Two-dimensional spatial heterodyne spectrometer for atmospheric nitrogen dioxide observations

Area of Science:

• Atmospheric science
• Spectroscopy
• Optical instrumentation

Background:

• Accurate measurement of atmospheric nitrogen dioxide (NO2) is crucial for air quality monitoring and climate studies.
• Existing spectroscopic methods may face limitations in spectral range, resolution, or portability.

Purpose of the Study:

• To develop and validate a broadband monolithic spatial heterodyne spectrometer (SHS) for atmospheric NO2 measurements.
• To assess the performance characteristics and accuracy of the newly fabricated SHS system.

Main Methods:

• Fabrication of a novel broadband monolithic spatial heterodyne spectrometer (SHS).
• Calibration and testing using Hg, Kr, Xe lamps, and a monochromator with a white light source.
• Measurement of direct solar-irradiance spectra in the NO2 absorption band.
• Analysis using the direct sun - differential optical absorption spectroscopy (DS-DOAS) method.

Main Results:

• The SHS system demonstrates an effective spectral range of 425-495 nm with >40% efficiency.
• Achieved maximum fringe visibility of ~0.85 and spectral resolution of ~0.073 nm.
• Negligible phase distortion effects were observed in the 2-D SHS system.
• Measured spectra align with Modtran6 simulations and show close agreement with OMI satellite data for NO2 vertical column content.

Conclusions:

• The developed broadband monolithic SHS is a viable and accurate instrument for atmospheric NO2 monitoring.
• The system's performance, including spectral range and resolution, meets requirements for atmospheric measurements.
• The SHS system's measurements are validated by comparison with established simulation models and satellite observations.