Browsing by Author "Ram S. Singh"

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Aerosol chemistry, transport, and climatic implications during extreme biomass burning emissions over the Indo-Gangetic Plain
(Copernicus GmbH, 2018) Nandita Singh; Tirthankar Banerjee; Made P. Raju; Karine Deboudt; Meytar Sorek-Hamer; Ram S. Singh; Rajesh K. Mall
The large-scale emissions of airborne particulates from burning of agricultural residues particularly over the upper Indo-Gangetic Plain (IGP) have often been associated with frequent formation of haze, adverse health impacts, and modification in aerosol climatology and thereby aerosol impact on regional climate. In this study, short-term variations in aerosol climatology during extreme biomass burning emissions over the IGP were investigated. Sizesegregated particulate concentration was initially measured and submicron particles (PM1:1) were found to dominate particulate mass within the fine mode (PM2:1). Particulatebound water-soluble ions were mainly secondary in nature and primarily composed of sulfate and nitrate. There was evidence of gaseous NH3 dominating neutralization of acidic aerosol species (SO2- 4 ) in submicron particles, in contrast to crustal-dominating neutralization in coarser particulates. Diurnal variation in black carbon (BC) mass ratio was primarily influenced by regional meteorology, while gradual increase in BC concentration was consistent with the increase in Delta-C, referring to biomass burning emissions. The influence of biomass burning emissions was established using specific organic (levoglucosan), inorganic (K+ and NH+ 4), and satellite-based (UV aerosol index, UVAI) tracers. Levoglucosan was the most abundant species within submicron particles (649±177 ngm-3), with a very high ratio (> 50) to other anhydrosugars, indicating exclusive emissions from burning of agriculture residues. Spatiotemporal distribution of aerosol and a few trace gases (CO and NO2) was evaluated using both spaceborne active and passive sensors. A significant increase in columnar aerosol loading (aerosol optical depth, AOD: 0.98) was evident, with the presence of absorbing aerosols (UVAI > 1.5) having low aerosol layer height (∼1:5 km). A strong intraseasonality in the aerosol cross-sectional altitudinal profile was even noted from CALIPSO, referring to the dominance of smoke and polluted continental aerosols across the IGP. A possible transport mechanism of biomass smoke was established using cluster analysis and concentration-weighted air mass back trajectories. Short-wave aerosol radiative forcing (ARF) was further simulated considering intraseasonality in aerosol properties, which resulted in a considerable increase in atmospheric ARF (135Wm-2) and heating rate (4.3Kday-1) during extreme biomass burning emissions compared to the non-dominating period (56Wm-2, 1.8Kday-1). Our analysis will be useful to improve understanding of short-term variation in aerosol chemistry over the IGP and to reduce uncertainties in regional aerosol-climate models. © 2018 Author(s).
Community structure of methanogenic archaea and methane production associated with compost-treated tropical rice-field soil
(2012) Alpana Singh; Ram S. Singh; Siddh N. Upadhyay; Chaitanya G. Joshi; Ajay K. Tripathi; Suresh K. Dubey
The diversity and density of methanogenic archaea and methane production were investigated ex situ at different growth stages of rice plant cultivated in compost-treated tropical rice fields. The qPCR analysis revealed variation in methanogens population from 3.40 × 106 to 1.11 × 107 copies g-1 dws, in the year 2009 and 4.37 × 106 to 1.36 × 107 copies g-1 dws in the year 2010. Apart from methanogens, a large number of bacterial (9.60 × 109-1.44 × 1010 copies g-1 dws) and archaeal (7.13 × 107-3.02 × 108 copies g-1 dws) communities were also associated with methanogenesis. Methanogen population size varied in the order: flowering > ripening > tillering > postharvest > preplantation stage. The RFLP-based 16S rRNA gene-targeted phylogenetic analysis showed that clones were closely related to diverse group of methanogens comprising members of Methanomicrobiaceae, Methanosarcinaceae, Methanosaetaceae and RC I. Laboratory incubation studies revealed higher amount of cumulative CH4 at the flowering stage. The integration of methanogenic community structure and CH4 production potential of soil resulted in a better understanding of the dynamics of CH4 production in organically treated rice-field soil. The hypothesis that the stages of plant development influence the methanogenic community structure leading to temporal variation in the CH4 production has been successfully tested. © 2012 Federation of European Microbiological Societies.
