Evidence for the Importance of Semivolatile Organic\nAmmonium Salts in Ambient Particulate Matter
Bibliographic record
Abstract
The\ngas/particle phase partitioning behavior of NH<sub>3</sub>/NH<sub>4</sub><sup>+</sup> and other semivolatile constituents was measured\nby a custom-designed Denuder-MOUDI-Denuder integrated sampling system\nin Toronto, Canada. In this setup, upstream denuders were used to\ncapture alkaline and acidic gaseous components, and particle phase\ncomponents were captured by the filters on MOUDI stages. Downstream\ndenuders captured any alkaline and acidic gases that exited the MOUDI\napparatus, likely representing semivolatile constituents. In the ambient\ngas phase HCOOH was the most abundant acidic gas, with an average\nmixing ratio ∼2–3 times higher than that of SO<sub>2</sub> and HNO<sub>3</sub>. It was found that the majority (49–96%)\nof filter-collected NH<sub>4</sub><sup>+</sup> volatilized during\ncollection. NO<sub>3</sub><sup>–</sup> volatilization could\nonly explain 0.9–15% of NH<sub>4</sub><sup>+</sup> loss from\nthe filters. Instead, a strong correlation and nearly 1:1 molar ratio\nbetween downstream HCOO<sup>–</sup> and NH<sub>4</sub><sup>+</sup> indicated that most of the semivolatile NH<sub>4</sub><sup>+</sup> was originally balanced by organic acids in the ambient particle\nphase. The thermodynamic properties of HCOOH/HCOO<sup>–</sup> suggest that it should not have been present at high levels in the\nambient particle phase, and we interpret its detection in the downstream\ndenuder as evidence for larger organic acids that reacted to generate\nHCOOH prior to our offline measurement.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.398 | 0.001 |
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; both teacher heads agree on what is shown here.
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".