Role of Water in the Formation, Transformation and Fate of Secondary Organic Aerosol
Bibliographic record
Abstract
Particle-phase water is the most abundant atmospheric aerosol constituent, yet the importance of water for the formation, transformation and fate of secondary organic aerosol (SOA) remains not fully characterized. In order to address this knowledge gap, this thesis explores the role of water in SOA formation, chemical aging and fate as cloud condensation nuclei. The formation of SOA from the photooxidation of isoprene in the presence of various sulfate seed particles was investigated using a flow tube reactor. Under constant environmental conditions, particle-phase water was found to have the largest effect on the amount of SOA formed where this additional organic material was highly oxidized, likely arising from enhanced uptake of organic acids due to their high water solubility. The amount of high molecular weight compounds increases with acidity, suggesting the role of acidity in governing organic composition. The relative humidity (RH) dependence of SOA aging by photolysis was examined using particles containing water-soluble α-pinene SOA material in an environmental chamber at three RH conditions (5, 45 and 85 %). Photolysis led to substantial mass loss where the rate of mass loss increased with increasing RH, suggesting that moisture-induced changes in SOA phase have implications to particle reactivity. Aging of ambient SOA sampled at Whistler, British Columbia found that aging by both gas and aqueous-phase OH increased the degree of oxygenation and CCN activity of the organic material, confirming the hypothesis that there is a simple relationship between the hygroscopicity of organic aerosol and its oxygen-to-carbon ratio. Addition of various types of organic material onto sulfate particles resulted in the suppression of water uptake during droplet growth. Experiments using sulfate particles with different acidity suggest that high molecular weight compounds, formed via acid-catalyzed condensed phase reactions, are the species affecting water uptake kinetics.
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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".