Degradation kinetics and metabolites in continuous biodegradation of isoprene
(Elsevier Ltd, 2016) Navnita Srivastva; Ram S. Singh; Siddh N. Upadhyay; Suresh K. Dubey
The kinetic parameters of isoprene biodegradation were studied in a bioreactor, comprising of bioscrubber and polyurethane foam packed biofilter in series and inoculated with Pseudomonas sp., using a Michaelis-Menten type model. The maximum elimination capacity, ECmax; substrate constant, Ks and ECmax/Ks values for bioscrubber were found to be 666.7 g m-3 h-1, 9.86 g m-3 and 67.56 h-1, respectively while those for biofilter were 3333 g m-3 h-1, 13.96 g m-3 and 238.7 h-1, respectively. The biofilter section exhibited better degradation efficiency compared to the bioscrubber unit. Around 62-75% of the feed isoprene got converted to carbon dioxide, indicating the efficient capability of bacteria to mineralize isoprene. The FTIR and GC-MS analyses of degradation products indicated oxidative cleavage of unsaturated bond of isoprene. These results were used for proposing a plausible degradation pathway for isoprene. © 2016 Elsevier Ltd.
Efficacy of wood charcoal and its modified form as packing media for biofiltration of isoprene
(Academic Press, 2017) Navnita Srivastva; Ram S. Singh; Suresh K. Dubey
The efficacy of wood charcoal (WC) and nutrient-enriched wood charcoal (NWC) as biofilter packing media were assessed for isoprene biodegradation in a bioreactor comprising bioscrubber and a biofilter connected in series and inoculated with Pseudomonas sp. The bioreactors using WC and NWC exhibited >90% removal efficiency and around 369 g m−3 h−1 elimination capacity at around 404 g m−3 h−1 inlet loading rate. In both the bioreactors, the biofilter component showed better degradation capacity compared to the bioscrubber unit. The kinetic parameters, maximum elimination capacity, ECmax; substrate constant, Ks and ECmax/Ks for Michaelis-Menten model were evaluated. The lower Ks for the WC packed bioreactor indicated that ECmax achieved, was faster compared to others, while higher ECmax and ECmax/Ks for the NWC packed bioreactor suggests its superiority in isoprene abatement in the continuous mode. A comparison of the available published information on biofiltration of isoprene reflected polyurethane foam as the superior packing media. © 2017 Elsevier Ltd
Ethanolysis of 4- (N, N-dimethylaminomemylene)-2-aryl-2-oxazolin-5-ones with sodium ethoxide in ethanol at reflux temperature: Unusual formation of N-acyl-α-amino acids
(1998) Ram S. Singh
The ethanolysis of 4-(N, N - dimethylaminomethylene)-2-aryl-2-oxazolin-5-ones 1 with sodium ethoxide in ethanol at reflux temperature leads to the formation of N-acyl-α-amino acids 3. Further, the reaction of 4-hydroxymethylene-2-phenyl-2-oxazolin-5 one 4 with sodium ethoxide in ethanol at reflux temperature also gives product 3a. The plausible mechanism has been proposed.
