Update of the HITRAN collision-induced absorption section

. In a 3.5-year long study, the long-term
performance of a mobile, solar absorption Bruker EM27/SUN spectrometer, used
for greenhouse gas observations, is checked with respect to a co-located
reference Bruker IFS 125HR spectrometer, which is part of the Total Carbon
Column Observing Network (TCCON). We find that the EM27/SUN is stable on
timescales of several years; the drift per year between the EM27/SUN and the
official TCCON product is 0.02 ppmv for X CO2 and 0.9 ppbv for
X CH4 , which is within the 1 σ precision of the comparison,
0.6 ppmv for X CO2 and 4.3 ppbv for X CH4 . The bias between
the two data sets is 3.9 ppmv for X CO2 and 13.0 ppbv for
X CH4 . In order to avoid sensitivity-dependent artifacts, the EM27/SUN
is also compared to a truncated IFS 125HR data set derived from
full-resolution TCCON interferograms. The drift is 0.02 ppmv for
X CO2 and 0.2 ppbv for X CH4 per year, with 1 σ 
precisions of 0.4 ppmv for X CO2 and 1.4 ppbv for X CH4 ,
respectively. The bias between the two data sets is 0.6 ppmv for
X CO2 and 0.5 ppbv for X CH4 . With the presented long-term
stability, the EM27/SUN qualifies as an useful supplement to the existing
TCCON network in remote areas. To achieve consistent performance, such an
extension requires careful testing of any spectrometers involved by
application of common quality assurance measures. One major aim of the
COllaborative Carbon Column Observing Network (COCCON) infrastructure is to
provide these services to all EM27/SUN operators. In the framework of COCCON
development, the performance of an ensemble of 30 EM27/SUN spectrometers was
tested and found to be very uniform, enhanced by the centralized inspection
performed at the Karlsruhe Institute of Technology prior to deployment.
Taking into account measured instrumental line shape parameters for each
spectrometer, the resulting average bias across the ensemble with respect to
the reference EM27/SUN used in the long-term study in X CO2 is
0.20 ppmv, while it is 0.8 ppbv for X CH4 . The average standard
deviation of the ensemble is 0.13 ppmv for X CO2 and 0.6 ppbv for
X CH4 . In addition to the robust metric based on absolute differences,
we calculate the standard deviation among the empirical calibration factors.
The resulting 2 σ uncertainty is 0.6 ppmv for X CO2 and
2.2 ppbv for X CH4 . As indicated by the executed long-term study on
one device presented here, the remaining empirical calibration factor deduced
for each individual instrument can be assumed constant over time. Therefore
the application of these empirical factors is expected to further improve the
EM27/SUN network conformity beyond the scatter among the empirical
calibration factors reported above.

/pdf/building-the-collaborative-carbon-column-observing-network-1jxktg4w6l.pdf

Building the COllaborative Carbon Column Observing Network (COCCON): long-term stability and ensemble performance of the EM27/SUN Fourier transform spectrometer

. Five portable Bruker EM27/SUN FTIR (Fourier transform infrared) spectrometers have been used for the accurate and precise observation of column-averaged abundances of CO2 and CH4 around the major city Berlin. In the work by Frey et al. (2015), a calibration procedure is developed and applied to the set of spectrometers used for the Berlin campaign. Here, we describe the observational setup of the campaign and aspects of the data analysis, and we present the recorded time series of XCH4 and XCO2. We demonstrate that the CO2 emissions of Berlin can be clearly identified in the observations. A simple dispersion model is applied which indicates a total strength of the Berlin source of about 0.8 t CO2 s−1. In the Supplement of this work, we provide the measured data set and auxiliary data. We hope that the model community will exploit this unique data set for state-of-the art inversion studies of CO2 and CH4 sources in the Berlin area.

