ABSTRACT A total of 61 samples, from six vertical profiles between surface and 1800 m from the Ar... more ABSTRACT A total of 61 samples, from six vertical profiles between surface and 1800 m from the Arabian Sea, have been analysed for uranium concentration to assess its behaviour in oxic and sub-oxic waters. These samples cover a wide range of dissolved oxygen concentration, from 0.14 to 230 μM. Uranium concentration in most of the samples fall in the range of 3.2 ± 0.2 μg l–1. In general, uranium exhibits a conservative behaviour in the Arabian Sea water column and denitrification processes do not seem to influence its abundance. The mean uranium/salinity ratio in waters with dissolved oxygen 100 μM, and in waters from other oceanic regions (9.34 ± 0.56) × 10–8 g g–1. In one of the profiles (18°N, 64°E) collected during summer monsoon (SK115/6; August 1996), two samples from 300 and 600 m have uranium concentration ∼10–15% lower than that expected based on salinity. Further studies are needed to confirm these results and to characterize the process(es) contributing to depletion of uranium at these depths.
Atmospheric transport of chemical constituents from the Indo-Gangetic Plain (IGP) to the Bay of B... more Atmospheric transport of chemical constituents from the Indo-Gangetic Plain (IGP) to the Bay of Bengal is a conspicuous seasonal feature that occurs during the late NE-monsoon (December-March). With this perspective, aerosol composition and abundance of mineral dust have been studied during November 2009 - March 2010 from a sampling site (Kharagpur: 22.3 N, 87.3E) in the IGP, representing the atmospheric outflow to the Bay of Bengal. The chemical composition of PM2.5 suggests the dominance of nss-SO42- (6.9 – 24.3 µg m-3); whereas the abundance of mineral dust varied from 3 to 18 µg m-3. The concentration of aerosol iron (FeTot) and its fractional solubility (Fews % = Fews/FeTot *100, where Fews is the water-soluble fraction of FeTot) varied from 60 to 1144 ng m-3 and from 6.7 to 26.5 %, respectively. A striking similarity in the temporal variability of total inorganic acidity (TIA = NO3- + nss-SO42-) and Fews (%) provides evidence for acid processing of mineral dust (alluvium) during atmospheric transport from the IGP. The contribution of TIA to water-soluble inorganic species [(nss-SO42- + NO3-)/ΣWSIS], mass ratios of Ca/Al and Fe/Al, abundance of dust (%) and Fews (%) in the IGP-outflow are similar to the aerosol composition over the Bay of Bengal. With the rapid increase in anthropogenic activities over south and south-east Asia, the enhanced fractional solubility of aerosol iron (attributed to acid processing of mineral dust) has implications to further increase the air-sea deposition of Fe to the surface ocean.
ABSTRACT We report here temporal changes in the measured oceanic geochemical properties of the Ar... more ABSTRACT We report here temporal changes in the measured oceanic geochemical properties of the Arabian Sea and the equatorial Indian Ocean by reoccupying six stations investigated during the GEOSECS expedition nearly two decades earlier in 1977 and 1978. Observed differences are interpreted in terms of plausible changes in environment and climate that have occurred in response to natural or anthropogenic processes. The depth-profiles of major parameters such as dissolved oxygen, CO2, major nutrients (silicate, nitrate and phosphate), and radiocarbon in dissolved inorganic carbon were measured during the cruises between 1994 and 1998 along with temperature and salinity. Most stations in the Arabian Sea show an increase in salinity by ~ 0.2 to 0.3 salinity units in the top 400 m whereas one station in the equatorial Indian Ocean show a decrease in salinity by ~ 0.1 units, indicating a likely change in the evaporation-precipitation (E-P) balance. The CO2 show average increase by 8 M within the top 1200 m of the Arabian Sea. The depth-profiles of nitrate and dissolved oxygen for the central Arabian Sea stations show significant variations, while only marginal changes are seen for silicate and phosphate relative to the GEOSECS data. Decrease in 14C of surface waters is due to steady decrease in atmospheric 14C concentration since GEOSECS and 14C increase in sub-surface waters is attributed to the downward vertical diffusion of bomb-radiocarbon interpreted in terms of atmosphere to ocean transfer and lateral advection of water masses.
