follow lane discipline. The propagation speed of small disturbance (PSSD), conventionally defined from the two-dimensional flow–density relationship, is reformulated for each class using a three-dimensional flow–concentration surface. Using the proposed PSSD and a speed–area occupancy (speed-AO) relationship, a second-order continuum model for multi-class traffic is formulated. The speed–AO relationship captures class-specific congestion and replicates the gap-filling behaviour commonly observed in lane-indisciplined traffic. Properties of the proposed model are validated theoretically where possible, and through numerical simulation when theoretical derivations are cumbersome. Numerical simulation of the proposed multi-class traffic model replicates field-observed phenomena such as shockwaves and rarefaction waves, local cluster effect, and gap-filling behaviour. Finally, the model is calibrated using field traffic data collected on a road section with bottleneck, and is found to replicate class-wise vehicle flows and speeds, and stop-and-go phenomena. © 2021 Elsevier B.V.

Physica A: Statistical Mechanics and its Applications

Multi-class traffic flow model based on three dimensional flow–concentration surface

Delhi is one of the most polluted cities globally, with frequent severe air pollution episodes and haze events occurring in recent years, thereby compelling us to understand the sources to develop effective mitigation plans. Complete chemical characterization of fine particulate matter (PM2.5) components (non-refractory, refractory and elements) with high time resolution has been done during the summer season (June-July 2019). The total PM equivalent (PM2.5(eq)) was 28.7 +/- 13.2 mu g m(-3) of which elements dominated the PM2.5(eq) with 34\% contribution followed by organics (28\%), black carbon (BC) (17\%), SO42- (10\%), Cl- (5\%) NH4+ (3.5\%) and NO3(2.5\%). The contributions from organic aerosols (OA) and SO42- were observed to be more than Cl- and NO3- . The total elemental mass concentration (PMEl) was mostly contributed (similar to 96\%) by Si, S, Cl, Ca, K, Fe and Al with Si and S alone contributing around 50\% of PMEl. Crustal elements (Al, Fe, Ca and Si) were highly enhanced in summer than elements emitted from anthropogenic emissions (Cl, S, K, Pb and Zn). Source apportionment (SA) of PM was performed using positive matrix factorization (PMF) together with ME-2 (multilinear engine) for OA and elements, separately. PMF on both datasets helped resolve sources such as combustion, industrial, dust-related, incineration and traffic. OA PMF identified three factors related to primary emissions: hydrocarbon-like OA (HOA, 12.3\%), solid fuel combustion (SFC, 16.2\%) and cooking OA (COA, 7.3\%) and two oxygenated OA (OOA): semi-volatile OOA (SVOOA, 15.2\%) and low-volatile OOA (LVOOA, 49.1\%). The elemental PMF resolved 8 factors: dust (52.5\%), S-rich (16.2\%), Cl-rich (10.7\%), 2 SFC factors (10.5\%), non-exhaust (7.2\%), Cu-rich (1.5\%) and industrial (1.4\%). The contribution of BC to total PM mass is shown to increase in the summer compared to previous studies reported for the winter season. The secondary oxidized sources dominated both the OA and elements SA during the summer with 64.3\% and 27\% (dust not considered) contribution, respectively. The domination of secondary sources implies that it is crucial to control the secondary aerosols' precursors in Delhi for developing pollution control strategies. The ME-2 resolved factors, coupled with concentration weighted trajectory (CWT) showed the probable major elemental source regions of local origin (Delhi-National Capital Region (Delhi-NCR)) as well as regional (from Punjab, Haryana, Uttar Pradesh and Pakistan). The local sources included Cu-rich (Haryana) and SFC-II (Delhi and Uttar Pradesh), while the regional sources were dust (southwest (SW)), industrial, Cl-rich (north-west (NW)), SFC-I (east and south-east (SE)) and S-rich (SE).

ATMOSPHERIC ENVIRONMENT

Real-time quantification and source apportionment of fine particulate matter including organics and elements in Delhi during summertime

Using polymer modification and warm mix modification together can result in modified binders having superlative performance along with normal mixing and compaction temperature. Over the decades, different experimental methods have been used to study rutting and fatigue performances of asphalt binders and mixes. Currently, advanced performance evaluation tests like multiple stress creep and recovery, linear amplitude sweep, wheel rut tester, and four-point bending beam test are being used. In the present study, warm mix polymer modified binder was prepared by using both polymer modifier, i.e. styrene butadiene styrene and warm mix modifier, i.e. zycotherm together. Then by using these advanced tests, rutting and fatigue performances of asphalt binder and mix were evaluated at different stress levels and temperatures. A correlation was established between the asphalt binder and mix performance. Stress susceptibility was also evaluated. Using both the modification methods did not show any compatibility problems. Mixes prepared using warm mix polymer modified binder were found to have improved performance along with lower production temperature. further performance evaluation tests of asphalt binder and mixes were found to have a very good correlation with each other. © 2021 Informa UK Limited, trading as Taylor & Francis Group.

