Sulfur Hexafluoride (SF6): Global Environmental Effects and Toxic Byproduct Formation

ABSTRACT

This work provides information concerning possible global environmental implications and personnel safety aspects that should be considered during the commercial uses of sulfur hexafluoride (SF₆). SF₆ is an anthropogenically produced compound, mainly used as a gaseous dielectric in gas insulated switchgear power installations. It is a potent greenhouse gas with a high global warming potential, and its concentration in the earth atmosphere is rapidly increasing. During its working cycle, SF₆ decomposes under electrical stress, forming toxic byproducts that are a health threat for working personnel in the event of exposure. Several precautions are recommended to avoid personnel exposure to toxic byproducts: oxyfluoride levels or other byproduct concentrations in the operating gas matrix should be traced to predetermine the overall gas toxicity; contaminants should be systematically considered during maintenance, chamber evacuation and system opening process; small SF₆ quantities leaking into air or stagnated pollutant concentrations in the operating field should be analyzed and compared to the threshold limit values and permissible exposure levels. New system design rules (i.e., hermetically sealed gas compartments, gas recycling or disposal in the field area) and different handling policies—both during maintenance and final disposal—now should be considered globally to provide for environmental and personnel safety.     

Surface solar ultraviolet radiation: A theoretical approach of the SUVR reaching the ground in Athens, Greece

Daily total ozone observations made during 1985–1993 by both the Total Ozone Mapping Spectrometer (TOMS) flown on the Satellite Nimbus-7 and the Dobson Spectrophotometer have been used in order to investigate the fluctuations of the daily broad-band and spectral solar ultraviolet radiation reaching the ground. This investigation has been performed by employing a recently developed parametric algorithm for the estimation of the spectral and broad-band solar ultraviolet radiation which takes the total ozone variations into consideration. Total ozone reductions during the summertime from 1985 to 1993 over Athens, Greece (37.6° N, 23.4° E), cause an increase in the ultraviolet irradiance which reaches the ground of 0.54 %, 0.98 %, 2.60 % and 0.79 % per decade for the months of July at 300 nm, 312 nm, 320 nm and UVB (280-320 nm), respectively.     

A multi-criteria approach for the dumping of dredged material in the Thermaikos Gulf,Northern Greece

A multi-criteria approach was applied for the disposal into the sea of ～1 100 000 m³ of sediment, dredged from a coastal area in the northeastern part of the Thermaikos Gulf. This sediment (classified as muddy) is distributed vertically into two distinct Layers (A and B) with the thickness of the surficial sedimentary unit ranging from 7 to 54 cm. Its geochemistry reveals increased Cr and Ni concentrations, which may be attributed to natural enrichment through the erosion of the adjacent igneous and metamorphic rocks. In addition, a low to moderate contamination from urban-originated heavy metals, like Cu, Pb and Zn as well as from aliphatic and polycyclic hydrocarbons was identified for the upper Layer A. However, the limited proportion (5.5%) of the polluted Layer A in the total volume of the dredged material could not affect the good quality (assessed by the Sediment Quality Guidelines) of the bulk sediment. The identification of the optimum marine dumping site was based on (a) the physicochemical similarity (detected by the application of a cluster analysis) of the dredged material with the surficial deposits of potential dumping sites in the Outer Thermaikos Gulf, and (b) the consideration, based on previous studies, of various criteria related to the disposal area such as deep-water circulation, influence on living resources, impact on economical (aquaculture, fishing, navigation), recreational (fishing) and military activities.     

Kinetic and Mechanistic Studies of NO X Selective Catalytic Reduction Over In/Al2O3 and N2O Decomposition Over Ru/Al2O3

Detailed kinetic studies are presented for two reactions: the nitric oxide (NO) selective catalytic reduction (SCR) by propene over indium/alumina (In/Al₂O₃) and the nitrous oxide (N₂O) reduction over ruthenium/alumina (Ru/Al₂O₃). Both reactions were studied in the presence of excess oxygen (O₂) to simulate the composition of flue gases. Apparent activation energies and apparent orders of reaction were calculated in experiments performed under differential reaction conditions. We used our experimental results to propose the reaction mechanism that leads to nitrogen formation over the two catalysts. The NO reduction proceeds through the initial formation of C _X H _Y O _Z N, a reaction intermediate that reacts with activated nitrogen oxides (NO _X ). Nitrous oxide is catalytically decomposed to nitrogen (N₂) over Ru/Al₂O₃.