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| Titel |
The CU 2-D-MAX-DOAS instrument – Part 1: Retrieval of 3-D distributions of NO2 and azimuth-dependent OVOC ratios |
| VerfasserIn |
I. Ortega, T. Koenig, R. Sinreich, D. Thomson, 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. 6 ; Nr. 8, no. 6 (2015-06-08), S.2371-2395 |
| Datensatznummer |
250116427
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| Publikation (Nr.) |
 copernicus.org/amt-8-2371-2015.pdf |
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| Zusammenfassung |
| We present an innovative instrument telescope and describe a retrieval method
to probe three-dimensional (3-D) distributions of atmospheric trace gases
that are relevant to air pollution and tropospheric chemistry. The University
of Colorado (CU) two-dimensional (2-D) multi-axis differential optical
absorption spectroscopy (CU 2-D-MAX-DOAS) instrument measures
nitrogen dioxide (NO2), formaldehyde (HCHO), glyoxal (CHOCHO), oxygen
dimer (O2–O2, or O4), and water vapor (H2O); nitrous
acid (HONO), bromine monoxide (BrO), and iodine monoxide (IO) are among other
gases that can in principle be measured. Information about aerosols is
derived through coupling with a radiative transfer model (RTM). The 2-D
telescope has three modes of operation: mode 1 measures solar scattered
photons from any pair of elevation angle
(−20° < EA < +90° or zenith; zero is
to the horizon) and azimuth angle
(−180° < AA < +180°; zero being
north); mode 2 measures any set of azimuth angles (AAs) at constant elevation
angle (EA) (almucantar scans); and mode 3 tracks the direct solar beam via a
separate view port. Vertical profiles of trace gases are measured and used to
estimate mixing layer height (MLH). Horizontal distributions are then derived
using MLH and parameterization of RTM (Sinreich et al., 2013). NO2 is
evaluated at different wavelengths (350, 450, and 560 nm), exploiting the
fact that the effective path length varies systematically with wavelength.
The area probed is constrained by O4 observations at nearby wavelengths
and has a diurnal mean effective radius of 7.0 to 25 km around the
instrument location; i.e., up to 1960 km2 can be sampled with high time
resolution. The instrument was deployed as part of the Multi-Axis DOAS
Comparison campaign for Aerosols and Trace gases (MAD-CAT) in Mainz, Germany,
from 7 June to 6 July 2013. We present first measurements (modes 1 and 2
only) and describe a four-step retrieval to derive (a) boundary layer
vertical profiles and MLH of NO2; (b) near-surface horizontal
distributions of NO2; (c) range-resolved NO2 horizontal
distribution measurements using an "onion-peeling" approach; and (d) the
ratios HCHO to NO2 (RFN), CHOCHO to NO2
(RGN), and CHOCHO to HCHO (RGF) at 14 pre-set azimuth
angles distributed over a 360° view. Three-dimensional distribution
measurements with 2-D-MAX-DOAS provide an innovative, regional perspective of
trace gases as well as their spatial and temporal concentration gradients,
and they maximize information to compare near-surface observations with
atmospheric models and satellites. |
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