Atomic oxygen is a main component of the mesosphere and lower thermosphere (MLT). The photochemistry and the energy balance of the MLT are governed by atomic oxygen. In addition, it is a tracer for dynamical motions in the MLT. It is difficult to measure with remote sensing techniques. Concentrations can be inferred indirectly from the oxygen air glow or from observations of OH, which is involved in photochemical processes related to atomic oxygen. Such measurements have been performed with several satellite instruments such as SCIAMACHY, SABER, WINDII and OSIRIS. However, the methods are indirect and rely on photochemical models and assumptions such as quenching rates, radiative lifetimes, and reaction coefficients. The results are not always in agreement, particularly when obtained with different instruments.

We have explored an alternative approach, namely the observation of the ³P₁ → ³P₂ fine-structure transition of atomic oxygen at 4.7 THz (63 µm) using the German Receiver for Astronomy at Terahertz Frequencies (GREAT) on board of SOFIA, the Stratospheric Observatory for Infrared Astronomy. GREAT is a heterodyne spectrometer providing high sensitivity and high spectral resolution as low as 76 kHz. This method enables the direct measurement without involving photochemical models to derive the atomic oxygen concentration. The night-time measurements have been performed during a SOFIA flight along the west coast of the US. These are the first measurements which resolve the line shape of the 4.7-THz transition. From the spectra the concentration profiles and radiances of atomic oxygen were derived with a radiative transfer model. The observed radiances range from 1.5 to 2.2 nW cm^-2 sr^-1 and the the altitude profiles agree within the measurement uncertainty with SABER data and the NRLMSISE-00 model [1].

In conclusion, THz heterodyne spectroscopy is a powerful method to measure atomic oxygen in the MLT. With the current progress in THz technology balloon-borne and space-borne 4.7-THz heterodyne spectrometers become feasible [2, 3]. Combining such a THz spectrometer with optical instruments similar to SABER or SCIAMACHY will be even more advantageous for the determination of atomic oxygen in the MLT.

[1] H. Richter et al., Direct measurements of atomic oxygen in the mesosphere and lower thermosphere using terahertz heterodyne spectroscopy, accepted for publication in Communications Earth & Environment (2021).

[2] M. Wienold et al, A balloon-borne 4.75 THz-heterodyne receiver to probe atomic oxygen in the atmosphere, to appear in: Proceedings of the 45^th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) (Buffalo, NY, 2020).

[3] S. P. Rea et al., The low-cost upper-atmosphere sounder (LOCUS), Proceedings of the 26th International Symposium on Space Terahertz Technology (Cambridge, MA, 2015).

How to cite: Hübers, H.-W., Richter, H., Buchbender, C., Güsten, R., Higgins, R., Klein, B., Stutzki, J., and Wiesemeyer, H.: Atomic oxygen in the mesosphere and lower thermosphere measured by terahertz heterodyne spectroscopy   , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7658, https://doi.org/10.5194/egusphere-egu21-7658, 2021.

We present a portable, multichannel laser heterodyne spectroradiometer (MLHS) with a spectral resolution of 0.0013 cm-1 for precision column measurements and vertical profiling of atmospheric greenhouse gases (GHG). Sample spectra of CO₂ and CH₄ absorption lines obtained by direct Sun observations have allowed us to measure GHG column abundance with a precision of 0.5% for CO₂ and 10% for CH₄, as well as to retrieve their vertical profiles and to get a vertical profile of the stratospheric wind Rodin et al. (2020). The fundamentals and specifics of the multichannel configuration implementation of heterodyne receivers are presented in Zenevich et al. (2020). This work presents the first data of atmospheric CO₂ and CH₄ measurements, which were taken in a 4-channel configuration of the heterodyne receiver. Such configuration has allowed us to get atmospheric spectra with the SNR 300-500 within 2 minutes period of signal integration and keep the high spectral resolution. The results of retrieving CO₂ and CH₄ vertical concentration profiles and vertical profiles of the stratospheric wind are also presented.

Acknowledgments

This work has been supported by the Russian Foundation for Basic Research grants # 19-29-06104  (A.V. Rodin, M. V. Spiridonov, I.Sh. Gazizov) and # 19-32-90276 (S. G. Zenevich).

References:

Zenevich S. et al.: The improvement of dark signal evaluation and signal-to-noise ratio of multichannel receivers in NIR heterodyne spectroscopy application for simultaneous CO2 and CH4 atmospheric measurements, OSA Continuum, 3, 7, 1801-1810, doi:10.1364/OSAC.395094, 2020.

Rodin, A. et al.: Vertical wind profiling from the troposphere to the lower mesosphere based on high-resolution heterodyne near-infrared spectroradiometry, Atmos. Meas. Tech., 13, 2299–2308, doi:10.5194/amt-13-2299-2020, 2020.

How to cite: Zenevich, S., Gazizov, I., Churbanov, D., Spiridonov, M., and Rodin, A.: Multichannel Heterodyne Spectroradiometer for Atmospheric Greenhouse Gas Measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3674, https://doi.org/10.5194/egusphere-egu21-3674, 2021.

How to cite: Miller, J. H., Flores, M., and Bomse, D.: Statistical Characterization of Temperature and Pressure Vertical Profiles for the Analysis of Laser Heterodyne Data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6802, https://doi.org/10.5194/egusphere-egu21-6802, 2021.

Laser heterodyne spectroscopic measurement technique^[1] has been proved to be a powerful and effective remote sensing tool for measurements of greenhouse gases in the atmospheric column^[2-6]. In the present work, we report the development of a portable all-fiber coupled dual-channel laser heterodyne radiometer (LHR) and its field deployment. Two DFB lasers operating at 1650.9 nm and 1603.6 nm are used for the remote measurements of column CH₄ and CO₂, respectively. A fiber optic switch is used to modulate and split the collected sunlight into two channels for simultaneous measurements of both target greenhouse gases. Custom-made preamplifiers combined with digital lock-in amplifiers are used to extract the laser heterodyne signals. The spectral resolution of the instrument is about 0.00442 cm^-1, and the signal-to-noise ratio of the measured spectrum of about 250 is achieved with 0.8 s average time per sampling datum. The developed LHR instrument was successfully deployed to a field atmospheric observation experiment (in Dachaidan district, Qinghai province, China).

