28 Aug 2020
28 Aug 2020
Airborne measurements of oxygen concentration from the surface to the lower stratosphere and pole to pole
- 1National Center for Atmospheric Research, Boulder, Colorado, USA
- 2Scripps Institution of Oceanography, La Jolla, California, USA
- 3Harvard University, Cambridge, Massachusetts, USA
- anow at: Picarro, Inc., Santa Clara, California, USA
- 1National Center for Atmospheric Research, Boulder, Colorado, USA
- 2Scripps Institution of Oceanography, La Jolla, California, USA
- 3Harvard University, Cambridge, Massachusetts, USA
- anow at: Picarro, Inc., Santa Clara, California, USA
Abstract. We have developed in situ and flask sampling systems for airborne measurements of variations in the O2/N2 ratio at the part per million level. We have deployed these instruments on a series of aircraft campaigns to measure the distribution of atmospheric O2 from 0–14 km and 87° N to 85° S throughout the seasonal cycle. The NCAR airborne oxygen instrument (AO2) uses a vacuum ultraviolet (VUV) absorption detector for O2 and also includes an infrared CO2 sensor. The VUV detector has a precision in 5 seconds of ±1.25 per meg (1σ) δ(O2/N2), but thermal fractionation and motion effects increase this to ±2.5–4.0 per meg when sampling ambient air in flight. The NCAR/Scripps airborne flask sampler (Medusa) collects 32 cryogenically dried air samples per flight under actively controlled flow and pressure conditions. For in situ or flask O2 measurements, fractionation and surface effects can be important at the required high levels of relative precision. We describe our sampling and measurement techniques, and efforts to reduce potential biases. We also present a selection of observational results highlighting the individual and combined instrument performance. These include vertical profiles, O2 : CO2 correlations, and latitudinal cross sections reflecting the distinct influences of terrestrial photosynthesis, air-sea gas exchange, burning of various fuels, and stratospheric dynamics. When present, we have corrected the flask δ(O2/N2) measurements for fractionation during sampling or analysis, with the use of the concurrent δ(Ar/N2) measurements. We have also corrected the in situ δ(O2/N2) measurements for inlet fractionation and humidity effects by comparison to the corrected flask values. A comparison of Ar/N2-corrected Medusa flask δ(O2/N2) measurements to regional Scripps O2 Network station observations shows no systematic biases over 10 recent campaigns (+0.2 ± 8.2 per meg, mean and standard deviation, n = 86). For AO2, after resolving sample drying and inlet fractionation biases previously on the order of 10–100 per meg, independent AO2 δ(O2/N2) measurements over 6 more recent campaigns differ from coincident Medusa flask measurements by −0.3 ± 7.2 per meg (mean and standard deviation, n = 1361), with campaign-specific means ranging from −5 to +5 per meg.
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Britton B. Stephens et al.


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RC1: 'Review of Stephens et al.', Anonymous Referee #1, 06 Oct 2020
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AC1: 'Response to Referee #1', Britton Stephens, 06 Dec 2020
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AC1: 'Response to Referee #1', Britton Stephens, 06 Dec 2020
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RC2: 'Review report on: Airborne measurements of oxygen concentration from the surface to the lower stratosphere and pole to pole... by Stephens et al', Anonymous Referee #2, 08 Nov 2020
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AC2: 'Response to Referee #2', Britton Stephens, 06 Dec 2020
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AC2: 'Response to Referee #2', Britton Stephens, 06 Dec 2020


-
RC1: 'Review of Stephens et al.', Anonymous Referee #1, 06 Oct 2020
-
AC1: 'Response to Referee #1', Britton Stephens, 06 Dec 2020
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AC1: 'Response to Referee #1', Britton Stephens, 06 Dec 2020
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RC2: 'Review report on: Airborne measurements of oxygen concentration from the surface to the lower stratosphere and pole to pole... by Stephens et al', Anonymous Referee #2, 08 Nov 2020
-
AC2: 'Response to Referee #2', Britton Stephens, 06 Dec 2020
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AC2: 'Response to Referee #2', Britton Stephens, 06 Dec 2020
Britton B. Stephens et al.
