Trend and lifetime of sulfur hexafluoride at mid-latitudes deduced from ACE-FTS occultation measurements
Bibliographic record
Abstract
Sulfur hexafluoride (SF6) is one of the strongest greenhouse gases on a per molecule basis, with a global warming potential of 22800 (100-yr horizon). This is an extremely stable gas in the atmosphere, which results in a very long lifetime, with large uncertainties. The value adopted by IPCC is 3200 years, but some studies suggest shorter lifetimes, as low as 800 years. Surface concentrations are now about 7 ppt, with reported trends indicating a steady and strong increase of 0.3 ppt/yr. Most emissions are of anthropogenic origin, related to its use as an insulator in high-voltage electrical installations. Secondary contributions result from magnesium and aluminum production as well as from the manufacturing of semiconductors (see e.g. Levin et al., 2010; Rigby et al., 2010 and references therein). In this contribution, we use occultation measurements performed by the ACE-FTS (Atmospheric Chemistry Experiment Fourier Transform Spectrometer) instrument, launched in August 2003 onboard the Canadian SCISAT satellite (Bernath et al., 2005). ACE-FTS is still in operation to date, with no significant degradation in its performance. This spectrometer achieves a spectral resolution of 0.02 cm-1 in the broad 750-4400 cm-1 range which covers the unresolved nu-3 band Q branch of SF6 centered at 947.9 cm-1. Signal-to-noise ratios of 200-300 are typically obtained in the spectral region of interest. Version 3 retrievals performed by University of Waterloo give volume mixing ratio profiles of SF6 in the 11-32 km altitude range. We consider all available sunrise and sunset occultation measurements obtained at midlatitudes in both hemispheres to derive the trend of SF6 in the lower stratosphere, from late February 2004 onwards. Consistency between both hemispheres will be investigated. In addition, concurrent N2O measurements are used to evaluate the atmospheric lifetime of SF6, following a method used previously for other long-lived gases (e.g. Zander et al, 1996). Comparisons with trends derived from in situ surface measurements or from ground-based remote-sensing observations (e.g. at the Jungfraujoch station, 46.5ºN) are also included.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".