Spectroscopic detection of short-lived gaseous nitrous acid (HONO) at 1254.85 cm⁻¹ was realized by off-beam coupled quartz-enhanced photoacoustic spectroscopy (QEPAS) in conjunction with an external cavity quantum cascade lasers (EC-QCL). High sensitivity monitoring of HONO was performed within a very small gas-sample volume (of ∼40 mm³) allowing a significant reduction (of about 4 orders of magnitude) of air sampling residence time which is highly desired for accurate quantification of chemically reactive short-lived species. Calibration of the developed QEPAS-based HONO sensor was carried out by means of lab-generated HONO samples whose concentrations were determined by direct absorption spectroscopy involving a ∼109.5 m multipass cell and a distributed feedback QCL. A minimum detection limit (MDL) of 66 ppbv (1 σ) HONO was achieved at 70 mbar using a laser output power of 50 mW and 1 s integration time, which corresponded to a normalized noise equivalent absorption coefficient of 3.6 × 10⁻⁸cm⁻¹ W/Hz^1/2. This MDL was down to 7 ppbv at the optimal integration time of 150 s. The corresponding 1σ minimum detected absorption coefficient is ∼1.1 × 10⁻⁷cm⁻¹ (MDL ∼ 3 ppbv) in 1 s and ∼1.1 × 10⁻⁸cm⁻¹ (MDL ∼ 330 pptv) in 150 s, respectively, with 1 W laser power.

A room-temperature continuous-wave (CW) quantum cascade laser (QCL)-based methane (CH₄) sensor operating in the mid-infrared near 8 μm was developed for continuous measurement of CH₄ concentrations in ambient air. The well-isolated absorption line (7F_2,4 ← 8F_1,2) of the ν₄ fundamental band of CH₄ located at 1255.0004 cm⁻¹ was used for optical measurement of CH₄ concentration by direct absorption in a White-type multipass cell with an effective path-length of 175 m. A 1σ (SNR = 1) detection limit of 33.3 ppb in 218 s was achieved with a measurement precision of 1.13%. The developed sensor was deployed in a campaign of measurements of time series CH₄ concentration on a site near a suburban traffic road in Dunkirk (France) from 9th to 22nd January 2013. An episode of high CH₄ concentration of up to ~3 ppm has been observed and analyzed with the help of meteorological parameters combined with back trajectory calculation using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model of NOAA.

The concentration of greenhouse gases in the atmosphere plays an important role in the radiative effects in the Earth’s climate system. Therefore, it is crucial to increase the number of atmospheric observations in order to quantify the natural sinks and emission sources. We report in this paper the development of a new compact lightweight spectrometer (1.8 kg) called AMULSE based on near infrared laser technology at 2.04 µm coupled to a 6-m open-path multipass cell. The measurements were made using the Wavelength Modulation Spectroscopy (WMS) technique and the spectrometer is hence dedicated to in situ measuring the vertical profiles of the CO₂ at high precision levels (σ_Allan = 0.96 ppm in 1 s integration time (1σ)) and with high temporal/spatial resolution (1 Hz/5 m) using meteorological balloons. The instrument is compact, robust, cost-effective, fully autonomous, has low-power consumption, a non-intrusive probe and is plug & play. It was first calibrated and validated in the laboratory and then used for 17 successful flights up to 10 km altitude in the region Champagne—Ardenne, France in 2014. A rate of 100% of instrument recovery was validated due to the pre-localization prediction of the Météo—France based on the flight simulation software.

Methane plays an important role in the radiative balance of the Earth climate: about 20% of the manmade global warming is related to methane emissions. To contribute to the study of CH₄ trends, we have developed a compact lightweight spectrometer (2.5 kg) by combining an antimonide laser diode at 3.24 µm with an 8 m optical multipass path cell open to the atmosphere. This laser sensor is to be operated from weather balloons to provide with regular in situ methane soundings from ground level up to ~ 25 km. In this paper, the laser sensor is described as well as the processing of the absorption spectra and the calibration of the instrument. The concentration data obtained from recent stratospheric balloon flights are reported and discussed.