The Δ <sup>17</sup> O and δ <sup>18</sup> O values of simultaneously collected atmospheric nitrates from anthropogenic sources – Implications for polluted air masses
Bibliographic record
Abstract
Abstract. There are clear motivations for better understanding the atmospheric processes that transform nitrogen (N) oxides (NOx) emitted from anthropogenic sources into nitrates (NO3−), two of them being that NO3− contributes to acidification and eutrophication of terrestrial and aquatic ecosystems, and particulate nitrate may play a role in climate dynamics. For these reasons, oxygen isotope ratios (δ18O, Δ17O) have been applied to infer the chemical pathways leading to the observed distribution of wet (w-NO3−), particulate (p-NO3−), and the sum of p-NO3− and gaseous HNO3, while the gaseous form (HNO3) has never been separately characterized for 17O. Previous research studies have investigated w-NO3−, p-NO3− or p-NO3− + HNO3 from non-polluted or polluted air masses, and inferred seasonal changes in the dominance of oxidation pathways to account for higher δ18O and Δ17O values in winter relative to summer. However, none of the polluted air studies collected samples specific to targeted emission sources. Here we have used a wind-sector-based, multi-stage filter sampling system and precipitation collector to simultaneously sample HNO3 and p-NO3−, and co-collect w-NO3−, downwind from five different anthropogenic sources. Overall, the w- and p-NO3 δ18O and Δ17O values show expected differences between cold and warm seasons, but only the Δ17O values of HNO3 follow this pattern. The HNO3 δ18O ranges are distinct from the w- and p-NO3− patterns. Interestingly, the Δ17O differences between p-NO3− and HNO3 shifts from positive during cold sampling periods to negative during warm periods. The summer pattern may be due to the presence of nitrates derived from NOx that has not yet reached isotopic equilibrium with O3 and subsequent differences in dry deposition rates, while the larger proportion of p-NO3− formed via the N2O5 pathway can explain the fall-winter pattern. Very low p-NO3− Δ17O values observed during warm months may be due to this non-equilibrated NOx, though contribution from RO2 oxidation remains a possibility. Our results show that the isotopic signals of HNO3, w-NO3− and p-NO3− are not interchangeable and that their differences can further our understanding of NOx oxidation and deposition. Future research should investigate all tropospheric nitrate species as well as NOx to refine our understanding of nitrate worldwide and to develop effective emission reduction strategies.
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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 | 0.000 | 0.000 |
| 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".