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| Titel |
Ground-based direct-sun DOAS and airborne MAX-DOAS measurements of the collision-induced oxygen complex, O2O2, absorption with significant pressure and temperature differences |
| VerfasserIn |
E. Spinei, A. Cede, J. Herman, G. H. Mount, E. Eloranta, B. Morley, S. Baidar, B. Dix, I. Ortega, T. Koenig, R. Volkamer |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 2 ; Nr. 8, no. 2 (2015-02-18), S.793-809 |
| Datensatznummer |
250116136
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| Publikation (Nr.) |
 copernicus.org/amt-8-793-2015.pdf |
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| Zusammenfassung |
The collision-induced O2 complex, O2O2, is a very important
trace gas for understanding remote sensing measurements of aerosols, cloud
properties and atmospheric trace gases. Many ground-based multi-axis differential optical absorption spectroscopy
(MAX-DOAS) measurements of
the O2O2 optical depth require correction factors of 0.75 ±
0.1 to reproduce radiative transfer modeling (RTM) results for a nearly pure
Rayleigh atmosphere. One of the potential causes of this discrepancy is
uncertainty in laboratory-measured O2O2 absorption cross section
temperature and pressure dependencies due to difficulties in replicating
atmospheric conditions in the laboratory environment.
This paper presents ground-based direct-sun (DS) and airborne multi-axis
(AMAX) DOAS measurements of O2O2 absorption optical depths under
actual atmospheric conditions in two wavelength regions (335–390 and
435–490 nm). DS irradiance measurements were made by the Washington State
University research-grade Multi-Function Differential Spectroscopy
Instrument instrument from 2007 to 2014 at seven
sites with significant pressure (778 to 1013 hPa) and O2O2
profile-weighted temperature (247 to 275 K) differences. Aircraft MAX-DOAS
measurements were conducted by the University of Colorado (CU) AMAX-DOAS
instrument on 29 January 2012 over the Southern Hemispheric subtropical
Pacific Ocean. Scattered solar radiance spectra were collected at altitudes
between 9 and 13.2 km, with O2O2 profile-weighted temperatures of
231 to 244 K and nearly pure Rayleigh scattering conditions.
Due to the well-defined DS air-mass factors during ground-based measurements
and extensively characterized atmospheric conditions during the aircraft
AMAX-DOAS measurements, O2O2 "pseudo" absorption cross sections,
σ, are derived from the observed optical depths and estimated
O2O2 column densities. Vertical O2O2 columns are
calculated from the atmospheric sounding temperature, pressure and specific
humidity profiles.
Based on the ground-based atmospheric DS observations, there is no pressure
dependence of the O2O2 σ within the measurement errors
(3%). Two data sets are combined to derive the peak σ temperature
dependence of the 360 and 477 nm dimer absorption bands from 231 to 275 K.
DS and AMAX-derived peak σ ( O2O2) as a function of T can be
described by a quadratic function at 360 nm and linear function at
477 nm
with about 9% ± 2.5% per 44 K rate.
Recent laboratory-measured O2O2 cross sections by Thalman and
Volkamer (2013) agree with these "DOAS apparent" peak σ( O2O2) at
233, 253 and 273 K within 3%. Changes in the
O2O2 spectral band shape at colder temperatures are observed for
the first time in field data. Temperature effects on spectral band shapes
can introduce errors in the retrieved O2O2 column abundances if a
single room temperature σ( O2O2) is used in the DOAS
analysis. Simultaneous fitting of σ( O2O2) at temperatures
that bracket the ambient temperature range can reduce such errors.
Our results show that laboratory-measured σ( O2O2) (Hermans, 2011, at 296 K and Thalman and Volkamer, 2013) are applicable for
observations over a wide range of atmospheric conditions. Column densities
derived using Hermans (2011) σ at 296 K require very small
correction factors (0.94 ± 0.02 at 231 K and 0.99 ± 0.02 at 275 K)
to reproduce theoretically calculated slant column densities for DS
and AMAX-DOAS measurements. Simultaneous fitting of σ( O2O2)
at 203 and 293 K further improved the results at UV and
visible wavelengths for AMAX-DOAS. |
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