Ammonia in the summertime Arctic marine boundary layer: sources, sinks, and implications
Bibliographic record
Abstract
Continuous hourly measurements of gas-phase ammonia (NH 3(g) ) were taken from 13 July to 7 August 2014 on a research cruise throughout Baffin Bay and the eastern Canadian Arctic Archipelago. Concentrations ranged from 30 to 650 ng m −3 (40–870 pptv) with the highest values recorded in Lancaster Sound (74°13′ N, 84°00′ W). Simultaneous measurements of total ammonium ([NH x ]), pH and temperature in the ocean and in melt ponds were used to compute the compensation point ( χ ), which is the ambient NH 3(g) concentration at which surface–air fluxes change direction. Ambient NH 3(g) was usually several orders of magnitude larger than both χ ocean and χ MP (< 0.4–10 ng m 3 ) indicating these surface pools are net sinks of NH 3 . Flux calculations estimate average net downward fluxes of 1.4 and 1.1 ng m −2 s −1 for the open ocean and melt ponds, respectively. Sufficient NH 3(g) was present to neutralize non-sea-salt sulfate (nss-SO 4 2− ) in the boundary layer during most of the study. This finding was corroborated with a historical data set of PM 2.5 composition from Alert, Nunavut (82°30′ N, 62°20′ W) wherein the median ratio of NH 4 + /nss-SO 4 2− equivalents was greater than 0.75 in June, July and August. The GEOS-Chem chemical transport model was employed to examine the impact of NH 3(g) emissions from seabird guano on boundary-layer composition and nss-SO 4 2− neutralization. A GEOS-Chem simulation without seabird emissions underestimated boundary layer NH 3(g) by several orders of magnitude and yielded highly acidic aerosol. A simulation that included seabird NH 3 emissions was in better agreement with observations for both NH 3(g) concentrations and nss-SO 4 2− neutralization. This is strong evidence that seabird colonies are significant sources of NH 3 in the summertime Arctic, and are ubiquitous enough to impact atmospheric composition across the entire Baffin Bay region. Large wildfires in the Northwest Territories were likely an important source of NH 3 , but their influence was probably limited to the Central Canadian Arctic. Implications of seabird-derived N-deposition to terrestrial and aquatic ecosystems are also discussed.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| 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".