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| Titel |
First in situ detection of HO2 radical in a smog chamber by cw-CRDS |
| VerfasserIn |
M. Djehiche, J. Tarmoul, A. Tomas, C. Fittschen, P. Coddeville |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250019484
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| Zusammenfassung |
| The hydroperoxyl radical HO2 belongs to these trace species of the atmosphere which play a
crucial role in the tropospheric chemistry. In particular, it is responsible for the
formation of OH radicals through the HO2 + NO reaction, the OH radical being the
most important oxidant in the troposphere. The detection and quantification of
the HO2 radical during laboratory experiments in environmental chambers have
been a challenge for a long time due to its short lifetime and consequently weak
concentrations.
We have thus developed a new quartz photochemical reactor of 120 L which has been
coupled to an in-situ cw-CRDS detector in the near IR. Preliminary tests on stable
molecules like CO (~ 1570 nm) and CH2O (~ 1510 nm) allowed us to determine the
absorption sensitivity of the spectrometer. An αmin of 1 × 10-9 cm-1 has been
obtained, leading to an HO2 detection limit of about 2 × 1010 molecule cm-3at
6625 cm-1. We then investigated the photolysis of methyl nitrite CH3ONO at 365
nm:
CH3ONO + hν → CH3O + NO
CH3O + O2 → CH2O + HO2
HO2 + NO → OH + NO2
For the first time, the HO2 radical has been directly observed duringthe photolysis of
CH3ONO. Experiments have been conducted at 50 Torr total pressure and absolute HO2
photostationary concentrations of (0.8 – 1.5) × 1011 molecules cm-3 have been determined,
depending on the reaction conditions. The simultaneous measurements of the products (NO2
and CH2O) in the same wavelength region allow us to simulate the explicit chemical
mechanism. The obtained results will be discussed and the perspectives in term of use of this
new setup will be presented. |
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