# Terahertz Rotational Spectroscopy of Greenhouse Gases Using Long Interaction Path-Lengths
## 4 Conclusions
In particular, the versatility of the electronic sources will allows performing time-resolved quantitative spectroscopies of reactants, oxidants and products involved in targeted reactions occurring in the high altitude atmospheric layers. Moreover, it will be interesting to measure in CHARME, at different pressures, the THz self-continuum of water absorption with the AMC coupled to MultiCHARME and to compare our spectra with those recently performed with the coherent THz synchrotron radiation coupled to the White-type cell shown in Figure 1 (right part) [40]. Finally, the high-finesse THz cavity hasalso to be employed for the detection of stable N2O and unstable O3 GHG. Next studies will be dedicated to verify if N2O and O3 submm-wave transitions could be measured at tropospheric (330 ppb) and stratospheric (7500 ppb) concentrations by FP-TAS. conceptualization, A.C. and V.B. ; methodology, A.C., F.H., G.M., R.B., J.D., E.F. and V.B. ; software, F.H. ; validation, A.C. and V.B. ; investigation, C.B., J.B., J.D., E.F, A.P. and A.C.; formal analysis, C.B., J.B., J.D., A.P. and V.B. ; writing--original draft preparation, A.C.; writing--review and editing, F.H., R.B., J.B. and V.B. ; supervision, A.C., G.M. and F.H. ; project administration, A.C., V.B. and G.M. ; funding acquisition, A.C., G.M. and E.F. All authors have read and agreed to the published version of the manuscript. This work was supported by the CaPPA project (Chemical and Physical Properties of the Atmosphere) funded by the French National Research Agency (ANR-11-LABX-0005-01) and the CLIMIBIO program supported by the Hauts-de-France Regional Council, the French Ministry of Higher Education and Research and the European Regional Development Fund. C.B. and J.D. were also funded by CLIMIBIO. The photomixing cw-THz spectrometer has been funded both by the Delegation Generale pour l'Armement (DGA, ProjetANR-11-ASTR-0035), the Institut de Recherche en Environement Industiel (IRENI) and the European Commission via the Interreg IVA-2 seas (Cleantech Project). MultiCHARME was founded by the University of Litttoral and its Research Quality Bonus. The THz cavity and A.P. were funded by the Salt-Nord (project Teraspec-M0407), the French ANR (ANR-15-CE29-0017) and the European Regional Development Fund (INTERREG V FR-WA-VL 1.2.11). We thank: (i) the AILES beamline team for the synchrotron-based FT-THz experiments, especially the beamline manager [PERSON] and [PERSON] in charge of the FT-FIR measurements in the White type cell; (ii) [PERSON] and [PERSON] from the Anhui Institut of Optics and Fine Mechanics (Hefei, China) for the development of the Chernin cell; (iii) [PERSON], [PERSON] and [PERSON] from LPCA (Dunkirk, France) for their assistance during the measurements in the CHARME chamber. The authors declare no conflict of interest. The following abbreviations are used in this manuscript:  
ACE & Atmospheric Chemistry Experiment  
AILES & Advanced Infrared beamLine Exploited for Spectroscopy  
AMC & Amplified Multiplier Chains  
CFCs/HCFCs & ChloroFluoroCarbons  
CHARME & CHamber for the Atmospheric Reactivity and the Metrology of the Environment  
cw-THz & continuous-wave Terahertz  
FFT & Fast Fourier Transform  
FP-TAS & Fabry-Perot Terahertz Absorption Spectroscopy  
FSR & Free Spectral Range  
FTS & Fourier Transform Spectrometer  
GHG & Greenhouse gas  
HITRAN & HIgh-resolution TRANmission molecular absorption database  
IASI & Infrared Atmospheric Sounding Interferometer  
IR & InfraRed  
LOD & Level of Detection  
LTG-AsGa & Low-Temperature Grown--Arsenide Gallium  
MLS & Microwave Limb Sounder  
NEP & Noise Equivalent Power  
SCISAT & SCIence Satellite  
SNR & Signal to Noise Ratio  
SOLEIL & Source Optimisee de Lumiere d'Energie Intermediaire du LURE  
STDS & Spherical-Top Data System  
TALIS & THz Atmospheric Limb Sounder  
TES & Tropospheric Emission Spectrometer  
TFMeCaSba & TetraFluoroMethane Calculated Spectroscopic Databases