Chemical evolution of secondary organic aerosol from OH-initiated heterogeneous oxidation
Bibliographic record
Abstract
Abstract. The heterogeneous oxidation of laboratory Secondary Organic Aerosol (SOA) particles by OH radicals was investigated. SOA particles, produced by reaction of α-pinene and O3, were exposed to OH radicals in a flow tube, and particle chemical composition, size, and hygroscopicity were measured to assess modifications due to oxidative aging. Aerosol Mass Spectrometer (AMS) mass spectra indicated that the degree of oxidation of 200 nm diameter SOA particles was significantly enhanced due to OH-initiated oxidation, as evidenced by the increase in the fraction of m/z 44 fragment of total organic mass concentration (F44). F44 values of the SOA particles, initially in the range F44=0.04–0.07, increased by up to ΔF44~0.01 under equivalent atmospheric aging timescales of 2 weeks, assuming a 24-h average OH concentration of 106 cm−3. Particle O/C ratios calculated from F44 values, initially in the range O/C=0.25–0.35, rose by a maximum of ΔO/C~0.04 units for 2 weeks of aging. Particle densities also increased with heterogeneous oxidation, consistent with the observed increase in the degree of oxidation. Minor reductions in particle size, with volume losses of up to 10%, were observed due to volatilization of oxidation products. The SOA particles activated more readily to form cloud droplets with an increase in the κ hygroscopicity parameter of up to a factor of two for the equivalent of 2 weeks of OH atmospheric exposure. These results indicate that OH heterogeneous oxidation of typical SOA needs to be considered as an atmospheric organic aerosol aging mechanism, most likely of higher relative importance away from VOC source regions, where other aging mechanisms are less dominant.
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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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.013 | 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 teacher head, 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".