Long-term observation of black carbon aerosols at an urban location over the central Indo-Gangetic Plain, South Asia
(Universidad Nacional Autonoma de Mexico, 2019) Sambhawika Srivastava; Manish Kumar; Ram S. Singh; Birendra N. Rai; Rajesh K. Mall; Tirthankar Banerjee
The first ever long-term measurement of black carbon (BC) aerosols over an urban location at the central Indo-Gangetic Plain (IGP) is presented. Both short- and long-term variations in BC during the period 2009-2013 are discussed with specific emphasis on variation in BC sources, meteorology, trend and possible transport pathways across the IGP. High BC mass loading was noted with a 5-yr composite mean (± SD) of 11.8 (± 8.6) μg m-3, having strong and consistent seasonal variations (median: 8.8; range: 1.4-48.0 μg m-3). Winter (21.5 ± 9.9μ gm-3) and post-monsoon (17.4 ± 10.2 μg m-3) specific rises in BC mass were consistent with the increase in household emissions, and from agricultural residue burning. The BC mass concentration was mostly influenced by local sources, while sudden change in BC was consistent with the change in Delta-C, indicating emissions primarily from biomass burning. Beside sources, atmospheric boundary layer height was noted to considerably influence short-term variations in BC concentration. A statistically significant monotonic increasing trend in BC concentration (0.9 μg m-3 yr-1) was computed along with its 95% uncertainty bounds (0.38-1.52 μ gm-3 yr-1). Increase in BC concentration was consistent with a rise in BC sources across the IGP and over India. Furthermore, clear evidence of local and regional scale transport of BC aerosols was found using the particle Lagrangian model. © 2019 Universidad Nacional Autónoma de México, Centro de Ciencias de la Atmósfera.; Se presentan las primeras mediciones a largo plazo de aerosoles de carbono negro (CN) en una ubicación urbana de la llanura indogangética media (IGP, por sus siglas en inglés). Tanto las variaciones a corto como a largo plazo en CN de 2009 a 2013 se analizan con énfasis específico en la variación de las fuentes de CN, la meteorología, la tendencia y el posible mecanismo de transporte a través de la IGP. Se observó una carga de CN excepcionalmente alta con una media (± DE) de 11.8 (± 8.6), con un patrón estacional fuerte y constante (mediana: 8.8; rango: 1.4-48.0 μg m-3). El aumento específico en el invierno (21.5 ± 9.9 μg m-3) y la temporada post monzón (17.4 ± 10.2 μg m-3) fue consistente con el aumento de las emisiones domésticas y la quema de residuos agrícolas. La masa de CN fue influenciada principalmente por fuentes locales, mientras que el cambio repentino en la concentración de CN fue consistente con el cambio en Delta-C, lo cual indica que las emisiones provienen principalmente de fuentes biogénicas de CN. Además de las fuentes, la altura de la capa límite atmosférica influyó considerablemente en la carga de CN. También se calculó una tendencia creciente monotónica estadísticamente significativa en la concentración de CN (0.9 μg m-3 yr-1) junto con sus correspondientes límites de incertidumbre de 95% (0.38-1.52 μg m-3 yr-1). Tal aumento gradual en CN fue consistente con el aumento potencial en sus fuentes. Además, se encontró evidencia clara del transporte local y regional de aerosoles de utilizando el modelo lagrangiano de partículas. © 2019 Universidad Nacional Autónoma de México, Centro de Ciencias de la Atmósfera.
Methyl 3-arylamino-2-benzoylaminopropenoates in the synthesis of 4- arylaminomethylene-2-phenyl-2-oxazolin-5-ones: Unexpected formation of bis- oxazolones
(1999) Manoj K. Singh; Ram S. Singh; Radhey M. Singh
The reaction of methyl 3-arylamino-2-benzoylaminopropenoates 2 with phosphorus oxychloride in pyridine at 70°C for 30 min leads to the unexpected formation of N-aryl-N-bis-(5-oxo-2-phenyl-4, 5- dihydro-oxazol-4- ylmethylene) amines 4. In contrast, 4-arylaminomethylene-2-phenyl-2-oxazolin- 5-ones 3 are obtained in only 2 min from compounds 2 under similar reaction conditions, which subsequently give compounds 4 on treatment with POCl3 in pyridine. A tentative mechanism to account the following conversion is suggested.
