Salu Jacob

Winter time chemical characteristics of aerosols over the Bay of Bengal: continental influence.

As part of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB) conducted under the Geosphere Biosphere Programme of Indian Space Research Organisation, ship-based aerosol sampling was carried out over the marine environment of Bay of Bengal (BoB) during the northern winter months of December 2008 to January 2009. About 101 aerosol samples were collected, covering the region from 3.4° to 21° N latitude and 76° to 98° E longitude—the largest area covered—including the south east (SE) BoB for the first time. These samples were subjected to gravimetric and chemical analysis and the total aerosol loading as well the mass concentration of the ionic species namely F−, Cl−, Br−, NO2−, NO3−, PO42−, SO42−, NH4+, etc. and the metallic species, Na, Mg, Ca, K, Al, Fe, Mn, Zn, and Pb were estimated for each sample. Based on the spatial distribution of individual chemical species, the air flow pattern, and airmass back trajectory analysis, the source characteristics of aerosols for different regions of BoB were identified. Significant level of continental pollution was noticed over BoB during winter. While transport of pollution from Indo-Gangetic Plain (IGP) contributed to aerosols over north BoB, those over SE BoB were influenced by SE Asia. A quantitative study on the wind-induced production of sea salt aerosols and a case study on the species dependent effect of rainfall are also presented in this paper.

Analysis of Trace Additives in Copper Alloys for Space Applications: A Comparison between Graphite Furnace Atomic Absorption Spectrometry and Inductively Coupled Plasma Atomic Emission Spectrometry

Cu-Cr-Zr-Ti alloy is a special type of copper alloy being used as thrust chamber material in cryogenic engine, owing to its good thermal conductivity and mechanical properties at high temperature. Presence of alloying elements like chromium, zirconium and titanium in lower percentage has considerable effect on the thermal and mechanical properties of the thrust chamber material. Hence the accurate estimation of alloying elements as well as trace impurities is an important part of the quality control process in the manufacture of these materials. In analytical methods like XRF, F-AAS etc. which are used for chemical analysis of alloys, the intensity of analytical signal is highly dependent on matrix composition and hence precise matching of sample and standard matrices is required for drawing accurate results. ICP-AES is well-established analytical technique offers better detection limit, wide linear dynamic range, high precision, good accuracy, and practically negligible chemical interferences for the estimation of alloying elements. An accurate and precise technique for quantitative estimation of the elements viz. chromium, zirconium, titanium, iron, manganese, nickel, lead etc. in Cu-Cr-Zr-Ti alloy has been successfully developed using ICP-AES and GF-AAS. Merits and demerits of the two analytical techniques are also compared with respect to the result obtained.

In situ measured seasonal characteristics of near-surface aerosols over Bay of Bengal and MODIS-retrieved columnar properties: A multicampaign analysis

Seasonal changes in near-surface aerosol mass loading and their chemical characteristics over the marine environment of Bay of Bengal (BoB) have been investigated, based on the ship-based experiments carried out as part of three major field campaigns in premonsoon, winter, and monsoon seasons. These spatiotemporal properties of in situ measured near-surface aerosols were compared with the columnar aerosol optical depth (AOD), Angstrom exponent, effective radius, mass concentration, fine-mode AOD, and large-mode AOD retrieved by Moderate Resolution Imaging Spectroradiometer (MODIS). The spatial heterogeneity in the chemical nature of aerosols for the three contrasting seasons has been addressed. In all the seasons, BoB is found to be polluted by anthropogenic aerosols as revealed by their chemical composition. North BoB exhibits highest near-surface aerosol loading, columnar AOD, and aerosol mass concentration irrespective of the season. While the high AOD in winter is due to fine-mode anthropogenic aerosols, that in monsoon is due to large-sized sea-salt aerosols. The fine-mode AOD over BoB contributes 45% in monsoon, 69% in premonsoon, and 73% in winter. The column AOD in winter and premonsoon is ~50% of its monsoonal value. The e-fold scale distances of total aerosol mass loading and those of various chemical species over BoB are also investigated. The column mass concentration has been estimated from the in situ measured near-surface aerosol mass loading and compared with that retrieved from MODIS. Regions where low near-surface aerosol mass loading was observed; the satellite-retrieved columnar loading was found to be overestimated suggesting seasonal and regional differences in scale height.