Aqueous Photoreactions of Wood Smoke Brown Carbon
Bibliographic record
Abstract
A dominant source of light-absorbing aerosol particles, brown carbon (BrC), to the atmosphere is smoke from biomass burning. Aqueous aging of biomass burning organic aerosol can increase BrC absorbance, which may extend its atmospheric lifetime in aerosol particles, cloud droplets, and fog droplets. This study investigates the aqueous aging of biomass burning BrC and the connection between absorbance and chemical composition. The water-soluble component of laboratory-generated wood smoke BrC was analyzed using aerosol-chemical ionization mass spectrometry, liquid chromatography–mass spectrometry (electrospray ionization), UV–vis spectroscopy, and NMR spectroscopy as it was exposed to UV-B light and OH oxidation to simulate photo-oxidation in the atmosphere. During UV-B light exposure, absorbance at 400 nm increased by greater than a factor of 2 and remained high for the 6 h exposure period. A similar increase in absorbance was observed during OH oxidation, up to an OH exposure of 4 × 10–10 M·s. At a cloud water OH concentration of 1 × 10–14 M, this OH exposure corresponds to ∼11 h of aqueous OH oxidation. Further OH oxidation led to a net loss of absorbance after an OH exposure of 1.5 × 10–9 M·s (∼42 h of aqueous OH oxidation). The increase in absorbance in both cases was linked to the formation of aromatic dimer compounds and functionalized products only during OH oxidation. The loss of absorbance with extended OH oxidation correlated with a loss of aromatic compounds and breakdown to smaller molecules. These results show that aqueous aging of the biomass burning material through photo-oxidation primarily increases the absorbance of BrC and may result in longer-lived BrC 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 | 0.000 |
| 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 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".