Long open-path measurements of greenhouse gases in air using near-infrared Fourier transform spectroscopy
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 a...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2018-03-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/11/1549/2018/amt-11-1549-2018.pdf |
| _version_ | 1818242115529867264 |
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| author | D. W. T. Griffith D. Pöhler S. Schmitt S. Hammer S. N. Vardag S. N. Vardag U. Platt |
| author_facet | D. W. T. Griffith D. Pöhler S. Schmitt S. Hammer S. N. Vardag S. N. Vardag U. Platt |
| author_sort | D. W. T. Griffith |
| collection | DOAJ |
| description | 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.<br><br>In this pilot study we present the first open-path near-infrared
(4000–10 000 cm<sup>−1</sup>, 1.0–2.5 µm) FTS measurements of CO<sub>2</sub>,
CH<sub>4</sub>, O<sub>2</sub>, H<sub>2</sub>O 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
CO<sub>2</sub> and a few tens of ppb for CH<sub>4</sub> 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. |
| first_indexed | 2024-12-12T13:40:06Z |
| format | Article |
| id | doaj.art-54b26e104d2b4e5ebed7a3aa3c3f0ebe |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-12T13:40:06Z |
| publishDate | 2018-03-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-54b26e104d2b4e5ebed7a3aa3c3f0ebe2022-12-22T00:22:49ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482018-03-01111549156310.5194/amt-11-1549-2018Long open-path measurements of greenhouse gases in air using near-infrared Fourier transform spectroscopyD. W. T. Griffith0D. Pöhler1S. Schmitt2S. Hammer3S. N. Vardag4S. N. Vardag5U. Platt6Centre for Atmospheric Chemistry, University of Wollongong, Wollongong, AustraliaInstitute of Environmental Physics, University of Heidelberg, Heidelberg, GermanyInstitute of Environmental Physics, University of Heidelberg, Heidelberg, GermanyInstitute of Environmental Physics, University of Heidelberg, Heidelberg, GermanyInstitute of Environmental Physics, University of Heidelberg, Heidelberg, Germanynow at: Heidelberg Centre for the Environment, University of Heidelberg, Heidelberg, GermanyInstitute of Environmental Physics, University of Heidelberg, Heidelberg, GermanyIn 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.<br><br>In this pilot study we present the first open-path near-infrared (4000–10 000 cm<sup>−1</sup>, 1.0–2.5 µm) FTS measurements of CO<sub>2</sub>, CH<sub>4</sub>, O<sub>2</sub>, H<sub>2</sub>O 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 CO<sub>2</sub> and a few tens of ppb for CH<sub>4</sub> 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.https://www.atmos-meas-tech.net/11/1549/2018/amt-11-1549-2018.pdf |
| spellingShingle | D. W. T. Griffith D. Pöhler S. Schmitt S. Hammer S. N. Vardag S. N. Vardag U. Platt Long open-path measurements of greenhouse gases in air using near-infrared Fourier transform spectroscopy Atmospheric Measurement Techniques |
| title | Long open-path measurements of greenhouse gases in air using near-infrared Fourier transform spectroscopy |
| title_full | Long open-path measurements of greenhouse gases in air using near-infrared Fourier transform spectroscopy |
| title_fullStr | Long open-path measurements of greenhouse gases in air using near-infrared Fourier transform spectroscopy |
| title_full_unstemmed | Long open-path measurements of greenhouse gases in air using near-infrared Fourier transform spectroscopy |
| title_short | Long open-path measurements of greenhouse gases in air using near-infrared Fourier transform spectroscopy |
| title_sort | long open path measurements of greenhouse gases in air using near infrared fourier transform spectroscopy |
| url | https://www.atmos-meas-tech.net/11/1549/2018/amt-11-1549-2018.pdf |
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