The experimental detail including the LHR instrument integration, dual-channel measurement results of column CH₄ and CO₂ and preliminary data inversion results will be presented and discussed.

Acknowledgments. The project was supported by the national key R&D program of China (2017YFC0209705). The authors thank the financial supports from the CPER CLIMIBIO program, the Labex CaPPA project (ANR-10-LABX005).

References

[1] D. Weidmann, T. Tsai, N. A. Macleod, G. Wysocki, Opt. Lett. 36 (2011) 1951-1953.

[2] E. L. Wilson, A. J. DiGregorio, G. Villanueva, C. E. Grunberg, et al., Appl. Phys. B 125 (2019) 211-219.

[3] D. S. Bomse, J. E. Tso, M. M. Flors, J. H. Miller, Appl. Opt. 59 (2020) B10-B17.

[4] J. Wang, G. Wang, T. Tan, G. Zhu, C. Sun, Z. Cao, W. Chen, X. Gao, Opt. Express 27 (2019) 9610-9619

[5] A. Rodin, A. Klimchuk, A. Nadezhdinskiy, D. Churbanov, et al., Opt. Express 22 (2014) 13825-13834.

[6] E. L. Wilson, M. L. McLinden, J. H. Miller, H. R. Melroy, et al., Appl. Phys. B 114 (2014) 385-393.

How to cite: Wang, J., Tan, T., Xue, Z., Gao, X., and Chen, W.: A portable dual-channel laser heterodyne radiometer for simultaneous remote measurements of CH4 and CO2 in the atmospheric column, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16428, https://doi.org/10.5194/egusphere-egu21-16428, 2021.

Advances in optical technology have led to the commercialization and widespread use of broadband optical frequency combs for multiplexed measurements of trace-gas species. Increasingly available in the mid-infrared spectral region, these devices can be leveraged to interrogate the molecular fingerprint region where many fundamental rovibrational transitions occur. Here we present a cross-dispersed spectrometer employing a virtually imaged phased array etalon and ruled diffraction grating coupled with a difference frequency generation comb centered near 4.5 µm. The spectrometer achieves sub-GHz spectral resolution with a 30 cm^-1 instantaneous bandwidth. Laboratory results for nitrous oxide isotopic abundance retrieval will be presented. Challenges relating to characterizing the instrument lineshape function, constructing a frequency axis traceable to the comb, and accurate spectral modelling will be addressed and progress towards incorporating a more compact laser frequency comb source into the system will be discussed.

How to cite: Bailey, D. M., Zhao, G., and Fleisher, A. J.: Precision Mid-Infrared Frequency Comb Spectroscopy using a Cross-Dispersed Spectrometer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12235, https://doi.org/10.5194/egusphere-egu21-12235, 2021.

The development of increasingly sensitive and robust instruments and new methodologies are essential to improve our understanding of the Earth’s climate and air pollution. In this context, Dual-Comb spectroscopy (DCS) appears as an emerging spectroscopy methodology to detect in situ, without air-sampling, atmospheric trace-gases.

DCS is a Fourier-transform type experiment that takes advantage of mode-locked femtosecond (fs) pulses. This methodology appears highly relevant for atmosphere remote-sensing studies because of its very fast acquisition rate (>kHz) that reduces the impact of atmospheric turbulences on the retrieved spectra. DCS has been successfully applied in near-infrared (NIR) spectral ranges for atmospheric greenhouse gas monitoring (water vapor, carbon dioxide, and methane) [1-2].

Its implementation in the UV range would offer a new spectroscopic intrumentation to target the most reactive species of the atmosphere (OH, HONO, BrO...) as they have their greatest absorption cross-sections in the UV range. UV-DCS would therefore be an answer to the lack of variability of today operationnal and in situ monitoring instrument for those reactive molecules.

We will present a potential light source for remote sensing UV-DCS and discuss the degree of immunity of UV-DCS to atmospheric turbulences. We will show to which extent the characteristics of the currently available UV sources are compatible with the unambiguous identification of UV absorbing gases by UV-DCS. We will finally present the performances of UV-DCS in terms of concentration detection limit for several UV absorbing molecules (OH, BrO, NO₂, OClO, HONO, CH₂O, SO₂). This sensitivity study has been recently published [3] and the main results will be presented.

[1] Rieker, G.B.; Giorgetta, F.R.; Swann, W.C.; Kofler, J.; Zolot, A.M.; Sinclair, L.C.; Baumann, E.; Cromer, C.;Petron, G.; Sweeney, C.; et al. « Frequency-comb-based remote sensing of greenhouse gases over kilometer air Paths ». Optica 1, p. 290–298 (2014)

[2] Oudin, J.; Mohamed, A.K.; Hébert, P.J. "IPDA LIDAR measurements on atmospheric CO2 and H2O using dual comb spectroscopy," Proc. SPIE 11180, International Conference on Space Optics — ICSO 2018, p. 111802N (12 July 2019)

[3] Galtier, S.; Pivard, C.; Rairoux, P. Towards DCS in the UV Spectral Range for Remote Sensing of Atmospheric Trace Gases. Remote Sens., 12, p.3444 (2020)

How to cite: Pivard, C., Galtier, S., and Rairoux, P.: Towards Remote Sensing of Atmospheric Trace Gases in the UV spectral range using Dual-Comb spectroscopy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12337, https://doi.org/10.5194/egusphere-egu21-12337, 2021.

Tunable diode laser absorption spectroscopy (TDLAS) based on multi-pass cell (MPC) ^[1-4] is a powerful analytical tool for field applications in air quality monitoring, industrial process control and medical diagnostics. However, the conventional MPC as a core component in TDLAS devices has a large size, low utilization efficiency of the mirror surfaces and tight optical alignment tolerances ^[5]. Design of miniaturized long-path MPC for the development of handheld portable high sensitivity sensing devices is one of the mainstream trends nowadays. In this work, we designed and fabricated a mini-MPC with an effective optical absorption path length of 4.2 m and dimensions of 4×4×6 cm³, which to our best knowledge is the current smallest MPC in terms of the same optical path length. The mini-MPC generates a seven-nonintersecting-circle dense spot pattern on two 25.4 mm spherical mirror surfaces providing a high fill factor of 21 cm^-2. A fiber-coupled collimator and an InGaAs photodetector are integrated into the mini-MPC via a high-resolution 3D-printed frame, hence removing the requirement of active optical alignment. Using a 1.65 μm distributed-feedback laser, the performance of this mini-MPC for methane detection was evaluated in terms of linearity, flow response time, stability, minimum detectable limit and measurement precision. Continuous measurements of methane near a sewer and in the atmosphere were performed to demonstrate the stability and robustness of the highly integrated mini-MPC based gas sensor. This work paves the way towards a sensitive, low-cost, miniature trace gas sensor inherently suitable for large-scale deployment of distributed sensor networks and for handheld mobile devices.

