Atmospheric emissions from waste recovery centers are strictly regulated by industrial emission directives which stipulate that they should be continuously monitored. In this work, we demonstrate and evaluate the capacity of terahertz rotational spectroscopy for real-time diagnosis and monitoring of gases of environmental interest on industrial sites. A spectrometer based on the use of a frequency multiplication chain operating at 530-620 GHz has been constructed, enabling the detection of most of the regulated compounds in waste incineration. The detection limits obtained are compatible with regulatory emission limit values. The installation of the instrument at the waste recovery center in Dunkirk demonstrated its ability to perform real-time quantitative multi-component in situ monitoring in an industrial environment. Continuous measurements of SO2 and CO over more than 24 h are compared with the measurements performed by two certified infrared instruments. The agreement between the three sets of measurements is excellent, demonstrating that high-resolution terahertz spectroscopy is relevant for real-time in situ monitoring of regulated industrial emissions gases, constituting an interesting alternative to other techniques thanks to a higher degree of selectivity.

The largest share of greenhouse gas (GHG) emissions related to livestock originates from methane (CH4) 4 ) and nitrous oxide (N2O) 2 O) which have a far higher influence on global warming, it is therefore necessary to accurately monitor CH4 4 and N2O 2 O emissions to provide theoretical and practical basis for further estimating and regulating GHG emissions from livestock and improving livestock production performance. For the purpose of sensing CH4 4 and N2O 2 O emissions during livestock living process in real time, an optical sensor based on continuous-wave (CW) external cavity quantum cascade laser (EC-QCL) operating at room temperature was developed. CH4 4 and N2O 2 O absorption lines, located around 8 mu m, of the v4 4 and v1 1 fundamental vibrational bands, respectively, were chosen for direct absorption spectroscopy, which allows for sensitive, selective and simultaneous measurement of CH4 4 and N2O 2 O concentrations. Use of a Herriot multi-pass cell with an effective path-length of 100 m, 1a (SNR = 1) limits of detection of 26.8 ppbv, 20.3 ppbv and 0.01 % for CH4, 4 , N2O 2 O and H2O 2 O vapor were achieved, respectively. Field measurement of CH4 4 and N2O 2 O emissions from horses has been carried out in a stable over two weeks at the Vernaelde farm in Couderkerque Branche city, France. Concentrations of CH4 4 and N2O 2 O up to 10 times and 1.5 times higher than their levels in the local ambient air ( 2.12 ppmv and 427 ppbv) were observed, respectively.

Abstract. We have developed MULTICHARME, a modified Chernin-type multi-pass cell especially designed for IR and THz long-path absorption measurements in the CHamber for Atmospheric Reactivity and Metrology of the Environment (CHARME). By measuring the output power using a near-IR diode-laser and a THz amplified multiplication chain, we have established that the effective reflectivity of MULTICHARME is better than 94 % over approximately three decades of frequency. Absorption measurements of N2O have been performed by probing highly excited rovibrational transitions in the near-IR and ground state rotational transitions at submillimetre wavelengths. In each case the linearity of the absorbance with the pathlengths was verified. Finally, we demonstrate that THz spectroscopy is able to study the isotopic composition of greenhouse polar gases such as N2O and to absolutely quantify stable (N2O) and reactive (O3) species at trace levels. Moreover, a THz monitoring at low pressure of the ozone decay in the chamber has been performed. The deduced ozone lifetime of 3.4 ± 0.1 h is shorter compared with previous measurements performed in CHARME at atmospheric pressure. For the first time, the ability of THz rotational spectroscopy to monitor, with a very high degree of selectivity, stable and reactive polar compounds at trace level in an atmospheric simulation chamber is demonstrated. However, the sensitivity of the THz monitoring needs to be improved to reach the atmospheric trace levels. For this purpose, it is necessary to figure out the baseline variations as well as possible induced by the multiple standing waves present in MULTICHARME.

