Irreversible loss of ice nucleation active sites in mineral dust particles caused by sulphuric acid condensation

Abstract

During the FROST-2 (FReezing Of duST) measurement campaign conducted at the Leipzig Aerosol Cloud Interaction Simulator (LACIS), we investigated changes in the ice nucleation properties of 300 nm Arizona test dust mineral particles following thermochemical processing by varying amounts and combinations of exposure to sulphuric acid vapour, ammonia gas, water vapour, and heat. The processed aerosol's heterogeneous ice nucleation properties were determined in both the water subsaturated and supersaturated humidity regimes at −30 °C and −25 °C using Colorado State University's continuous flow diffusion chamber. The amount of sulphuric acid coating material was estimated by an aerosol mass spectrometer and from CCN-derived hygroscopicity measurements. The condensation of sulphuric acid decreased the dust particles' ice nucleation ability in proportion to the amount of sulphuric acid added. Heating the coated particles in a thermodenuder at 250 °C – intended to evaporate the sulphuric acid coating – reduced their freezing ability even further. We attribute this behaviour to accelerated acid digestion of ice active surface sites by heat. Exposing sulphuric acid coated dust to ammonia gas produced particles with similarly poor freezing potential; however a portion of their ice nucleation ability could be restored after heating in the thermodenuder. In no case did any combination of thermochemical treatments increase the ice nucleation ability of the coated mineral dust particles compared to unprocessed dust. These first measurements of the effect of identical chemical processing of dust particles on their ice nucleation ability in both water subsaturated and mixed-phase supersaturated cloud conditions revealed that ice nucleation was more sensitive to all coating treatments in the water subsaturated regime. The results clearly indicate irreversible impairment of ice nucleation activity in both regimes after condensation of concentrated sulphuric acid. This implies that the sulphuric acid coating caused permanent chemical and/or physical modification of the ice active surface sites; the possible dissolution of the coating during droplet activation did not restore all immersion/condensation-freezing ability

Characterization of Ice‐Nucleating Particles Over Northern India

“…Differences between upwind and downwind were ranging from 0 to 5 L −1 at −16 °C. This has also been observed in laboratory studies using sulphuric acid coatings (Cziczo et al, ; Sullivan, Petters, et al, ) and ozone (Kanji et al, ). Thomson et al (), however, noted an increase in INP activity due to ocean ship emissions.…”

Changes in precipitating snow chemistry with location and elevation in the California Sierra Nevada

“…The low concentrations of soluble Ca 2+ and Mg 2+ was likely a result of less aged or heterogeneously processed dust, particularly during the March sample collection, which would prevent dissolution of insoluble mineral species [ Savoie and Prospero , ; Wang et al ., ]. Cloud processing of the mineral dust can have implications for modulating INP properties of the dust, subsequently impacting its role in ice and precipitation formation processes in Sierra Nevada orographic clouds [ Cziczo et al ., ; Sullivan et al ., , ]. Additionally, Ca 2+ and Mg 2+ were strongly correlated with Cl − and SO 4 2− , indicating that the dust may have been cloud processed with marine air (and inorganic ions from sea salt) during transport or underwent riming during precipitation.…”

“…Several studies have utilized bulk soluble components of precipitation to elucidate sources and atmospheric processing of aerosols involved in precipitation [ Henning et al ., ; Lafreniere and Sinclair , ; Shrestha et al ., ; Sorooshian et al ., ; Xu et al ., ]. However, the primary aerosols that act as ice nucleating particles (INPs)—mineral dust, soot, and primary biological particles—are typically insoluble, irregularly shaped, and relatively large compared to particles that are poor INPs, such as those originating from pollution (i.e., containing sulfate or nitrate) [ Andreae and Rosenfeld , ; Christner et al ., ; Creamean et al ., ; Klein et al ., ; Sullivan et al ., , ]. These effective INPs contain surface sites that enable ice crystal formation at temperatures higher than homogeneous nucleation (−36 °C) [ Pruppacher and Klett , ; Vali et al ., ].…”

The role of time in heterogeneous freezing nucleation

“…Specifically, these experiments use the CFDC or similar techniques [ Welti et al ., ; Niedermeier et al ., ; Sullivan et al ., ], immerse a single dust particle of a known size inside a droplet, and process it through air that is supersaturated with respect to ice. At the outlet of the instrument, an optical particle counter characterizes the fraction of droplets that form ice at a given temperature [ Rogers et al ., ].…”

“…Additionally, data from Sullivan et al . [, ] show an increase in activated fraction at a given temperature for an increase in particle size. There are clear discrepancies in the data that suggest that current experimental uncertainties surrounding the CFDC measurements are too large to either prove or disprove the validity of the moderate size dependence predicted by the model extrapolation of our experimental results.…”