Acknowledgments

The project is sponsored by National Key R&D Program of China (2017YFA0304203), National Natural Science Foundation of China (NSFC) (61622503, 61575113, 61805132, 11434007), Outstanding Innovative Teams of Higher Learning Institutions of Shanxi, Foundation for Selected Young Scientists Studying Abroad, Sanjin Scholar (2017QNSJXZ-04) and Shanxi “1331KSC”. Frank K. Tittel acknowledges support by the Robert Welch Foundation (Grant #C0586).

References

[1] L. Dong; F. K. Tittel; C. Li; N. P. Sanchez; H. Wu; C. Zheng, Y. Yu, A. Sampaolo, R. J. Griffin, Opt. Express 24 (2016) A528.

[2] K. Liu, L. Wang, T. Tan, G. S. Wang, W. J. Zhang, W. D. Chen, X. M. Gao, Sensor. Actuat. B-Chem. 220 (2015) 1000.

[3] R. Cui, L. Dong, H. Wu, S. Li, L. Zhang, W. Ma, W. Yin, L. Xiao, S. Jia, F. K. Tittel, Opt. Express 26 (2018) 24318.

[4] C. T. Zheng, W. L. Ye, J. Q. Huang, T. S. Cao, M. Lv, J. M. Dang, Y. D Wang, Sensor. Actuat. B-Chem. 190 (2014) 249.

[5] P. Weibring, D. Richter, A. Fried, J. G. Walega, C. Dyroff, Appl. Phys. B 85 (2006) 207.

How to cite: Cui, R., Dong, L., Wu, H., Ma, W., Xiao, L., Jia, S., Chen, W., and Tittel, F. K.:  3D-Printed Miniature Fiber-Coupled Multi-pass Cell with Dense Spot Pattern for ppb-level Methane Detection Using a Near-IR Diode Laser, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-479, https://doi.org/10.5194/egusphere-egu21-479, 2021.

Differential Optical Absorption Spectroscopy (DOAS) has proven to be very useful to study the composition and dynamics of Earth’s atmosphere. Compact grating spectrographs (GSs) with moderate spectral resolution (ca. 1nm) allow to quantify the absorption of many trace gases along atmospheric light paths from ground to space borne platforms.

Since the width of a rovibronic absorption line of a small molecule in the UV to near IR spectral range is in the picometre range, increasing the spectral resolution of DOAS measurements largely increases their selectivity and in many cases also their sensitivity. In addition, further trace gases (e.g. OH radicals) or isotopes of trace gases could be detected, while common problems due to Fraunhofer line undersampling were reduced. However, since high resolution GSs are bulky (immobile) instruments with a strongly reduced light throughput, hardly any high resolution DOAS measurements have been performed.

Since more than a century, Fabry Pérot Interferometers (FPIs) have been successfully used for high resolution spectroscopy in many scientific fields, where their light throughput advantage over grating spectrographs for higher resolving powers is well known. However, except for a few studies, FPIs
received hardly any attention in atmospheric trace gas remote sensing. We examine the light throughput of GSs and FPI spectrographs regarding spectral resolution and spectrograph size (i.e. mobility). We find that robust and mobile high resolution FPI spectrograph implementations can be by orders of magnitude smaller than GSs with the same spectral resolution. A compact high resolution FPI spectrograph prototype was already successfully tested in the field. Further, the light throughput can be optimised to allow for passive scattered sunlight measurements with similar SNR as moderate resolution DOAS measurements while, at the same time, attaining spectral resolutions in the picometre range.

High resolution FPI spectrographs might allow for a multitude of applications in atmospheric remote sensing. A few examples include scattered sunlight absorption measurements of many atmospheric trace gases and their isotopes, the quantification of tropospheric and volcanic OH radicals, high resolution O2 measurements for radiative transfer investigation and aerosol studies, and solar induced chlorophyll fluorescence quantification using Fraunhofer lines.

How to cite: Kuhn, J., Bobrowski, N., Wagner, T., and Platt, U.: Towards DOAS measurements with a picometre spectral resolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2504, https://doi.org/10.5194/egusphere-egu21-2504, 2021.

Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) is a well-established measurement technique for the detection of atmospheric aerosol and trace gases: ultra-violet and visible radiation spectra of skylight are analyzed to obtain information on different atmospheric parameters. An appropriate set of spectra recorded under different viewing geometries ("Multi-Axis") allows retrieval of aerosol and trace gas vertical distributions as well as aerosol properties by applying numerical inversion methods. Currently one of the method’s major limitations in ground-based applications is the limited information contained in the measurements that reduces the sensitivity, particularly at higher altitudes.

It is well known but not yet used in MAX-DOAS profile retrievals that measuring skylight of different polarisation directions provides additional information: The degree of polarisation for instance strongly depends on the atmospheric aerosol content and the aerosol properties and – since the light path differs for the light of different polarisation -  the set of geometries available for the inversion is extended. We present a novel polarization-sensitive MAX-DOAS instrument (PMAX-DOAS) and a corresponding inversion algorithm, capable of using polarimetric information to significantly extend the information content of the measurements. The improvement over conventional “unpolarised” MAX-DOAS approaches will be discussed, based on both, synthetic data and real measurements.

How to cite: Tirpitz, J.-L., Frieß, U., and Platt, U.: The information content of skylight polarisation in MAX-DOAS trace gas- and aerosol profiling applications , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10338, https://doi.org/10.5194/egusphere-egu21-10338, 2021.