Even if on-board mm-wave/THz heterodyne receivers have been developed to measure greenhouse gases (GHGs) atmospheric profiles, rotational spectroscopy rests under-exploited for their monitoring unlike IR rovibrational spectroscopy. The present study deals with the ability of THz spectroscopy using long interaction path-lengths for GHG laboratory investigations. High-resolution THz signatures of non-polar greenhouse molecules may be observed by probing very weak centrifugal distortion induced rotational transitions. To illustrate, new measurements on CH4 and CF4 have been carried out. For CH4, pure rotational transitions, recorded by cw-THz photomixing up to 2.6 THz in a White type cell adjusted to 20 m, have allowed to update the methane line list of atmospheric databases. Concerning CF4, Fabry-Perot THz absorption spectroscopy with a km effective pathlength was required to detect line intensities lower than 10−27 cm−1/(moleccm−2). Contrary to previous synchrotron-based FT-FIR measurements, the tetrahedral splitting of CF4 THz lines is fully resolved. Finally, quantitative measurements of N2O and O3 gas traces have been performed in an atmospheric simulation chamber using a submm-wave amplified multiplier chain coupled to a Chernin type multi-pass cell on a 200 m path-length. The THz monitoring of these two polar GHGs at tropospheric and stratospheric concentrations may be now considered.

The hydroxyl radical (OH) is considered as a primary agent responsible to remove a majority of trace gas in the atmosphere [1]. It is also responsible to initiate the reactions leading to the formation of a wide range of secondary species such as ozone (O3) and secondary organic aerosols (SOAs) [2]. Reliable and real-time assessment of the OH radical concentration change and related chemical process in the atmosphere is a key factor to understand and determinate the oxidation capacity of the atmosphere. Because of its very high reactivity, very short lifetime (≤ 1 s) associated with very low atmospheric concentration (~106 OH/cm3), the development of optical instrument allowing accurate, interference-free and ultra-high sensitivity in-situ direct measurement of OH concentration presents a great challenge for atmospheric science and climate change research.We report in this paper our recent development of an OH sensor based on Faraday Rotation Spectroscopy (FRS) [3]. FRS exploits magnetic circular birefringence (MCB) observed in the vicinity of Zeeman split absorption line of paramagnetic species such as O2, NO, NO2, OH. The Q(1,5e) and Q(1,5f) double lines of OH at 3568,52 cm-1 and 3568,41 cm-1 were chosen for quantification of OH radicals [4,5]. In order to enhance the detection sensitivity, multi-pass absorption approach was coupled to FRS. A 1σ (SNR=1) detection limit of about 5×107 OH/cm3 was achieved. The experimental detail and the preliminary results will be presented and discussed. Acknowledgments The authors thank the financial supports from the CPER CLIMIBIO program and the Labex CaPPA project (ANR-10-LABX005). References [1] D.E. Heard, M.J. Pilling, Chem. Rev. 103 (2003) 5163-5198. [2] D. Stone, L.K. Whalley, and D.E. Heard, Chem. Soc. Rev. 41 (2012) 6348-6404. [3] G. Litfin, C.R. Pollock, R.F. Curl, F.K. Tittel, J. Chem. Phys. 72 (1980) 6602-6605. [4] W. Zhao, G. Wysocki, W. Chen, et al., Opt. Express 19, (2011) 2493-2501. [5] W. Zhao, G. Wysocki, W. Chen, W. Zhang, Appl. Phys. B 109 (2012) 511-519.

In this Letter, the development of a custom-designed incoherent broadband cavity enhanced absorption spectrometer (IBBCEAS) and its application to in situ measurement of aerosol extinction near the ground surface are described in an effort to address the issue of missing data in the light detection and ranging (lidar) blind zone in the first hundreds of meters of the observation range. Combined measurements of aerosol extinction at the same location using lidar remote sensing at 355 nm and in situ IBBCEAS operating in the UV spectral region around 370 nm showed results with a good correlation ( R 2 = 0.90 ) between the two measurement techniques. This Letter highlights a new strategy for near-end lidar calibration, using a ground-based compact and robust IBBCEAS located at the lidar measurement site to determine the vertical profile of the aerosol extinction coefficient with a higher accuracy.

A compact isotope ratio sensor based on laser absorption spectroscopy at 2.7 μm was developed for high precision and simultaneous measurements of the D/H, 18O/16O and 17O/16O isotope ratios in glacier water. Measurements of the oxygen and hydrogen isotope ratios in glacier water demonstrate a 1σ precision of 0.3‰ for δ18O, 0.2‰ for δ17O, and 0.5‰ for δ2H, respectively. The δ values of the working standard glacier water obtained by the calibrated sensor system is basically identical to the IRMS measurement results with a very high calibration accuracy from 0.17‰ to 0.75‰. Preliminary results on the reproducibility measurements display a standard deviation of 0.13‰ for δ18O, 0.13‰ for δ17O, and 0.64‰ for δ2H, respectively.

