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

Abstract

Ice-nucleating particles (INPs) impact global climate by altering cloud formation and properties. The ability of aerosol particles to nucleate ice is in part determined by particle composition. Here, we demonstrate that the addition of common fluorinated pollutants to seawater can enhance the ice nucleation activity of resulting simulated sea spray particles, although we note that ambient sea spray will have additional organic components not considered here. We quantified the ice supersaturation at the onset of ice nucleation, fractional INP activation, and ice nucleation active site density for inorganic sea salt, assemblages of per- and poly-fluorinated alkyl substances (PFASs), and internally mixed particles. Particles composed solely of PFASs or sea salt mixed with PFASs nucleated ice heterogeneously in a temperature (−50 ≤ T ≤ −40 °C) and ice supersaturation (1.0 ≤ S ice ≤ 1.5) range relevant to cirrus cloud formation. Conversely, the temperature and relative humidity trajectories considered here precluded heterogeneous ice nucleation of particles composed solely of inorganic sea salt. Our active site density calculations indicate that PFAS-containing sea salt aerosol exhibits ice nucleation activities similar to other effective INPs. Since the PFAS concentrations in our aerosolized solutions were similar to those observed in the ocean, our findings indicate that the addition of anthropogenic pollutants such as PFASs to seawater may enhance the ice-nucleating abilities of sea spray aerosols in the cirrus cloud regime. Further studies should investigate the interactions of PFASs with other marine organic matter to ascertain the impacts of particle composition on ambient sea spray’s ice nucleation activity.

PFAS on atmospheric aerosol particles: a review

“…45 Recent evidence even suggests that PFAS may enhance ice nucleation by aerosol particles. 46,47 However, relatively few studies have explored impacts of PFAS on cloud formation through either CCN or ice nucleating particles.…”

Aerosol Composition, Mixing State, and Phase State of Free Tropospheric Particles and Their Role in Ice Cloud Formation

“…In particular, organic matter is a common type of aerosol found in the atmosphere, but its effect on IN is poorly understood because its abundance in INPs has been confirmed only using advanced analytical techniques . The reduction of INP activity is believed to be caused by reducing the availability of IN active sites or changing the water activity of the core particle. − Conversely, some coating materials are found to enhance IN activity. , For example, several studies reported the significant potential of organic aerosol to act as INPs, although not as efficiently as mineral dust particles. ,,− The ubiquity of organic matter in a photochemically active environment affects the IN properties of aerosol by influencing their phase state (liquid to solid) and morphology. ,− The phase of organic aerosol affects the IN activity and the pathway to form ice. It is widely accepted that INPs contain insoluble and/or solid substrates that aid in the formation of ice crystals .…”

Emerging investigator series: surfactants, films, and coatings on atmospheric aerosol particles: a review

“…For example, surface-active per- and polyfluoroalkyl substances (PFAS) 293 likely affect ice nucleation of aerosol particles. 294 Interestingly, PFOA (perfluorooctanoic acid, a C8 carboxylic acid) can nucleate freezing at −16 °C, but PFOS (perfluorooctane sulfonic acid, a C8 sulfonic acid) is ineffective due to the bulky, disordered sulfonate head groups. 295 Furthermore, pH matters: neutral PFOA allows for ice nucleation, but anionic PFOA does not.…”