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| Titel |
Airborne CARIBIC measurements in the UTLS: Distribution, seasonal cycle and variability of acetone |
| VerfasserIn |
Felix Geiger, Marco Neumaier, Carl A. M. Brenninkmeijer, Detlev Sprung, Joel Brito, Andreas Zahn |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250056543
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| Zusammenfassung |
| In the Earth´s atmosphere volatile organic compounds (VOCs) have multifaceted functions,
e.g. controlling (together with reactive nitrogen) the photochemical production of ozone or
influencing directly (via e.g. acetone) or indirectly (via ozone) the Earth´s oxidation capacity.
The UTLS region (upper troposphere / lower stratosphere) plays a key role in the climate
system. Any change in its structure and chemical composition results in changes in the
radiative forcing of the atmosphere and thus in climate change. The UTLS is – in spite of the
immense importance – still one of the least understood regions of the atmosphere. The
need for a better understanding of the dynamics across the tropopause is therefore
obvious.
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 within the UTLS (9-12 km
altitude).
Acetone (CH3COCH3), as one of the most abundant oxygenated volatile organic
compounds (OVOCs) in the atmosphere, can be used to gain more information about the
dynamic processes and chemical cycles. The presented measurements have been carried out
by the PTR-MS instrument (proton-transfer-reactions mass spectrometry) onboard CARIBIC.
Because of the meteorological and geographical variance of the atmospheric layering, the
tropopause is crossed up to 20 times during one (quasi-horizontal) long-range flight. Thereby
tropospheric and stratospheric air is sampled to fractions of ~60 % and ~40 %, respectively.
The stratospheric flight sections largely occur in the extra-tropical tropopause (transition)
layer (exTL).
With an average of four long-distance flights per month between Germany and the major
destinations in North- and South-America, as well as South-East Asia, the largest airborne
dataset of acetone on a nearly worldwide scale has been composed.
The following major findings in the analysis of the collected data are shown:
A strong seasonal variation of acetone occurs at the mid-latitude tropopause with
maxima of approximately 900 pptv (parts per 1012 vol) in summer and minima
of approximately 200 pptv in midwinter.
This seasonality propagates into the LMS (lowermost stratosphere) in ~6 weeks
with rapidly decreasing concentrations and increasing phase shifts reaching 2 km
above the tropopause.
Probability density functions (PDFs) and the course of the seasonal variation of
acetone relative to the tropopause are interpreted regarding the in-mixing and
subsequent dispersion of acetone in the LMS.
The production of HOx due to the photolysis of acetone is compared with the
one following the photolysis of ozone and subsequent reaction of O(1D) with
water vapour. |
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