Mixing ratios of 15 carbonyls and BTEX (benzene, toluene, ethyl benzene, xylenes) were measured for the first time in ambient air of Kolkata, India at three sites from March to June 2006 and their photochemical reactivity was evaluated. Day and nighttime samples were collected on weekly basis. Formaldehyde was the most abundant carbonyl (mean concentration ranging between 14.07 microg m(-3) to 26.12 microg m(-3) over the three sites) followed by acetaldehyde (7.60-18.67 microg m(-3)) and acetone (4.43-10.34 microg m(-3)). Among the high molecular weight aldehydes, nonanal showed the highest concentration. Among the mono-aromatic VOCs, mean concentration of toluene (27.65-103.31 microg m(-3)) was maximum, closely followed by benzene (24.97-79.18 microg m(-3)). Mean formaldehyde to acetaldehyde (1.4) and acetaldehyde to propanal ratios (5.0) were typical of urban air. Based on their photochemical reactivity towards OH. radical, the concentrations of the VOCs were scaled to formaldehyde equivalent, which showed that the high molecular weight carbonyls and xylenes contribute significantly to the total OH-reactive mass of the VOCs. Due to the toxic effect of the VOCs studied, an assessment for both cancer risk and non-cancer hazard due to exposure to the population were calculated. Integrated life time cancer risk (ILTCR) due to four carcinogens (benzene, ethyl benzene, formaldehyde and acetaldehyde) and non-cancer hazard index for the VOCs at their prevailing level were estimated to be 1.42E-04 and 5.6 respectively.
The Sundarban mangrove forest (4,264 km 2 ) constitutes about 3% of the total area of the world mangrove. We measured diurnal and seasonal variations of air-water CO 2 exchange in relation to the occurrence of phytoplankton during January-December 2001. Diurnal variations of airflows showed that the minimum and maximum CO 2 flux of Ϫ16.2 mol m Ϫ2 h Ϫ1 and 49.9 mol m Ϫ2 h
Ϫ1, respectively, occurred during the higher sea breeze. The average ratio of dissolved inorganic nitrogen (DIN ϭ 13.85 Ϯ 7.19 mol L Ϫ1 ) to dissolved inorganic phosphorus (DIP ϭ 1.23 Ϯ 0.57 mol L Ϫ1 ) was 11 Ϯ 4 and the surface water was undersaturated with respect to dissolved oxygen. The mean value of 0.1 Ϯ 0.08 for the ratio of phytoplankton production (P) to community respiration (R) indicated that the ecosystem was heterotrophic. The saturation of dissolved carbon dioxide with respect to the atmosphere varied seasonally between 59% and 156%, with minimum levels in postmonsoon and maximum levels in premonsoon/early monsoon (June/July). Out of the 36 genera of diatoms, 1 blue green alga, and 3 dinoflagellates that occurred throughout the year, only 6 reached bloom proportions in postmonsoon, when mangrove water was a sink of atmospheric CO 2 . Although 59.3% of the emitted CO 2 was removed from the atmosphere by biological processes, on an annual basis, the Sundarban mangrove forest supplies 13.8 kg C ha Ϫ1 yr Ϫ1 of CO 2 from water surface to the atmosphere. Even though it is important to compare all in and out fluxes, there is no direct link between CO 2 emission and the later CO 2 removal by biological processes.
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 world's largest rivers, the Ganges with a flow of 15,646 m3 s-1 (1.6% of the world's 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%.
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