Surface snow bromide and nitrate at Eureka, Canada in early spring and implications for polar boundary layer chemistry
Bibliographic record
Abstract
Abstract. This study explores the role of snowpack in polar boundary layer chemistry, especially as a di-rect source of reactive bromine (BrOX=BrO+Br) and nitrogen (NOX=NO+NO2) in the Arctic springtime. Surface snow samples were collected daily from a Canadian high Arctic location at Eureka, Nunavut (80° N, 86° W) from the end of February to the end of March in 2018 and 2019. The snow was sampled at several sites representing distinct environments: sea ice, inland close to sea level, and a hilltop ~600 m above sea level (asl). At the inland sites, surface snow salinity has a double-peak distribution with the first and low-est peak at 0.001–0.002 practical salinity unit (psu), which corresponds to the precipitation ef-fect, and the second peak at 0.01–0.04 psu, likely due to the condensation effect. Snow salinity on sea ice has a triple-peak distribution; its first and second peaks overlap with the inland peaks, and the third peak at 0.2–0.4 psu can be clearly attributed to sea water contamination. At all sites, sodium and chloride concentrations in surface snow increase by almost 10-fold from the top 0.2 cm to ~1 cm in depth. Bromide in surface snow is significantly enriched, indi-cating that surface snow at Eureka is a net sink of atmospheric bromine. Moreover, daily data show that top surface snow bromide at all sampling sites has an increasing trend over the measurement time period (late February to late March), with mean slopes of 1.9 and 1.3 ppb d-1 in the 0–0.2 cm and the 0.2–0.5 cm layers, respectively. At the sea level sites, snow nitrate also shows a significant increasing trend, with mean slopes of 12.1, 12.4, and 4.3 ppb d-1 in the top 0.2 cm, 0.2–0.5 cm, and 0.5–1.5 cm layers, respectively. Using these trends, we derive a novel method to calculate deposition flux of bromide and nitrate to the snowpack. For bromide, the integrated deposition flux is 1.29×107 molecules cm-2 s-1 at sea level and 1.01×107 molecules cm-2 s-1 at ~600 m. For nitrate, the integrated deposition flux is 2.4×108 molecules cm-2 s-1 at sea level and -1.0×108 molecules cm-2 s-1 at ~600 m; the negative flux indicates that snow at the hilltop sites is losing nitrate. The smaller vertical gradient of bromide deposition flux strongly indicates that local snowpack emission on sea ice and inland is not likely to be a large source of reactive bromine. In contrast, nitrate deposition flux has a large vertical gradient, e.g., with a positive flux at sea level and a negative flux at ~600 m, indicating that snowpack at sea level is a large source of reactive nitrate. In addition, we found a significant correlation (with coefficient R values of 0.48-0.76) between surface snow nitrate and bromide at the inland sites. The [NO3-] / [Br-] ratio ranges from 4 to 7, highlighting the effect of reactive bromine in accelerating the atmospheric NOX-to-nitrate con-version. This is the first time we see such an effect over the course of one day.
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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 | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".