Validation of modeling approach to evaluate congener-specific concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans in air and soil near a solid waste incinerator.

A concise modeling approach using long-term averaged meteorological data was developed to estimate site-specific concentrations of congeners of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) near a solid waste incinerator. This approach consists of calculation of atmospheric dispersion, dry and wet deposition of gaseous and particle-bound congeners, and non-steady-state concentrations in soil. The predictability of this approach was evaluated by comparison of calculated concentrations of congeners in soil with those measured at eight locations near a municipal solid waste incinerator (MSWI). The variation of these concentrations due to variability of meteorological parameters is small. A considerable number of mean values show good agreement with measured concentrations within a factor of three. The reasonable agreement between calculated and measured concentrations indicates that algorithms for the calculation of vapor-phase deposition and non-steady-state concentrations in soil must be included in the modeling approach for an accurate estimation of the concentrations of congeners of PCDD/Fs emitted from MSWIs to the atmosphere. For a detailed estimation of site-specific concentrations, it is important to specify the bulk density of soil in the evaluated area, together with meteorological parameters.     

Role of carbonic anhydrase in the supply of inorganic carbon to the giant clam—zooxanthellate symbiosis

The mechanism whereby inorganic carbon (C_i) is acquired by the symbiotic association between the giant clam (Tridacna derasa) and zooxanthellae (Symbiodinium sp.) has been investigated. C_i in the haemolymph of the clam is in equilibrium with the surrounding sea water. The photosynthesis rate exhibited by the intact clam varies as a function of the C_i concentration in the clam haemolymph. The gill tissue contains high carbonic anhydrase activity which may be important in adjusting the C_i equilibrium between haemolymph and sea water. Zooxanthellae (Symbiodinium sp.) isolated from the clam mantle prefer CO₂ to HCO ₃ ^- as a source of inorganic carbon. The zooxanthellae have low levels of carbonic anhydrase on the external surface of the cell; however, mantle extracts display high carbonic anhydrase activity. Carbonic anhydrase is absent from the mantle of aposymbiotic clams (T. gigas), indicating that this enzyme may be essential to the symbiosis. The enzyme is probably associated with the zooxanthellae tubes in the mantle. The results indicate that carbonic anhydrase plays an important role in the supply of carbon dioxide within the clam symbiosis.     

Validation of modeling approach to evaluate congener-specific concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans in air and soil near a solid waste incinerator

A concise modeling approach using long-term averaged meteorological data was developed to estimate site-specific concentrations of congeners of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) near a solid waste incinerator. This approach consists of calculation of atmospheric dispersion, dry and wet deposition of gaseous and particle-bound congeners, and non-steady-state concentrations in soil. The predictability of this approach was evaluated by comparison of calculated concentrations of congeners in soil with those measured at eight locations near a municipal solid waste incinerator (MSWI). The variation of these concentrations due to variability of meteorological parameters is small. A considerable number of mean values show good agreement with measured concentrations within a factor of three. The reasonable agreement between calculated and measured concentrations indicates that algorithms for the calculation of vapor-phase deposition and non-steady-state concentrations in soil must be included in the modeling approach for an accurate estimation of the concentrations of congeners of PCDD/Fs emitted from MSWIs to the atmosphere. For a detailed estimation of site-specific concentrations, it is important to specify the bulk density of soil in the evaluated area, together with meteorological parameters.     

Natural purification effects in the river in consideration with domestic wastewater pollutant discharge reduction effects

The first social experiment program in Japan to reduce domestic wastewater pollutant discharge by “soft interventions” in households has been conducted in the Yamato-gawa River drainage area since 2005. The Yamato-gawa River has been listed as one of the worst water quality rivers in Japan because of the larger annual average BOD. “Hard interventions” including deployment of wastewater treatment facilities and artificial installation of natural purification facilities in the river has been conducted in these years to improve river water quality. At the first Yamato-gawa River social experiment program (YR-SEP) in March 2005, BOD at the monitoring point near the river mouth decreased about 6% during the Program. Natural purification e ect along the river was evaluated in this article with one-dimensional water quality model for the six river sections. Larger biological oxygen consumption rate, kb, was estimated in the sections with artificially installed natural purification facilities. The e ect of “soft interventions” in households in the YR-SEP was estimated as 25% BOD decrease in the nearest monitoring point to the river mouth, when all the households participate in the Program and BOD discharge reduction rate with “soft interventions” in households was 40%.     

Experiments and numerical simulation on methane flame quenching by water mist

The study of extinguishment using water mist has been motivated due to the phase-out of the use of halens and the search for alternative means that preserve all of the benefits of a clean total flooding agent without adverse environmental impact. With the numerical simulation, we analyzed a gas–liquid two-phase problem including water (liquid), air and methane (gas) using Eulerian equations for the liquid phase and the full Navier–Stokes equations for the gas phase. Gaseous mass, momentum and energy equations are integrated simultaneously by a Harten–Yee explicit non-MUSCL modified-flux type TVD scheme for the convective terms and a central difference scheme for the viscous terms. Liquid phase conservation equations are solved with an application of a flux-vector-splitting scheme. In the experiments in an open room (500×500×500 mm) we observed an interaction of the diffusion flame with the water mists. The results show remarkable flame quenching and a good agreement between the numerical and experimental results.     

The cost of stratospheric climate engineering revisited

Stratospheric aerosol injection (SAI) has been receiving increasing attention as a possible option for climate engineering. Its direct cost is perceived to be low, which has implications for international governance of this emerging technology. Here, we critically synthesize previous estimates of the underlying parameters and examine the total costs of SAI. It is evident that there have been inconsistencies in some assumptions and the application of overly optimistic parameter values in previous studies, which have led to an overall underestimation of the cost of aircraft-based SAI with sulfate aerosols. The annual cost of SAI to achieve cooling of 2 W/m² could reach US$10 billion with newly designed aircraft, which contrasts with the oft-quoted estimate of “a few billion dollars.” If existing aircraft were used, the cost would be expected to increase further. An SAI operation would be a large-scale engineering undertaking, possibly requiring a fleet of approximately 1,000 aircraft, because of the required high altitude of the injection. Therefore, because of its significance, a more thorough investigation of the engineering aspects of SAI and the associated uncertainties is warranted.