Bibliographic record
Abstract
Brown carbon (BrC) is a type of carbonaceous aerosol, primarily emitted from biomass burning sources such as wildfires. These aerosol particles have significant implications on climate through their ability to absorb light, and potentially contributing to warming effects. Due to the expected increase of wildfire activity in the upcoming years, this source of particulate emission is also expected to increase. Oxidative and photochemical aging in the atmosphere, however, can change BrC’s light absorbing properties as well as its chemical composition. Significant uncertainties remain when estimating BrC’s impact on climate due to its chemical complexity and the range of atmospheric aging processes that can change its composition and optical properties.This thesis focused on elucidating the changes in absorption and chemical composition of biomass burning brown carbon aerosol from atmospheric aging. Targeting daytime photochemical aging by light exposure, we found that UVA light enhanced the ability of the particles to absorb visible light on short timescales of hours or less. This was accompanied by an increase in the oxidation state of the organic aerosols. The role that oxygen, and the subsequent reactive species formed by the presence of oxygen, plays in this absorption enhancement was also investigated. In particular, UV light exposure in the absence of oxygen does not lead to absorption enhancement in the visible region of the spectrum, pointing to the central role it plays in this photochemistry in the atmosphere. Using a singlet oxygen scavenger, we found that around 33% of the absorption increase was due to the formation of this reactive species, with no indication of OH radical formation. This has implications for anoxic, solid-like particles, where oxygen availability is low. Lastly, the enhancement in the absorption properties of biomass burning aerosols by short-term (1 hour) aging with low mixing ratios of NO3 radicals, one of the most important nighttime oxidants. We found that prior aging by either OH radicals or UVB light exposure significantly suppresses the subsequent absorption enhancement from NO3 radical aging, indicating that the aging mechanisms are in competition with each other. Overall, this thesis highlights the rapid optical and chemical transformations of BrC via photochemical and oxidative processing, and advances our understanding of how such particles evolve, with associated impacts on climate.
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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".