Real-time, controlled OH-initiated oxidation of biogenic secondary organic aerosol
Bibliographic record
Abstract
Abstract. The chemical complexity of atmospheric organic aerosol (OA) requires novel methods for characterization of its components and description of its atmospheric processing-induced transformations. We present the first field deployment of the Toronto Photooxidation Tube (TPOT), a field-deployable flow reactor for the controlled exposure of ambient aerosol to OH radicals. The system alternates between sampling of (1) (unreacted) ambient aerosol, (2) aerosol exposed to UV light and subjected to a ~4 to 10 °C temperature increase, and (3) aerosol that is oxidized by OH (in addition to the aforementioned UV exposure/temperature increase). This allows both characterization of the aging process and classification of aerosol in terms of its volatility and reaction-based properties. Summertime measurements by an aerosol mass spectrometer coupled to the TPOT were performed in the remote forest of western Canada, resulting in aerosol dominated by biogenic secondary organic aerosol. Volatilization/UV exposure resulted in an approximately 10 to 25% decrease in organic mass and resulted in a slight increase in oxygenation. OH oxidation resulted in a further organic mass decrease (additional ~25%) and yielded an aerosol with O:C values comparable to those characteristic of low volatility, highly oxygenated OA. Most OH-induced changes occurred within ~3 day-equivalents of atmospheric processing, with further reactions generally proceeding at a greatly reduced rate. Positive matrix factorization (PMF) analysis of the TPOT data yielded five factors. One factor is related to primary biomass burning organic aerosol, while the others describe oxygenated organic aerosol (OOA) components in terms of reactivity and volatility: (1) volatile and reactive; (2) non-volatile and reactive; (3) non-volatile and reactive early-generation product; (4) non-volatile and non-reactive product. This PMF classification of aerosol components directly in terms of reactivity and volatility is enabled by the TPOT-modulated perturbation of aerosol composition, and is not otherwise accessible. The particle-phase reaction end products have mass spectra similar to the low-volatility oxygenated organic aerosol (LV-OOA) factors widely reported in the literature, providing supporting evidence for aged organic aerosol formation from OH-driven oxidation processes.
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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".