研究目的
To develop and demonstrate a new passive remote sensing instrument for measuring 2-D distributions of NO2 slant column densities with high spatiotemporal resolution, overcoming limitations of existing methods like grating spectrometers.
研究成果
The AOTF-based NO2 camera successfully measures 2-D NO2 distributions with high spatiotemporal resolution, enabling detailed study of plume dynamics and chemistry. It demonstrates capabilities for emission monitoring and correction of SO2 camera data. Future improvements include temperature stabilization and use of CMOS detectors for higher temporal resolution.
研究不足
The instrument has a temporal resolution of 3 minutes, which is slower than SO2 cameras (1 Hz). Wavelength drift due to temperature changes can introduce uncertainties in cross-section measurements. The need for homogeneous background illumination and optically thin plumes limits applicability in certain conditions. Detection limit is around 5e16 molecules cm-2, which may not suffice for very low concentrations.
1:Experimental Design and Method Selection:
The instrument uses an acousto-optical tunable filter (AOTF) for spectral selection, allowing high-resolution imaging of NO2 absorption features. It is based on the ALTIUS instrument concept, with a telecentric optical design to ensure spectral homogeneity.
2:Sample Selection and Data Sources:
Measurements were conducted during the AROMAT-2 campaign at a coal-fired power plant in Romania, focusing on NO2 plumes from stacks. Background and plume areas were imaged simultaneously.
3:List of Experimental Equipment and Materials:
Key components include an AOTF (Gooch & Housego TeO2 crystal), a Princeton Instrument Pixis 512B CCD detector, polarizers, lenses, and driving electronics.
4:Experimental Procedures and Operational Workflow:
The AOTF is tuned to specific wavelengths (e.g.,
5:8 nm, 3 nm) to capture spectral images. Sequences involve acquiring images at multiple wavelengths with the AOTF on and off for dark current subtraction. Data are averaged to improve signal-to-noise ratio. Data Analysis Methods:
4 NO2 slant column densities are retrieved using a mathematical model based on Beer-Lambert law, involving normalization by background signals, correction for instrument response, and error estimation. Cross-section data from Vandaele et al. (1998) are used.
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