Experimental Determination of the Relationship Between Organic Aerosol Viscosity and Ice Nucleation at Upper Free Tropospheric Conditions. Issue 16 (12th August 2022)

• Record Type: Journal Article
• Authors: Kasparoglu, Sabin; Perkins, Russell; Ziemann, Paul J.; DeMott, Paul J.; Kreidenweis, Sonia M.; Finewax, Zachary; Deming, Benjamin L.; DeVault, Marla P.; Petters, Markus D.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 16(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-12
• Subjects: organic aerosol -- ice nucleation -- aerosol phase state -- aerosol viscosity; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2021JD036296
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: This work presents measurements of the ice nucleating ability of secondary organic material recorded between −40 and −70°C and relative humidity with respect to ice (RHice ) between 150% and 220%. For a subset of systems, temperature and humidity dependence of particle viscosity as well as dry glass transition temperature were characterized using the dual tandem differential mobility analyzer method. Eleven unique monoterpene, sesquiterpene and aromatic precursors were used to generate secondary organic material (SOM) using either an oxidation flow reactor (OFR) or an environmental chamber (EC). For the SOM for which viscosity was measured, the particle glass transition temperatures varied between 6 and 23°C ( n = 8). Measurements were performed to verify that increased relative humidity did not plasticize the particles below −10°C at residence times similar to those in the ice nucleation instrument. No heterogeneous ice nucleation was observed at the ∼0.5% onset threshold for any of the materials generated. The ice nucleation occurs by the freezing of SOM solution droplets consistent with homogeneous freezing indicating that they form an aqueous solution, or the SOM particles required water saturation to freeze, indicating that they were hydrophobic. Experiments exploring the influence of functional groups and mass loading did not reveal any obvious influence of particle chemistry or generation conditions on the results. Close structural matches between known organic ice nucleating particles as precursor or formed products did not yield materials that promoted freezing. These experiments suggest that heterogeneous ice formation of glassy secondary organic materials is likely uncommon under upper free tropospheric conditions. Key Points: Glass transition of terpene‐derived secondary organic material ranges between 6 and 23°C. Carene‐derived aerosol did not plasticize below −10°C at 120 s residence time No heterogeneous ice nucleation was observed for secondary organic material generated from terpene and aromatic precursors The presence of ONO2 moieties or of close structural matches between known organic ice nucleating particles and products did not promote freezing