Continuous measurements of atmospheric monochloroacetic acid: Evidence of photochemical formation
Bibliographic record
Abstract
Monochloroacetic acid (MCAA) is a regulated disinfection byproduct in drinking water due to toxicity, but its presence in environmental samples unrelated to disinfection is poorly understood. Here, we apply two online mass spectrometry-based techniques to quantify atmospheric MCAA: chemical ionization mass spectrometry with acetate reagent ion for 1 Hz measurements of gas-phase MCAA and ambient ion monitoring ion chromatography mass spectrometry for hourly measurements of MCAA in the gas and particle phases. Sampling campaigns in Toronto, Canada determined average gas-phase MCAA mixing ratios of 0.57 ± 0.44 pptv from February – April 2022 and 1.4 ± 1.0 pptv from June – August 2022. No MCAA was detected in particulate matter (PM2.5), suggesting particles were not reservoirs of MCAA. Summer MCAA gas-phase data displayed clear diurnal trends and correlated with UV irradiance and known secondary pollutants ozone and formic acid. Thus, we propose MCAA is photochemically formed from volatile precursors. Modelling MCAA from three known precursors accounted for < 0.2% of the measured MCAA in July, suggesting unknown MCAA precursors including the potential for it to be a product of chlorine atom-initiated photochemistry.
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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 | 0.000 |
| 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".