Relative Humidity Effect on the Formation of Highly Oxidized Molecules and New Particles during Monoterpene Oxidation
Bibliographic record
Abstract
Abstract. It has been widely observed around the world that the frequency and intensity of new particle formation (NPF) events are reduced during periods of high relative humidity (RH). The current study focuses on how RH affects the formation of highly oxidized molecules (HOMs), which are key components of NPF and initial growth caused by oxidized organics. The ozonolysis of α-pinene, limonene, and △3-carene, with and without OH-scavenger, were carried out under low NOx conditions under a range of RH (from ~3 % to ~90 %) in a temperature-controlled flow tube. A Scanning Mobility Particle Sizer (SMPS) was used to measure the size distribution of generated particles and a novel transverse-ionization chemical ionization inlet with a high-resolution time-of-fight mass spectrometer detected HOMs. A major finding from this work is that neither the detected HOMs nor their abundance changed significantly with RH, which indicates that the detected HOMs must be formed from water-independent pathways. In fact, the distinguished OH- and O3-derived peroxy radicals (RO2), HOM monomers, and HOM dimers could mostly be explained by the autoxidation of RO2 followed by bimolecular reactions with other RO2 or hydroperoxy radicals (HO2), rather than from a water-influenced pathway like through the formation of a stabilized Criegee intermediate (sCI). However, as RH changed from 3 to 90 % the particle number concentrations decreased by a factor of 2~3 while particle mass concentrations increased or decreased slightly within a factor of 2. These observations show that, while high RH appears to inhibit NPF as evident by the decreasing number concentration, this reduction is not caused by a decrease in RO2-derived HOMs formation. One possible explanation is the existence of other extremely low volatility compounds (ELVOCs), like gas phase formed sCI-included accretion products, which are responsible for the very first steps of NPF but are not detected by nitrate-based chemical ionization mass spectrometry. These ELVOCs may be preferentially reduced at high RH compared to more volatile compounds, the latter of which mainly determine the final mass concentration of particles. Another possibility is that a fraction of HOMs cluster with water (but detected as the declustered molecules) at high RH in such a way that they may no longer be able to participate in cluster formation, thereby suppressing NPF.
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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".