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646 results on '"Balasubramanian, Rajasekhar"'

214. Observing and understanding the Southeast Asian aerosol system by remote sensing: An initial review and analysis for the Seven Southeast Asian Studies (7SEAS) program

Author

Reid, Jeffrey S., primary, Hyer, Edward J., additional, Johnson, Randall S., additional, Holben, Brent N., additional, Yokelson, Robert J., additional, Zhang, Jianglong, additional, Campbell, James R., additional, Christopher, Sundar A., additional, Di Girolamo, Larry, additional, Giglio, Louis, additional, Holz, Robert E., additional, Kearney, Courtney, additional, Miettinen, Jukka, additional, Reid, Elizabeth A., additional, Turk, F. Joseph, additional, Wang, Jun, additional, Xian, Peng, additional, Zhao, Guangyu, additional, Balasubramanian, Rajasekhar, additional, Chew, Boon Ning, additional, Janjai, Serm, additional, Lagrosas, Nofel, additional, Lestari, Puji, additional, Lin, Neng-Huei, additional, Mahmud, Mastura, additional, Nguyen, Anh X., additional, Norris, Bethany, additional, Oanh, Nguyen T.K., additional, Oo, Min, additional, Salinas, Santo V., additional, Welton, E. Judd, additional, and Liew, Soo Chin, additional

Published
2013
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220. Variation in global chemical composition of PM2:5: emerging results from SPARTAN.

Author

Snider, Graydon, Weagle, Crystal L., Murdymootoo, Kalaivani K., Ring, Amanda, Ritchie, Yvonne, Stone, Emily, Walsh, Ainsley, Akoshile, Clement, Nguyen Xuan Anh, Balasubramanian, Rajasekhar, Brook, Jeff, Qonitan, Fatimah D., Jinlu Dong, Griffith, Derek, Kebin He, Holben, Brent N., Kahn, Ralph, Lagrosas, Nofel, Lestari, Puji, and Zongwei Ma

Subjects
ATMOSPHERIC composition, CLIMATE change, PARTICULATE matter, OPTICAL properties of atmospheric aerosols
Abstract

The Surface PARTiculate mAtter Network (SPARTAN) is a long-term project that includes characterization of chemical and physical attributes of aerosols from filter samples collected worldwide. This paper discusses the ongoing efforts of SPARTAN to define and quantify major ions and trace metals found in fine particulate matter (PM2:5). Our methods infer the spatial and temporal variability of PM2:5 in a cost-effective manner. Gravimetrically weighed filters represent multi-day averages of PM2:5, with a collocated nephelometer sampling air continuously. SPARTAN instruments are paired with AErosol RObotic NETwork (AERONET) sun photometers to better understand the relationship between ground-level PM2:5 and columnar aerosol optical depth (AOD). We have examined the chemical composition of PM2:5 at 12 globally dispersed, densely populated urban locations and a site at Mammoth Cave (US) National Park used as a background comparison. So far, each SPARTAN location has been active between the years 2013 and 2016 over periods of 2-26 months, with an average period of 12 months per site. These sites have collectively gathered over 10 years of quality aerosol data. The major PM2:5 constituents across all sites (relative contribution±SD) are ammoniated sulfate (20%±11%), crustal material (13.4% ±9.9%), equivalent black carbon (11.9%±8.4%), ammonium nitrate (4.7%±3.0%), sea salt (2.3%± 1.6%), trace element oxides (1.0%±1.1%), water (7.2% ±3.3%) at 35% RH, and residual matter (40%±24%). Analysis of filter samples reveals that several PM2:5 chemical components varied by more than an order of magnitude between sites. Ammoniated sulfate ranges from 1.1 µgm-3 (Buenos Aires, Argentina) to 17 µgm-3 (Kanpur, India in the dry season). Ammonium nitrate ranged from 0.2 µgm-3 (Mammoth Cave, in summer) to 6.8 µgm-3 (Kanpur, dry season). Equivalent black carbon ranged from 0.7 µgm-3 (Mammoth Cave) to over 8 µgm-3 (Dhaka, Bangladesh and Kanpur, India). Comparison of SPARTAN vs. coincident measurements from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network at Mammoth Cave yielded a high degree of consistency for daily PM2:5 (r² = 0.76, slopeD1.12), daily sulfate (r² = 0.86, slopeD1.03), and mean fractions of all major PM2:5 components (within 6%). Major ions generally agree well with previous studies at the same urban locations (e.g. sulfate fractions agree within 4% for 8 out of 11 collocation comparisons). Enhanced anthropogenic dust fractions in large urban areas (e.g. Singapore, Kanpur, Hanoi, and Dhaka) are apparent from high Zn : Al ratios. The expected water contribution to aerosols is calculated via the hygroscopicity parameter Kv for each filter. Mean aggregate values ranged from 0.15 (Ilorin) to 0.28 (Rehovot). The all-site parameter mean is 0.20±0.04. Chemical composition and water retention in each filter measurement allows inference of hourly PM2:5 at 35% relative humidity by merging with nephelometer measurements. These hourly PM2:5 estimates compare favourably with a beta attenuation monitor (MetOne) at the nearby US embassy in Beijing, with a coefficient of variation r² = 0.67 (n = 3167), compared to r² = 0.62 when Kv was not considered. SPARTAN continues to provide an open-access database of PM2:5 compositional filter information and hourly mass collected from a global federation of instruments. [ABSTRACT FROM AUTHOR]

