Revisiting chloroform emissions from the pulp and paper sector: a brief communication
Bibliographic record
Abstract
Abstract Halogenated very short-lived substances (VSLS) represent a growing source of chlorine to the stratosphere where they may contribute to ozone layer depletion. Chloroform (CHCl 3 ) is a prominent VSLS with poorly constrained anthropogenic sources that include its unintentional production when wood pulp is bleached for paper production. Recent assessments of the global CHCl 3 budget have relied on emission factors (EFs) for the pulp/paper (PP) sector derived some 35 years ago when industrial practices were markedly different. Here, we analysed data from the Pollutant Release and Transfer Registers of the USA, Canada and Japan. Combined with data on the national number of pulp mills and bleached wood pulp production volume, we derive plausible lower and upper limit EFs. These factors show a downward trend since the early 2000s, which we attribute to a continued phase-down in the use of ‘elemental chlorine’ bleaching in favour of ‘elemental chlorine free’ bleaching. The derived mean EFs for the period 2000–2020, expressed as the mass of CHCl 3 per air–dried tons (adt) of bleached pulp, are in close agreement for the regions considered: USA (39.8 ± 32 g/adt), Canada (38.6 ± 29.8 g/adt) and Japan (30.1 ± 8.6 g/adt). Assuming these factors are broadly representative of other world regions, a mean annual global CHCl 3 source of 3 (1–6) Gg yr −1 from the PP sector is estimated for the approximate 2000–2020 period. We conclude that the sector’s contribution to the global CHCl 3 budget has likely decreased considerably since the 1990s and that the use of older EFs to calculate present-day emissions should be avoided.
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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 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".