Long open-path measurements of greenhouse gases in air using near-infrared Fourier transform spectroscopy

Abstract. In complex and urban environments, atmospheric trace gas composition is highly variable in time and space. Point measurement techniques for trace gases with in situ instruments are well established and accurate, but do not provide spatial averaging to compare against developing high-resolution atmospheric models of composition and meteorology with resolutions of the order of a kilometre. Open-path measurement techniques provide path average concentrations and spatial averaging which, if sufficiently accurate, may be better suited to assessment and interpretation with such models. Open-path Fourier transform spectroscopy (FTS) in the mid-infrared region, and differential optical absorption spectroscopy (DOAS) in the UV and visible, have been used for many years for open-path spectroscopic measurements of selected species in both clean air and in polluted environments. Near infrared instrumentation allows measurements over longer paths than mid-infrared FTS for species such as greenhouse gases which are not easily accessible to DOAS.In this pilot study we present the first open-path near-infrared (4000–10 000 cm−1, 1.0–2.5 µm) FTS measurements of CO2, CH4, O2, H2O and HDO over a 1.5 km path in urban Heidelberg, Germany. We describe the construction of the open-path FTS system, the analysis of the collected spectra, several measures of precision and accuracy of the measurements, and the results a four-month trial measurement period in July–November 2014. The open-path measurements are compared to calibrated in situ measurements made at one end of the open path. We observe significant differences of the order of a few ppm for CO2 and a few tens of ppb for CH4 between the open-path and point measurements which are 2 to 4 times the measurement repeatability, but we cannot unequivocally assign the differences to specific local sources or sinks. We conclude that open-path FTS may provide a valuable new tool for investigations of atmospheric trace gas composition in complex, small-scale environments such as cities.

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Long open path measurements of greenhouse gases in air using near infrared Fourier transform spectroscopy

10.5194/amt-2017-272 ◽

2017 ◽

Author(s):

David W. T. Griffith ◽

Denis Pöhler ◽

Stefan Schmitt ◽

Samuel Hammer ◽

Sanam N. Vardag ◽

...

Keyword(s):

Near Infrared ◽

Measurement Techniques ◽

Trace Gas ◽

Small Scale ◽

Gas Composition ◽

Spatial Averaging ◽

Mid Infrared ◽

Open Path ◽

Atmospheric Trace Gas

Abstract. In complex and urban environments, atmospheric trace gas composition is highly variable in time and space. Point measurement techniques for trace gases with in situ instruments are well established and accurate, but do not provide spatial averaging to compare against developing high resolution atmospheric models of composition and small scale meteorology with resolutions of the order of a kilometre. Open path measurement techniques provide path average concentrations and spatial averaging which, if sufficiently accurate, may be better suited to assessment and interpretation with such models. Open path Fourier Transform Spectroscopy (FTS) in the mid infrared region, and Differential Optical Absorption Spectroscopy (DOAS) in the UV and visible, have been used for many years for open path spectroscopic measurements of selected species in both clean air and in polluted environments. Compared to the mid infrared, near infrared instrumentation allows measurements over longer paths than mid IR FTS, for species such as greenhouse gases which are not easily accessible to DOAS. In this pilot study we present the first open path near infrared (4000–10 000 cm−1, 1.0–2.5 μm) FTS measurements of CO2, CH4, O2, H2O and HDO over a 1.5 km path in urban Heidelberg, Germany. We describe the construction of the open path FTS system, the analysis of the collected spectra, precision and accuracy of the measurements, and the results from a four-month trial measurement period in July–November 2014. The open path measurements are compared to calibrated in situ measurements made at one end of the open path. There are small but significant differences between in situ and open path measurements coincident in time which reflect local sources and sinks and the way in which they are sampled by the point and path-averaged measurements. Open path FTS may provide a valuable new tool for investigations of atmospheric trace gas composition in complex, small scale environments such as cities.

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Major ergot alkaloids in naturally contaminated cool-season barley grain grown under a cold climate condition in western Canada, explored with near-infrared (NIR) and fourier transform mid-infrared (ATR-FT/MIR) spectroscopy

Food Control ◽

10.1016/j.foodcont.2019.03.025 ◽

2019 ◽

Vol 102 ◽

pp. 221-230 ◽

Cited By ~ 5

Author(s):

Haitao Shi ◽

Warren Schwab ◽

Na Liu ◽

Peiqiang Yu

Keyword(s):

Fourier Transform ◽

Near Infrared ◽

Ergot Alkaloids ◽

Barley Grain ◽

Cold Climate ◽

Western Canada ◽

Climate Condition ◽

Cool Season ◽

Mid Infrared ◽

Mir Spectroscopy

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Level 2 processing for the imaging Fourier transform spectrometer GLORIA: derivation and validation of temperature and trace gas volume mixing ratios from calibrated dynamics mode spectra

Atmospheric Measurement Techniques ◽

10.5194/amt-8-2473-2015 ◽

2015 ◽

Vol 8 (6) ◽

pp. 2473-2489 ◽

Cited By ~ 19

Author(s):

J. Ungermann ◽

J. Blank ◽

M. Dick ◽

A. Ebersoldt ◽

F. Friedl-Vallon ◽

...

Keyword(s):

Fourier Transform ◽

Horizontal Resolution ◽

Trace Gas ◽

Radiative Transfer Model ◽

Transfer Model ◽

Ionization Mass ◽

Fourier Transform Spectrometer ◽

Upper Troposphere ◽

Mixing Ratios

Abstract. The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is an airborne infrared limb imager combining a two-dimensional infrared detector with a Fourier transform spectrometer. It was operated aboard the new German Gulfstream G550 High Altitude LOng Range (HALO) research aircraft during the Transport And Composition in the upper Troposphere/lowermost Stratosphere (TACTS) and Earth System Model Validation (ESMVAL) campaigns in summer 2012. This paper describes the retrieval of temperature and trace gas (H2O, O3, HNO3) volume mixing ratios from GLORIA dynamics mode spectra that are spectrally sampled every 0.625 cm−1. A total of 26 integrated spectral windows are employed in a joint fit to retrieve seven targets using consecutively a fast and an accurate tabulated radiative transfer model. Typical diagnostic quantities are provided including effects of uncertainties in the calibration and horizontal resolution along the line of sight. Simultaneous in situ observations by the Basic Halo Measurement and Sensor System (BAHAMAS), the Fast In-situ Stratospheric Hygrometer (FISH), an ozone detector named Fairo, and the Atmospheric chemical Ionization Mass Spectrometer (AIMS) allow a validation of retrieved values for three flights in the upper troposphere/lowermost stratosphere region spanning polar and sub-tropical latitudes. A high correlation is achieved between the remote sensing and the in situ trace gas data, and discrepancies can to a large extent be attributed to differences in the probed air masses caused by different sampling characteristics of the instruments. This 1-D processing of GLORIA dynamics mode spectra provides the basis for future tomographic inversions from circular and linear flight paths to better understand selected dynamical processes of the upper troposphere and lowermost stratosphere.

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