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| Titel |
A rapid method to derive horizontal distributions of trace gases and aerosols near the surface using multi-axis differential optical absorption spectroscopy |
| VerfasserIn |
Y. Wang, A. Li, P. H. Xie, T. Wagner, H. Chen, W. Q. Liu, J. G. Liu |
| 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 ; 7, no. 6 ; Nr. 7, no. 6 (2014-06-11), S.1663-1680 |
| Datensatznummer |
250115815
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| Publikation (Nr.) |
 copernicus.org/amt-7-1663-2014.pdf |
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| Zusammenfassung |
We apply a novel experimental procedure for the rapid measurement of the
average volume mixing ratios (VMRs) and horizontal distributions of trace
gases such as NO2, SO2, and HCHO in the boundary layer, which was
recently suggested by Sinreich et al. (2013). The method is based on
two-dimensional scanning multi-axis differential optical absorption
spectroscopy (MAX-DOAS). It makes use of two facts (Sinreich et al., 2013):
first, the light path for observations at 1° elevation angle
traverses mainly air masses located close to the ground (typically < 200 m); second, the light path length can be calculated using the
simultaneous measured absorption of the oxygen dimer O4. Thus, the
average value of the trace gas VMR in the atmospheric layer between the
surface and the particular altitude, for which this observation was sensitive, can be
calculated. Compared to the originally proposed method, we introduce several
important modifications and improvements: We apply the method only to
measurements at 1° elevation angle (besides zenith view), for
which the uncertainties of the retrieved values of the VMRs and surface
extinctions are especially small. Using only 1° elevation angle for
off-axis observation also allows an increased temporal resolution. We
determine (and apply) correction factors (and their uncertainties) directly
as function of the measured O4 absorption. Finally, the method is
extended to trace gases analysed at other wavelengths and also to the
retrieval of aerosol extinction. Depending on atmospheric
visibility, the typical uncertainty of the results ranges from about 20%
to 30%.
We apply the rapid method to observations of a newly-developed ground-based
multifunctional passive differential optical absorption spectroscopy
(GM-DOAS) instrument in the north-west outskirts near Hefei in China.
We report NO2, SO2, and HCHO VMRs and aerosol extinction for four
azimuth angles and compare these results with those from simultaneous
long-path DOAS observations. Good agreement is found (squares of the
correlation coefficients for NO2, SO2, and HCHO were 0.92, 0.85,
and 0.60, respectively), verifying the reliability of this novel method.
Similar agreement is found for the comparison of the aerosol extinction with
results from visibility meters. Future studies may conduct measurements
using a larger number of azimuth angles to increase the spatial resolution. |
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