CFC-11 and CCl4 in the Atmosphere: A free calibration standard for Proton-Transfer-Reaction Mass-Spectrometry (PTR-MS)
Bibliographic record
Abstract
The Proton-transfer-reaction mass spectrometer (PTR-MS) has become an important tool for real-time monitoring of volatile organic compounds (VOCs) in the atmosphere. PTR-MS is semi-quantitative in untargeted analysis if the transmission of the analytes is well constrained. The transmission at different m/z is determined by using commercial calibration standards.We present an additional method to constrain the instrument transmission using well-monitored ozone-depleting substances in the atmosphere. Ozone-depleting substances such as chlorofluorcarbons (CFCs) are banned and monitored through the Montreal Protocol, but their concentration in the atmosphere is relatively stable, and due to their long lifetime they are well mixed. Two of these banned substances can be detected using PTR-MS, namely Trifchloroluoromethane (CFC-11) and carbon tetrachloride (CCl4). Their major ion CCl3+ is measured at m/z 116.906. A clear signal at this mass is observed in all atmospheric measurements. Since the concentrations of CFC-11 and CCl4 in the atmosphere are measured frequently by global monitoring networks, they can be used to determine the transmission at m/z 116.906. We experimentally determined the pseudo-reaction rate constants of CFC-11 and CCl4. Utilizing this, the transmission of m/z 116.906 can be determined using any atmospheric measurements in the past or present. This innovative approach can be a useful tool for quality control of PTR-MS data and checking instrument performance during measurements.
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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 | 0.004 | 0.004 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.003 | 0.002 |
| Insufficient payload (model declined to judge) | 0.005 | 0.003 |
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".