Evidence for the Importance of Semivolatile Organic Ammonium Salts in Ambient Particulate Matter
Bibliographic record
Abstract
The gas/particle phase partitioning behavior of NH 3 /NH 4 + and other semivolatile constituents was measured by a custom-designed Denuder-MOUDI-Denuder integrated sampling system in Toronto, Canada. In this setup, upstream denuders were used to capture alkaline and acidic gaseous components, and particle phase components were captured by the filters on MOUDI stages. Downstream denuders captured any alkaline and acidic gases that exited the MOUDI apparatus, likely representing semivolatile constituents. In the ambient gas phase HCOOH was the most abundant acidic gas, with an average mixing ratio ∼2–3 times higher than that of SO 2 and HNO 3 . It was found that the majority (49–96%) of filter-collected NH 4 + volatilized during collection. NO 3 – volatilization could only explain 0.9–15% of NH 4 + loss from the filters. Instead, a strong correlation and nearly 1:1 molar ratio between downstream HCOO – and NH 4 + indicated that most of the semivolatile NH 4 + was originally balanced by organic acids in the ambient particle phase. The thermodynamic properties of HCOOH/HCOO – suggest that it should not have been present at high levels in the ambient particle phase, and we interpret its detection in the downstream denuder as evidence for larger organic acids that reacted to generate HCOOH prior to our offline measurement.
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 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".