Top-down and bottom-up estimates of anthropogenic methyl bromide emissions from eastern China
Bibliographic record
Abstract
Abstract. Methyl bromide (CH3Br) is a potent ozone-depleting substance (ODS) that has both natural and anthropogenic sources. CH3Br has been used mainly for preplant soil fumigation, post-harvest grain and timber fumigation, and structural fumigation. Most non-quarantine/pre-shipment (non-QPS) uses have been phased-out in 2005 for non-Article 5 (developed) countries and in 2015 for Article 5 (developing) countries under the Montreal Protocol on Substances that Deplete the Ozone Layer; some uses have continued under critical use exemptions (CUEs). Under the Protocol, individual nations are required to report annual data on CH3Br production and consumption for quarantine/pre-shipment (QPS) uses, non-QPS uses and CUEs to the United Nations Environment Programme (UNEP). In this study, we analyzed high precision, in situ measurements of atmospheric concentrations of CH3Br obtained at the Gosan station on Jeju island, Korea, from 2008 to 2019. The background concentrations of CH3Br in the atmosphere at Gosan declined from 8.5 ± 0.8 ppt in 2008 to 7.4 ± 0.6 ppt in 2019 at a rate of −0.13 ± 0.02 ppt yr−1. At Gosan, we also observed periods of persistent concentrations (pollution events) elevated above the decreasing background in continental air masses from China. Statistical back trajectory analyses showed that these pollution events predominantly trace back to CH3Br emissions from eastern China. Using an inter-species correlation (ISC) method with the reference trace species CFC-11 (CCl3F), we estimate anthropogenic CH3Br emissions from eastern China at 4.1 ± 1.3 Gg yr−1 in 2008–2019, approximately 2.9 ± 1.3 Gg yr−1 higher than the bottom-up emission estimates reported to UNEP. Possible non-fumigation CH3Br sources – rapeseed production and biomass burning – were assessed and it was found that the discrepancy is more likely due to unreported or incorrectly reported QPS and non-QPS fumigation uses. These largely-unreported anthropogenic emissions of CH3Br are confined to eastern China and account for 30–40 % of anthropogenic global CH3Br emissions. They are likely due to delays in the introduction of CH3Br alternatives, such as sulfuryl fluoride (SO2F2), heat, irradiation and a possible lack of industry awareness of the need for regulation of CH3Br production and use.
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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".