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The Total Carbon Column Observing Network (TCCON) and the Infrared Working Group of the Network for the Detection of Atmospheric Composition Change (NDACC-IRWG) are two ground-based networks that provide the retrieved concentrations of up to 30 atmospheric trace gases, using solar absorption spectrometry. Both networks provide reference measurements for the validation of satellites and models. TCCON concentrates on long-lived greenhouse gases (GHGs) for carbon cycle studies and validation. The number of sites is limited, and the geographical coverage is uneven, covering mainly Europe and the USA. A better distribution of stations is desired to improve the representativeness of the data for various atmospheric conditions and surface conditions and to cover a large latitudinal distribution. The two successive Fiducial Reference Measurements for Greenhouse Gases European Space Agency projects (FRM4GHG and FRM4GHG2) aim at the assessment of several low-cost portable instruments for precise measurements of GHGs to complement the existing ground-based sites. Several types of low spectral resolution Fourier transform infrared (FTIR) spectrometers manufactured by Bruker, namely an EM27/SUN, a Vertex70, a fiber-coupled IRCube, and a Laser Heterodyne spectro-Radiometer (LHR) developed by UK Rutherford Appleton Laboratory are the participating instruments to achieve the Fiducial Reference Measurements (FRMs) status. Intensive side-by-side measurements were performed using all four instruments next to the Bruker IFS 125HR high spectral resolution FTIR, performing measurements in the NIR (TCCON configuration) and MIR (NDACC configuration) spectral range. The remote sensing measurements were complemented by AirCore launches, which provided in situ vertical profiles of target gases traceable to the World Meteorological Organization (WMO) reference scale. The results of the intercomparisons are shown and discussed. Except for the EM27/SUN, all other instruments, including the reference TCCON spectrometer, needed modifications during the campaign period. The EM27/SUN and the Vertex70 provided stable and precise measurements of the target gases during the campaign with quantified small biases. As part of the FRM4GHG project, one EM27/SUN is now used as a travel standard for the verification of column-integrated GHG measurements. The extension of the Vertex70 to the MIR provides the opportunity to retrieve additional concentrations of N2O, CH4, HCHO, and OCS. These MIR data products are comparable to the retrieval results from the high-resolution IFS 125HR spectrometer as operated by the NDACC. Our studies show the potential for such types of spectrometers to be used as a travel standard for the MIR species. An enclosure system with a compact solar tracker and meteorological station has been developed to house the low spectral resolution portable FTIR systems for performing solar absorption measurements. This helps the spectrometers to be mobile and enables autonomous operation, which will help to complement the TCCON and NDACC networks by extending the observational capabilities at new sites for the observation of GHGs and additional air quality gases. The development of the retrieval software allows comparable processing of the Vertex70 type of spectra as the EM27/SUN ones, therefore bringing them under the umbrella of the COllaborative Carbon Column Observing Network (COCCON). A self-assessment following the CEOS-FRM Maturity Matrix shows that the COCCON is able to provide GHG data products of FRM quality and can be used for either short-term campaigns or long-term measurements to complement the high-resolution FTIR networks. [ABSTRACT FROM AUTHOR]