Water vapor (H₂O) is the strongest greenhouse gas in our atmosphere, and it plays a key role in multiple processes that affect weather and climate. Particularly, H₂O in the upper troposphere - lower stratosphere (UTLS) is of great importance to the Earth's radiative balance, and has a significant impact on the rate of global warming. Hence, accurate measurements of UTLS H₂O are crucial for understanding and projecting climate. Currently, the reference method used for in-situ measurements of UTLS H₂O aboard meteorological balloons is cryogenic frostpoint hygrometry (CFH) [1]. However, the cooling agent required for this technique (trifluoromethane) is phasing out as of 2020, due to its strong global warming potential. This represents a major challenge for the continuity of global, long-term stratospheric H₂O monitoring networks, such as the GCOS Reference Upper Air Network (GRUAN).

As an alternative to CFH, we developed a compact instrument based on mid-IR quantum-cascade laser absorption spectroscopy (QCLAS) [2]. The spectrometer, with a total weight of 3.9 kg, relies on a segmented circular multipass cell [3] that was specifically developed to meet the stringent requirements, in mass, size and temperature resilience, posed by the harsh environmental conditions of the UTLS. Quick response and minimal interference by H₂O outgassing from surfaces are achieved by an open-path approach. An elaborate thermal management system ensures excellent internal temperature stability, despite of outside temperature variations of up to 80 K.

In collaboration with the German Weather Service (DWD), two successful test flights were performed in December 2019 in Lindenberg, Germany. We will report on the results of these test flights, highlighting the instrument outstanding capabilities under UTLS and stratospheric conditions (up to 28 km altitude), and identifying some limitations. Further development activities triggered by the test flights, involving both hardware adaptations and spectral analysis modifications, will be also discussed.  The final validation will be addressed, in cooperation with the Swiss Federal Institute of Metrology (METAS), by laboratory experiments in a custom-made climate chamber, using dynamically generated, SI-traceable reference mixtures with H₂O amount fractions below 20 ppmv and uncertainty < 1%. The ultimate goal is to demonstrate the potential of QCLAS as a highly valuable technique for quantitative balloon-borne measurements of UTLS and stratospheric H₂O.

[1] Brunamonti et al. (2019), J. Geophys. Res. Atmos., doi.org/10.1029/2018JD030000.

[2] Graf et al. (2020), Atmos. Meas. Tech. Discuss., doi.org/10.5194/amt-2020-243 (Accepted 4 January 2021).

[3] Graf, Emmenegger and Tuzson (2018), Opt. Lett., doi.org/10.1364/OL.43.002434.

How to cite: Brunamonti, S., Graf, M., Emmenegger, L., and Tuzson, B.: Quantum-cascade laser absorption spectroscopy for balloon-borne measurements of stratospheric H2O, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5558, https://doi.org/10.5194/egusphere-egu21-5558, 2021.

A narrow-band optical hygrometer FIRH (Fast Infrared Hygrometer, Nowak et al., 2016), based on absorption of laser light at wavelength λ=1364.6896 nm was used for contactless measurements of humidity inside the measurement volume of LACIS-T (turbulent Leipzig Aerosol Cloud Interaction Simulator, Niedermeier et al., 2020). LACIS-T is a multi-purpose moist-air wind tunnel for investigating atmospherically relevant interactions between turbulence and cloud microphysical processes under well-defined and reproducible laboratory conditions. Main goals of the experiment were:

1) characterization and evaluation of the FIRH hygrometer in controlled conditions,

2) characterization of fast turbulent humidity fluctuations inside LACIS-T.

Collected results indicate, that FIRH can be used to characterize turbulent fluctuations of humidity in scales of tens of centimeters with the temporal resolution of 2 kHz and presumably more. Interestingly, scanning of LACIS-T measurement volume indicated existence of turbulence and wave-like features for the investigated measurement setup in its  central part, where air streams of different thermodynamical properties, yet the same mean velocity mix intensively. , However, the setup for cloud measurements include an additional flow (i.e., an aerosol flow) in the central part strongly reducing the wave-like features. In other words, cloud process studies are most likely unaffected by these features.

Finally, the experiments proved that contactless measurements of humidity conducted from outside the measurement volume of LACIS-T are useful, on condition of corrections of glass window transmission and interferences.

Niedermeier, D., Voigtländer, J., Schmalfuß, S., Busch, D., Schumacher, J., Shaw, R. A., and Stratmann, F. (2020): Characterization and first results from LACIS-T: a moist-air wind tunnel to study aerosol–cloud–turbulence interactions, Atmos. Meas. Tech., 13, 2015-2033, doi:10.5194/amt-13-2015-2020.

Nowak J., Magryta P., Stacewicz T., Kumala W., Malinowski S.P., 2016: Fast optoelectronic sensor of water concentration, Optica Applicata, vol. 46(4) , pp. 607-618 , doi: 10.5277/oa160408

How to cite: Grosz, R., Nowak, J., Niedermeier, D., Mijas, J., Frey, W., Ort, L., Malinowski, S., Schmalfuss, S., Stacewicz, T., and Voigtländer, J.: Contactless and high-frequency optical hygrometry in LACIS-T, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14538, https://doi.org/10.5194/egusphere-egu21-14538, 2021.

Peroxy radicals (HO₂+RO₂) are crucial intermediates in many key atmospheric processes and contribute to the formation of major air pollutants, such as ozone and secondary organic aerosols¹. Due to their high reactivity and their extremely low concentrations (typically <100 pptv), in-situ real time and interference-free measurements of peroxy radicals remain challenging. In the present work, photoacoustic spectroscopy (PAS)² is applied, for the first time to our best knowledge, to the measurements of peroxy radicals with the help of the well established chemical amplification approach. Peroxy radical chemical amplification (PERCA)³ is based on chemical conversion of peroxy randicals into NO₂ and followed by chemical amplification to achieve the necessary measurement sensitivity for the measurement of atmospheric peroxy radical concentration. The resulting NO₂ concentration is measured by PAS to infer the total concentration of peroxy radicals. The performance of the developed PERCA-PAS approach was demonstrated with a reference ECHAMP chemical amplification system using cavity attenuated phase shift spectroscopy (CAPS) for NO₂ monitoring. The determined amplification gains (referred to as chain length, CL) of the ECHAMP system using PAS are well consistent with the values determined using CAPS. A 1-σ limit of detection of ~12 pptv for peroxy radicals was achieved in an integration time of 90 s at a relative humidity of about 9.8%. The detection limit of the current ECHAMP-PAS system can be further improved by using higher laser power and increasing the number of microphones in the photoacoustic spectrophone, which would allow reaching sub-pptv detection limits for the measurements of peroxy radicals in the atmosphere.

