Atmospheric applications IFS 125HR

Importance of the topic

The accurate detection and quantification of atmospheric trace gases are essential for understanding chemical processes in the stratosphere and troposphere, monitoring air quality, and assessing the impact of human activities on climate. High-resolution Fourier transform infrared (FT-IR) spectrometry enables precise identification of molecular absorption features, making it a key tool for long-term environmental observations and pollutant surveillance.

Objectives and study overview

This application note presents the flexibility and performance of the Bruker IFS 125HR FT-IR spectrometer for atmospheric research. Two installation scenarios are described:

• A multi-channel observatory setup in Shenzhen, China, for simultaneous solar absorption and emission measurements across a broad spectral range.
• Polar night observations using lunar radiation as an infrared source to extend measurement periods in high-latitude regions.

Methodology and measurement approach

The IFS 125HR features a permanently aligned cube-corner Michelson interferometer, providing stable beam alignment without active adjustment. Dual-channel DigiTect™ detection combined with dichroic beam splitters allows parallel acquisition in two spectral windows, each optimized with dedicated detectors. For solar absorption studies, a precisely tracked solar beam is fed into the spectrometer via an A547N/2 solar tracker and controlled by CamTracker image-processing software. During polar night, the moon serves as a weaker IR source; the dual-channel design ensures sufficient sensitivity even at reduced signal levels.

Instrumentation

• IFS 125HR ultra-high resolution FT-IR spectrometer
• A547N/2 solar tracker system with CamTracker software
• Dichroic and reflective 3×120° beam splitters for spectral division
• DigiTect™ dual-channel detector modules covering MIR, NIR, and VIS/UV regions

Main results and discussion

In Shenzhen, three compact IFS 125HR units operate in parallel to capture solar absorption and atmospheric emission signals in the full mid-IR to near-UV range (600 cm⁻¹ to 33 000 cm⁻¹) without manual reconfiguration. This arrangement enabled continuous monitoring of trace gases under clean (sea) and polluted (urban) backgrounds. Polar night measurements demonstrated detection of stratospheric species such as HNO₃, HCl, HF, and ClONO₂ using the moon as a radiation source. Spectra recorded at 0.02 cm⁻¹ resolution revealed distinct absorption lines, confirming the system’s high sensitivity under low-light conditions.

Benefits and practical applications of the method

• Unmatched spectral resolution and long-term stability for atmospheric monitoring.
• Modular optical bench allows rapid adaptation to different spectral ranges.
• Parallel dual-channel acquisition accelerates data collection and extends observation windows.
• Solar and lunar tracking options enable continuous operation in diverse geographic and seasonal conditions.

Future trends and potential applications

Advances in detector technology and real-time data processing will further improve sensitivity and temporal resolution. Integration of multiple high-resolution FT-IR stations into global networks can enhance coverage of trace gas distributions. Machine learning algorithms applied to the rich spectral datasets may enable automated anomaly detection and rapid source attribution in air quality monitoring.

Conclusion

The Bruker IFS 125HR spectrometer offers exceptional flexibility and sensitivity for atmospheric trace gas analysis. Its permanently aligned interferometer, dual-channel detection, and remote tracking accessories make it uniquely suited for high-resolution solar and lunar absorption studies. No other commercial FT-IR system matches its combination of resolution, stability, and modularity for demanding environmental applications.

References

1. M. Gisi et al., "CamTracker: a new camera controlled high precision solar tracker system for FT-IR spectrometers," Atmospheric Measurement Techniques, 4 (2011), 47–54.
2. J. Notholt, O. Schrems, "Ground-based FT-IR spectroscopic absorption measurements of stratospheric trace gases in the Arctic with the sun and the moon as light sources," Journal of Molecular Structure, 347 (1995), 407–416.
3. N. M. Deutscher et al., "Total column CO₂ measurements at Darwin," Atmospheric Measurement Techniques, 3 (2010), 947–958.
4. R. Kohlhepp et al., "Observed and simulated time evolution of HCl, ClONO₂, and HF total column abundances," Atmospheric Chemistry and Physics, 12 (2012), 3527–3556.