Quantum Yields of Hydroxyl Radical and Nitrogen Dioxide from the Photolysis of Nitrate on Ice
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Bibliographic record
Abstract
Nitrate photolysis proceeds via two major channels at illumination wavelengths above 290 nm: NO 3 - + h ν (+H + ) → NO 2 + • OH (1) and NO 3 - + h ν → NO 2 - + O( 3 P) (2). A recent study determined the quantum yield of reaction 1 on ice by measuring NO 2 production, but suggested their values might be lower bounds because of incomplete recoveries of NO 2 . We measured the quantum yield of pathway 1 using an alternate approach, i.e., by following the formation of • OH. Our quantum yields for • OH (Φ OH ) at 263 K were independent of nitrate concentration and illumination wavelength (λ > 300 nm), but were dependent upon pH. Values of Φ OH decreased from (3.6 ± 0.6) × 10 -3 at pH 7.0 to (2.1 ± 0.8) × 10 -3 at pH 2.0, where the listed pH values are those of the sample solution prior to freezing. Temperature dependence experiments (239−318 K; pH 5.0) showed that values of Φ OH in ice pellets and aqueous solutions were both well described by the same regression line, ln(Φ OH ) = ln(Φ 1 ) = −(2400 ± 480)(1/ T ) + (3.6 ± 0.8) (where errors represent ±1σ), suggesting that the photolysis of nitrate on ice occurs in a “quasi-liquid layer” rather than in the bulk ice. Our ice quantum yields between 268 and 240 K are 3−9 times higher, respectively, than Φ 1 values determined previously in ice. Applying our quantum yields to past field experiments indicates that nitrate photolysis can account for the flux of NO x from sunlit snow in the Antarctic and at Summit, Greenland, but that nitrate was only a minor source of the snowpack NO x measured during the Alert 2000 campaign in the Canadian Arctic. Additional calculations show that the photolysis of nitrate on cirrus clouds in the upper troposphere is a minor source of NO x that cannot account for the apparent underestimation of the ratio of NO x /HNO 3 in current numerical models.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.000 | 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 it