On the use of isotopic composition measurements of volatile organic compounds to determine the “photochemical age” of an air mass
Bibliographic record
Abstract
It is shown that stable carbon isotope ratio measurements in atmospheric volatile organic compounds can be used to determine the photochemical age of the studied compounds. This “Isotopic Hydrocarbon Clock” has several advantages compared to the conventional “Hydrocarbon Clock”. Due to the small Kinetic Isotope Effects for the reaction of hydrocarbons with OH‐radicals, the photochemical ages derived from changes in isotopic composition are the correct linearly averaged age of the studied compounds, independent of the mixing of air parcels with different photochemical ages. The uncertainties of photochemical ages derived from isotopic composition measurements of atmospheric non‐methane hydrocarbons depend primarily on the accuracy of stable carbon isotope ratio measurements, the Kinetic Isotope Effect for the reaction of hydrocarbons with OH‐radicals and the variability of isotopic composition of hydrocarbon sources. Uncertainty analysis shows that the “Isotopic Hydrocarbon Clock” is not only a theoretical possibility but a viable method to determine the photochemical age of atmospheric hydrocarbons.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".