The High Resolution Stereo Camera (HRSC) has been orbiting the planet Mars since January 2004 onb... more The High Resolution Stereo Camera (HRSC) has been orbiting the planet Mars since January 2004 onboard the European Space Agency (ESA) Mars Express mission and delivers imagery which is being used for topographic mapping of the planet. The HRSC team has ...
U–Th decay series isotopes, δ18O and Si measurements in the river estuarine waters and sediments ... more U–Th decay series isotopes, δ18O and Si measurements in the river estuarine waters and sediments of the polluted Hooghly estuary as well as the surface waters of the Bay of Bengal, its high salinity end member, are reported. Dissolved Si indicates that there are probably two mixing regimes, dissolved U behaviour is nonconservative and δ18O behaves conservatively in the overall
ABSTRACT Laboratory inter-comparison is one of the methods used for regularly assessing the accur... more ABSTRACT Laboratory inter-comparison is one of the methods used for regularly assessing the accuracy of the analytical data produced by laboratories for particular measurements. A working group at the 2010 GEOTRACES Asia Planning Workshop in Taipei recommended that a Ra inter-comparison experiment be conducted in the surface sea water of the Asian coastal region. In May 2011, we organized the Asian Ra Inter-comparison experiment. Analytes included 223Ra, 224Ra, 226Ra, 228Ra, and 228Th. Nine laboratories joined this activity. One sample set was collected in the coastal region of the Yellow Sea, near Qingdao, China (YS1, YS2) and another in Tolo Harbor of Hong Kong (HK1, HK2). These waters are relatively high in Ra and low in suspended matter and can be considered representative of coastal waters in the region. The results show that most of the data reported by different labs is within two standard deviations of the mean. Radium extraction efficiencies based on two Mn-fiber columns attached in series averaged 95–99%. Results for 226Ra, 223Ra, and 228Th in the Asia Inter-comparison are considerably less scattered than in the GEOTRACES Atlantic Inter-comparison. For 228Ra the Asia and GEOTRACES results are similar; but for 224Ra, the Asia results are considerably more scattered than the GEOTRACES results.
228 Ra and 226 Ra have been measured in the surface waters of the western Bay of Bengal during fi... more 228 Ra and 226 Ra have been measured in the surface waters of the western Bay of Bengal during five cruises conducted between 1988 and 1999. The ranges and mean (given in brackets) concentrations for 228 Ra and 226 Ra are 6.8 -42.1 (17.8 Ϯ 7.9) dpm/100 kg and 6.0 -16.7 (9.2 Ϯ 2.2) dpm/ 100 kg, respectively. ( 228 Ra/ 226 Ra) Activity Ratio (henceforth denoted as [228/226]) ranges from 0.8 to 3.4 with a mean of 1.9 Ϯ 0.5. Both 228 Ra and 226 Ra show inverse correlation with salinity, the former much stronger.
Bed sediments of the Yamuna River and its tributaries in the Himalaya (Yamuna River System, YRS) ... more Bed sediments of the Yamuna River and its tributaries in the Himalaya (Yamuna River System, YRS) have been analyzed for major elements and trace metals (Sr, Ba, Ni, Cu, Co, Zn, Pb and Cr). These results have been used to characterize chemical weathering and transport in the Himalaya, to assess relative mobility of elements during weathering and to understand heavy metal association. Concentrations of major and trace elements of YRS sediments vary between 20 and 50%. In general, elemental variability reduces when data are analyzed individually for the major rivers, suggesting that tributaries draining diverse lithology contribute significant variations. Comparison of sediment chemistry with composition of source rocks and average Upper Continental Crust (UCC) suggests significant loss of Na, K, Ca and Mg from source rocks during weathering, the degree of loss being more for Ca and Na. Chemical index of alteration (CIA) for YRS sediments averages at 59, indicating that weathering in the basin is of moderate intensity. This inference is also supported by major ion chemistry of YRS waters and is attributed to steep gradient and enhanced physical erosion in the basin. Available results seem to indicate that Na and Sr are effectively more mobile than Ba, which is thought to be a combined effect of higher solubility of Na and Sr, and the affinity of Ba to be adsorbed onto solid phase. Heavy metals show significant positive correlation with Al and weak correlation with Fe, Mn and P. These observations suggest that metal concentrations are controlled mainly by clay mineral abundances, and that Fe-Mn oxides and organic matter may be playing less significant role. Heavy metal concentrations of YRS sediments are lower than those of suspended particulates of the Yamuna river, presumably due to higher clay mineral abundances in the latter. Strong association of metals with Al, and lower metal concentrations in bed sediments compared to suspended matter underscores the importance of sediment transport and mineral sorting in influencing the YRS sediment chemistry. Enrichment factor and geo-accumulation index calculated for heavy metals in YRS sediments suggest that they are mainly of natural origin and that anthropogenic activities exert little influence on their abundances.
