Enhancement of the Heterogeneous Ice Nucleation by the Changing Phase State of Secondary Organic Aerosols
Notice bibliographique
Résumé
Cirrus clouds and their effects on earth’s radiative balance are major sources of uncertainties in predicting future climate. These clouds also dehydrate air ascending to the tropopause, thereby reducing water content in the stratosphere. However, the formation of cirrus clouds is not well understood. Data from field sites and campaigns have shown that organic aerosols (OAs) is a major component of the non-refractory aerosols in the free troposphere where ice cirrus clouds typically form. Measurements by aerosol mass spectrometers in the free troposphere above forests indicate a high mass fraction of these OAs are derived from the atmospheric oxidation of isoprene and other volatile organic compounds (VOCs). Despite their abundance, the effects of these OAs on ice nucleation (IN) is controversial. Previously, these OAs were assumed to be homogeneously mixed liquids, which limits their INabilities. Recent studies have shown that depending on the ambient humidity and temperature, OAs can exist in semi-solid or solid phase states, which can potentially increase INactivity. This laboratory study systematically examines the effects of aerosol-phase state on IN properties of secondary organic aerosols (SOA) produced by the environmental chamber by simultaneously measuring their chemical composition and ice nucleation properties. Selected types of SOA particles were generated by reacting the respective volatile organic compounds (VOCs) with either ozone and/or OH radicals in the MIT environmental chamber and a potential aerosol mass (PAM) oxidation flow reactor. Four kinds of SOA, namely a-pinene SOA, toluene SOA, -caryophyllene SOA, and IEPOX-derived SOA were generated and passed through a temperature control apparatus, where the temperature of the aerosols can be varied between -42°C and 20°C before entering the spectrometer for ice nucleation (SPIN, Droplet Measurement Technologies, Inc.) for determining ice nucleation activity. A scanning mobility particle sizer (SMPS) and an aerosol mass spectrometer (AMS, Aerodyne Inc.) measured the number-diameter distribution and chemical composition of the particles upstream of the SPIN. An optical particle counter downstream of the SPIN measured the optical signatures of the ice particles and some of the large bare organic particles. The SPIN operating temperature was between -38°C and -46°C. Our results show that pre-cooling the aerosol particles to -25 to -42°C enhances the IN onset relative humidity (RH) and the active fraction of IN when compared with non-pre-cooling conditions only for -caryophyllene SOA and IEPOX-derived SOA. Coupled with viscosity and glass transition temperature calculations, we show that the aerosol phase state changes due to the pre-cooling explains this enhancement. By combining the ice nucleation results with chemical analysis of the SOA, our study suggests that the chemical composition influences of these organic aerosols alter the hygroscopicity and the phase state of these organic aerosols, which eventually affects their INproperties. As the phase state of the organic aerosols changes from liquid to semi-solid or solid, their INonset relative humidity decreases, suggesting certain types of SOA (including b-caryophyllene and isoprene SOA) could be potentially important ice nuclei in the free troposphere.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».