This work provides a promising technique to develop novel compact and very cost-effective (compared to all methods currently used) sensors, which will allow readily developing network measurements and investigation of the spatial distribution of peroxy radicals in the atmosphere.

Acknowledgments. This work is supported by the French national research agency (ANR) under MABCaM and LABEX-CaPPA contracts, the European Funds for Regional Economic Development through the CaPPA project, the CPER-CLIMIBIO program, the LEFE/CHAT INSU program. It is also supported by the National Natural Science Foundation of China (22073013), Natural Science Foundation of Chongqing (cstc2018jcyjAX0050) and Fundamental Research Funds for the Central Universities (2020CDJXZ002).

Reference

[1] J. J. Orlando, G. S. Tyndall, Laboratory studies of organic peroxy radical chemistry: an overview with emphasis on recent issues of atmospheric significance, Chem. Soc. Rev. 41(2012) 6294-6317.

[2] W. Chen et al., Photonic Sensing of reactive atmospheric species, in Encyclopedia of Analytical Chemistry © 2017 John Wiley & Sons, Ltd. DOI: 10.1002/9780470027318.a9432.

[3] C. Cantrell, D. Stedman, A possible technique for the measurement of atmospheric peroxy radicals, Geophys. Res. Lett. 9 (1982) 846-849.

How to cite: Chen, W., Wang, G., Lahib, A., Duncianu, M., Gou, Q., Stevens, P. S., Dusanter, S., Tomas, A., and Sigrist, M. W.: Peroxy radical measurements by photoacoustic spectroscopy coupled to chemical amplification, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-502, https://doi.org/10.5194/egusphere-egu21-502, 2021.

Solar occultation flux (SOF) and Mobile extractive FTIR (MeFTIR) are techniques used for over 20 years to quantify industrial emissions of VOCs, CH₄, and others, from refineries in the USA, Europe, and Asia. Here, they were combined to assess methane (CH₄) and ammonia (NH₃) from concentrated animal feeding operations (CAFOs) in the San Joaquin Valley (SJV), California. SOF and MeFTIR were used to measure NH₃ column, and ground concentrations of NH₃ and CH₄, respectively. SOF retrieves the gas column concentration from the solar spectra using a solar track, directing the light to a FTIR spectrometer, while crossing the gas plume. Subsequently, a direct flux approach combines the retrieved columns with wind information to obtain the mass fluxes of ammonia. In this survey, the wind information was acquired by a wind LIDAR, which measures wind speed and direction in the interval of 10 – 300 m. On the other hand, Methane emissions were quantified using a unique indirect flux approach by combining the estimated ammonia fluxes and the NH₃:CH₄ ratios measured from the ground concentration using MeFTIR.

Two field campaigns performed in spring and autumn studied emissions from 14 single dairy CAFOs. The daily emissions from the single farms averaged 96.4 ± 38.4 kg_NH3 h^-1and 411 ± 185.4 kg_CH4h^-1, respectively, for NH₃ and CH₄ with the corresponding emission factors (EF) per animal unit of 11.3 ± 3.8 g_NH3h^-1AU^-1and 50.3 ± 24.1 g_CH4h^-1AU^-1. The uncertainty of ammonia measurements was 17 % in a standard confidence interval (CI) and 37 % in a 95 % CI, with the largest uncertainty associated with the wind measurements. Furthermore, the methane uncertainty estimations averaged 27 % in a standard CI, and 52 % in a 95 % CI, dominated by the ammonia fluxes uncertainty. Comparison between Annual or daily EFs obtained by SOF to other quantification approaches, have to take into consideration the SOF measurement conditions, day-time and sunny weather, due to their effects on the NH₃ emissions. The study contributed to develop the knowledge of dairy CAFOs emission, and to strengthen the role of optical remote sensing techniques, bridging the gap between satellites and stationary measurement approaches.

How to cite: Vechi, N. T., Mellqvist, J., Offerle, B., Samuelsson, J., and Scheutz, C.: Mobile Optical Remote Sensing for quantification of Ammonia and Methane emissions from Dairy Farms in California., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10911, https://doi.org/10.5194/egusphere-egu21-10911, 2021.

The hydroxyl (OH) free radical plays an important role in atmospheric chemistry due to its high reactivity with volatile organic compounds (VOCs) and trace species (CH_4, CO, SO₂, etc) [1]. Due to its very short lifetime (~1 s or less) and very low concentration in the atmosphere (in the order of 10⁶ cm^-3), in situ and direct measurement of OH concentration in the atmosphere is challenging [2].

We report in this paper our recent work on developing a compact spectroscopic instrument based on off-axis integrated cavity output spectroscopy (OA-ICOS) [3] for optical monitoring of OH radicals. In the present work, OH radicals of ~10¹² OH radicals/cm³ were generated from continue micro-wave discharge at 2.45 GHz of water vapor at low pressure (0.2-1 mbar), and were used as sample for validation of the developed OA-ICOS approaches. Two experimental approaches are designed for the measurements of OH radicals: (1) OA-ICOS [4] and wavelength modulation enhanced OA-ICOS (WM OA-ICOS) [5]. A distributed feedback (DFB) laser operating at 2.8 µm was employed for probing the Q (1.5e) and Q (1.5f) double-line transitions of the ²Π_3/2state at 3568.52382 and 3568.41693 cm^-1, respectively. A 1s detection limit of ~2.7×10¹⁰ cm^-3  was obtained for an averaging time of 125 s using a simple OA-ICOS scheme. This limit of detection is further improved by a factor of 3.4 using a WM OA-ICOS approach.

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]  U. Platt, M. Rateike, W. Junkermann, J. Rudolph, and D. H. Ehhalt, New tropospheric OH measurements, J. Geophys. Res. 93 (1988) 5159-5166.

[2]  D. E. Heard and M. J. Pilling, Measurement of OH and HO₂ in the Troposphere, Chem. Rev. 103 (2003) 5163-5198.

[3]  J. B. Paul, L. Lapson, J. G. Anderson, Ultrasensitive absorption spectroscopy with a high-finesse optical cavity and off-axis alignment, Appl. Opt. 40 (2001) 4904-4910.

