Comparison of two closed-path cavity-based spectrometers for measuring air–water CO<sub>2</sub> and CH<sub>4</sub> fluxes by eddy covariance
In recent years several commercialised closed-path cavity-based spectroscopic instruments designed for eddy covariance flux measurements of carbon dioxide (CO<sub>2</sub>), methane (CH<sub>4</sub>), and water vapour (H<sub>2</sub>O) have become available. Here...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2016-11-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/9/5509/2016/amt-9-5509-2016.pdf |
| _version_ | 1818560256452591616 |
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| author | M. Yang J. Prytherch E. Kozlova M. J. Yelland D. Parenkat Mony T. G. Bell |
| author_facet | M. Yang J. Prytherch E. Kozlova M. J. Yelland D. Parenkat Mony T. G. Bell |
| author_sort | M. Yang |
| collection | DOAJ |
| description | In recent years several commercialised closed-path cavity-based spectroscopic
instruments designed for eddy covariance flux measurements of carbon dioxide
(CO<sub>2</sub>), methane (CH<sub>4</sub>), and water vapour (H<sub>2</sub>O) have become
available. Here we compare the performance of two leading models – the
Picarro G2311-f and the Los Gatos Research (LGR) Fast Greenhouse Gas Analyzer
(FGGA) at a coastal site. Both instruments can compute dry mixing ratios of
CO<sub>2</sub> and CH<sub>4</sub> based on concurrently measured H<sub>2</sub>O, temperature,
and pressure. Additionally, we used a high throughput Nafion dryer to
physically remove H<sub>2</sub>O from the Picarro airstream. Observed air–sea
CO<sub>2</sub> and CH<sub>4</sub> fluxes from these two analysers, averaging about 12 and
0.12 mmol m<sup>−2</sup> day<sup>−1</sup>
respectively, agree within the
measurement uncertainties. For the purpose of quantifying dry CO<sub>2</sub> and
CH<sub>4</sub> fluxes downstream of a long inlet, the numerical H<sub>2</sub>O
corrections appear to be reasonably effective and lead to results that are
comparable to physical removal of H<sub>2</sub>O with a Nafion dryer in the mean.
We estimate the high-frequency attenuation of fluxes in our closed-path
set-up, which was relatively small ( ≤ 10 %) for CO<sub>2</sub> and CH<sub>4</sub>
but very large for the more polar H<sub>2</sub>O. The Picarro showed significantly
lower noise and flux detection limits than the LGR. The hourly flux
detection limit for the Picarro was about 2 mmol m<sup>−2</sup> day<sup>−1</sup> for
CO<sub>2</sub> and 0.02 mmol m<sup>−2</sup> day<sup>−1</sup> for CH<sub>4</sub>. For the LGR these
detection limits were about 8 and 0.05 mmol m<sup>−2</sup> day<sup>−1</sup>. Using global maps of monthly mean air–sea CO<sub>2</sub> flux
as reference, we estimate that the Picarro and LGR can resolve hourly
CO<sub>2</sub> fluxes from roughly 40 and 4 % of the world's oceans respectively. Averaging over longer timescales would be required in regions
with smaller fluxes. Hourly flux detection limits of CH<sub>4</sub> from both
instruments are generally higher than the expected emissions from the open
ocean, though the signal to noise of this measurement may improve closer to
the coast. |
| first_indexed | 2024-12-14T00:36:10Z |
| format | Article |
| id | doaj.art-f80139b9690142839c128e6c752a385d |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-14T00:36:10Z |
| publishDate | 2016-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-f80139b9690142839c128e6c752a385d2022-12-21T23:24:38ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482016-11-0195509552210.5194/amt-9-5509-2016Comparison of two closed-path cavity-based spectrometers for measuring air–water CO<sub>2</sub> and CH<sub>4</sub> fluxes by eddy covarianceM. Yang0J. Prytherch1E. Kozlova2M. J. Yelland3D. Parenkat Mony4T. G. Bell5Plymouth Marine Laboratory, Prospect Place, Plymouth, UKInstitute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, UKCollege of Life and Environmental Sciences, University of Exeter, North