Impact of NO <sub> <i>x</i> </sub> on secondary organic aerosol (SOA) formation from <i>α</i> -pinene and <i>β</i> -pinene photooxidation: the role of highly oxygenated organic nitrates
Bibliographic record
Abstract
The formation of organic nitrates (ONs) in the gas phase and their impact on mass formation of secondary organic aerosol (SOA) was investigated in a laboratory study for α -pinene and β -pinene photooxidation. Focus was the elucidation of those mechanisms that cause the often observed suppression of SOA mass formation by NO x , and therein the role of highly oxygenated multifunctional molecules (HOMs). We observed that with increasing NO x concentration (a) the portion of HOM organic nitrates (HOM-ONs) increased, (b) the fraction of accretion products (HOM-ACCs) decreased, and (c) HOM-ACCs contained on average smaller carbon numbers. Specifically, we investigated HOM organic nitrates (HOM-ONs), arising from the termination reactions of HOM peroxy radicals with NO x , and HOM permutation products (HOM-PPs), such as ketones, alcohols, or hydroperoxides, formed by other termination reactions. Effective uptake coefficients γ eff of HOMs on particles were determined. HOMs with more than six O atoms efficiently condensed on particles ( γ eff >0.5 on average), and for HOMs containing more than eight O atoms, every collision led to loss. There was no systematic difference in γ eff for HOM-ONs and HOM-PPs arising from the same HOM peroxy radicals. This similarity is attributed to the multifunctional character of the HOMs: as functional groups in HOMs arising from the same precursor HOM peroxy radical are identical, vapor pressures should not strongly depend on the character of the final termination group. As a consequence, the suppressing effect of NO x on SOA formation cannot be simply explained by replacement of terminal functional groups by organic nitrate groups. According to their γ eff all HOM-ONs with more than six O atoms will contribute to organic bound nitrate (OrgNO 3 ) in the particulate phase. However, the fraction of OrgNO 3 stored in condensable HOMs with molecular masses > 230 Da appeared to be substantially higher than the fraction of particulate OrgNO 3 observed by aerosol mass spectrometry. This result suggests losses of OrgNO 3 for organic nitrates in particles, probably due to hydrolysis of OrgNO 3 that releases HNO 3 into the gas phase but leaves behind the organic rest in the particulate phase. However, the loss of HNO 3 alone could not explain the observed suppressing effect of NO x on particle mass formation from α -pinene and β -pinene. Instead we can attribute most of the reduction in SOA mass yields with increasing NO x to the significant suppression of gas phase HOM-ACCs, which have high molecular mass and are potentially important for SOA mass formation at low-NO x conditions.
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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".