S. Sen

Seasonal effects on the air–water carbon dioxide exchange in the Hooghly estuary, NE coast of Bay of Bengal, India

Monthly variation of CO2 fugacity (fCO2) in surface water and related atmospheric exchanges were measured in the Hooghly estuary which is one of the most important estuaries, since it is fed by one of the worlds largest rivers, the Ganges with a flow of 15,646 m3 s-1 (1.6% of the worlds combined river flow). Carbon dioxide fluxes averaged over the entire estuary are in the range of -2.78 to 84.4 mmol m-2 d-1. This estuary acts as a sink for CO2 during monsoon months and seasonal variation of its flux is controlled by dilution of seawater by river water. Since the solubility of CO2 and the disassociation of carbonic acid in estuarine water are controlled by temperature and salinity, the observed variations of CO2 fluxes are compared with those predicted from seasonal changes in temperature, salinity and the ratio of gross primary production to community respiration using empirical equations with an explained variability of 55%.

Impact of Sundarban mangrove biosphere on the carbon dioxide and methane mixing ratios at the NE Coast of Bay of Bengal, India

Abstract Diurnal and seasonal variations in carbon dioxide and methane fluxes between Sundarban biosphere and atmosphere were measured using micrometeorological method during 1998–2000. Study of the diurnal variation of micrometeorological conditions in the atmosphere was found to be necessary to determine the duration of neutral stability when flux estimation was reliable. Neutral stability of the atmosphere occurred in the limited micrometeorological conditions, when friction velocity ranged between 0.360 and 0.383 m s −1 . The value of drag coefficient (1.62–20.6)×103 obtained at variable wind speed could be deemed specific for this particular surface. 58.2% drop of carbon dioxide and 63.4% drop of methane in the atmosphere at 1 m height were observed during day time, between dawn and early evening. Diurnal variations in methane and carbon dioxide mixing ratios showed a positive correlation with Richardsons number (Ri). This environment acted as a net source for carbon dioxide and methane. The mixing ratios of methane were found to vary between 1.42 and 2.07 ppmv , and that of carbon dioxide, between 324.3 and 528.7 ppmv during the study period. The biosphere–atmosphere flux of carbon dioxide ranged between −3.29 and 34.4 mg m −2 s −1 , and that of methane, between −4.53 and 8.88 μg m −2 s −1 . The overall annual estimate of carbon dioxide and methane fluxes from this ecosystem to atmosphere were estimated to be 694 Tg yr −1 and 184 Gg yr −1 , respectively. Considerable variations in mixing ratios of carbon dioxide and methane at the NE coast of Bay of Bengal were observed due to the seasonal variations of their fluxes from the biosphere to the atmosphere. The composition was inferred by fitting model prediction to measurements.

Formation, transformation, and removal of aerosol over a tropical mangrove forest

[1] A comprehensive size-segregated characterization of the chemical properties (watersoluble inorganic fraction) of the sea-salt aerosol originated from the surf zone at the land-ocean boundary of Sundarban Mangrove forest, NE coast of Bay of Bengal, and an analysis of the relevant meteorological parameters revealed how the combined effect of anthropogenic gases and aerosol advected to the virgin mangrove forest and micrometeorological conditions could change the marine character of the aerosol before the onset of SW monsoon. The average aerosol mass concentration was 99.94 ± 41.9 μg m -3 with production rate of 0.19 μg m -2 s -1 (during January) to 4.29 μg m -2 s -1 (during April) and dry deposition rate of 0.019 μg m -2 s -1 (during January) to 13.21 μg m -2 s -1 (during June). 72.35% of the total aerosol mass was leachable by water, and relatively large concentrations of phosphorus were observed. More chloride depletion from the coarse (2.0 2.0 μm. Distributions of Na + , K + , Ca 2+ , Mg 2+ , NH + 4 , Cl - , NO 2 , NO 3 , SO 2- 4 , and PO 3- 4 in different size modes were considered to collate their source apportionment. The proximity of Calcutta and Haldia metropolis to the mangrove forest could influence the forest air quality and depositional processes.

Interactions of Cu (II) and Fe (III) with mangal humic substances studied by synchronous fluorescence spectroscopy and potentiometric titration

Humic (HA) and fulvic (FA) acids isolated from mangrove sediments of Sundarban, the largest delta on earth in the estuarine phase of the river Ganges, were studied and attempts were made to characterize their binding sites by quenching of Synchronous fluorescence (SyF) bands with Fe (III) and Cu (II). A modified Stern-Volmer relationship applicable for static quenching was applied for the determination of conditional stability constants and the data were compared with those determined by potentiometric titration. In the excited state HA and FA showed different acidity constant compared to the ground state. Values of the conditional stability constant (log Kc) for Fe (III) and Cu (II) indicated that binding sites were bidentate in nature. FA were better chelators than the HA fractions. High energy binding sites of both FA & HA were occupied by Fe(III) and the low energy binding sites, mainly responsible for mobilization and immobilization of metal, were occupied by Cu(II).

Contribution from the primary and secondary sources to the atmospheric formaldehyde in Kolkata, India

A novel and straight forward method is adopted to segregate the contribution of primary and secondary sources of formaldehyde based on the rates of its formation and removal at different times in the urban atmosphere of Kolkata. To achieve the above objective, the diurnal and seasonal mixing ratios of formaldehyde were measured during dry season at two busy roadside locations. The maximal secondary formation fluxes of formaldehyde during summer and winter were found to be 6.63 x 10(7) and 1.23 x 10(7) molecules cm(-3) s(-1), respectively. Apart from formaldehyde (C(1)), several other carbonyls were quantified in this study. An overall good correlation between acetaldehyde (C(2)) and propanal (C(3)) indicates the contribution of vehicular emission to the carbonyl budget. The secondary formaldehyde contributions in summer and winter were about 71% and 32%, respectively. The relative mean contributions of C(1), C(2) and ozone towards generation of OH fluxes in summer were found to be 1.56 x 10(7), 6.96 x 10(5), and 1.29 x 10(7)molecules cm(-3) s(-1), respectively, which were 3.2, 3.4 and 1.6 times higher than those in winter.