Chlorine in the atmosphere

Perner D., Arnold T., Crowley J., Kliipfel T., Martinez M., and Seuwen R. (1999) The measurements of active chlorine in the atmosphere by chemical amplification. J. Atmos. Chem. 34, 9-20. 

The dominant chemical form of chlorine in the atmosphere is HC1 185 it is produced mainly from aerosols of marine origin. The role of Cl compounds as catalysts for the recombination of oxygen was discussed and shown to play no major role in the normal atmosphere. The molecular motions of liquid and of paraelectric solid HC1 have been studied by analysis of Raman lineshapes.185... 

The chemical state of HCl on ice can greatly influence the heterogeneous reactions leading to the release of active chlorine in the atmosphere.A lot of studies have been recently dedicated to the HCl adsorption on ice/ each aiming at a better understanding of the dissociation/solvatation mechanism of HCl, but sometimes reporting contradictory conclusions. " ... 

These and continuing actions on a worldwide scale have had a significant impact on the amount of chlorine in the atmosphere. Its concentration in the atmosphere is known to have peaked in the mid-1990s and is now declining. There is hope that the ozone layer may recover within the next 50 years or so due to this worldwide effort to address a very serious environmental problem. It is hoped that during this time the G1 concentration will drop to the pre-ozone—hole level of around 2 ppb. 

Although chlorine is an abimdant element in nature, it does not go through a biogeochemical cycle like sulfur and nitrogen do. There tends to be very little chlorine in the atmosphere (from any natural sources at least) as either the pure element or in compounds. On land, chlorine mostly stays locked up in rock salt and other minerals. In the ocean the splashing of salt water releases some salt into the air, which would include NaCl but in NaCl, chlorine is present as the chloride ion (Cl ), not as chlorine atoms. Chloride ions are not particularly reactive and are more likely just to fall back into the ocean than to combine with other substances in the atmosphere. 

The ozone layer in the stratosphere filters the high-energy ultraviolet radiation out of the sunlight and in this way enables life on earth. Since midst of the seventies a drastic decrease in the ozone concentration above the antarctic region has been observed in September and October every year, and since 1990 also above the arctic region. Investigating the role of chlorine in the atmospheric chemistry it was found, that chlorofluorocarbons can reach the stratosphere, where they decompose and release halogens that affect the ozone layer [357]. 

In the atmosphere, ozone is attacked by chlorine atoms primarily introduced via polutants. The destruction of ozone is self-sustaining via these reactions ... 

Solvent resistance This varies from very poor (for chlorinated rubbers) to good (for polyurethanes). All paint binders have specific susceptibilities and the presence of small quantities of the appropriate solvent in the atmosphere in the region of an item of plant can cause rapid failure. 

Chlorine (sixteenth most abundant element) is found as Cl- in water soluble salt deposits, such as NaCl, and in salt waters. The element, Cl2, is not found in the atmosphere. 

A major difficulty is that so many applicahons employ polymers as though they were readily disposable, despite the fact that they are, in reality, among the more inert of chemical pollutants. In particular, plashc packaging tends to make a single use of a fabricated polymer which is then thrown away. Even when disposed of responsibly, packaging materials are the source of a serious pollution problem. Municipal authorities dispose of such materials by one of two routes, landfilling and incineration, of which the latter cannot be readily used for chlorinated polymers, such as PVC, because of the additional problems caused by organochlorine species in the atmosphere. 

The chlorine atoms in the upper atmosphere come from the breakdown of CF2 CI2 and other similar chlorofluorocarbons (CFCs), known commercially as Freons. Production of these compounds was more than one million tons in 1988, largely for use in relrigerators and air conditioners. Once released into the atmosphere, CFCs diffuse slowly upward in the atmosphere until they reach the ozone layer. There, ultraviolet light Irom the sun splits off chlorine atoms. These react with ozone, with dramatic results. Annual ozone decreases have exceeded 50% above Antarctica. The background photo shows the Antarctic hole (red-violet) on September 24, 2003. 

