Ice nucleation ability of Ammonium Sulfate aerosol particles internally mixed with Secondary Organics

Abstract

Abstract. The abundance of aerosol particles and their ability to catalyze ice nucleation are key parameters to correctly understand and describe the aerosol indirect effect on the climate. Cirrus clouds strongly influence the Earth's radiative budget, but their effect is highly sensitive to their formation mechanism, which is still poorly understood. Sulfate and organics are among the most abundant aerosol components in the troposphere and have also been found in cirrus ice crystal residuals. Most of the studies on ice nucleation at cirrus cloud conditions looked at either purely inorganic or purely organic particles. However, particles in the atmosphere are mostly found as internal mixtures, the ice nucleation ability of which is not yet fully characterized. In this study, we investigated the ice nucleation ability of internally mixed particles composed of crystalline ammonium sulfate (AS) and secondary organic material (SOM) at temperatures between −50 °C and −65 °C. The SOM was generated from the ozonolysis of α-pinene. The experiments were conducted in a large cloud chamber, which also allowed to simulate various aging processes that the particles may experience during their transport in the atmosphere, like cloud cycling and redistribution of the organic matter. We found that the ice nucleation ability of the mixed AS/SOM particles is strongly dependent on the particle morphology. If the organic matter is evenly distributed around the AS crystals in a core-shell morphology, small organic mass fractions of 5–8 wt% are sufficient to completely mask the heterogeneous ice nucleation ability of the inorganic core. In this case, the ice nucleation onset increased from a saturation ratio with respect to ice Sice ~ 1.30 for the pure AS crystals to ≥ 1.45 for the SOM-coated AS crystals. However, if such SOM-coated AS crystals are subjected to the mentioned aging processes, they show an improved ice nucleation ability with the ice nucleation onset at Sice ~ 1.35. We suggest that the aging processes change the particle morphology. The organic matter might redistribute on the surface to form a partially engulfed structure, where the ice-active sites of the AS crystals are no longer completely masked by the organic coating, or the morphology of the organic coating layer might transform from a compact to a porous structure. Our results underline the complexity to represent the ice nucleation ability of internally mixed particles in cloud models. They also demonstrate the need to further investigate the impact of atmospheric aging and cloud processing on the morphology and related ice nucleation ability of internally mixed particles.

Enhanced Ice Nucleation of Simulated Sea Salt Particles with the Addition of Anthropogenic Per- and Polyfluoroalkyl Substances

“…They found that the critical S ice of compositionally-mixed particles fell between that of ammonium sulfate and α-pinenederived SOA. More recently, Bertozzi et al 92 have demonstrated that SOA coatings can both enhance and decrease the ice nucleation abilities of ammonium sulfate particles, depending on the composition and aging state of the SOA material.…”

Influence of the Neutralization Degree on the Ice Nucleation Ability of Ammoniated Sulfate Particles

“…The first was a stationary instrument permanently installed at the AIDA facility, called INKA (Ice Nucleation Chamber of the Karlsruhe Institute of Technology) (DeMott et al., 2018; Schiebel, 2017; Wagner et al., 2020). The second was a mobile version of INKA, called mINKA, which was developed for experiments in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at CERN (Bertozzi, 2021; M. Wang et al., 2022), but was also available for this study. Both INKA and mINKA are CFDCs with vertical cylindrical geometry (Rogers, 1988).…”

“…mINKA has shorter cylinder walls (85 cm) than INKA, but is operated without an evaporation section to maximize the residence time of the particles in the diffusion section where nucleation and growth of the ice crystals can take place. Further technical details and a thorough comparison of the performance of the two CFDCs for different types of aerosol particles are given in Bertozzi (2021). Both instruments were operated in the “humidity scan mode,” where the temperature experienced by the aerosol particles was kept constant and RH was increased from ice‐saturated to water‐saturated conditions at an average dS ice /dt rate of about 0.03 min −1 .…”

Ice nucleation on surrogates of boreal forest SOA particles: effect of water content and oxidative age

“…Heterogeneous ice formation by ice-nucleating particles (INPs) allows for the formation of cirrus clouds at lower humidity than required for ice formation by homogeneous freezing of solution droplets, which is determined by the water activity criterion (Koop et al, 2000). Typical cirrus cloud INPs are water-insoluble particles such as mineral dusts, fly ash, metallic particles (DeMott et al, 2003;Cziczo et al, 2013) or soot (Bond et al, 2013). Prompted by the realization that secondary organic aerosol (SOA) particles can exist in a highly viscous, (semi-)solid state (Zobrist et al, 2008;Virtanen et al, 2010), the possibility that SOA particles could act as INPs has been investigated in recent years (Möhler et al, 2008;Prenni et al, 2009;Wang et al, 2012;Ladino et al, 2014;Schill et al, 2014;Ignatius et al, 2016;Charnawskas et al, 2017;Wagner et al, 2017;Bertozzi et al, 2021).…”

“…Typical cirrus cloud INPs are water-insoluble particles such as mineral dusts, fly ash, metallic particles (DeMott et al, 2003;Cziczo et al, 2013) or soot (Bond et al, 2013). Prompted by the realization that secondary organic aerosol (SOA) particles can exist in a highly viscous, (semi-)solid state (Zobrist et al, 2008;Virtanen et al, 2010), the possibility that SOA particles could act as INPs has been investigated in recent years (Möhler et al, 2008;Prenni et al, 2009;Wang et al, 2012;Ladino et al, 2014;Schill et al, 2014;Ignatius et al, 2016;Charnawskas et al, 2017;Wagner et al, 2017;Bertozzi et al, 2021). SOA acting as INPs affect precipitation formation, cloud cover and the cloud albedo.…”