The Breathing of Halogenated Volatile Organic Compounds (HVOCs) from Human-impacted Ecosystems
Bibliographic record
Abstract
Atmospheric methyl chloride (CH3Cl) and methyl bromide (CH3Br) are the largest natural gaseous carriers of reactive chlorine and bromine, which contribute to stratospheric ozone depletion. Chloroform (CHCl3) also contributes to total stratospheric chlorine load and ozone destruction, with a much smaller impact. This dissertation investigates and quantifies emissions of these halogenated volatile organic compounds (HVOCs) from some natural ecosystems impacted by human activities.Chapter two describes a study on HVOCs flux measurements at an intermediate zone of coastal ecosystems in South Carolina, which are subject to seawater intrusion induced by storm surges combined with sea level rise. The degraded forested wetland showed significant CHCl3 emission rates and remained a net CH3Cl sink and a negligible CH3Br source/sink, unlike the saltmarsh which was a significant source for both. This study suggested that sea level rise and frequent storm surges derived from global climate change, in the long term, may increase CHCl3 emissions from coastal degraded forested wetlands and of methyl halides if salt marshes expand, with potential impacts for stratospheric ozone depletion.\nChapter three describes a project that measured life-cycle fluxes of CH3Cl, CH3Br and CH3I from rapeseed (Brassica napus “Empire”). The results showed that rapeseed emitted 5.3 ± 1.3 Gg CH3Cl year−1, 2.8 ± 0.7 Gg CH3Br year−1, and 4.0 ± 0.8 Gg CH3I year−1 as of 2018. Assuming the future global rapeseed production follows the same rate of increase as the past 60 years, the atmospheric sources of CH3Cl, CH3Br and CH3I may increase to 13.1 Gg year-1, 7.0 Gg year-1, and 9.8 Gg year-1, respectively by 2050, becoming an ever-larger global source. \nChapter four describes a study which showed that CuSO4, in conjunction with either hydrogen peroxide (H2O2) or solar radiation, significantly enhanced CH3Cl and CH3Br production from organic matter in soil or seawater. This study identified a new abiotic pathway of methyl halide production occurring in agricultural fields and water bodies facilitated by the widespread application of Cu (II) based pesticides, herbicides and fungicides. A rough quantification suggested this mechanism had the potential to account for a significant part of the missing sources of CH3Cl and CH3Br.\nThese aforementioned studies highlight the increasing contribution from natural sources of ozone depleting substances (ODSs) influenced by human activities, which may offset some of the ODSs reductions achieved by the Montreal Protocol.
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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) | 0.000 | 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 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".