Evaluation of the Effects of Ozone Oxidation on Redox-Cycling Activity of Two-Stroke Engine Exhaust Particles
Bibliographic record
Abstract
The effect of oxidation on the redox-cycling activity of engine exhaust particles is examined. Particles obtained from a two-stroke gasoline engine were oxidized in a flow tube with ozone on a one-minute time scale both in the presence and absence of substantial gas-phase exhaust components. Whereas ozone concentrations were high, the ozone exposures were approximately equivalent to 60 ppb ozone for 2-8 h. Oxidation led to substantial increases in redox-cycling of aqueous extracts of filtered particles, as measured using the dithiothreitol (DTT) assay. Increases in redox activity when the entire exhaust was oxidized were primarily driven by deposition of redox-active secondary organic aerosol (SOA), resulting in an upper-limit DTT activity of 8.6 ± 2.0 pmol DTT consumed per min per microgram of particles, compared to 0.73 ± 0.60 pmol min(-1) μg(-1) for fresh, unoxidized exhaust particles. Redox-cycling activity reached higher levels when VOC denuded exhaust was oxidized, with the highest DTT activity observed being 16.7 ± 1.6 pmol min(-1) μg(-1) with no upper limit reached for the range of ozone exposures used in this study. Our results provide laboratory support for the hypothesis that the toxicity of engine combustion particles due to redox-cycling may increase as they age in the atmosphere.
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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".