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| Titel |
Rate Constants for the Reactions of OH with CO, NO and NO2, and of HO2 with NO2 in the Presence of Water Vapour at Lower-Tropospheric Conditions |
| VerfasserIn |
Michael Rolletter, Hendrik Fuchs, Anna Novelli, Christian Ehlers, Andreas Hofzumahaus |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250129241
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| Publikation (Nr.) |
 EGU/EGU2016-9322.pdf |
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| Zusammenfassung |
| Recent studies have shown that the chemistry of gaseous nitrous acid (HONO) in the lower
troposphere is not fully understood. Aside from heterogenous reactions, the daytime HONO
formation in the gas-phase is not well understood (Li et al., Science, 2014). For a better
understanding of HONO in the gas-phase, we have reinvestigated the reaction rate
constants of important tropospheric reactions of the HOx radical family (OH and HO2)
with nitrogen oxides at realistic conditions of the lower troposphere (at ambient
temperature/pressure and in humid air). In this study we apply a direct pump and probe
technique with high accuracy, using small radical concentrations to avoid secondary
chemistry.
Pulsed laser photolysis/laser-induced fluorescence (LP/LIF) was used to investigate the
reaction rate constants of OH with CO, NO, NO2, and HO2 with NO2 in synthetic air at
different water vapor concentrations (up to 5 x 1017 molecules cm−3). Photolysis of ozone in
the presence of gaseous water was the source of OH. The reactions took place in a flow-tube
at room temperature and atmospheric pressure. The chemical decay of the radicals was
monitored by laser-induced fluorescence detection in a low-pressure cell, which sampled air
continuously from the end of the flow-tube. Knowing the reactant concentrations
subsequently allowed to calculate the bimolecular reaction rate constants at 1 atm from the
pseudo-first-order decays. In order to observe HO2 reactions, OH was converted into
HO2 with an excess of CO in the flow-tube. The newly measured rate constants
for OH with CO, NO and NO2 agree very well with current recommendations by
NASA/JPL and IUPAC and have an improved accuracy (uncertainty < 5%). These rate
coefficients are independent of the presence of water vapour. The measured rate
constant of HO2 with NO2 was found to depend significantly on the water-vapour
concentration (probably due to formation of HO2*H2O complexes) and to exceed current
recommendations by NASA/JPL and IUPAC by up to a factor of 2.6. Our experiments
confirm the existence of a water vapour influence similarly to the one reported
previously by Sander and Peterson (1984) for a lower total pressure (470 hPa). |
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