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

• Verfasst von: Griffith, David W. T. [VerfasserIn]
• Verfasst von: Pöhler, Denis [VerfasserIn]
• Verfasst von: Hammer, Samuel [VerfasserIn]
• Verfasst von: Vardag, Sanam Noreen [VerfasserIn]
• Verfasst von: Platt, Ulrich [VerfasserIn]
• Verfasst von: Schmitt, Stefan [VerfasserIn]
• Titel: Long open-path measurements of greenhouse gases in air using near-infrared Fourier transform spectroscopy
• Verf.angabe: David W.T. Griffith, Denis Pöhler, Stefan Schmitt, Samuel Hammer, Sanam N. Vardag, and Ulrich Platt
• E-Jahr: 2017
• Jahr: 21 Aug 2017
• Umfang: 30 S.
• Fussnoten: Gesehen am 21.05.2019
• Titel Quelle: Enthalten in: Atmospheric measurement techniques discussions
• Ort Quelle: Katlenburg-Lindau : Copernicus, 2008
• Jahr Quelle: 2017
• Band/Heft Quelle: 10(2017) Artikel-Nummer 272, 30 Seiten
• ISSN Quelle: 1867-8610
• DOI: doi:10.5194/amt-2017-272
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1569817340

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.