Micro-spectroscopic and freezing characterization of ice-nucleating particles collected in the marine boundary layer in the eastern North Atlantic

Abstract

Abstract. Formation of atmospheric ice plays a crucial role in the microphysical evolution of mixed-phase and cirrus clouds and thus climate. How aerosol particles impact ice crystal formation by acting as ice-nucleating particles (INPs) is a subject of intense research activities. To improve understanding of atmospheric INPs, we examined daytime and nighttime particles collected during the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) field campaign conducted in summer 2017. Collected particles, representative of a remote marine environment, were investigated for their propensity to serve as INPs in the immersion freezing (IMF) and deposition ice nucleation (DIN) modes. The particle population was characterized by chemical imaging techniques such as computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM/EDX) and scanning transmission X-ray microscopy with near-edge X-ray absorption fine-structure spectroscopy (STXM/NEXAFS). Four major particle-type classes were identified where internally mixed inorganic–organic particles make up the majority of the analyzed particles. Following ice nucleation experiments, individual INPs were identified and characterized by SEM/EDX. The identified INP types belong to the major particle-type classes consisting of fresh sea salt with organics or processed sea salt containing dust and sulfur with organics. Ice nucleation experiments show IMF events at temperatures as low as 231 K, including the subsaturated regime. DIN events were observed at lower temperatures of 210 to 231 K. IMF and DIN observations were analyzed with regard to activated INP fraction, ice-nucleation active site (INAS) densities, and a water activity-based immersion freezing model (ABIFM) yielding heterogeneous ice nucleation rate coefficients. Observed IMF and DIN events of ice formation and corresponding derived freezing rates demonstrate that the marine boundary layer aerosol particles can serve as INPs under typical mixed-phase and cirrus cloud conditions. The derived IMF and DIN parameterizations allow for implementation in cloud and climate models to evaluate predictive effects of atmospheric ice crystal formation.

Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubility

“…It is considered that the internal mixing of mineral dust and sea salt is formed by cloud processes (Niimura et al, 1998;Formenti et al, 2011). A recent study found internal mixing particles between aged sea salt, mineral dust, S, and OCs in submicron aerosols collected from the North Atlantic Ocean, of which OCs species were similar to those in SSA (Knopf et al, 2022). This result is similar to the microscopic observation results (Figs.…”

“…Similar internal mixing particles between mineral dust and SSA have been found not only in the Pacific Ocean, but also in other regions (Okada et al, 1990;Niimura et al, 1998;Wagner et al, 2008;Kandler et al, 2017;Adachi et al, 2020;Kwak et al, 2022;Knopf et al, 2022). It is considered that the internal mixing of mineral dust and sea salt is formed by cloud processes (Niimura et al, 1998;Formenti et al, 2011).…”

Ice-nucleating agents in sea spray aerosol identified and quantified with a holistic multimodal freezing model

“…Shadings with and without a dashed outline indicate freezing data from a MART or an LBWC, respectively. Previous J het measurements and uncertainty for IMF of particles stemming from a marine environment from Knopf et al ( 45 ) and Cornwell et al ( 60 ) are shown as the gray circles and diamonds, respectively. ( B ) Predicted number concentration of INPs, [INP], derived from the SFM compared with measured [INP] from previous CFDC, IS, and MOUDI-DFT experiments ( 12 ).…”

“…They observed a small fraction of ice crystal residuals classified as SSA particles, containing elevated concentrations of marine biogenic markers. Knopf et al ( 45 ) examined particles collected in the marine boundary layer in the eastern north Atlantic for their ability to induce IMF and DIN. INPs were identified by SEM with energy-dispersive analysis of x-rays (SEM/EDX), showing particles associated with sea salt and OM.…”

An automated size and time-resolved aerosol collector platform integrated with environmental sensors to study the vertical profile of aerosols

“…For example, collected samples can be utilized for offline analysis of phase state (55), phase separations (56), and morphology and mixing state of particles (57)(58)(59), and evaluate their size-resolved chemical composition (60). Particles collected on TEM grids can be probed to study hygroscopic behavior (61,62), and particles collected on Silicon nitride substrates can be utilized for ice nucleation studies (60,63). Furthermore, particles collected on lacey TEM grids will facilitate studies of optical properties (light absorption and scattering) of electron beam-resistant spherical particles using electron energy loss spectroscopy (64).…”