/pdf/application-of-portable-ftir-spectrometers-for-detecting-3l7pcfegwd.pdf

Application of portable FTIR spectrometers for detecting greenhouse gas emissions of the major city Berlin

. Remote sensing of the gaseous composition of non-eruptive, passively degassing volcanic plumes can be a tool to gain insight into volcano interior processes. Here, we report on a field study in September 2015 that demonstrates the feasibility of remotely measuring the volcanic enhancements of carbon dioxide (CO2), hydrogen fluoride (HF), hydrogen chloride (HCl), sulfur dioxide (SO2), and bromine monoxide (BrO) in the downwind plume of Mt. Etna using portable and rugged spectroscopic instrumentation. To this end, we operated the Fourier transform spectrometer EM27/SUN for the shortwave-infrared (SWIR) spectral range together with a co-mounted UV spectrometer on a mobile platform in direct-sun view at 5 to 10 km distance from the summit craters. The 3 days reported here cover several plume traverses and a sunrise measurement. For all days, intra-plume HF, HCl, SO2, and BrO vertical column densities (VCDs) were reliably measured exceeding 5  × 1016, 2  × 1017, 5  × 1017, and 1  × 1014 molec cm−2, with an estimated precision of 2.2  × 1015, 1.3  × 1016, 3.6  × 1016, and 1.3  × 1013 molec cm−2, respectively. Given that CO2, unlike the other measured gases, has a large and well-mixed atmospheric background, derivation of volcanic CO2 VCD enhancements (ΔCO2) required compensating for changes in altitude of the observing platform and for background concentration variability. The first challenge was met by simultaneously measuring the overhead oxygen (O2) columns and assuming covariation of O2 and CO2 with altitude. The atmospheric CO2 background was found by identifying background soundings via the co-emitted volcanic gases. The inferred ΔCO2 occasionally exceeded 2  ×  1019 molec cm−2 with an estimated precision of 3.7  ×  1018 molec cm−2 given typical atmospheric background VCDs of 7 to 8  ×  1021 molec cm−2. While the correlations of ΔCO2 with the other measured volcanic gases confirm the detection of volcanic CO2 enhancements, correlations were found of variable significance (R2 ranging between 0.88 and 0.00). The intra-plume VCD ratios ΔCO2 ∕ SO2, SO2 ∕ HF, SO2 ∕ HCl, and SO2 ∕ BrO were in the range 7.1 to 35.4, 5.02 to 21.2, 1.54 to 3.43, and 2.9  ×  103 to 12.5  ×  103, respectively, showing pronounced day-to-day and intra-day variability.

/pdf/remote-sensing-of-volcanic-co-2-hf-hcl-so-2-and-bro-in-the-58yga52xo8.pdf

Remote sensing of volcanic CO 2 , HF, HCl, SO 2 , and BrO in the downwind plume of Mt. Etna

. The portable FTIR (Fourier transform infrared) spectrometer EM27/SUN, dedicated to the precise and accurate observation of column-averaged abundances of methane and carbon dioxide, has been equipped with a second detector channel, which allows the detection of additional species, especially carbon monoxide. This allows an improved characterisation of observed carbon dioxide enhancements and makes the extended spectrometer especially suitable as a validation tool of ESA's Sentinel 5 Precursor mission, as it now covers the same spectral region as used by the infrared channel of the TROPOMI (TROPOspheric Monitoring Instrument) sensor. The extension presented here does not rely on a dichroic, but instead a fraction of the solar beam is decoupled near the aperture stop of the spectrometer using a small plane mirror. This approach allows maintaining the camera-controlled solar tracker set-up, which is referenced to the field stop in front of the primary detector. Moreover, the upgrade of existing instruments can be performed without alterating the optical set-up of the primary channel and resulting changes of the instrumental characteristics of the original instrument.

/pdf/addition-of-a-channel-for-xco-observations-to-a-portable-3lr1th4gpt.pdf

Addition of a channel for XCO observations to a portable FTIR spectrometer for greenhouse gas measurements

. A commercial low-resolution (0.5 cm−1) Fourier Transform Spectrometer (FTS) has been modified and is used for determining the total column XCO2 of the atmosphere by analysing direct solar radiation. The spectrometer has a small home-built solar tracker attached, so that it is a ready-to-use instrument. The results are validated with temporally coinciding on-site measurements taken with a high-resolution Total Carbon Column Observing Network (TCCON) FTIR spectrometer. For the whole comparison period of 5 months (26 measurement days) an agreement with TCCON results of (0.12 ± 0.08)% is achieved. This makes the spectrometer a promising candidate for a low-cost addition to the TCCON core FTIR sites, especially suitable for locations with limited infrastructure. An impressive mechanical and thermal stability is proved, enabling the spectrometer for use in field campaigns and for the monitoring of local sources.

/pdf/xco-2-measurements-with-a-tabletop-fts-using-solar-1n3gmehyqm.pdf

XCO 2 -measurements with a tabletop FTS using solar absorption spectroscopy

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XCO 2 -measurements with a tabletop FTS using solar absorption spectroscopy