Trends of stratospheric BrO (1995 to 2025) derived from ground-based DOAS observations at Kiruna, Northern Sweden
Bibliographic record
Abstract
Stratospheric bromine originates partly from natural and partly from anthropogenic sources. After the Montreal protocol and following amendments, anthropogenic emissions (halons and methyl bromide) were largely reduced. This reduction was not only seen in tropospheric in situ measurements, but also in a reduction of stratospheric bromine levels (estimated from BrO measurements) after about 2002.Here, we report on ground-based observations of stratospheric BrO carried out between 1995 and present in Kiruna (northern Sweden). The (slant) column density of BrO is analysed from UV spectra of zenith scattered sun light at solar zenith angles of 80° and 90°. Our measurements are in agreement with predictions predictions and existing observational data sets for the period before about 2019 for which a steady decline of the BrO levels is found. However, after 2019 the stratospheric BrO levels increased again, in contrast to the expected trend. The reason for this discrepancy is not yet known. Possible explanations might be increasing natural emissions of methyl bromide and/or very short lived bromine containing compounds, perhaps related to climate change (e.g. a warmer sea surface). Also recently again increasing anthropogenic emissions of methyl bromide might contribute. The variation of stratospheric aerosols is unlikely to explain the changed trend after 2019.
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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 | 0.001 | 0.001 |
| 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".