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| Titel |
CARIBIC passenger aircraft measurements in the UTLS: Distribution and seasonal variation of acetone and its impact on the production of HOx |
| VerfasserIn |
M. Neumaier, F. Geiger, E. Christner, R. Ruhnke, C. A. M. Brenninkmeijer, A. Zahn |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069564
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| Zusammenfassung |
| Volatile Organic Compounds (VOCs) are key players in tropospheric chemistry. VOCs
e.g. control (together with NOx) the photochemical production of ozone or they
contribute directly (e.g. via acetone) or indirectly to the oxidation capacity of the
atmosphere.
The UTLS region (upper troposphere / lower stratosphere) plays a key role in the climate
system and any change of its structure and chemical composition can lead to changes in the
Earth’s radiative forcing.
Since May 2005 the CARIBIC passenger aircraft (Civil Aircraft for the Regular
Investigation of the atmosphere Based on an Instrument Container – Lufthansa, Airbus
340-600) measures ~100 trace gases and aerosol components in the UTLS (9-12 km altitude)
on four long-distance flights per month. Acetone is measured using a PTR-MS
(proton-transfer-reaction mass spectrometer). Over the years the largest airborne in-situ
dataset of acetone on a nearly worldwide scale has been composed. Acetone (CH3COCH3)
with a typical lifetime of ~3-6 weeks and an estimated source strength of 40-100 Tg/year is
one of the most abundant oxygenated volatile organic compounds (OVOCs) in the
atmosphere.
The coverage of the acetone dataset was expanded by folding the CARIBIC data with
5-day back trajectories from the ECMWF model. In winter acetone mixing ratios of around
300 pptv were observed on average between 8 km altitude up to the tropopause with hints for
biomass burning over North Africa. In summer elevated values >1500 pptv can be observed
especially between 35Ë - 70Ë N.
The data were used to estimate the rate of OH production due to acetone photolysis and
the findings were contrasted to the rate of OH production from ozone (O3+ hÏ
–> O(1D) +
O2 and O(1D) + H2O –> 2 OH). It is shown that around the tropopause the OH production
from acetone photolysis can compete with OH production from ozone photolysis. Due to the
vertically strongly decreasing acetone concentration the OH production from acetone
photolysis however becomes a minor channel above the tropopause, i.e. in the lowermost
stratosphere. |
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