The Total Carbon Column Observing Network (TCCON) measures column-average mole fractions of several greenhouse gases (GHGs) beginning in 2004 from over 30 current or past measurement sites around the world, using solar absorption spectroscopy in the near infrared region. TCCON GHG data have been used extensively for multiple purposes, including in studies of the carbon cycle and anthropogenic emissions as well as to validate and improve observations made from space based sensors. Here, we describe an update to the retrieval algorithm used to process the TCCON near IR solar spectra and the associated data product. This version, called GGG2020, was initially released in April 2022. It includes updates and improvements to all steps of the retrieval, including but not limited to: converting the original interferograms into spectra, the spectroscopic information used in the column retrieval, post hoc airmass dependence correction, and scaling to align with the calibration scales of in situ GHG measurements. All TCCON data are available through tccondata.org and hosted on CaltechDATA (data.caltech.edu). Each TCCON site has a unique DOI for its data record. An archive of all sites’ data is also available with the DOI 10.14291/TCCON.GGG2020 (Total Carbon Column Observing Network (TCCON) Team, 2022). The hosted files are updated approximately monthly, and TCCON sites are required to deliver data to the archive no later than one year after acquisition. Full details of data locations are provided in the data availability section. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) and Methane (CH4) are two important greenhouse gases in the atmosphere. In 2019, midinfrared (MIR) solar absorption spectra were recorded by a Bruker Vertex 70 spectrometer and a Bruker IFS 125HR spectrometer at Sodankylä, Finland at spectral resolutions of 0.2 cm−1 and 0.005 cm−1, respectively. The N2O and the CH4 retrievals from high-resolution MIR spectra have been well investigated within the Network for Detection of Atmospheric Composition Change (NDACC), but not for MIR spectra gathered with instruments operating at low spectral resolution. In this study, N2O and CH4 retrieval strategies and retrieval uncertainties from the Vertex 70 MIR low-resolution spectra are discussed and presented. The accuracy and precision of the Vertex 70 N2O and CH4 retrievals are assessed by comparing them with the colocated 125HR retrievals and AirCore measurements. The relative differences between the N2O total columns retrieved from 125HR and Vertex 70 spectra are -0.3±0.7(1σ)% with a correlation coefficient (R) of 0.93. Regarding CH4 total column, we first used the same retrieval microwindows for 125HR and Vertex 70 spectra, but there is an underestimation in the Vertex 70 retrievals, especially in summer. The relative differences between the CH4 total columns retrieved from the 125HR and Vertex spectra are -1.3±1.1% with a R value of 0.77. To improve the Vertex 70 CH4 retrievals, we propose an alternative retrieval microwindows. The relative differences between the CH4 total columns retrieved from the 125HR and Vertex spectra in these new windows become 0.0±0.8%, along with an increase in R value to 0.87. The co-located AirCore measurements confirm that the Vertex 70 CH4 retrievals using the latter window choice are better, with the relative mean differences between the Vertex CH44 retrievals and AirCore measurements of -1.9% for the standard NDACC mircrowindows, and of 0.13% for the alternative microwindows. This study provides an insight into the N2O and CH4 retrievals from the low-resolution (0.2 cm−1 ) MIR spectra observed with a Vertex 70 spectrometer, and demonstrates the suitability of this kind of instruments for contributing to satellite validation, model verification, and other scientific campaigns with the advantage of their transportability and lower cost compared to standard NDACC-type FTIR instruments. [ABSTRACT FROM AUTHOR]

We compare the atmospheric column-averaged dry-air mole fractions of carbon dioxide (XCO2) and methane (XCH4) measured with a pair of COllaborative Carbon Column Observing Network (COCCON) spectrometers at Kiruna and Sodankylä (boreal areas). We compare model data provided by the Copernicus Atmosphere Monitoring Service (CAMS) between 2017 and 2019 with XCH4 data from the recently launched Sentinel-5 Precursor (S5P) satellite between 2018 and 2019. In addition, measured and modeled gradients of XCO2 and XCH4 (Δ XCO2 and Δ XCH4) on regional scales are investigated. Both sites show a similar and very good correlation between COCCON retrievals and the modeled CAMS XCO2 data, while CAMS data are biased high with respect to COCCON by 3.72 ppm (±1.80 ppm) in Kiruna and 3.46 ppm (±1.73 ppm) in Sodankylä on average. For XCH4 , CAMS values are higher than the COCCON observations by 0.33 ppb (±11.93 ppb) in Kiruna and 7.39 ppb (±10.92 ppb) in Sodankylä. In contrast, the S5P satellite generally measures lower atmospheric XCH4 than the COCCON spectrometers, with a mean difference of 9.69 ppb (±20.51 ppb) in Kiruna and 3.36 ppb (±17.05 ppb) in Sodankylä. We compare the gradients of XCO2 and XCH4 (Δ XCO2 and Δ XCH4) between Kiruna and Sodankylä derived from CAMS analysis and COCCON and S5P measurements to study the capability of detecting sources and sinks on regional scales. The correlations in Δ XCO2 and Δ XCH4 between the different datasets are generally smaller than the correlations in XCO2 and XCH4 between the datasets at either site. The Δ XCO2 values predicted by CAMS are generally higher than those observed with COCCON with a slope of 0.51. The Δ XCH4 values predicted by CAMS are mostly higher than those observed with COCCON with a slope of 0.65, covering a larger dataset than the comparison between S5P and COCCON. When comparing CAMS Δ XCH4 with COCCON Δ XCH4 only in S5P overpass days (slope = 0.53), the correlation is close to that between S5P and COCCON (slope = 0.51). CAMS, COCCON, and S5P predict gradients in reasonable agreement. However, the small number of observations coinciding with S5P limits our ability to verify the performance of this spaceborne sensor. We detect no significant impact of ground albedo and viewing zenith angle on the S5P results. Both sites show similar situations with the average ratios of XCH4 (S5P/COCCON) of 0.9949±0.0118 in Kiruna and 0.9953±0.0089 in Sodankylä. Overall, the results indicate that the COCCON instruments have the capability of measuring greenhouse gas (GHG) gradients on regional scales, and observations performed with the portable spectrometers can contribute to inferring sources and sinks and to validating spaceborne greenhouse gas sensors. To our knowledge, this is the first published study using COCCON spectrometers for the validation of XCH4 measurements collected by S5P. [ABSTRACT FROM AUTHOR]

