Segmented flow coil equilibrator for continuous measurement of volatile organic compounds in seawater of the polar oceans
Bibliographic record
Abstract
Volatile organic compounds (VOCs) are a group of molecules that influence aspects of atmospheric chemistry such as oxidation chemistry and particle formation. Most VOCs are produced from a variety of anthropogenic and natural sources; with emissions from the oceans least well known/ quantified. In this thesis I focus on methanol, acetone, acetaldehyde, DMS and isoprene. Uncertainty persists as to the factors influencing their variability in seawater concentrations. The polar oceans are particularly undersampled regions with few to no measurements of these compounds, which is partially due to a lack of suitable instrumentation. \n \nTo increase available instrumentation, this thesis describes the development of a Segmented Flow Coil Equilibrator coupled to a commercially available Proton Transfer Reaction-Mass Spectrometer for measurements of VOCs in seawater. Its main advantage lies in its ability to measure underway and discrete samples. \n \nThe method is used to make depth profile and underway measurements in the Canadian Arctic Archipelago during sea ice melt season. Highest VOC concentrations are generally observed at the surface, apart from DMS and isoprene which sometimes display a subsurface maximum. Generally, highest surface concentrations of VOCs are observed in partial ice cover. Concentrations of acetone and acetaldehyde were about 30 – 50 % higher in partial ice cover compared to ice-free waters. \n \nThis thesis also presents ambient air, underway and depth profile measurements from a transect in the subpolar Southern Ocean, used to calculate surface saturations and air – sea fluxes. Correlations with other biogeochemical data allowed me to elucidate factors controlling seawater concentrations of these VOCs. This dataset contains the first evidence of a statistically significant, but small diel change (on the order of 8 – 26 %) in seawater isoprene, acetone and acetaldehyde concentrations in the open ocean. \n \nThe measurements presented in this thesis will be useful to constrain ocean source/sink strength. The analysis points towards factors controlling the global variability of these compounds in the ocean.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.002 |
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".