Data sets
START-08 Airborne Oxygen Instrument B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.5065/D6DJ5CZ5
HIPPO-1 Airborne Oxygen Instrument B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.5065/D6J38QVV
HIPPO-2 Airborne Oxygen Instrument B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.5065/D67H1GXJ
HIPPO-3 Airborne Oxygen Instrument B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.5065/D65Q4TF0
HIPPO-4 Airborne Oxygen Instrument B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.5065/D679431D
HIPPO-5 Airborne Oxygen Instrument B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.5065/D6WW7G0D
HIPPO-1 Multiple Enclosure Device for Unfractionated Sampling of Air (MEDUSA) Flask Data B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.26023/J0VT-J67P-330R
HIPPO-1 Multiple Enclosure Device for Unfractionated Sampling of Air (MEDUSA) Kernel Data B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.26023/4NM6-3MPG-WC14
HIPPO-2 Multiple Enclosure Device for Unfractionated Sampling of Air (MEDUSA) Flask Data B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.26023/30T9-FZ21-4G04
HIPPO-2 Multiple Enclosure Device for Unfractionated Sampling of Air (MEDUSA) Kernel Data B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.26023/P4PE-KKYS-FZ07
HIPPO-3 Multiple Enclosure Device for Unfractionated Sampling of Air (MEDUSA) Flask Data B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.26023/MYW6-DQQ6-PZ0R
HIPPO-3 Multiple Enclosure Device for Unfractionated Sampling of Air (MEDUSA) Kernel Data B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.26023/GA02-K0FR-C10M
HIPPO-4 Multiple Enclosure Device for Unfractionated Sampling of Air (MEDUSA) Flask Data B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.26023/XQW5-YHPP-XG0M
HIPPO-4 Multiple Enclosure Device for Unfractionated Sampling of Air (MEDUSA) Kernel Data B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.26023/FF65-2RZM-ZB00
HIPPO-5 Multiple Enclosure Device for Unfractionated Sampling of Air (MEDUSA) Flask Data B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.26023/R8JN-Z3TG-2E0N
HIPPO-5 Multiple Enclosure Device for Unfractionated Sampling of Air (MEDUSA) Kernel Data B. Stephens, R. Keeling, J. Bent, A. Watt, S. Shertz, and W. Paplawsky https://doi.org/10.26023/X9KY-CK34-VR10
ORCAS Airborne Oxygen Instrument B. Stephens, J. Bent, A. Watt, R. Keeling, E. Morgan, and S. Afshar https://doi.org/10.5065/D6N29VC6
ORCAS Medusa Flask Sampler Flask Data B. Stephens, J. Bent, A. Watt, R. Keeling, E. Morgan, S. Afshar, and W. Paplawsky https://doi.org/10.5065/D6H130FW
ORCAS Medusa Flask Sampler Kernel Data B. Stephens, J. Bent, A. Watt, R. Keeling, E. Morgan, S. Afshar, and W. Paplawsky https://doi.org/10.5065/D6MS3R6C
ATom: L2 In Situ Measurements from the NCAR Airborne Oxygen Instrument (AO2) B. Stephens, E. Morgan, A. Watt, J. Bent, S. Afshar, R. Keeling, and W. Paplawsky https://doi.org/10.3334/ORNLDAAC/1704
ATom: L2 Measurements from Medusa Whole Air Sampler (Medusa) E. Morgan, B. Stephens, J. Bent, A. Watt, S. Afshar, W. Paplawsky, and R. Keeling https://doi.org/10.3334/ORNLDAAC/1729
Britton B. Stephens et al.
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Cited
2 citations as recorded by crossref.
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- Gravitational separation of Ar∕N<sub>2</sub> and age of air in the lowermost stratosphere in airborne observations and a chemical transport model B. Birner et al. 10.5194/acp-20-12391-2020