We compare the atmospheric column-averaged dry-air mole fractions of carbon dioxide (XCO2) and methane (XCH4) measured with a pair of COCCON spectrometers at Kiruna and Sodankylä sites in boreal areas with model data provided by the Copernicus Atmosphere Monitoring Service (CAMS) and with XCH4 from the recently launched Sentinel-5 Precursor (S5P) satellite. Both sites show a similar and very good correlation between COCCON retrievals and the modeled CAMS XCO2 and CH4 data. CAMS data are biased high with respect to COCCON in both XCO2 and XCH4, while the S5P satellite generally measures lower atmospheric XCH4 than the COCCON spectrometers. The gradients of XCO2 and XCH4 (ΔXCO2 and ΔXCH4) between Kiruna and Sodankylä derived from CAMS reanalysis and COCCON and S5P measurements are investigated to study the capability of detecting sources and sinks on regional scales. CAMS, COCCON and S5P predict gradients in reasonable agreement. However, the small number of observations coinciding with S5P limits our ability to verify the performance of this sensor. Overall, the results indicate that the COCCON instrument has the capability of measuring greenhouse gas (GHG) gradients on regional scales and observations performed with the portable spectrometers can contribute to inferring sources and sinks and to validating space borne greenhouse gas sensors. [ABSTRACT FROM AUTHOR]

Fourier transform spectrometer (FTS) observations at Sodankylä, Finland (67.4° N, 26.6° E) have been performed since early 2009. The FTS instrument is participating in the Total Carbon Column Observing Network (TCCON) and has been optimized to measure abundances of the key greenhouse gases in the atmosphere. Sodankylä is the only TCCON station in the Fennoscandia region. Here we report the measured CO2 time series over a 7-year period (2009- 2015) and provide a description of the FTS system and data processing at Sodankylä.We find the lowest monthly column CO2 values in August and the highest monthly values during the February-May season. Inter-annual variability is the highest in the June-September period, which correlates with the growing season. During the time period of FTS measurements from 2009 to 2015, we have observed a 2.2±0.2 ppm increase per year in column CO2. The monthly mean column CO2 values have exceeded 400 ppm level for the first time in February 2014. [ABSTRACT FROM AUTHOR]

Fourier Transform Spectrometer (FTS) measurements of atmospheric carbon dioxide andmethane were established at Sodankylä (67.4∘ N, 26.6∘ E) in early 2009. The instrumentrecords high-resolution solar spectra in the near-infrared spectral region. Column-averagedabundances of methane, carbon dioxide and other gases are derived from the measuredspectra. The FTS at Sodankylä participates in the Total Carbon Column Observing Network(TCCON). Here we present data from ten years of measurements at Sodankylä andcomparisons with satellite borne observations. In order to guarantee the optimal performanceof the ground based FTS, we have checked and adjusted the optical alignment of theinstrument on regular basis. The instrument line shape measurements show that thederived modulation efficiency at maximum optical path difference has remainedrelatively stable, indicating that the alignment has been maintained. Relevant satellitemissions during the recent ten-year time period include the TROPOspheric MonitoringInstrument (TROPOMI) on board of the Copernicus Sentinel-5 Precursor satellite,the Orbiting Carbon Observatory-2 (OCO-2); the Greenhouse Gases ObservingSatellite (GOSAT); the SCanning Imaging Absorption spectroMeter for AtmosphericCHartographY (SCIAMACHY) and TanSat. Finally we compare the remote sensingobservations with in situ measurements at Sodankylä. The in-situ measurementswere performed at a tower near the FTS site and by using a balloon-borne AirCoreinstrument. [ABSTRACT FROM AUTHOR]

