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| Titel |
Ship emissions of SO2 and NO2: DOAS measurements from airborne platforms |
| VerfasserIn |
N. Berg, J. Mellqvist, J.-P. Jalkanen, J. Balzani |
| 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 ; 5, no. 5 ; Nr. 5, no. 5 (2012-05-15), S.1085-1098 |
| Datensatznummer |
250002866
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| Publikation (Nr.) |
 copernicus.org/amt-5-1085-2012.pdf |
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| Zusammenfassung |
A unique methodology to measure gas fluxes of SO2 and NO2 from
ships using optical remote sensing is described and demonstrated in a
feasibility study. The measurement system is based on Differential Optical
Absorption Spectroscopy using reflected skylight from the water surface as
light source. A grating spectrometer records spectra around 311 nm and 440 nm,
respectively, with the telescope pointed downward at a 30° angle
from the horizon. The mass column values of SO2 and NO2 are
retrieved from each spectrum and integrated across the plume. A simple
geometric approximation is used to calculate the optical path. To obtain the
total emission in kg h−1 the resulting total mass across the plume is
multiplied with the apparent wind, i.e. a dilution factor corresponding to
the vector between the wind and the ship speed. The system was tested in two
feasibility studies in the Baltic Sea and Kattegat, from a CASA-212 airplane
in 2008 and in the North Sea outside Rotterdam from a Dauphin helicopter in
an EU campaign in 2009. In the Baltic Sea the average SO2 emission out
of 22 ships was (54 ± 13) kg h−1, and the average NO2 emission was
(33 ± 8) kg h−1, out of 13 ships. In the North Sea the average SO2
emission out of 21 ships was (42 ± 11) kg h−1, NO2 was not measured
here. The detection limit of the system made it possible to detect SO2
in the ship plumes in 60% of the measurements when the described method
was used.
A comparison exercise was carried out by conducting airborne optical
measurements on a passenger ferry in parallel with onboard measurements. The
comparison shows agreement of (−30 ± 14)% and (−41 ± 11)%,
respectively, for two days, with equal measurement precision of about
20%. This gives an idea of the measurement uncertainty caused by errors
in the simple geometric approximation for the optical light path neglecting
scattering of the light in ocean waves and direct and multiple scattering in
the exhaust plume under various conditions. A tentative error budget
indicates uncertainties within 30–45% but for a reliable error analysis
the optical light path needs to be modelled.
A ship emission model, FMI-STEAM, has been compared to the optical
measurements showing an 18% overestimation and a correlation coefficient
(R2) of 0.6. It is shown that a combination of the optical method with
modelled power consumption can estimate the sulphur fuel content within
40%, which would be sufficient to detect the difference between ships
running at 1% and at 0.1%, limits applicable within the IMO regulated
areas. |
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