International Journal of Pavement Engineering

Investigating the performance of polymer and warm mix modified asphalt binders and mixtures

Changes in mean and extreme precipitation characteristics with changing climate may lead to an increase in frequency of hydrological extremes. For studying the impacts of the changing climate on hydrological systems, General Circulation Model (GCM)/Regional Climate Model (RCM) simulated precipitation are used. However, these products should be bias-corrected before used in hydrological simulations to predict hydrological extremes. Most of the existing bias-correction techniques suffer from either of two limitations – (a) they only reduce bias in selected precipitation quantile (either mean or extreme values), and/or (b) they exclude zero values from the analysis, even though their presence is significant in daily precipitation. In this study, a stochastic copula-based bias-correction method (Maity et al., J. Hydrometeorol., 20, 2019, 595), henceforth RMPH method, is used that corrects the bias in any quantile (mean and/or extreme values) of daily precipitation including zero values. The RMPH method is applied across Indian mainland to correct bias in simulated precipitation from the Coordinated Regional Climate Downscaling Experiment (CORDEX). Due to diverse climatic conditions across India, the quality of bias-corrected precipitation is studied separately for different meteorologically homogenous regions of the country. Despite non-uniform distribution of raingauge stations for observed precipitation, the superiority of the bias-corrected precipitation (from RMPH method) in correcting bias and retaining the seasonal variation across the country is evident when compared with tradition bias-correction approach like quantile mapping. The new bias-corrected precipitation dataset developed is particularly suited for hydrological simulations, formulating extreme event mitigation strategies and climate change adaptation strategies. © 2021 The Authors. Geoscience Data Journal published by Royal Meteorological Society and John Wiley & Sons Ltd.

Geoscience Data Journal

Precipitation of Mainland India: Copula‐based bias‐corrected daily CORDEX climate data for both mean and extreme values

Most of the existing studies on meteorological drought suggest more intense and frequent drought events due to changing climate. However, basin-scale assessment of future agricultural drought is lacking due to many reasons. In this study, the intensity and frequency of future agricultural drought (characterized by the Standardized Soil Moisture Index, SSMI) for 226 sub-basins across India are analyzed, and vulnerable basins are identified. The prediction of the future agricultural drought status is achieved using the wavelet-based drought temporal consequence modeling of meteorological drought with the best performing bias-corrected Coordinated Regional Downscaling Experiment (CORDEX) simulations, selected by Multi-Criteria Decision-Making frameworks. This study reveals a geographically contrasting change in future agricultural drought that indicates more intense agricultural drought in north, north-east, and central India as compared with south India. The area under drought is also expected to increase, and about 20 and 50% of the Indian mainland is expected to suffer from extreme (SSMI < 2) and moderate (SSMI < 1) agricultural drought conditions by the end of this century. Sub-basins lying in north and central India are expected to have a longer time under drought conditions. Thus, the findings of this study will be useful for future planning and preparedness against agricultural productivity. © 2021 The Authors.

Journal of Water and Climate Change

Assessment of basin-wise future agricultural drought status across India under changing climate

It is known that some organic materials show a good capacity for selective removal of Cr(VI) from contaminated water; however, the exact mechanism of such removal has yet to be investigated and established. In this study, coconut husk, a waste material with no or low cost, has been used as a representative material to investigate the exact mechanism of Cr(VI) removal by organic matter from synthetic wastewater. The investigation has been carried out in two significant stages. First, the adsorption phenomenon was studied using batch kinetic and column studies to determine the isotherms and kinetic models and effects of process parameters like solution pH and contact time. 100% Cr(VI) removal was achieved at pH 2 within 30 min at a stirring rate of 300 rpm. Although an impressive adsorption capacity of 222.22 mg/g was calculated using the Langmuir model, there was a poor fit of the observed data with the known adsorption models, leading to the inference that the mechanism of removal involved processes other than simple adsorption. The virgin and exhausted material were further characterized using field emission-scanning electron microscope (FE-SEM), thermal analysis, Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). From the characterization results, it was found that Cr(VI) was first adsorbed at the functional groups followed by oxidation of major components like hemicelluloses, cellulose, and lignin, present in the adsorbent, resulting in the formation of ethers, carboxylic groups, and other carbonyl functionalities. Cr(VI) itself got reduced to Cr(III) and precipitated as Cr(OH)3 inside the pores of the adsorbent. The study conclusively established that Cr(VI) removal by organic matters such as coconut husk is essentially a sorption coupled redox process. © 2021