Published
2016
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221. Three-Dimensional Graphene-Based Porous Adsorbents for Postcombustion CO2 Capture.

Author

Chowdhury, Shamik and Balasubramanian, Rajasekhar

Subjects
*GRAPHENE, *POROUS materials, *POROSITY, *SORBENTS, *ADSORPTION (Chemistry), *GRAPHENE oxide
Abstract

Three-dimensional (3D) crumpled graphene-based porous adsorbents with highly interconnected networks were synthesized through a facile one-step physical activation method using reduced graphene oxide (RGO) as precursor, for separation of carbon dioxide (CO2) from postcombustion flue gas mixtures. Due to their large surface area (above 1300 m2 g-1), high pore volume (over 1 cm3 g-1), and well-defined bimodal microporous-mesoporous structure, these hierarchical porous graphene-based materials demonstrate rapid, stable, reversible, and high CO2 uptake of 2.45 mmol g-1 at 25 °C and 1 bar. Importantly, the CO2 over nitrogen (N2) adsorption selectivity is among the best at partial pressures relevant to capturing CO2 emanating from postcombustion power plants fueled with either coal or natural gas. Moreover, the isosteric heat of adsorption of only -27.42 kJ mol-1 at zero coverage reflects the ease of adsorbent regeneration with significantly low energy consumption, which in turn might reduce the costs of carbon capture and sequestration. [ABSTRACT FROM AUTHOR]

Published
2016
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222. Recent advances and progress in the development of graphene-based adsorbents for CO2 capture.

Author

Balasubramanian, Rajasekhar and Chowdhury, Shamik

Abstract

With the current high consumption of fossil fuels and the rapid increase in atmospheric CO2 concentrations, there is a strong need for energy efficient and selective capture of CO2 from fossil-fuelled power plants and other large industrial sources. Among the various adsorbents explored by the scientific community for CO2 removal from flue gases, graphene is receiving increased attention because of its unique molecular structure and many exciting properties such as high mechanical strength, excellent thermal conductivity, good chemical stability, large accessible surface area, and tunable porosity. In addition, the facile surface functionalization of graphene leads to production of innovative graphene-based materials that have the potential to be applied as advanced next-generation CO2 adsorbents. As a consequence, graphene and its derivatives have been the subject of intense experimental investigations and theoretical studies in recent years, probing their unmatched structural versatility for CO2 abatement. This review aims at bringing together the latest developments in the rapidly evolving cross-disciplinary field of graphene-mediated CO2 adsorption and it provides new research directions for making further advances toward practical deployment of graphene-based CO2 adsorbents. [ABSTRACT FROM AUTHOR]

Published
2015
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