Atmosphere methyl bromide

Salt marshes, mixed with the mangroves in certain warm regions, account for the formation of 10% of the atmospheric methyl bromide and methyl chloride. These two gases react with stratospheric ozone (Rhew 2000). 

M. E. Hines, and R. C. Harriss, Rapid Degradation of Atmospheric Methyl Bromide in Soils, Nature, 377, 717-719 (1995). 

Yagi, K., J. Williams, N.-Y. Wang, and R. J. Cicerone, Atmospheric Methyl Bromide (CH,Br) from Agricultural Soil Fumigations, Science, 267, 1979-1981 (1995). 

Varner RK, Crill PM, Talbot RW (1999) Wetlands A Potentially Significant Source of Atmospheric Methyl Bromide and Methyl Chloride. Geophys Res Lett 26 2433... 

Jeffers, P.M. and Wolfe, NL. Green plants A terrestrial sink for atmospheric methyl bromide. Geophy. Res. Lett. 25 43-46, 1998. 

Cicerone R. J., Heidt L. E., and Pollack W. H. (1988) Measurements of atmospheric methyl-bromide and bromo-form. J. Geophys. Res. 93, 3745-3750. 

Varner R. K., Grill P. M., and Talbot R. W. (1999) Wetlands a potentially significant source of atmospheric methyl bromide and methyl chloride. Geophys. Res. Lett. 26, 2433-2436. 

As a soil fumigant methyl bromide leaves no toxic residue in soils. The volatile gas rises into the atmosphere. Methyl bromide is an ozone-depleting substance. Although methyl bromide is very soluble in water, its high vapor pressure in various soil types indicates a low tendency to adsorb to soils and rapid evaporation. Methyl bromide has a half-life in air estimated from 0.3 to 1.6 years. Degradation is primarily due to photolysis. In soils, the half-life is 0.2-0.5 days. In water, a half-life of 3 h was calculated. 

Methyl bromide is nonflammable over a wide range of concentrations in air at atmospheric pressure and offers practically no fire hazard. With an intense source of ignition, flame propagation within a narrow range from 13.5 to 14.5% by volume has been reported. The material has no flash point. Thermal decomposition in a glass vessel begins somewhat above 400°C. 

Grosjean D (1991) Atmospheric chemistry of toxic contaminants. 4. Saturated halogenated aliphatics methyl bromide, epichlorhydrin, phosgene. J Air Waste Manage Assoc 41 56-61. 

Methyl bromide has been identified as an ozone-depleting substance and is being gradually removed from world markets. Current legislation and plans call for the elimination of methyl bromide in most industrial countries by 2005, with possible exemptions for quarantine (UNEP, 1996). Currently there is an extensive search worldwide for products that are alternatives to methyl bromide (Kawakami, 1999). These alternatives are broadly defined and include components of management plans such as sanitation, monitoring, contact insecticides, heat treatments, and modified atmospheres, in addition to new fumigants (Batchelor, 1998). 

Due to its gaseous nature it may have an effect on the stratospheric ozone layer [281, 402, 404]. After injection into soil for fumigation, methyl bromide rapidly diffuses through the soil pore space to the soil surface and then into the atmosphere [159,162,163,405,406]. Since a plastic sheet typically covers the soil surface, the rate of emission into the atmosphere depends upon the thickness and density of the plastic, if other conditions are the same [159, 406]. Other routes of disappearance from soil include chemical hydrolysis, methylation to soil organic matter through free radical reactions, and microbial degradation [ 136,159,405,407]. Several reports appeared on the study of the microbial transformations of methyl bromide, summarized as follows ... 

Watson RT, Albritton DL, Anderson SO, Lee-Bapty S (1992) Methyl bromide its atmospheric science technology and economics. United Nations Environmental Programme, United Nations Headquarters, Nairobi, Kenya... 

Bond EJ, Dumas T. 1987. Concentrations of methyl bromide inside flour mills and in the atmosphere around the mills during and after fumigation. Proc Entomol Soc Ont 118 1-6. 

Robbins DE. 1976. Photodissociation of methyl chloride and methyl bromide in the atmosphere. Geophys Res Lett 3 213-216. 

The highly toxic pesticide, methyl bromide or CHsBr, is diffusing through air. Estimate the mean velocity and mean free path of the methyl bromide molecules at an atmospheric pressure of 1 atm and a room temperature of 20° C. 