[4]  W. Chen, A. A. Kosterev, F. K. Tittel, X. Gao, W. Zhao, "H₂S trace concentration measurements using Off-Axis Integrated Cavity Output Spectroscopy in the near-infrared", Appl. Phys. B 90 (2008) 311-315

[5] W. Zhao, X. Gao, W. Chen, W. Zhang, T. Huang, T. Wu, H. Cha, Wavelength modulation off-axis integrated cavity output spectroscopy in the near infrared, Appl. Phys. B 86 (2007) 353-359

How to cite: Ngo, M. N., Ba, T. N., Petitprez, D., Cazier, F., Zhao, W., and Chen, W.: Measurement of OH radicals using off-axis integrated output spectroscopy (OA-ICOS) at 2.8 µm, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16416, https://doi.org/10.5194/egusphere-egu21-16416, 2021.

Nitrogen Oxide (NO_x) emissions from vehicles are a major cause of poor air quality in urban areas. The emissions per vehicle are regulated by the EURO Norm (EURO V: 2000mg/kWh, EURO VI: 460mg/kWh). Existing possibilities to measure whether the vehicles comply with the regulations (e.g. PEMS: Portable Emission Measurement System) are rare and costly. Within the framework of the EU project CARES (City Air Remote Emission Sensing) different remote emission sensing techniques and instruments are further developed. ‘Plume Chasing’ is one of them. With the Plume Chasing method, the emissions of a vehicle are measured in the wake of the investigated vehicle, i.e. in the diluted emission plume. This is done with a for this purpose optimized ICAD NO_x-CO₂ instrument (Airyx GmbH), that allows fast (1s time resolution) and simple measurements with high accuracy (sub ppb for NO_x) with a high measurement range (0-5000ppb). With these characteristics, it is perfectly suitable to detect malfunctioning or illegally manipulated emission control systems like SCR (selective catalytic reduction).

Several validation studies of Plume Chasing against the established PEMS have shown very good correlations. During a 3-day study in Sweden in November 2019, Plume Chasing measurements of a EURO V and a EURO VI truck were performed with activated as well as deactivated emission control system for several hours in different driving conditions. The derived Plume Chasing NO_x emission values even for short measurement times of one and two minutes showed excellent correlation with the averaged PEMS NO_x data of the trucks with R²~0.9. The study demonstrated the robustness of the Plume Chasing method in detecting high emitter trucks. To further test and optimise different measurement configurations and data analysis algorithms, within the CARES project several ICAD NO_x-CO₂ instruments are installed together with e.g. LICOR CO2-sensors or Condensation Particle Counters in a measurement vehicle from TNO, Netherlands.

Studies on German and Austrian highways in 2018 and 2019 showed that among several hundreds of trucks up to 35% of the EURO V trucks and up to 25% of the EURO VI trucks showed consistently high emissions exceeding the EURO norm limit, which provides strong evidence for a high number of defect or manipulated emission control systems. A recent study in Denmark showed 9,7% of the vehicles exceeding the standards. The vehicles were afterwards inspected by the police and defects or manipulations of the emission control system could be confirmed.

How to cite: Schmidt, C., Pöhler, D., Engel, T., Horbanski, M., Lampel, J., Schmitt, S., and Platt, U.: Real Driving NOx Emission Measurements of Vehicles with ICAD instruments for Plume Chasing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1646, https://doi.org/10.5194/egusphere-egu21-1646, 2021.

Nitrous acid (HONO) is one of the important atmospheric trace gases due to its contribution to the cycles of nitrogen oxides (NOx) and hydrogen oxides (HOx). In particular it acts as a precursor of tropospheric OH radicals, which is responsible for the self-cleansing capacity of the atmosphere [1,2]. We developed an instrument based on incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) for automatic measurement of HONO in a rural area in a summer period during a field "Campagne d’OBservation Intensive des Aérosols et précurseurs à Caillouël-Crépigny (COBIACC)" in France. IBBCEAS technique is now extensively used in field applications for the measurements of both trace gases and aerosols [3,4].

Real-time in situ measurements of HONO and NO₂ have been simultaneously carried out. The IBBCEAS instrument performance has been demonstrated and validated through lab-based tests, and in particular through field intercomparison via side-by-side measurements of temporal concentration profiles of HONO and NO₂ in the rural area. The intercomparison of the concentration measurements between IBBCEAS and an instrument called MARGA (Monitor for AeRosols and Gases in Ambient air) for HONO, and IBBCEAS vs. a reference NOx analyzer for NO₂. Good agreements have been observed which demonstrated the performance of the developed IBBCEAS instrument for the measurement of atmospheric HONO concentration (<5 ppb) in a rural area.

The preliminary experimental results will be presented and discussed.

Acknowledgments This work was supported by the CPER CLIMIBIO program and the Labex CaPPA project (ANR-10-LABX005). The authors highly appreciate the offers of Mr. Eric Wetzels from Polyfluor Plastics bv for the help in our instrumental conception involving Teflon pipe.

References

[1] X. Li, T. Brauers, R. Häseler, R. Bohn, H. Fuchs, A. Hofzumahaus, F. Holland, S. Lou, et al., Exploring the atmospheric chemistry of nitrous acid (HONO) at a rural site in Southern China, Atmos. Chem. Phys. 12 (2012) 1497-1513.

[2] H. Su, Y. Cheng, M. Shao, D. Gao, Z. Yu, L. Zeng, J. Slanina, et al., Nitrous acid (HONO) and its daytime sources at a rural site during the 2004 PRIDE‐PRD experiment in China, J. Geophys. Res. 113 (2008) D14312.

[3] T. Wu, Q. Zha, W. Chen, Z. Xu, T. Wang, X. He, Development and deployment of a cavity enhanced UV-LED spectrometer for measurements of atmospheric HONO and NO₂ in Hong Kong, Atmos. Environ. 95 (2014) 544-551.

[4] L. Meng, G. Wang, P. Augustin, M. Fourmentin, Q. Gou, E. Fertein, T. N. Ba, C. Coeur, A. Tomas, W. Chen, Incoherent broadband cavity enhanced absorption spectroscopy-based strategy for direct measurement of aerosol extinction in lidar blind zone, Opt. Lett. 45 (2020) 1611-1614.

How to cite: Meng, L., Wang, G., Coeur, C., Tomas, A., Wu, T., Fu, H., and Chen, W.: Development of an incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument for autonomous field measurements of HONO and NO2 in a rural area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16417, https://doi.org/10.5194/egusphere-egu21-16417, 2021.