We report here the first measurements of dissolved rare earth elements (REE) in the headwaters of... more We report here the first measurements of dissolved rare earth elements (REE) in the headwaters of the Yamuna river draining through the southern slopes of Himalaya. Due to intense weathering of the surface rocks of different lithologies and influence of tributaries, Yamuna river waters have variable dissolved REE contents (87 < ÂREE < 1374 ng L -1 , mean = 288.6 ng L -1 ) and exhibit negative Eu anomaly (0.49 < Eu/Eu* < 0.73, mean = 0.63). While most of the samples do not show discernable Ce anomalies; a negative Ce anomaly, however, found in a few of them, which can be explained by the colloidal pool preferentially enriched in Ce. A comparison among the river waters and bed sediments suggests that dissolved composition of REE is strongly fractionated and is enriched in MREE (Nd-Gd) with respect to sediments; presumably due to preferential dissolution of phosphate minerals such as apatite during weathering processes.
Measurements of five cosmogenic 325i vertical profiles in Atlantic waters (27°N to 60°S) are pres... more Measurements of five cosmogenic 325i vertical profiles in Atlantic waters (27°N to 60°S) are presented. The amounts of dissolved SiO 2 extracted range from 2 to 54 g; the amounts of water from which SiO 2 was extracted range between 540 kg and 270,000 kg. In additon, SiO 2 recovered from four surface particulate composites (64 °N to 61 ° S) were also analyzed for 32Si. 32Si measurements were made by milking and counting the daughter activity, 32p. The net 32p activities range from 0.7 to 6.8 cph; typical errors in measurements of the 32p activities are 20-30%.
Measurements of five cosmogenic 32Si vertical profiles in Atlantic waters (27°N to 60°S) are pres... more Measurements of five cosmogenic 32Si vertical profiles in Atlantic waters (27°N to 60°S) are presented. The amounts of dissolved SiO2 extracted range from 2 to 54 g; the amounts of water from which SiO2 was extracted range between 540 kg and 270,000 kg. In additon, SiO2 recovered from four surface particulate composites (64°N to 61°S) were also analyzed for 32Si.
The 228Ra concentrations of the Dead Sea waters range from 0.13 to 1.48 dpm kg-1, two to three or... more The 228Ra concentrations of the Dead Sea waters range from 0.13 to 1.48 dpm kg-1, two to three orders of magnitude higher than those of ocean waters and lake waters. However, the 228Ra/226Ra activity ratios, (0.12-1.29) × 10-2, are in the range reported for the hydrosphere. The surface waters of the Dead Sea are enriched in 228Ra by a factor of about three over the near-bottom waters. There is a factor of about two spatial variability in the mid-depth Ra concentrations at the two profile stations. The near-bottom 228Ra gradients yield vertical eddy diffusivity coefficient (K) of 2.0 and 0.4 cm2 s-1 at profile locations 1 and 2 respectively. These values are comparable to those measured in oceans and lakes.
Radiometric and compositional studies of a gravity core from the Tapti salt marsh region is repor... more Radiometric and compositional studies of a gravity core from the Tapti salt marsh region is reported. The sediment accumulation rate of 3 mm/yr. Determined by the 210Pb excess method is indicative of the apparent rate of sea level rise in the region (as a lower ...
