Mercury point source

Mercury point sources and rates of particle scavenging are key factors in atmospheric transport rates to sites of methylation and subsequent entry into the marine food chain (Rolfhus and Fitzgerald 1995). Airborne soot particles transport mercury into the marine environment either as nuclei for raindrop formation or by direct deposition on water (Rawson etal. 1995). In early 1990, both dimethylmercury and monomethylmercury were found in the subthermocline waters of the equatorial Pacific Ocean the formation of these alkylmercury species in the low oxygen zone suggests that Hg2+ is the most likely substrate (Mason and Fitzgerald 1991 Figure 5.1). 

An elevated concentration of mercury (i.e., >1.0 mg/kg FW), usually as methylmercury, in any biological sample is often associated with proximity to human use of mercury. The elimination of mercury point-source... 

The Hg-electrolysis technology is one of the major point sources of Hg contamination, and its impact on the environment has been studied worldwide [23-26]. Although mercury cell chlor-alkali industry is obsolete in most of the European Union countries [27], in Spain it will be allowed until the end of 2010. 

In aquatic environments where point sources of industrial contamination have been identified, the elimination of mercury discharges has usually improved environmental quality. Such improvement has been reported for Minamata Bay (Table 5.4) for sediments in Saguenay Fjord, Quebec,... 

OSPAR facilitated these technical efforts by setting up an Intersessional Correspondence Group (ICG) - a loose group of experts drawn from industry and government - which reports to OSPAR s annual meeting on point sources of pollution (known, creatively, as POINT). This work culminated in a two-day chlor-alkali workshop ( WOCAI ) in Madrid in September 1999 at which very full technical presentations were made on every aspect of the mercury issue. The conclusions of this workshop supported some, but not all, of industry s views. Where areas of technical disagreement still existed these were referred back to the ICG for resolution. 

High intensity, microwave powered emission sources have recently been developed that are reported to provide substantially higher DUV output than classical electrode discharge mercury lamps 76). These sources suffer from self-absorption of the intense 254 nm emission but have a relatively high output in a band between 240 and 280 nm. They are extended sources of finite size rather than point sources, and they must also be an integral part of a tuned, resonant microwave cavity. Consequently, extensive condenser design work would be required in order to utilize the microwave powered sources in projection printers. 

High-pressure mercury lamps operate at pressures of about 10 atm, and there are essentially two types used in industrial applications. The point source... 

High-pressure mercury lamps operate at pressures about 10 atmospheres and essentially two types are used in industrial applications. The point source lamp focuses on a small-diameter spot, thus delivering an intense radiation to that spot. The capillary lamp is used for narrow webs up to approximately 20 cm (8 in.) wide.4 They are capable of producing a wider spectrum than the medium-pressure lamps and operate with higher power (150-2880 W/cm). Their disadvantage is a relatively short operating life, typically hundreds of hours. 

The human-related sources of mercury to the environment are numerous and widespread. Most direct inputs of mercury from point sources to aquatic systems have largely been contained in most developed countries. Inputs of mercury to the environment via the atmosphere are of the greatest concern. These emissions, coupled with long-distance transport of elemental mercury, have resulted in elevated concentrations of mercury in fish from locations that are removed from anthropogenic sources (e.g., open-ocean, and semi-remote regions in the United States, Canada, Scandinavia Wiener et al., 2002). A summary of the fluxes from major sources (for 1995) is shown... 

Fig- 36. Point source, high-pressure mercury arc, 200 W. From ref. 9. 

A more detailed estimate of national mercury emission rates for various categories of sources is shown in Table 5-4. As shown in this table, point sources of anthropogenic mercury emissions appear to represent the greatest contribution of mercury releases, with combustion sources representing 85% of all emissions. 

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