Methyl chloride oceans

Lovelock and co-workers [228,229] determined methyl fluoride, methyl chloride, methyl bromide, methyl iodide, and carbon tetrachloride in the Atlantic Ocean. This shows a global distribution of these compounds. Murray and Riley [230,231] confirmed the presence of carbon tetrachloride, and also found low concentrations of chloroform and tri- and tetrachloroethylene in Atlantic surface waters. 

Thousands of tonnes of methyl chloride are produced naturally every day, primarily in the oceans. Other significant natural sources include forest and brush fires and volcanoes. Although the atmospheric budget of methyl chloride can be accounted for by volatilization from the oceanic reservoir, its production and use in the manufacture of silicones and other chemicals and as a solvent and propellant can make a significant impact on the local atmospheric concentration of methyl chloride. It has been detected at low levels in drinking-water, groundwater, surface water, seawater, effluents, sediments, in the atmosphere, in fish samples and in human milk samples (Holbrook, 1993 United States National Library of Medicine, 1998). Tobacco smoke contains methyl chloride (lARC, 1986). 

Exposure to methyl chloride may occur in its production, and in the production of silicones and various other chemical products. Methyl chloride is produced naturally, primarily in oceans, and it is widely detected in ambient air and water. 

Methyl iodide is produced by many marine photosynthetic organisms and therefore the ocean is thought to be a major natural source of methyl iodide. Some of this is released to the atmosphere and some reacts with seawater to form methyl chloride. Industrial emissions of methyl iodide may occur in conjunction with its use as a methylating agent and in organic synthesis. Humans are exposed to methyl iodide from the ambient air and from ingesting seafood (United States National Library of Medicine, 1998). 

Moore RM, Groszko W, Niven JS (1996) Ocean-Atmosphere Exchange of Methyl Chloride Results from NW Atlantic and Pacific Ocean Studies. J Geophys Res 101 28529... 

The Oceans as a Source of Gases to the Atmosphere 2.1 Dimethyl sulfide Methyl mercaptan Carbonyl sulfide Carbon disulfide Hydrogen sulfide Methyl iodide Methyl chloride Chloroform Nitrous oxide Methane... 

Moore R. M., Groszko W., and Niven S. J. (1996a) Ocean-atmosphere exchange of methyl chloride results from NW Atlantic Ocean and Pacific Ocean studies. J. Geophys. Res. 101, 28529-28538. 

Many of these naturally produced gases play important roles in atmospheric chemistry. For example, OCS may maintain the stratospheric sulfate layer 10,11). Changes in the concentration of this aerosol layer could alter the global temperature. Dimethyl sulfide is produced in the ocean and is released to the atmosphere where it probably is rapidly oxidized to SO2, which contributes substantially to the background acidity of rainwater 12). Methyl chloride, which is produced in the ocean, is the dominant... 

As we have mentioned already, the Cl/ClO cycle is also important in stratosphere. The natural source of atomic chlorine. Cl, is methyl chloride gas, CH3CI, produced at the Earth s surface, mainly in the oceans as a result of the interaction of chloride ions with decaying vegetation. Only a portion of methyl chloride gas is destroyed in the troposphere. When intact molecules of it reach the stratosphere, they react photochemically decomposed by UV-C or attacked by OH radicals (reactions (15) and (16))... 

Methyl chloride supplies about 0.5 ppb of chlorine to the stratosphere. Prior to 1996, the atmospheric input of CH3CI was assumed to be a result of biological processes in the ocean. Tropical terrestrial sources, biomass burning and tropical plants, are now believed to be important. The dominant sink of CH3CI is reaction with the OH radical in the... 

However, the removal of chlorine and its reservoir species (HCl and CIONO2) by physical processes is slow. Consequently, chlorine is a serious threat to stratospheric ozone. To amplify this concern, the natural level of chlorine is about 0.6 part per billion (ppb) and results from methyl chloride (CH3CI) released from the oceans [3]. As of 1989, the total chlorine level from all known sources was 3.7 ppb [3], nearly six times the natural level of chlorine. Prior to 1987 there were no controls over the production of chlorofluorocarbons from industrial sources however, in 1987, international agreements were drawn up to limit the production and use of CFCs, with the expected complete phaseout of these materials by the year 2000 [4-6]. Now the question that must be addressed is the following What are the atmospheric implications of the new materials found to replace the chlorofluorocarbons ... 

Yvon-Lewis, S. A., D. B. King, R. Tokarczyk, K. D. Goodwin, E. S. Saltzman and J. H. Butler (2004) Methyl bromide and methyl chloride in the Southern Ocean. Journal of Geophysical Research 109, C02008, doi 10.1029/2003JC001809... 

There are no naturally occurring CFCs, but some natural sources contribute chlorine and bromine to the atmosphere, and, just like halogens from CFC, these naturally occurring Cl and Br atoms can participate in ozone-depleting reactions. The principal natural sources are methyl bromide and methyl chloride, which are emitted from the oceans. It is estimated that these molecules contribute less than a third of the total Cl and Br in the atmosphere the remaining two-thirds is a result of human activities. 

Methyl chloride, CH3CI 600 ppt Uniform Emissions from ocean, 3 Biomass burning, 0.7 Reaction with OH 1.3 yr... 

Methyl halides such as methyl chloride CH3CI, methyl bromide CHsBr, and methyl iodide CH3I are natural origin species emitted from terrestrial and oceanic sources, but anthropogenic emissions are also important for CH3Br. Among these, CH3I are photolyzed mostly by the actinic flux in the troposphere. 

As an example of homogeneous catalysis, I shall describe the havoc that a chlorine atom. Cl, can bring about in the upper atmosphere. Chlorine atoms are produced by the impact of solar radiation on methyl chloride, CH3CI, 5, once widely used as a propellant in aerosol cans and which drifted high into the atmosphere after its propellant duties were done. Methyl chloride is also formed as a by-product of reactions between chloride ions. Cl", and decaying vegetation in salty oceans. 

Natural acidity is contributed from emissions of acidic or acidifying compounds from volcanoes (Pyle et al., 1996 Camuffo, 1992), including compounds of S, N, Cl (chloride), and NH3 (ammonia), from the ocean (e.g., methyl sulfonate) (Charlson et al., 1987), and from wetlands (e.g., H2S) (Gorham et al., 1987). 

The possibility that the depletion of chloride in the marine aerosol is due to fractionation during the formation of sea-salt particles by bursting bubbles can be discounted. Laboratory studies of Chesselet et al (1972b) and Wilkness and Bressan (1972) showed no deviation of the Cl /Na+ mass ratio from seawater in the bubble-produced sea-salt particles. It may be mentioned in passing that bromide in marine aerosols shows a deficit similar to chloride, whereas iodide is present in excess. The latter observation is attributed to both chemical enrichment at the sea s surface and scavenging of iodine from the gas phase. A portion of iodine is released from the ocean as methyl iodide, which in the atmosphere is subject to photodecomposition and thereby provides a source of scavengable iodine. The process has been reviewed by Duce and Hoffman (1976). In continental aerosols, chloride and bromide are partly remnants of sea salt, but there exists also a contribution from the gas phase. 

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