LARA: Laser-based air pollution monitoring

• Research unit: EU RFP
• Project number: 95.0796

Key words (English)

Tunable infrared lasers; laser spectroscopy; photoacoustic sensor; trace gas monitoring

Alternative project number (English)

EU project number: SMT4-CT96-2108

Research programs (English)

EU-programme: 4. Frame Research Programme - 2.2 Measurements and testing

Short description (English)

See abstract

Further information (English)

Full name of research-institution/enterprise:
ETH Zürich
Institut für Quantenelektronik
Laboratorium für Laserspektroskopie und Umweltanalytik

Partners and International Organizations (English)

University Heidelberg (D) (Coordinator), T.R.I., Scanzorosciate (I), Attila Jozsef University, Szeged (HU), JRC, Europ. Ref. Lab. of Air Pollution, Ispra (I), Thomson-CSF, Lab. Central de Recherches, Orsay (F), Thomson-CSF, Optronique, Orsay (F)

Abstract (English)

The judgement of the air quality (emission, workplace, public health, etc.) requires novel measurement techniques for the sensitive and selective monitoring of trace gases. The objective of this joint project was to develop and implement an instrument on the basis of narrowband tunable infrared lasers and photoacoustic detection with multi-component capability and detection sensitivities at the ppm to ppb (mg/m3) level.
After having demonstrated the feasibility of both our narrowband difference frequency (DFG) laser source and our novel photoacoustic sensor with a multi-microphone array, we focused our research acitivities In the third project year on the further improvement of system performance (essentially detection sensitivity and selectivity) as well as on measurements and analyses of multi-component gas mixtures. Problems to be addressed were external noise sources, water vapor contamination of the gas cell and handling system, fitting of measured spectra as well as overall system stability.
The external noise was efficiently attenuated by a special noise-insulating box. The system stability was found to be most probably determined by parasitic oscillations of the laser source that results in pulse-to-pulse wavelength and linewidth fluctuations of the emitted radiation. These instabilities and the spectral interference by water vapor currently represent limiting factors for ultimate sensitivity.
Measurements have been performed on various gas mixtures, notably on a calibrated benzene - toluene - p-xylene - (BTX) - mixture supplied by the JRC partner. Good agreement between measurement and fit was obtained. Detection limits are in the 50-100 ppb range. Under water vapor interference-free conditions a 1 ppb sensitivity is realistic.
Within this project we developed and implemented a working system for trace gas sensing. Attractive features are the extremely broad laser tuning range and the efficient photoacoustic detection scheme which allow sensitive monitoring of any gas with good sensitivity and selectivity.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 95.0796