It is important to characterize the composition of aerosol particles in air, which causes adverse health effects and millions of deaths each year. Aerosol, or particulate matter (PM), is difficult to characterize because of its wide range of particle sizes; constituents (various organic and inorganic compounds); concentration; morphology; state (liquid or solid); and time-dependent modification.
Infrared (IR) spectroscopy is a non-destructive method, which provides useful chemical information about the constituents. Current methods for collecting samples use filters that are made of materials which interferes with the IR spectra and thus lowers detection capabilities. Hence, collection on an IR-transparent substrate is desirable. In order to make a good quantitative measurement of the composition of the aerosol using IR-spectroscopy, a collector design should achieve some objectives. Low size-dependence, low chemical interference, and high collection efficiency are required to collect an aerosol sample that is identical to the aerosol in air. Furthermore, high spatial uniformity in deposition pattern is required to reduce optical artefacts or spectrometer dependence, and high collection mass flux is required to reduce the collection time needed for making a confident claim.
Electrostatic precipitation (ESP) is a versatile method of aerosol collection and does not suffer from high pressure drop (which can modify the aerosol chemical composition, for example in filtration), or from bounce-off effects (which preferentially samples the size range and liquids, for example in impaction). ESP devices for particle deposition are present in either a translationally symmetric design (linear system) or a radially symmetric design (radial system). Most ESP designs in the public domain have been designed for different purposes and face limitations for fulfilling objectives stated above. Hence, a new device is necessary to meet performance objectives.
Our design is based on an analytical, dimensionless (scalable) mathematical model that embodies the physics of particle migration trajectories due to fluid dynamics and electrostatics that lead to particle capture in a two-stage ESP device. This model allowed us to evaluate the tradeoffs among objectives to arrive at a design optimized across multiple objectives, and across multiple length scales (due to its dimensionless form). We validated this model against numerical simulations using COMSOL Multiphysics software, which is considered to be accurate but can only be run for a limited number of configurations (with respect to geometry and operating parameters) due to its high computational cost. Using the validated analytical model, we investigate the relationship among device geometry, methods of particle introduction, operational parameters, and deposited particle positions (which determines collection efficiency, uniformity, and size dependence), to arrive at a range of designs that meet design criteria.
We further report the fabrication of a suitable embodiment using 3D-printing while incorporating ease of operation and handling. Measurement capabilities and limits of the device using different laboratory-generated aerosol are reported.

How to cite: Dudani, N. and Takahama, S.: Method and apparatus for quantitative measurement of aerosol composition using controlled collection of airborne particles, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16389, https://doi.org/10.5194/egusphere-egu21-16389, 2021.

Atmospheric particulate matter (PM) is composed of up to 90% of organic matter [1]. Chemical characterization of PM organic fraction can be achieved by transmission mode Fourier transform infrared spectroscopy (TM-FTIR). FTIR is fast and inexpensive for qualitative and quantitative analysis of functional groups (FG) [2]. However, the applicability of TM-FTIR strongly depends on the filter support properties onto which particles are collected. Indeed, Teflon filters may negatively affect the effectiveness of the technique because of the symmetric and asymmetric stretching of -CF2 bonds covering the spectral range of  1100-1300 cm^-1, and the polymeric matrix causes diffusion of the incident radiation leading to baseline distortion in the 1500 - 4000 cm^-1 region. Additionally, high loads of NH₄NO₃ cause the “Christiansen peak effects” - refractive index of the samples matches that of the surrounding medium - which produces an anomalous transmittance of radiation and a distorted absorbance [3]. Moreover, FTIR analysis cannot be directly applied on quartz filters (QF) due to their strong IR absorbance that prevents the radiation source to cross the filter. 

In order to overcome these drawbacks, we applied attenuated total reflectance - Fourier transform infrared (ATR-FTIR) spectroscopy on solvent extracts of PM_2.5 directly transferred onto a ZnSe crystall employing electrospray (ES). The ES-ATR-FTIR technique is characterized by a rapid solvent evaporation favouring the formation of thin films [4]. This enables us to improve the sensitivity and efficiency of the technique obtaining transmission-mode-like spectra of methanol extracted samples characterized by a high solvent/analyte ratio. 

In this work, 403 samples of atmospheric PM_2.5 collected in Zürich-Kaserne site from March 2016 to April 2017 are analyzed using TM-FTIR. The spectra were initially employed to evaluate the FGs composition of PM_2.5 and the fraction of organic matter (OM) which resulted into an average of 40-50%. Successively, PM_2.5 co-sampled on QF filters from Zürich-Kaserne site were analysed by ES-ATR-FTIR. The technique was performed on a reduced number of representative samples selected from clusters with different FGs profile. The ES-ATR-FTIR spectra of ambient samples were collected and compared to those obtained by TM-FTIR on Teflon filters. While the OM/OC for each cluster is comparable to the OM/OC estimated from the Teflon filters, both OM and OC estimes of ATR mode are 40% of the transmission estimates due to the extraction limitation.

Further insights on the PM chemical composition are explored by appying non-negative matrix factorization (NMF) to ATR spectra. Throught NMF analysis, inorganic and organic spectral features and they relative contributions are identified and quantified over the year and indicating the contribution of biogenic sources in summer and residential wood burning in winter. 

In conclusion, ES-ATR-FTIR enables the acquisition of spectra of PM_2.5 samples without interference of supporting material. Additionally, further insights on the PM chemical composition due to extended accessible spectral region are discussed.

Bibliography 

[1] J. L. Jimenez et al., Sci., 326, 5959,1525-1529

[2] S. Takahama. et al., Aer. Sci. Tech. 47, 310, 325, 2013.

[3] M. A. Jarzembski. et al., Appl. Opt., 42, 2003.

[4] A. M. Arangio et al., App. Spec., 73,  6, 638-65.

How to cite: Arangio, A., Yazdani, A., Reggente, M., Zellweger-Fasi, C., Nenes, A., Hüglin, C., and Takahama, S.: Characterization of Organic Matter in PM2.5 sampled on different filter by FITR and Electrospray ATR-FTIR, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7625, https://doi.org/10.5194/egusphere-egu21-7625, 2021.