ABSTRACT Daily variability in the chemical composition of atmospheric PM2.5 and PM10 has been stu... more ABSTRACT Daily variability in the chemical composition of atmospheric PM2.5 and PM10 has been studied from an urban site (Ahmedabad) in western India over a span of 30 days during winter. The PM2.5 and PM10 mass concentrations ranged from 32 to 106 μg m− 3 and 121 to 327 μg m− 3, respectively. On average, PM2.5 constitutes ~ 33% of PM10, indicating dominance of coarse mode aerosols in the urban atmosphere. The particulate EC and OC show higher abundances in PM2.5 (average: 3.0 ± 0.9 and 18.3 ± 5.9 μg m− 3 respectively) whereas those in PM10 are 4.4 ± 2.4 and 29.8 ± 11.2 μg m− 3 respectively. A linear increasing trend and representative OC/EC ratio of 6.2 indicate their primary source from biomass burning emissions. The water-soluble organic carbon (WSOC: 4.0–14.7 μg m− 3) and its linear relationship with K+ (0.6–1.7 μg m− 3) in PM2.5 further support biomass burning emissions as a dominant source for carbonaceous aerosol. Among water-soluble inorganic species, SO42− is the most abundant (range: 3.2–22.5 μg m− 3); almost all of it occurs in fine mode (PM2.5) and exhibits near-quantitative neutralization with NH4+ (r = 0.98, slope: 1.3). The water-soluble Ca2+ and Mg2+ mainly abundant in the coarse mode, suggest significant contribution from mineral dust. Documenting large temporal variability in the chemical composition of coarse and fine mode aerosol is essential in order to assess the changing regional emission scenario over mega-cities and their down-wind transport.
Air pollution in rural China has often been ignored, especially for the less developed west China... more Air pollution in rural China has often been ignored, especially for the less developed west China. Atmospheric polycyclic aromatic hydrocarbons (PAHs) were measured monthly at 11 rural sites (5 rural villages and 6 rural fields) together with 7 urban stations in northern China between April 2010 and March 2011. PAH concentrations at rural village sites were similar to those in urban areas and significantly higher than those in rural fields, indicating severe contamination in rural villages. PAH concentrations in the west were similar to those in the more developed North China Plain, and higher than those along the coast. Such a geographical distribution is mainly caused by the differences in residential energy consumption and meteorological conditions, which can explain approximately 48% of the total variation in PAH concentrations. With heavy dependence on biofuel combustion for heating, seasonality in rural areas is more profound than that in urban areas.
ABSTRACT A total of 61 samples, from six vertical profiles between surface and 1800 m from the Ar... more ABSTRACT A total of 61 samples, from six vertical profiles between surface and 1800 m from the Arabian Sea, have been analysed for uranium concentration to assess its behaviour in oxic and sub-oxic waters. These samples cover a wide range of dissolved oxygen concentration, from 0.14 to 230 μM. Uranium concentration in most of the samples fall in the range of 3.2 ± 0.2 μg l–1. In general, uranium exhibits a conservative behaviour in the Arabian Sea water column and denitrification processes do not seem to influence its abundance. The mean uranium/salinity ratio in waters with dissolved oxygen 100 μM, and in waters from other oceanic regions (9.34 ± 0.56) × 10–8 g g–1. In one of the profiles (18°N, 64°E) collected during summer monsoon (SK115/6; August 1996), two samples from 300 and 600 m have uranium concentration ∼10–15% lower than that expected based on salinity. Further studies are needed to confirm these results and to characterize the process(es) contributing to depletion of uranium at these depths.
Atmospheric transport of chemical constituents from the Indo-Gangetic Plain (IGP) to the Bay of B... more Atmospheric transport of chemical constituents from the Indo-Gangetic Plain (IGP) to the Bay of Bengal is a conspicuous seasonal feature that occurs during the late NE-monsoon (December-March). With this perspective, aerosol composition and abundance of mineral dust have been studied during November 2009 - March 2010 from a sampling site (Kharagpur: 22.3 N, 87.3E) in the IGP, representing the atmospheric outflow to the Bay of Bengal. The chemical composition of PM2.5 suggests the dominance of nss-SO42- (6.9 – 24.3 µg m-3); whereas the abundance of mineral dust varied from 3 to 18 µg m-3. The concentration of aerosol iron (FeTot) and its fractional solubility (Fews % = Fews/FeTot *100, where Fews is the water-soluble fraction of FeTot) varied from 60 to 1144 ng m-3 and from 6.7 to 26.5 %, respectively. A striking similarity in the temporal variability of total inorganic acidity (TIA = NO3- + nss-SO42-) and Fews (%) provides evidence for acid processing of mineral dust (alluvium) during atmospheric transport from the IGP. The contribution of TIA to water-soluble inorganic species [(nss-SO42- + NO3-)/ΣWSIS], mass ratios of Ca/Al and Fe/Al, abundance of dust (%) and Fews (%) in the IGP-outflow are similar to the aerosol composition over the Bay of Bengal. With the rapid increase in anthropogenic activities over south and south-east Asia, the enhanced fractional solubility of aerosol iron (attributed to acid processing of mineral dust) has implications to further increase the air-sea deposition of Fe to the surface ocean.