Reaction of 4-substituted aminomethylene-2-phenyl-2-oxazolin-5-ones with primary amines
(1997) Manoj K. Singh; Kumar K. Singh; Ram S. Singh; Radhey M. Singh
The regioselective reactions of 4-(N,N-dimethyIaminbmethylene)-2-phenyl-2-oxa2olin-5-one 2b and 4-anilinomethylene-2-phenyl-2-oxazolin-5-one 2c with primary alkyl amines in acetonitrile afford the corresponding 4-alkylaminomethylene-2-oxazolin-5-ones 4 in excellent yields. Oxazolones 2b and 2c are resistant to aminolysis with primary aryl amines. However, compound 2c gives 3-anilino-2-benzoylaminoacrylanilide 9 with aniline in acetonitrile containing catalytic amount of acetic acid, via 1, 5-bond cleavage. The regioselectivity is explained by the hard-soft acid-base (HSAB) principle.
Temporal evolution of submicron particles during extreme fireworks
(Springer International Publishing, 2019) Sunil K. Yadav; Manish Kumar; Yashasvi Sharma; Prashant Shukla; Ram S. Singh; Tirthankar Banerjee
Evolution of submicron particles in terms of particle number concentration and mobility-equivalent diameter was measured during Diwali festival–specific intensive pyrotechnic displays in Varanasi over central Indo-Gangetic Plain (IGP). A scanning mobility particle sizer coupled with an optical particle sizer was used to fit in an overlapping size range, and particle number concentration was analyzed to have an insight into the new particle formation and subsequent evolution of particles from nucleation to accumulation mode. Further, variation in black carbon (BC) concentration and aerosol ionic composition was measured simultaneously. Frequent fluctuation in particle number concentration in and around Diwali festival was evidenced, primarily influenced by local emission sources and meteorology, with three distinct peaks in number concentrations (dN/dlogDp, 3.1–4.5 × 104 cm3) coinciding well with peak firework emission period (18:00–23:00 h). Submicron particle size distribution revealed a single peak covering a size range of 80–130 nm, and for all instances, number concentration maximum coincided with geometric mean minimum, indicating the emission primarily in the ultrafine range (< 0.1 μm). Interestingly, during peak firework emissions, besides rise in accumulation mode, an event of new particle formation was identified with increase in nucleation and small Aitken mode, before being dispersed to background aerosols. On an integral scale, a clear distinction was noted between a normal and an episodic event, with a definite shift in the formation of ultrafine particles compared with the accumulation mode. The BC diurnal profile was typical, with a prominent nocturnal peak (12.0 ± 3.9 μg m-3) corresponding to a decrease in the boundary layer height. A slight variation in maximum BC concentration (16.8 μg m-3) was noted in the night of the event coinciding well with firework emissions. An increase in some specific ionic species was also noted in combination with an increase in the overall cation to anion ratio, which was explained in terms of heterogeneous transformation of NOx and catalytic conversion of SO2. [Figure not available: see fulltext.]. © 2019, Springer Nature Switzerland AG.
Unusual reactions of 2-aryl-4-(N,N-dimethylaminomethylene)-2-oxazolin5-ones with O-nucleophiles: Synthesis of 2-aryl-4-hydi oxymethylene- 2-oxazolin-5-ones
(1998) Kumar K. Singh; Ram S. Singh; Radhey M. Singh
The reactions of 2-aryl-4-(N,N-dimethyIaminomethylene)-2- oxazolin-5-ones 2 with aqueous or ethanolic KOH and sodium ethoxide lead to the formation of 2-aryl-4-hydroxymethylene-2-oxazolin-5ones 4, 1,5-bond remaining unaffected. However, the reactions of 2 with aqueous or methanolic KOH afford methyl 2-acylamino-3-dimethylaminopropenoates 9 along with 4. These observations are explained by the hard-soft acid-base (HSAB) principle. Further, compounds 9 on treatment with POCl3 in pyridine and ethanolic KOH give the corresponding cyclized products 2 and 4, respectively.