Bi‐directional air‐surface exchange of atmospheric ammonia: A review of measurements and a development of a big‐leaf model for applications in regional‐scale air‐quality models
Bibliographic record
Abstract
The air‐surface exchange of atmospheric ammonia (NH 3 ) and measurements of the canopy and stomatal compensation points ( χ cp and χ st , respectively) and the stomatal and soil emission potentials (Γ st and Γ g , respectively) are reviewed. A database of these values has been developed, to be used for the development of input parameters and for model evaluation. The compensation points are dependent on canopy type, nitrogen (N) status, temperature, growth stage, and meteorological conditions. Canopies that receive high atmospheric nitrogen input generally have high χ cp values. χ cp values also tend to be higher over intensively managed vegetated surfaces than semi‐natural vegetation, due to the higher nitrogen content in these surfaces. Increased nitrogen concentrations from fertilization and cutting practices have been observed to increase the compensation points and therefore the emission from these canopies. The decomposition of litter leaves has been found to play a dominant role and significantly increase the values of χ cp over agricultural vegetation and fertilized grasslands. By modifying an existing big‐leaf dry deposition model to allow NH 3 emission from leaf stomata and soil surfaces, a bi‐directional air‐surface exchange model has been developed for applications in regional‐scale air‐quality models. The model predicts χ cp values that vary with canopy type, nitrogen content, and meteorological conditions. χ cp values predicted by the model are around 1–2 μ g m −3 over forest canopies and 4–10 μ g m −3 over grasslands and agricultural canopies during a typical summer daytime; χ cp values are ∼10 and ∼3 times lower over forests and agricultural lands, respectively, in nighttime and/or winter conditions. These results are similar to the range of measured values. The new bi‐directional air‐surface exchange model will reduce the dry deposition fluxes by 20–100 ng m −2 s −1 compared to the original dry deposition model over low‐N forests and agricultural lands during typical summer daytime conditions, which can be the difference between whether deposition or emission occurs. For example, this new model produces emissions fluxes of 0–90 ng m −2 s −1 over croplands when the atmospheric NH 3 concentrations are below 10 μ g m −3 .
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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 | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".