ABSTRACT We report here temporal changes in the measured oceanic geochemical properties of the Ar... more ABSTRACT We report here temporal changes in the measured oceanic geochemical properties of the Arabian Sea and the equatorial Indian Ocean by reoccupying six stations investigated during the GEOSECS expedition nearly two decades earlier in 1977 and 1978. Observed differences are interpreted in terms of plausible changes in environment and climate that have occurred in response to natural or anthropogenic processes. The depth-profiles of major parameters such as dissolved oxygen, CO2, major nutrients (silicate, nitrate and phosphate), and radiocarbon in dissolved inorganic carbon were measured during the cruises between 1994 and 1998 along with temperature and salinity. Most stations in the Arabian Sea show an increase in salinity by ~ 0.2 to 0.3 salinity units in the top 400 m whereas one station in the equatorial Indian Ocean show a decrease in salinity by ~ 0.1 units, indicating a likely change in the evaporation-precipitation (E-P) balance. The CO2 show average increase by 8 M within the top 1200 m of the Arabian Sea. The depth-profiles of nitrate and dissolved oxygen for the central Arabian Sea stations show significant variations, while only marginal changes are seen for silicate and phosphate relative to the GEOSECS data. Decrease in 14C of surface waters is due to steady decrease in atmospheric 14C concentration since GEOSECS and 14C increase in sub-surface waters is attributed to the downward vertical diffusion of bomb-radiocarbon interpreted in terms of atmosphere to ocean transfer and lateral advection of water masses.
The High Resolution Stereo Camera (HRSC) has been orbiting the planet Mars since January 2004 onb... more The High Resolution Stereo Camera (HRSC) has been orbiting the planet Mars since January 2004 onboard the European Space Agency (ESA) Mars Express mission and delivers imagery which is being used for topographic mapping of the planet. The HRSC team has ...
U–Th decay series isotopes, δ18O and Si measurements in the river estuarine waters and sediments ... more U–Th decay series isotopes, δ18O and Si measurements in the river estuarine waters and sediments of the polluted Hooghly estuary as well as the surface waters of the Bay of Bengal, its high salinity end member, are reported. Dissolved Si indicates that there are probably two mixing regimes, dissolved U behaviour is nonconservative and δ18O behaves conservatively in the overall
ABSTRACT Laboratory inter-comparison is one of the methods used for regularly assessing the accur... more ABSTRACT Laboratory inter-comparison is one of the methods used for regularly assessing the accuracy of the analytical data produced by laboratories for particular measurements. A working group at the 2010 GEOTRACES Asia Planning Workshop in Taipei recommended that a Ra inter-comparison experiment be conducted in the surface sea water of the Asian coastal region. In May 2011, we organized the Asian Ra Inter-comparison experiment. Analytes included 223Ra, 224Ra, 226Ra, 228Ra, and 228Th. Nine laboratories joined this activity. One sample set was collected in the coastal region of the Yellow Sea, near Qingdao, China (YS1, YS2) and another in Tolo Harbor of Hong Kong (HK1, HK2). These waters are relatively high in Ra and low in suspended matter and can be considered representative of coastal waters in the region. The results show that most of the data reported by different labs is within two standard deviations of the mean. Radium extraction efficiencies based on two Mn-fiber columns attached in series averaged 95–99%. Results for 226Ra, 223Ra, and 228Th in the Asia Inter-comparison are considerably less scattered than in the GEOTRACES Atlantic Inter-comparison. For 228Ra the Asia and GEOTRACES results are similar; but for 224Ra, the Asia results are considerably more scattered than the GEOTRACES results.