Park Road, Exeter, UKNational Oceanography Centre, European Way, Southampton, UKInter University Centre for Development of Marine Biotechnology, School of Marine Sciences, Cochin University of Science and Technology, Cochin, IndiaPlymouth Marine Laboratory, Prospect Place, Plymouth, UKIn recent years several commercialised closed-path cavity-based spectroscopic instruments designed for eddy covariance flux measurements of carbon dioxide (CO<sub>2</sub>), methane (CH<sub>4</sub>), and water vapour (H<sub>2</sub>O) have become available. Here we compare the performance of two leading models – the Picarro G2311-f and the Los Gatos Research (LGR) Fast Greenhouse Gas Analyzer (FGGA) at a coastal site. Both instruments can compute dry mixing ratios of CO<sub>2</sub> and CH<sub>4</sub> based on concurrently measured H<sub>2</sub>O, temperature, and pressure. Additionally, we used a high throughput Nafion dryer to physically remove H<sub>2</sub>O from the Picarro airstream. Observed air–sea CO<sub>2</sub> and CH<sub>4</sub> fluxes from these two analysers, averaging about 12 and 0.12 mmol m<sup>−2</sup> day<sup>−1</sup> respectively, agree within the measurement uncertainties. For the purpose of quantifying dry CO<sub>2</sub> and CH<sub>4</sub> fluxes downstream of a long inlet, the numerical H<sub>2</sub>O corrections appear to be reasonably effective and lead to results that are comparable to physical removal of H<sub>2</sub>O with a Nafion dryer in the mean. We estimate the high-frequency attenuation of fluxes in our closed-path set-up, which was relatively small ( ≤ 10 %) for CO<sub>2</sub> and CH<sub>4</sub> but very large for the more polar H<sub>2</sub>O. The Picarro showed significantly lower noise and flux detection limits than the LGR. The hourly flux detection limit for the Picarro was about 2 mmol m<sup>−2</sup> day<sup>−1</sup> for CO<sub>2</sub> and 0.02 mmol m<sup>−2</sup> day<sup>−1</sup> for CH<sub>4</sub>. For the LGR these detection limits were about 8 and 0.05 mmol m<sup>−2</sup> day<sup>−1</sup>. Using global maps of monthly mean air–sea CO<sub>2</sub> flux as reference, we estimate that the Picarro and LGR can resolve hourly CO<sub>2</sub> fluxes from roughly 40 and 4 % of the world's oceans respectively. Averaging over longer timescales would be required in regions with smaller fluxes. Hourly flux detection limits of CH<sub>4</sub> from both instruments are generally higher than the expected emissions from the open ocean, though the signal to noise of this measurement may improve closer to the coast.https://www.atmos-meas-tech.net/9/5509/2016/amt-9-5509-2016.pdf |
| spellingShingle | M. Yang J. Prytherch E. Kozlova M. J. Yelland D. Parenkat Mony T. G. Bell Comparison of two closed-path cavity-based spectrometers for measuring air–water CO<sub>2</sub> and CH<sub>4</sub> fluxes by eddy covariance Atmospheric Measurement Techniques |
| title | Comparison of two closed-path cavity-based spectrometers for measuring air–water CO<sub>2</sub> and CH<sub>4</sub> fluxes by eddy covariance |
| title_full | Comparison of two closed-path cavity-based spectrometers for measuring air–water CO<sub>2</sub> and CH<sub>4</sub> fluxes by eddy covariance |
| title_fullStr | Comparison of two closed-path cavity-based spectrometers for measuring air–water CO<sub>2</sub> and CH<sub>4</sub> fluxes by eddy covariance |
| title_full_unstemmed | Comparison of two closed-path cavity-based spectrometers for measuring air–water CO<sub>2</sub> and CH<sub>4</sub> fluxes by eddy covariance |
| title_short | Comparison of two closed-path cavity-based spectrometers for measuring air–water CO<sub>2</sub> and CH<sub>4</sub> fluxes by eddy covariance |
| title_sort | comparison of two closed path cavity based spectrometers for measuring air water co sub 2 sub and ch sub 4 sub fluxes by eddy covariance |
| url | https://www.atmos-meas-tech.net/9/5509/2016/amt-9-5509-2016.pdf |
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