High Time Resolution Ambient Observations of Gas-Phase Perfluoroalkyl Carboxylic Acids: Implications for Atmospheric Sources
Bibliographic record
Abstract
Atmospheric formation of persistent perfluoroalkyl carboxylic acids (PFCAs) is a route to global contamination, including drinking water sources. We present high time resolution measurements of C 2 –C 6 PFCAs in ambient air made over 6 weeks each in winter and summer 2022 in Toronto, Canada. Observations were made using chemical ionization mass spectrometry with acetate ionization, with care taken to avoid system contamination. Measurements of trifluoroacetic acid (C 2 PFCA) are reported at 1 min time resolution, while those for C 3 –C 6 PFCAs are at 10 min time resolution. Variations with time and relationships to meteorology and other pollutants show evidence of secondary formation of all observed PFCAs except perfluoropropionic acid (C 3 PFCA). High time resolution data allow these unique observations, allowing for improved process and source understanding moving forward. Mixing ratios of TFA were larger than predicted from models that describe TFA formation from known precursors, indicating additional atmospheric sources of this molecule have yet to be identified.
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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 | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 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".