The amount of CH3Br that is applied to soils as a fumigant and that escapes to the atmosphere is also uncertain. For example, Cicerone and co-workers (Yagi et al., 1993, 1995) measured a range from 34 to 87% of the methyl bromide applied to a field that escaped to the atmosphere. Since approximately 80% of synthetic CH3Br use is due to soil fumigation (Shorter et al.,... 

These data also demonstrate the impact of bromine chemistry on the stratosphere (see Chapter 12.D). The initial ODP for methyl bromide is 15, due primarily to the large a factor associated with bromine chemistry. However, since it is removed by reaction with OH in the troposphere as well as by other processes such as hydrolysis in the oceans and uptake by soils and foliage (see Chapter 12.D), it has a short atmospheric lifetime of 1.3 years and hence the ODP decreases rapidly with time, toward a long-term steady-state value. 

Grosjean, D., Atmospheric Chemistry of Toxic Contaminants. 4. Saturated Halogenated Aliphatics Methyl Bromide, Epichlorhy-drin, Phosgene, J. Air Waste Manage. Assoc., 41, 56-61 (1991b). 

Second, reaction 8.9 and other relevant reactions appear to occur preferentially on available solid surfaces, which are often ice crystals but may also be particles of sulfate hazes from volcanic eruptions or human activity. Third, volatile bromine compounds are even more effective (via Br atoms) than chlorine sources at destroying ozone methyl bromide is released into the atmosphere naturally by forest fires and the oceans, but anthropogenic sources include the use of organic bromides as soil fumigants (methyl bromide, ethylene dibromide) and bromofluorocarbons as fire extinguishers (halons such as CFsBr, CF2BrCl, and C2F4Br2). 

Tmdinger CM, Etheridge DM, Sturrock GA, Fraser PJ, Krummel PB, McCulloch A (2004) Atmospheric Histories of Halocarbons from Analysis of Antarctic Fim Air Methyl Bromide, Methyl Chloride, Chloroform, and Dichloromethane. J Geophys Res 109 D22310... 

Butler JH, Rodriguez JM (1996) Methyl Bromide in the Atmosphere. In Bell CH, Price N, Chakrabarti B (eds) The Methyl Bromide Issue. Wiley, Chichester, UK, p 27... 

Reeves CE (2003) Atmospheric Budget Implications of the Temporal and Spatial Trends in Methyl Bromide Concentration. J Geophys Res 108 4343... 

Various other workers have reported on the determination of volatile organic compounds in soils [186,187] and landfill soils [188]. Soil fumigants such as methyl bromide have also been determined by this technique [189]. Trifluoroacetic acid is a breakdown product of hydrofluorocarbons and hydrochlorofluorocarbon refrigerant products in the atmosphere and, as such, due to the known toxicity of trifluoroacetic acid, it is important to be able to determine it in the atmosphere, water and in soil from an environmental point of view [190]. In this method the trifluoroacetic acid is extracted from the soil sample by sulfuric acid and methanol, which is then followed by the derivatisation of it to the methyl ester. The highly volatile methyl ester is then analysed with a recovery of 87% using headspace gas chromatography. Levels of trifluoroacetic acid in soil down to 0.2 ng/g can be determined by the procedure. 

Hydrolysis can explain the attenuation of contaminant plumes in aquifers where the ratio of rate constant to flow rate is sufficiently high. Thus 1,1,1-trichloroethane (TCA) has been observed to disappear from a mixed halocarbon plume over time, while trichlo-roethene and its biodegradation product 1,2-dichloroethene persist. The hydrolytic loss of organophosphate pesticides in sea water, as determined from both laboratory and field studies, suggests that these compounds will not be long-term contaminants despite runoff into streams and, eventually, the sea (Cotham and Bidleman, 1989). The oceans also can provide a major sink for atmospheric species ranging from carbon tetrachloride to methyl bromide. Loss of methyl bromide in the oceans by a combination of hydrolysis... 

Robbins, D.E. (1976) Photodissociation of methyl chloride and methyl bromide in the atmosphere. Geophys. Res. Letter 3, 213-216. Robbins, G.A., Wang, S., Stuart, J.D. (1993) Using the static headspace method to determine Henry s law constants. Anal. Chem. 65, 3113-3118. 

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