Journal of Cleaner Production

Comprehensive investigation of the mechanism for Cr(VI) removal from contaminated water using coconut husk as a biosorbent

Numerical modeling of upstream propagation of a positive surge wave in an open-channel flow caused by a sudden rise of downstream water level, either by gate operation or by tidal influence, remains an important challenge from many aspects. A perusal of literature suggests that the Serre-Green-Naghdi (SGN) models have not been methodically explored for a positive surge flow modeling. In this study, the SGN equations for variable bed profiles are solved for simulating the positive surge waves. The governing equations are reformulated in the form of a conservation law, which is solved using a hybrid finite volume-finite difference method. The eddy-viscosity type wave breaking model is coupled with the governing equations for simulating a breaking surge. The performance of second- and fourth-order time stepping schemes and second- and fourth-order accurate schemes for determining the numerical flux is assessed. The results indicate that using an overall fourth-order accurate scheme is preferred for an accurate depiction of the positive surge waves. A comparison is also made with laboratory observations from a wide range of experiments conducted under different discharge, Froude number and bed slope conditions, which demonstrates that the proposed model can accurately reproduce the key free surface characteristics corresponding to positive surge waves. The importance of computing an accurate initial gradually varied flow profile before applying the transient downstream condition, such as a gate closure, is highlighted. Further, the significance of considering full non-linearity is demonstrated through numerical tests as the weakly non-linear Boussinesq-type equations are found to perform poorly in predicting the secondary undulations for an undular surge. The non-hydrostatic pressure field occurring during the propagation of an undular surge has rarely been reported from laboratory experiments. In this study, the bed pressure beneath a propagating undular surge is measured and compared with that computed according to the SGN equations. Finally, the results obtained from the proposed SGN model are compared with those obtained from Large Eddy Simulation results available in the literature. © 2021

Applied Mathematical Modelling

Modeling positive surge propagation in open channels using the Serre-Green-Naghdi equations

Turbulent flow characteristics over an abrupt step change in bed roughness from smooth to rough are studied measuring the flow field by a Particle Image Velocimetry (PIV) system. The smooth and rough beds are referred to as the upstream and downstream beds, respectively. The velocity color maps and profiles show that an abrupt step change in bed roughness causes flow retardation in the downstream bed owing to the combined effects of roughness-induced and separated flows. The results of the Reynolds stresses reveal that the profiles in the downstream bed exhibit discriminable bulges, whose size increases with an increase in the streamwise distance. The stress color maps illustrate the creation of a roughness-induced layer that grows over the downstream bed as the streamwise distance increases. The bed shear stress evidences an overshooting behavior immediate downstream of the abrupt step change in bed roughness to reach its peak magnitude. The third-order correlations indicate that the effects of the abrupt step change in bed roughness produce an inrush of rapidly moving fluid streaks in the near-bed flow and arrival of slowly moving fluid streaks in the away-bed flow. Regarding the turbulent kinetic energy (TKE) budget, the enhanced magnitudes of the TKE budget terms within the roughness-induced layer are prevalent. The TKE dissipation rate lags the production rate, and the negative TKE diffusion rate implies an addition in the TKE production. Bursting analysis endorses that the sweeps govern the near-bed flow on the downstream bed and the ejections prevail far from the bed. © 2021 Author(s).

Physics of Fluids

Turbulent flow characteristics over an abrupt step change in bed roughness

Turbulence characteristics in a fully developed flow over a gradually varied bed roughness are investigated. The results of the Reynolds stress profiles indicate that they increase with an increase in bed roughness height. Their peaks occur within the wall-shear layer close to the bed. Besides, the bed shear stress rises in accordance with the roughness height. The roughness-induced layer grows as the roughness height increases with the streamwise distance. The velocity profiles fitted with the logarithmic law reveal that the zero-velocity level is elevated as the roughness height increases, but the zero-plane displacement is not influenced by the roughness. The turbulent kinetic energy (TKE) flux results indicate that an inrush of faster moving fluid parcels composing the sweep event is the dominant mechanism in the near-bed flow zone. The magnitude of the sweep event escalates, as the roughness height increases. On the other hand, a process of slowly moving fluid parcels forming the ejection event prevails in the outer flow layer. The TKE flux results agree with those obtained from the bursting analysis. Concerning the TKE budget, the peaks of the TKE production, dissipation, and pressure energy diffusion rates being positive appear near the bed and grow as the roughness height increases, whereas the peak of the TKE diffusion rate being negative behaves in the similar way as the other terms of the TKE budget behave. © 2021 Author(s).