228 Ra and 226 Ra have been measured in the surface waters of the western Bay of Bengal during fi... more 228 Ra and 226 Ra have been measured in the surface waters of the western Bay of Bengal during five cruises conducted between 1988 and 1999. The ranges and mean (given in brackets) concentrations for 228 Ra and 226 Ra are 6.8 -42.1 (17.8 Ϯ 7.9) dpm/100 kg and 6.0 -16.7 (9.2 Ϯ 2.2) dpm/ 100 kg, respectively. ( 228 Ra/ 226 Ra) Activity Ratio (henceforth denoted as [228/226]) ranges from 0.8 to 3.4 with a mean of 1.9 Ϯ 0.5. Both 228 Ra and 226 Ra show inverse correlation with salinity, the former much stronger.
Bed sediments of the Yamuna River and its tributaries in the Himalaya (Yamuna River System, YRS) ... more Bed sediments of the Yamuna River and its tributaries in the Himalaya (Yamuna River System, YRS) have been analyzed for major elements and trace metals (Sr, Ba, Ni, Cu, Co, Zn, Pb and Cr). These results have been used to characterize chemical weathering and transport in the Himalaya, to assess relative mobility of elements during weathering and to understand heavy metal association. Concentrations of major and trace elements of YRS sediments vary between 20 and 50%. In general, elemental variability reduces when data are analyzed individually for the major rivers, suggesting that tributaries draining diverse lithology contribute significant variations. Comparison of sediment chemistry with composition of source rocks and average Upper Continental Crust (UCC) suggests significant loss of Na, K, Ca and Mg from source rocks during weathering, the degree of loss being more for Ca and Na. Chemical index of alteration (CIA) for YRS sediments averages at 59, indicating that weathering in the basin is of moderate intensity. This inference is also supported by major ion chemistry of YRS waters and is attributed to steep gradient and enhanced physical erosion in the basin. Available results seem to indicate that Na and Sr are effectively more mobile than Ba, which is thought to be a combined effect of higher solubility of Na and Sr, and the affinity of Ba to be adsorbed onto solid phase. Heavy metals show significant positive correlation with Al and weak correlation with Fe, Mn and P. These observations suggest that metal concentrations are controlled mainly by clay mineral abundances, and that Fe-Mn oxides and organic matter may be playing less significant role. Heavy metal concentrations of YRS sediments are lower than those of suspended particulates of the Yamuna river, presumably due to higher clay mineral abundances in the latter. Strong association of metals with Al, and lower metal concentrations in bed sediments compared to suspended matter underscores the importance of sediment transport and mineral sorting in influencing the YRS sediment chemistry. Enrichment factor and geo-accumulation index calculated for heavy metals in YRS sediments suggest that they are mainly of natural origin and that anthropogenic activities exert little influence on their abundances.
We report here the first measurements of dissolved rare earth elements (REE) in the headwaters of... more We report here the first measurements of dissolved rare earth elements (REE) in the headwaters of the Yamuna river draining through the southern slopes of Himalaya. Due to intense weathering of the surface rocks of different lithologies and influence of tributaries, Yamuna river waters have variable dissolved REE contents (87 < ÂREE < 1374 ng L -1 , mean = 288.6 ng L -1 ) and exhibit negative Eu anomaly (0.49 < Eu/Eu* < 0.73, mean = 0.63). While most of the samples do not show discernable Ce anomalies; a negative Ce anomaly, however, found in a few of them, which can be explained by the colloidal pool preferentially enriched in Ce. A comparison among the river waters and bed sediments suggests that dissolved composition of REE is strongly fractionated and is enriched in MREE (Nd-Gd) with respect to sediments; presumably due to preferential dissolution of phosphate minerals such as apatite during weathering processes.
Measurements of five cosmogenic 325i vertical profiles in Atlantic waters (27°N to 60°S) are pres... more Measurements of five cosmogenic 325i vertical profiles in Atlantic waters (27°N to 60°S) are presented. The amounts of dissolved SiO 2 extracted range from 2 to 54 g; the amounts of water from which SiO 2 was extracted range between 540 kg and 270,000 kg. In additon, SiO 2 recovered from four surface particulate composites (64 °N to 61 ° S) were also analyzed for 32Si. 32Si measurements were made by milking and counting the daughter activity, 32p. The net 32p activities range from 0.7 to 6.8 cph; typical errors in measurements of the 32p activities are 20-30%.
