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- Title
The AOTF-based NO<sub>2</sub> camera.
- Authors
Dekemper, Emmanuel; Vanhamel, Jurgen; Van Opstal, Bert; Fussen, Didier
- Abstract
The abundance of NO2 in the boundary layer relates to air quality and pollution sources monitoring. Observing the spatio-temporal distribution of NO2 above well-delimited (flue gas stacks, volcanoes, ships) or more extended sources (cities) allows for several applications: monitoring emission fluxes or studying the plume dynamic chemistry and its transport. So far, most attempts to map the NO2 field from the ground have been made with visible-light scanning spectrometers. Benefiting from a high retrieval accuracy, they only achieve a relatively low temporal resolution that hampers the detection of dynamic features. We present a new type of passive remote sensing instrument aiming at the measurement of the 2-D distributions of NO2 slant column densities (SCD) with a high spatio-temporal resolution. The measurement principle has strong similarities with the popular filter-based SO2 camera as it relies on spectral images taken at wavelengths where the molecule absorption cross-section is different. Contrary to the SO2 camera, the spectral selection is performed by an acousto-optical tunable filter (AOTF) capable of resolving the target molecule's spectral features. The NO2 camera capabilities are demonstrated by imaging the NO2 abundance in the plume of a coal-fired power plant. During this experiment, the 2-D distribution of the NO2 SCD was retrieved with a temporal resolution of 3 minutes and a spatial sampling of 50 cm (over a 250 x 250 m² area). The detection limit was close to 5 x 1016 molecules cm-2, with a maximum detected SCD of 4 x 1017 molecules cm-2. Illustrating the added-value of the NO2 camera measurements, the data reveal the dynamics of the NO to NO2 conversion in the early plume with an unprecedent resolution: from its release in the air, and for 100 m upwards, the observed NO2 plume concentration increased at a rate of 0.75-1.25 g s-1. In joint campaigns with SO2 cameras, the NO2 camera could also help in removing the bias introduced by the NO2 interference in the SO2 measurements.
- Subjects
NITROGEN dioxide analysis; REMOTE sensing equipment; ACOUSTO-optical filters
- Publication
Atmospheric Measurement Techniques Discussions, 2016, p1
- ISSN
1867-8610
- Publication type
Abstract
- DOI
10.5194/amt-2016-237