Imaging of atmospheric trace gases in the UV and visible wavelength range provides insight into the spatial distribution of physical and chemical processes in the atmosphere. Instruments for this purpose ideally combine a high spatio-temporal resolution with a high trace gas selectivity. In addition, they have to be built robust and compact for field measurements.

Atmospheric trace gas remote sensing by Differential Optical Absorption Spectroscopy (DOAS) is common and allows to measure several trace gases simultaneously with high selectivity and sensitivity. On the downside, image acquisition requires spatial scanning as for instance implemented in so-called hyperspectral cameras (also known as Imaging DOAS, IDOAS). This, however, results in reduced spatio-temporal resolution. Another approach to trace gas imaging is to use band pass filters, as for example in SO₂ cameras, which has the benefit of fast image acquisition combined with a high spatial resolution, but this advantage comes at the expense of low spectral sensitivity. Hence, only very high trace gas abundances can be reliably quantified, and the measurement is vulnerable to broadband interferences e.g. by aerosol.

We report an imaging technique combining the IDOAS and filter-based cameras’ advantages by utilizing the periodic transmission features of a Fabry-Perot-Interferometer (FPI). The FPI is tuned to two positions, so that its transmission either correlates or anti-correlates with the approximately periodic absorption structures of the target trace gas. From the measured intensities the differential optical density and the column density of the trace gas can be obtained with a high selectivity. Compared to IDOAS (or hyperspectral cameras) we only measure two different wavelength channels, however with maximum trace gas specific information. This reduces the amount of recorded data by at least two orders of magnitude for the same measurement resolution. This can be crucial for the feasibility of field measurements.

We present a compact and field-ready Imaging-FPI-Correlation-Spectroscopy (IFPICS) prototype. The FPI settings (or different FPIs) can be adapted to detect several different trace gases, our set-ups have been optimized for sulphur dioxide (SO₂), bromine monoxide (BrO) or formaldehyde (HCHO).

We anticipate from laboratory studies using scattered skylight and HCHO cuvettes a detection limit of 4.7x10¹⁶ molec cm^-2 for an image of about 90x90 pixel and an integration time of 6s. Because of the similar absorption features of BrO we expect a detection limit of 1.6x10¹⁴ molec cm^{^-2}. Additionally, an outlook on the application of BrO imaging in volcanic plumes is given.

How to cite: Nies, A., Fuchs, C., Kuhn, J., Bobrowski, N., and Platt, U.: IFPICS: Combining the advantages of hyperspectral imaging and filter cameras for trace gas imaging, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2811, https://doi.org/10.5194/egusphere-egu21-2811, 2021.

In the context of climate change, atmospheric gas monitoring is of major interest. Accurate measurements of the concentration of CO₂, CH₄, NO₂, O₃, etc. are necessary to control their emissions. Indeed, these gases have impacts on climate change as well as on people’s health.

Good control of such emissions requires gas concentration measurements with high spatial, spectral and temporal resolutions. These acquisitions are mostly done with conventional dispersive hyperspectral imaging systems. However, these instruments result from a compromise between price, resolutions and size which not always allows concentration evaluation that are accurate enough. The Imaging Spectrometer On Chip (ImSPOC) device is based on a ground-breaking concept to overcome the compromise size versus performances allowing snapshot acquisition. Indeed, it is an interferometric imaging spectrometer, sized like a matches’ box, allowing acquisition of an interferogram by pixel instead of a spectrum. In this way, a snapshot acquisition with high spectral resolutions can be acquired from Nano-satellites, drones or ground. The device is composed of a matrix of Fabry-Perot interferometers of different thickness combined with a matrix of photodetectors. ImSPOC is then a competitive device for real-time acquisitions of the atmosphere. However, despite these advantages, the acquisition of interferograms requires ad hoc signal processing techniques to reconstruct the corresponding spectra used for the estimation of the gas concentration. As the interferogram acquisitions are only on a range of thicknesses, some information are missing and need to be compensated with the signal processing methods that are specially developed to provide accurate spectra allowing to evaluate the concentration of gases. The development of these algorithms is then quite challenging.

To validate the most recent ImSPOC prototype in the UV-visible range and the corresponding developed methods, zenith observations were acquired with the ImSPOC device and a classical dispersive hyperspectral spectrometer. These acquisitions allow the validation of ImSPOC at two different levels: 1) the reconstructed spectra are qualitatively compared to the spectra acquired by the classical device and 2) using the Differential Optical Absorption Spectroscopy (DOAS) method on both devices spectra, the evaluated concentrations of the gases are quantitatively compared. These comparisons allow us to validate the usefulness of the ImSPOC device for the evaluation of the gas concentration using zenith observations.  

How to cite: Dolet, A., Picone, D., Gousset, S., Dalla Mura, M., Le Coarer, E., and Voisin, D.: Using zenith observations for evaluation of an improved interferometric imaging spectrometer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2536, https://doi.org/10.5194/egusphere-egu21-2536, 2021.

The analysis of atmospheric trace gas distributions by absorption spectroscopy of scattered sunlight in the near UV to near IR spectral ranges has proven to be extremely useful. A central parameter for the achievable sensitivity and spatial resolution of spectroscopic instruments is the étendue (product of aperture angle and entrance area) of the spectrograph, which is at the heart of the instrument. The étendue of an instrument can be enhanced by (1) up-scaling all instrument dimensions or (2) by changing the instrument F-number, (3) by increasing the entrance area, or (4) by operating many instruments (of identical design) in parallel. While options (1) and (4) allow enhancement by (in principle) arbitrary factors, the effect of options (2) and (3) and measures like better grating efficiency is limited.

We present new ideas and considerations on how instruments for the spectroscopic determination of atmospheric gases could be optimized with respect to étendue per volume (or mass) by using new possibilities in spectrograph design and manufacturing. Particular emphasis is on arrays of massively parallel instruments for observations using scattered sunlight. Such arrays can reduce size and weight of instruments by orders of magnitude, while preserving spectral resolution and light throughput. We also discuss the optimal size of individual spectrographs in a spectrograph array and give examples of grating spectrograph systems for use on a (low Earth orbit) satellite including one with sub-km ground pixel size and daily global coverage.

How to cite: Platt, U., Wagner, T., Kuhn, J., and Leisner, T.: The “Ideal Spectrograph” for Atmospheric Observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-690, https://doi.org/10.5194/egusphere-egu21-690, 2021.