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| Titel |
Laboratory study on heterogeneous decomposition of methyl chloroform on various standard aluminosilica clay minerals as a potential tropospheric sink |
| VerfasserIn |
S. Kutsuna, L. Chen, K. Ohno, N. Negishi, K. Takeuchi, T. Ibusuki, K. Tokuhashi, A. Sekiya |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 3, no. 4 ; Nr. 3, no. 4 (2003-07-21), S.1063-1082 |
| Datensatznummer |
250001139
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| Publikation (Nr.) |
 copernicus.org/acp-3-1063-2003.pdf |
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| Zusammenfassung |
| Methyl chloroform (1,1,1-trichloroethane,
CH3CCl3) was found to decompose heterogeneously on seven types of standard clay minerals (23 materials) in dry air
at 313 K in the laboratory. All reactions proceeded through the elimination of
HCl; CH3CCl3
was converted quantitatively to CH2=CCl2. The activities
of the clay minerals were compared via their pseudo-first-order reaction rate constants
(k1). A positive correlation was observed between the k1
value and the specific surface area (S) of clay minerals, where the
S value was determined by means of the general Brunauer-Emmett-Teller (BET) equation. The
k1 value was anti-correlated with the value of n, which was a parameter of the general BET equation and related to the
average pore size of the clay minerals, and correlated with the water content that can
be removed easily from the clay minerals. The reaction required no special pretreatment
of clay minerals, such as heating at high temperatures; hence, the reaction can be
expected to occur in the environment. Photoillumination by wavelengths present in the
troposphere did not accelerate the decomposition of CH3CCl3, but it induced
heterogeneous photodecomposition of CH2=CCl2. The temperature dependence
of k1, the adsorption equilibrium coefficient of CH3CCl3
and CH2=CCl2, and the surface reaction rate constant of
CH3CCl3 were determined for an illite sample. The k1
value increased with increasing temperature. The amount of CH3CCl3 adsorbed
on the illite during the reaction was proportional to the partial pressure of
CH3CCl3. The reaction was sensitive to relative humidity and the
k1 value decreased with increasing relative humidity. However, the reaction was found to proceed at a relative humidity of
22% at 313 K, although the k1 value was about one-twentieth of the value in non-humidified air. The conditions
required for the reaction may be present in major desert regions of the world. A simple estimation
indicates that the possible heterogeneous decomposition of CH3CCl3 on the ground surface in arid regions
is worth taking into consideration when inferring the tropospheric lifetime of
CH3CCl3 and global OH concentration from the global budget concentration of
CH3CCl3. |
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