Marine environments atmospheres

Atmospheric corrosion results from a metal s ambient-temperature reaction, with the earth s atmosphere as the corrosive environment. Atmospheric corrosion is electrochemical in nature, but differs from corrosion in aqueous solutions in that the electrochemical reactions occur under very thin layers of electrolyte on the metal surface. This influences the amount of oxygen present on the metal surface, since diffusion of oxygen from the atmosphere/electrolyte solution interface to the solution/metal interface is rapid. Atmospheric corrosion rates of metals are strongly influenced by moisture, temperature and presence of contaminants (e.g., NaCl, SO2,. ..). Hence, significantly different resistances to atmospheric corrosion are observed depending on the geographical location, whether mral, urban or marine. 

Sulphur oxides These (SO2 is the most frequently encountered oxide) are powerful stimulators of atmospheric corrosion, and for steel and particularly zinc the correlation between the level of SO2 pollution and corrosion rates is good However, in severe marine environments, notably in the case of zinc, the chloride contamination may have a higher correlation coefficient than SO2. 

The purity of the zinc is unimportant, within wide limits, in determining its life, which is roughly proportional to thickness under any given set of exposure conditions. In the more heavily polluted industrial areas the best results are obtained if zinc is protected by painting, and nowadays there are many suitable primers and painting schemes which can be used to give an extremely useful and long service life under atmospheric corrosion conditions. Primers in common use are calcium plumbate, metallic lead, zinc phosphate and etch primers based on polyvinyl butyral. The latter have proved particularly useful in marine environments, especially under zinc chromate primers . 

Sulfides and disulfides can be produced by bacterial reactions in the marine environment. 2-Dimeth-ylthiopropionic acid is produced by algae and by the marsh grass Spartina alternifolia, and may then be metabolized in sediment slurries under anoxic conditions to dimethyl sulfide (Kiene and Taylor 1988), and by aerobic bacteria to methyl sulfide (Taylor and Gilchrist 1991). Further details are given in Chapter 11, Part 2. Methyl sulfide can also be produced by biological methylation of sulfide itself (HS ). Carbon radicals are not the initial atmospheric products from organic sulfides and disulfides, and the reactions also provide an example in which the rates of reaction with nitrate... 

A successful control agent probably should be sought in the marine environment for three reasons. First, this is where the problem is and if a natural control agent has developed, this is where it should be found. Second, the most potent chemical agents seem to be found in the ocean or in the atmosphere potency appears to be required because of the tremendous dilutions. Third, this is where we found what we believe to be a potentially useful control agent. 

Chabas, A. and D. Jeannette (2001), Weathering of marbles and granites in marine environment Petrophysical properties and special role of atmospheric salts, Environ. Geol. 40(3), 359-368. 

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). 

The global dispersion and deposition of debris from atmospheric nuclear weapons is by far the largest source of artificial radioactivity to the terrestrial and marine environment. Nevertheless, this caused only a slight increase in the total global inventory of radioactivity, with the major contributor being tritium ( H). Evidence for significant... 

Corrosion resistant piping should be provided where corrosive atmospheres exist, such as marine environment, chlorine plants, etc. 

Owens NJP (1987) Natural variations in N in the marine environment, Adv Mar Biol 24 390 51 Pagani M, Arthur MA, Freeman KH (1999a) Miocene evolution of atmospheric carbon dioxide, Paleoceanography 14 273-292... 

D. C. Cook, A C. Van Orden, J. Reyes, S.J.Oh, R. Balasubramanian, J.J. Carpio, H.E. Townsend, Atmospheric Corrosion in Marine Environments along the Gulf of Mexico, Marine Corrosion in Tropical Environments, ASTM STP 1399, S.W. Dean,... 

For special purposes, more complex equipment is occasionally used (not covered by 4665) which additionally attempts to simulate corrosive or polluted atmospheres. There is an ISO standard for plastics for a salt spray exposure test93 which could in principle be applied to rubber should such an exposure be needed. Cyclic exposure to corrosive atmosphere could be more representative of service94,95. One particular circumstance is exposure to a marine environment and there is an ISO standard covering this for plastics96. 

The mixture of organic constituents in the marine environment is extremely complex. Their origin is partly terrigenuous many compounds are produced in the marine environment itself. The different sources and their relative importance for the complexation of trace metals in estuaries, coastal seas and open ocean are riverine input, runoff from the coastal zone, resuspension, import of water mases, atmospheric input and in situ biological production. 

Assessments of the impacts of different radioactive sources on contamination of the Arctic marine environment including water basins, land, and atmosphere. 

Overall, widespread PAH contamination in the coastal sediments of Singapore is apparent. PAH distribution profiles in both regions were dominated by pyrogenically derived PAH sources, signifying that inputs to the marine environment are dominated by the atmospheric deposition of contaminated particulates. With reference to studies conducted elsewhere, sediments in Singapore can be classified as moderately contaminated. 

In thermospray interfaces, the column effluent is rapidly heated in a narrow bore capillary to allow partial evaporation of the solvent. Ionisation occurs by ion-evaporation or solvent-mediated chemical ionisation initiated by electrons from a heated filament or discharge electrode. In the particle beam interface the column effluent is pneumatically nebulised in an atmospheric pressure desolvation chamber this is connected to a momentum separator where the analyte is transferred to the MS ion source and solvent molecules are pumped away. Magi and Ianni (1998) used LC-MS with a particle beam interface for the determination of tributyl tin in the marine environment. Florencio et al. (1997) compared a wide range of mass spectrometry techniques including ICP-MS for the identification of arsenic species in estuarine waters. Applications of HPLC-MS for speciation studies are given in Table 4.3. 

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