Two-Phase Morphology and Drastic Viscosity Changes in Biomass Burning Organic Aerosol After Hydroxyl Radical Aging
Bibliographic record
Abstract
Understanding the impact of wildfire-derived biomass burning organic aerosol (BBOA) on air quality, climate, and atmospheric chemistry requires knowledge of its phase behavior and viscosity – properties that remain poorly characterized after atmospheric aging. We investigated how hydroxyl radical (OH) aging affects these properties in BBOA generated from smoldering pine wood. Samples were aged in an oxidative flow reactor with equivalent atmospheric aging times of 1.3, 5.2, and 8.6 days. Phase behavior was assessed using optical microscopy, and viscosity was measured using the poke-flow technique. Across all aging times and relative humidities (0–90% RH), particles consisted of a hydrophilic core and a hydrophobic shell. Under dry conditions, viscosity increased by 4–5 orders of magnitude with aging, and the most aged particles became glass-like. Viscosity was strongly RH-dependent. From these measurements, we estimated mixing times and glass formation in 200 nm particles throughout the troposphere. Aged BBOA is predicted to remain well mixed in the boundary layer, but in the free troposphere (~1–12 km), mixing times often exceed 1 hour and particles are frequently in a glassy state. These findings have implications for particle growth, evaporation, and ice nucleation, and suggest that OH aging alone cannot fully explain tar ball formation in the atmosphere.
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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 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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".