Within the EU-funded Readiness of Integrated carbon observation system (ICOS) for Necessities of integrated Global Observations (RINGO) project, vertical profile measurements have been explored using both AirCores and the ground-based Total Carbon Column Observing Network (TCCON) Fourier-transform infrared spectrometers (FTIRs) to enhance the link between ICOS ground-based stations, TCCON, and satellite measurements. AirCore is a long coiled stainless steel tube used for atmospheric sampling up to heights of around 30 km, which is launched on a weather balloon with one end open and the other end closed, and collects continuously ambient air samples during descent. The analysis results of the air samples for greenhouse and other trace gases mole fractions combined with the recorded in-flight information, e.g. coil temperatures, ambient pressure and altitude, allow for the retrieval of the vertical profiles. As for TCCON FTIRs, two-layer vertical profiles will be derived either by optimal estimation profile retrieval or by the use of a different gas (HF, N2O). In June 2018, an intensive AirCore comparison campaign took place at the TCCON site in Sodankylä, Finland. A total of 10 balloon flights were made, with combinations of different AirCores and/or the LIghtweight Stratospheric Air (LISA) sampler per balloon flight. The measured species include CO2, CH4, CO, O2, H2O by continuous cavity ring-down spectrometers (CRDS) at Sodankylä, and subsequent isotopic compositions of CO2 and CH4 and halogenated trace gases by delayed analyses of collected stratospheric air samples conducted later in several individual home laboratories. Here we present the first results from this campaign and compare the different AirCore/LISA profiles. The analyses are focused on 1) the accuracy of AirCore measurements of CO2, CH4 and CO mole fractions; 2) the accuracy of the altitude registration of AirCore profiles; 3) a comparison of AirCore observations with and without drying the air sample. Furthermore, we will evaluate the TCCON FTIR profile retrievals with collocated AirCore profiles. [ABSTRACT FROM AUTHOR]

The European Space Agency (ESA) funded project "Fiducial Reference Measurementsfor Ground-Based Infrared Greenhouse Gas Observations (FRM4GHG)" at theSodankylä (Finland) TCCON site was aimed at characterizing the performance of severallow-cost portable ground-based spectrometers in comparison to the standard TCCONFourier-transform Infrared spectrometer for precise solar absorption measurements of CO2,CH4 and CO dry-air column-averaged mixing ratios. The collocated measurements wereperformed continuously between March and Oktober in 2017 and 2018, when the sun wasabove the horizon. The TCCON instrument was also operated in a special low-resolutionmode, with a spectral resolution comparable to that of the other participating portablespectrometers. In addition, regular balloon-borne AirCore launches were performed from thesame site: these provided vertical profiles of CO2, CH4 and CO up to about 25 km altitude.The AirCore vertical profiles were calibrated to WMO reference standards and were used asreference profiles for the ground-based remote sensing measurements. The campaignCO and CH4 data have been compared to coincident Sentinel-5 Precursor (S-5P)products. In this presentation we will present the intercomparison results from these two years ofCO2, CH4 and CO measurements from the six participating instruments. We will discussinstrument related problems, like non-linearity effects that have been identified during thecampaign, and the methodologies that have been developed to correct for these issues. Wewill also show the validation results for the S5-P CH4 and CO data using the campaign data.Furthermore we will discuss guidelines for the deployment of these low-cost portableinstruments at new observation sites to complement the TCCON network and improve thevalidation capabilities for the existing and future satellite missions and models for greenhousegases. [ABSTRACT FROM AUTHOR]