Terpene Structure Governs Humidity-Enhanced New Particle Formation through an OH-Sensitive Ozonolysis Network
- 1Department of Chemistry
- 2University of Vermont
Abstract
Relative humidity (RH) impacts new particle formation (NPF) from monoterpene ozonolysis in a non-uniform way. Depending on the precursor, water vapor can either suppress particle formation or increase it, and the chemical origin of that contrast has remained uncertain. Here we use cyclohexane to remove OH and separate the OH-sensitive portion of the particle response from the residual OH-insensitive contribution for α-pinene, β-pinene, and camphene. Experiments were carried out at <0.1% and 60% RH using low monoterpene mixing ratios of 0.5 – 5 ppbv. In the absence of scavenger, the maximum number of particles formed (Nmax) increased strongly with RH for α-pinene and β-pinene (Enhancement Factor, ΔNmax = 1.06 and 0.76, respectively) but not for camphene. Once OH was scavenged, the humid conditions no longer produced higher Nmax compared to the corresponding dry ones. The dry-condition OH-sensitive fractions were 87.5% for α-pinene, 79.9% for β-pinene, and 53.7% for camphene. We then compared these results with literature ozonolysis OH-forming yields for a broader five-terpene set that also includes α-terpinene and γ-terpinene. The comparison shows a useful but limited role for OH yield: compounds with very low OH-forming propensity show little RH enhancement, yet the magnitude of the enhancement is not set by OH yield alone. α-Terpinene, for example, gives the largest ΔNmax response despite an intermediate OH yield, whereas γ-terpinene has a much higher OH yield but a smaller enhancement. We therefore place the RH effect within a structure-dependent OH-sensitive ozonolysis network in which Criegee Intermediate (CI) geometry, radical fate, autoxidation, and precursor concentration all influence whether additional water vapor ultimately produces more new particles.
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BibTeX
@misc{adeoye2026terpene,
title = {{Terpene Structure Governs Humidity-Enhanced New Particle Formation through an OH-Sensitive Ozonolysis Network}},
author = {Tijesuni J. Adeoye and Giuseppe A. Petrucci},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010918/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010918/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Terpene Structure Governs Humidity-Enhanced New Particle Formation through an OH-Sensitive Ozonolysis Network
AU - Tijesuni J. Adeoye
AU - Giuseppe A. Petrucci
PY - 2026
DA - 2026/10/22
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010918/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010918/v1
AB - Relative humidity (RH) impacts new particle formation (NPF) from monoterpene ozonolysis in a non-uniform way. Depending on the precursor, water vapor can either suppress particle formation or increase it, and the chemical origin of that contrast has remained uncertain. Here we use cyclohexane to remove OH and separate the OH-sensitive portion of the particle response from the residual OH-insensitive contribution for α-pinene, β-pinene, and camphene. Experiments were carried out at <0.1% and 60% RH using low monoterpene mixing ratios of 0.5 – 5 ppbv. In the absence of scavenger, the maximum number of particles formed (Nmax) increased strongly with RH for α-pinene and β-pinene (Enhancement Factor, ΔNmax = 1.06 and 0.76, respectively) but not for camphene. Once OH was scavenged, the humid conditions no longer produced higher Nmax compared to the corresponding dry ones. The dry-condition OH-sensitive fractions were 87.5% for α-pinene, 79.9% for β-pinene, and 53.7% for camphene. We then compared these results with literature ozonolysis OH-forming yields for a broader five-terpene set that also includes α-terpinene and γ-terpinene. The comparison shows a useful but limited role for OH yield: compounds with very low OH-forming propensity show little RH enhancement, yet the magnitude of the enhancement is not set by OH yield alone. α-Terpinene, for example, gives the largest ΔNmax response despite an intermediate OH yield, whereas γ-terpinene has a much higher OH yield but a smaller enhancement. We therefore place the RH effect within a structure-dependent OH-sensitive ozonolysis network in which Criegee Intermediate (CI) geometry, radical fate, autoxidation, and precursor concentration all influence whether additional water vapor ultimately produces more new particles.
ER -