Measurements of five cosmogenic 32Si vertical profiles in Atlantic waters (27°N to 60°S) are pres... more Measurements of five cosmogenic 32Si vertical profiles in Atlantic waters (27°N to 60°S) are presented. The amounts of dissolved SiO2 extracted range from 2 to 54 g; the amounts of water from which SiO2 was extracted range between 540 kg and 270,000 kg. In additon, SiO2 recovered from four surface particulate composites (64°N to 61°S) were also analyzed for 32Si.
The 228Ra concentrations of the Dead Sea waters range from 0.13 to 1.48 dpm kg-1, two to three or... more The 228Ra concentrations of the Dead Sea waters range from 0.13 to 1.48 dpm kg-1, two to three orders of magnitude higher than those of ocean waters and lake waters. However, the 228Ra/226Ra activity ratios, (0.12-1.29) × 10-2, are in the range reported for the hydrosphere. The surface waters of the Dead Sea are enriched in 228Ra by a factor of about three over the near-bottom waters. There is a factor of about two spatial variability in the mid-depth Ra concentrations at the two profile stations. The near-bottom 228Ra gradients yield vertical eddy diffusivity coefficient (K) of 2.0 and 0.4 cm2 s-1 at profile locations 1 and 2 respectively. These values are comparable to those measured in oceans and lakes.
Radiometric and compositional studies of a gravity core from the Tapti salt marsh region is repor... more Radiometric and compositional studies of a gravity core from the Tapti salt marsh region is reported. The sediment accumulation rate of 3 mm/yr. Determined by the 210Pb excess method is indicative of the apparent rate of sea level rise in the region (as a lower ...
ABSTRACT Daily variability in the chemical composition of atmospheric PM2.5 and PM10 has been stu... more ABSTRACT Daily variability in the chemical composition of atmospheric PM2.5 and PM10 has been studied from an urban site (Ahmedabad) in western India over a span of 30 days during winter. The PM2.5 and PM10 mass concentrations ranged from 32 to 106 μg m− 3 and 121 to 327 μg m− 3, respectively. On average, PM2.5 constitutes ~ 33% of PM10, indicating dominance of coarse mode aerosols in the urban atmosphere. The particulate EC and OC show higher abundances in PM2.5 (average: 3.0 ± 0.9 and 18.3 ± 5.9 μg m− 3 respectively) whereas those in PM10 are 4.4 ± 2.4 and 29.8 ± 11.2 μg m− 3 respectively. A linear increasing trend and representative OC/EC ratio of 6.2 indicate their primary source from biomass burning emissions. The water-soluble organic carbon (WSOC: 4.0–14.7 μg m− 3) and its linear relationship with K+ (0.6–1.7 μg m− 3) in PM2.5 further support biomass burning emissions as a dominant source for carbonaceous aerosol. Among water-soluble inorganic species, SO42− is the most abundant (range: 3.2–22.5 μg m− 3); almost all of it occurs in fine mode (PM2.5) and exhibits near-quantitative neutralization with NH4+ (r = 0.98, slope: 1.3). The water-soluble Ca2+ and Mg2+ mainly abundant in the coarse mode, suggest significant contribution from mineral dust. Documenting large temporal variability in the chemical composition of coarse and fine mode aerosol is essential in order to assess the changing regional emission scenario over mega-cities and their down-wind transport.
Air pollution in rural China has often been ignored, especially for the less developed west China... more Air pollution in rural China has often been ignored, especially for the less developed west China. Atmospheric polycyclic aromatic hydrocarbons (PAHs) were measured monthly at 11 rural sites (5 rural villages and 6 rural fields) together with 7 urban stations in northern China between April 2010 and March 2011. PAH concentrations at rural village sites were similar to those in urban areas and significantly higher than those in rural fields, indicating severe contamination in rural villages. PAH concentrations in the west were similar to those in the more developed North China Plain, and higher than those along the coast. Such a geographical distribution is mainly caused by the differences in residential energy consumption and meteorological conditions, which can explain approximately 48% of the total variation in PAH concentrations. With heavy dependence on biofuel combustion for heating, seasonality in rural areas is more profound than that in urban areas.
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Papers by R. Rengarajan