In homogeneous catalysis, both the catalyst and the reactants are in the same phase, i.e. all are molecules in the gas phase, or, more commonly, in the liquid phase. One of the simplest examples is found in atmospheric chemistry. Ozone in the atmosphere decomposes, among other routes, via a reaction with chlorine atoms ... 

The reaction of volatile chlorinated hydrocarbons with hydroxyl radicals is temperature dependent and thus varies with the seasons, although such variation in the atmospheric concentration of trichloroethylene may be minimal because of its brief residence time (EPA 1985c). The degradation products of this reaction include phosgene, dichloroacetyl chloride, and formyl chloride (Atkinson 1985 Gay et al. 1976 Kirchner et al. 1990). Reaction of trichloroethylene with ozone in the atmosphere is too slow to be an effective agent in trichloroethylene removal (Atkinson and Carter 1984). 

For polychlorinated biphenyls (PCBs), rate constants were highly dependent on the number of chlorine atoms, and calculated atmospheric lifetimes varied from 2 d for 3-chlorobiphenyl to 34 d for 236-25 pentachlorobiphenyl (Anderson and Hites 1996). It was estimated that loss by hydroxy-lation in the atmosphere was a primary process for the removal of PCBs from the environment. It was later shown that the products were chlorinated benzoic acids produced by initial reaction with a hydroxyl radical at the 1-position followed by transannular dioxygenation at the 2- and 5-positions followed by ring fission (Brubaker and Hites 1998). Reactions of hydroxyl radicals with polychlorinated dibenzo[l,4]dioxins and dibenzofurans also play an important role for their removal from the atmosphere (Brubaker and Hites 1997). The gas phase and the particulate phase are in equilibrium, and the results show that gas-phase reactions with hydroxyl radicals are important for the... 

Although reactions carried out by ozone have attracted enormous attention in the atmospheric environment, ozone has also been used extensively in the treatment of drinking water without the production of undesirable trihalomethanes from the use of molecular chlorine (Richardson et al. 1999). It has been examined for the removal of a number of contaminants, and ozone is considered to be a selective oxidant, even though quite complex reactions may occur. 

Larsson, P., C. Jarnmark, and A. Sodergren. 1992. PCBs and chlorinated pesticides in the atmosphere and aquatic organisms of Ross Island, Antarctica. Mar. Pollut. Bull. 25 9-12. 

Both models apply the same chemical scheme of mercury transformations. It is assumed that mercury occurs in the atmosphere in two gaseous forms—gaseous elemental HgO, gaseous oxidized Hg(II) particulate oxidized Hgpart, and four aqueous forms—elemental dissolved HgO dis, mercury ion Hg2+, sulphite complex Hg(S03)2, and aggregate chloride complexes HgnClm. Physical and chemical transformations include dissolution of HgO in cloud droplets, gas-phase and aqueous-phase oxidation by ozone and chlorine, aqueous-phase formation of chloride complexes, reactions of Hg2+ reduction through the decomposition of sulphite complex, and adsorption by soot particles in droplet water. 

Liquefaction of chlorine is always incomplete, because the non-condensable impurities carry chlorine at its vapour pressure as they leave the liquefaction process. This exit gas, or tail gas, is handled in any of several different ways. It is of course an intolerable plant emission, and the contained chlorine must at least be destroyed before the gas is released to the atmosphere. There is also a powerful economic incentive for recovering much of the chlorine in some usable form - Silver s estimate of the value of the chlorine in the tail gas produced in the United States alone in 1981 was 50 million [3]. 

In the electrolysis plant of Akzo Nobel in Rotterdam a hypochlorite production unit is in operation. This unit has two functions handling chlorine-containing waste gases from the plant and production of hypochlorite. The reaction is carried out in a two-step apparatus in which a liquid jet-loop reactor and a packed column are in series. In this way chlorine is converted to hypochlorite and emissions of chlorine to the atmosphere are avoided. 

Volpe C, Wahlen M, Spivack AJ (1998) Chlorine isotopic composition of marine aerosols Implications for the release of reactive chlorine and HCl cycling rates. Geophys Res Lett 25(20) 3831-3834 Volpe CM (1998) Stable Chlorine Isotope Variations in the Atmosphere. PhD Dissertation, University of California, San Diego, San Diego, California... 

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