Accurate measurement of atmospheric particulate matter (PM) absorption coefficient is highly required for study of earth climate change and for monitoring of air quality. In addition, multi-wavelength measurements of PM absorption can provide information on the PM chemical composition (black carbon or brown carbon). A multi-wavelengths photoacoustic (MW-PA) spectrophone operating at 444, 532 and 660 nm was developed and deployed for filter-free characterization of wavelength-dependent optical properties of PM mass absorption coefficient (MAC) and absorption Angstrom coefficient (AAC). It is worth noting that to date no any AAC of volcanic ashes determined by filter-free measurement have been reported. The developed MW-PA spectrophone was deployed to an intensive field campaign measurement of environmental PM in Grenoble (France). Side-by-side inter-comparison measurements of ambient PM showed a good correlation between the developed MW-PA spectrophone and a reference instrument aethalometer (Magee scientific, AE33).

A compact laser-based absorption sensor system associated with a 152-m path length absorption cell for simultaneous second harmonic (2f) detection of atmospheric nitrous oxide (N2O), methane (CH4), and water vapor (H2O) is presented. An 8 mu m external cavity quantum cascade laser (EC-QCL) was used as an excitation source to simultaneously target three neighboring absorption lines, N2O at 1255.424 cm(-1) , CH4 at 1255.000 cm(-1), and H2O at 1254.732 cm(-1) . Minimum detection limits (1 sigma) of 0.9 ppb for N2O, 4.8 ppb for CH4 and 31 ppm for H2O were achieved with a 1.s integration time at an optimum pressure of 50 Torr. Both laboratory and atmospheric environmental mixing ratios of these three gases associated with basic meteorological parameters were recorded and the corresponding emission sources were analyzed. In particular, the N2O emission was studied during extended time periods including rainy intervals.

A spectroscopic instrument based on an external cavity quantum cascade laser was developed for optical monitoring of dinitrogen pentoxide (N2O5) at the ppbv-level in a nocturnal tropospheric chemical reaction process in an atmospheric simulation chamber.

In the context of climate change mitigation, reuse of carbon dioxide (CO2) represents an alternative with important applications in chemical industry and power generation. For this purpose, CO2 must be purified. Combustion processes lead to high amounts of CO2 but still with impurities and also accompanied by toxic gases (mainly NO and CO). A catalytic reduction process of NO (to N-2) while oxidizing CO into CO2 is a promising method to purify the CO2 . However, nitrous oxide (N2O) with a global warming potential of 300 times greater than CO2 may be a by-product from this process. It is therefore necessary to optimize the chemical reaction conditions to minimize N2O production. A room-temperature continuous-wave (CW) external cavity quantum cascade laser (EC-QCL)-based optical sensor was developed for real-time monitoring N2O production during the whole catalytic reaction process. A well-isolated N2O absorption line, located at 1261.0598 cm(-1) , of the v(1) fundamental vibrational band was selected for sensitive and selective measurement of N2O concentration by direct absorption spectroscopy. Using a modified-Herriot multi-pass cell with an effective path-length of 50m, the limit of detection (l sigma) of 32.3 ppbv was obtained in 12 s with 1.1% relative uncertainty in measurement precision. N2O productions through the catalytic reduction of NO by CO over Pt/SiO2 catalyst under different temperatures were investigated. High N2O production of up to similar to 6.1 ppmv at 190 degrees C was observed. The optimal reaction conditions for zero N2O production were found at a temperature higher than 340 degrees C where 47% of NO was converted to N-2. (C) 2018 Elsevier Ltd. All rights reserved.

A photoacoustic spectroscopy based NO2 sensor was developed for measurement of ambient NO2 with a sensitivity of about 0.4 ppb (SNR=1) in 1 min, which was validated with side-by-side measurements using a referenced NOx analyzer.

An mid-infrared laser heterodyne radiometer was been developed for ground-based remote measurements of greenhouse gases (GHGs) in the atmospheric column.

A photoacoustic spectroscopy based NO2 sensor was developed for measurement of ambient NO2 with a sensitivity of about 0.4 ppb (SNR=1) in 1 min, which was validated with side- by-side measurements using a referenced NOx analyzer.

We will present our recent developments and applications of laser-based spectroscopic instruments to monitoring of climate-change related aerosols, which involve photoacoustic spectroscopy (PAS) and broadband cavity enhanced absorption spectroscopy (BBCEAS).