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DOAS measurements of NO2 from an ultralight aircraft during the Earth Challenge expedition

Author(s): A. Merlaud | M. Van Roozendael | J. van Gent | C. Fayt | J. Maes | X. Toledo | O. Ronveaux | M. De Mazière

Journal: Atmospheric Measurement Techniques Discussions
ISSN 1867-8610

Volume: 5;
Issue: 1;
Start page: 1947;
Date: 2012;
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We report on airborne Differential Optical Absorption Spectroscopy (DOAS) measurements of NO2 tropospheric columns above South Asia, Arabic peninsula, North Africa, and Italy in November and December 2009. The DOAS instrument was installed on an ultralight aircraft involved in the Earth Challenge project, an expedition of seven pilots flying on four ultralight aircraft between Australia and Belgium. The instrument recorded spectra in limb geometry with a large field-of-view, a set-up which provides a high sensitivity to the boundary layer NO2 while minimizing the uncertainties related to the attitude variations. We compare our measurements with OMI and GOME-2 tropospheric NO2 products when the latter are available. Above Rajasthan and the Po Valley, two areas where the NO2 field is homogeneous, data sets agree very well. Our measurements in this areas are respectively 0.1 ± 0.1 to 2.8 ± 1 × 1015 molec cm−2 and 2.5 ± 0.5 × 1016 molec cm−2. Flying downwind of Riyadh, our NO2 measurements show with a higher spatial resolution than OMI the structure of the megacities'exhaust plume. Moreover, our measurements indicate larger columns (up to 70%) than the one seen by satellites. We also derived tropopsheric columns when no satellite data was available, if it was possible to get information on the visibility from satellite measurements of aerosol optical thickness. The maximum column we measured was above Benghazi, with 5.7 ± 2 × 1016 molec cm−2. This experiment also provides a confirmation for the recent finding of a soil signature above desert.

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