Advancing Atmospheric Pollution Monitoring with Airborne THz Spectrometer

TL;DR

Real-time, spatially resolved monitoring of atmospheric pollutants is needed in challenging environments. This work presents a drone-mounted terahertz-continuous-wave spectrometer with an integrated 5-meter aspiration sampling system and a dedicated spectral library to enable in-flight identification and quantification of VOCs and multi-component mixtures. Ground-based and in-flight tests show that spectra match laboratory references and allow accurate deconvolution of complex mixtures, including the first THz detection of dichloromethane in a flight setting. The approach enables rapid, remote air-quality surveillance in difficult terrains and provides a foundation for scalable deployment and subsequent sensitivity enhancements via longer multipass cells and humidity-aware calibration.

Abstract

This study details the development and validation of an airborne THz spectrometer designed for real-time, remote detection of atmospheric pollutants. The platform couples a stabilized unmanned aerial system (UAS) with a high-resolution terahertz continuous-wave (THz-CW) laser source and detector, enabling flexible, in situ spectroscopic analysis of dispersed atmospheric vapours. This proof-of-concept investigation confirms the feasibility of UAS-THz-CW systems for spatially resolved environmental pollutant monitoring. The demonstrated capability of this terahertz sensor for remote, multi-component detection of atmospheric contaminants holds significant potential for advancing air pollutant monitoring technologies, providing a pathway for more effective and portable detection. This advancement can contribute to the necessary alert actions for minimizing contaminants impacting public and environmental health, thereby safeguarding human and ecosystem health.

Figures (5)

• Figure 1: a) The assembled UAS-THz-CW system in ground station; b) and c) in flight during in-field trials for stability test; d) UAS-THz-CW system in flight during remote sampling with the 5-meter aspiration tube for the collection of the targeted analyte.
• Figure 2: Schematic representations of: a) the assembled THz-on-drone system; b) CW spectrometer he radiation's optical path inside the sampling cell is reported in red.
• Figure 3: a) Absorption spectrum of water vapor (acquired in ambient air with a relative humidity (RH) of $\approx$ 35%). The peaks at 557.2, 752.3 and 987.9 GHz, linked to water vapour absorptions Slocum2013. b) Absorption spectrum of ammonia which presents a specific absorption fingerprints centered at 0.572 THz. c) Absorption spectrum of acetonitrile (MeCN) with specific fingerprints spaced approximately every 18.43 GHz. d) Absorption spectrum of dichloromethane (DCM) with specific fingerprints spaced approximately every 57.46 GHz. e) Absorption spectrum of acetone injected into the cell wich presents a broad band centered at 0.565 THz. f) Absorption spectrum of methanol (MeOH) with specific fingerprints spaced approximately every 49.36 GHz. All the measurements are carried out in ambient air in the range 0.2-1 THz. The water vapour absorption peaks are present at 557.2, 752.3 and 987.9 GHz Slocum2013 in every spectra.
• Figure 4: Comparison between the experimental mixture constituted by acetone, methanol, and dichloromethane aspirated inside the sampling cell and remotely investigated by the THz-on-drone system at a flight altitude from the soil level of 5 m and the spectrum obtained from the retrieved coefficients in the range 0.2-1 THz. Dotted vertical lines indicate water vapour absorptions frequencies (557.2, 752.3 and 987.9 GHz) Slocum2013.
• Figure 5: Comparison between the experimental mixture constituted by ammonia, acetonitrile, acetone, methanol, and dichloromethane aspirated inside the sampling cell and the spectrum obtained from the retrieved coefficients in the range 0.2-1 THz. Dotted vertical lines indicate water vapour absorptions frequencies (557.2, 752.3 and 987.9 GHz) Slocum2013.