Methyl chloroform , tropospheric

Taylor JA, Brasseur GP, Zimmermann PR, Cicerone RJ. 1991. A study of the sources and sinks of methane and methyl chloroform using a global three-dimensional Lagrangian tropospheric tracer transport model. Journal of Geophysical Research 96D 3013-3044. 

Rudolph J, von Czapiewski K, Koppmann R (2000) Emissions of Methyl Chloroform (CH3CCI3) from Biomass Burning and the Tropospheric Methyl Chloroform Budget. Geophys Res Lett 27 1887... 

Based on direct spectroscopic measurements of OH radical concentrations at close to ground level, peak daytime OH radical concentrations are typically (3-10) x 106 molecule cm-3 (see, for example, Brauers et al., 1996 Mather et al., 1997 Mount et al., 1997). A diur-nally, seasonally, and annually averaged global tropospheric OH radical concentration has been derived from the emissions, atmosphere concentrations, and OH radical reaction rate constant for methyl chloroform (CH3CC13), resulting in a 24-hr average OH radical concentration of 9.7 x 10s molecule cm 3 (Prinn et al., 1995). 

In such models the OH concentration field is computed using measured or estimated concentration fields of the precursor molecules and photon flux data. The resulting OH field is then tuned such that it correctly predicts the lifetime of methyl chloroform (CH3CCI3) with respect to OH radical attack. From measurements of the atmospheric turnover time of CH3CCI3 (4.8 years) [20], its lifetime with respect to loss in the stratosphere (45 years), and its lifetime with respect to loss in the oceans (85 years) the tropospheric lifetime of CH3CCI3 with respect to OH radical attack has been inferred to be 5.7 years [17,21], Methyl chloroform is the calibration molecule of choice because it has a long history of precise atmospheric measurements, it has no natural sources, its industrial production is well documented, and because the kinetics of reaction Eq. 20 are well established, feo = 1.8 x 10-12 exp(- 1500/T) cm3 molecule-1 s-1 [22]. 

Finlayson-Pitts BJ, Ezell MJ, Jayaweera TM, et al. 1992. Kinetics of the reactions of OH with methyl chloroform and methane implications for global tropospheric OH and the methane budget. 

Here Rs is again the total mass of methyl chloroform present in the troposphere divided by the cumulative emission up to time t. The residence time in the southern hemisphere depends on the interhemispheric exchange time,... 

The atmosphere consists of a lower layer, the troposphere, separated from the upper stratosphere by the tropopause, a boundary characterised by a sharp reversal of rate of change of temperature. The only non-fluorinated halocarbons found in the stratosphere are carbon tetrachloride, and some methyl chloroform and methyl chloride. The troposphere, however, contains a much wider range of chlorocarbons at detectable levels. 

In the troposphere, OH is produced mainly by reaction (11a) and it is responsible for the oxidation of many constituents such as methyl chloride, chloroform, and a certain number of chlorofluoromethanes. 

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