Repeatability of INP activation from the vapor

Abstract

Laboratory generated aerosols and aerosol sampled in a field campaign were studied to assess the repeatability of heterogeneous ice activation processes and verify if the ice nuclei particles maintained their nucleating capability. Experiments were performed using a filter technique, i.e. aerosol particles were sampled on black-gridded cellulose nitrate membrane filters and assessed for ice nucleating particles in a dynamic filter-processing chamber at our ISAC-CNR laboratory. The laboratory investigations used Arizona Test Dust (ATD) generated by nebulizing a suspension of ATD. After nebulization, the wet aerosol in the carrier gas was dried and then sampled on a filter. Aerosol field sampling (size range PM1 and PM10) was carried out in the Arctic (Ny-Ålesund, Svalbard) from 12 to 23 April 2019. The activation processes were repeated twice for each filter at temperatures of −22 °C and −18 °C. For aerosol, ATD runs were performed only in conditions of supersaturation (saturation ratio Sw = 1.02), while for the Arctic aerosol, conditions below saturation were also considered (Sw = 0.96). The experiments showed that approximately 40% of the ATD particles maintain their initial nucleating efficiency, both at T = −22 °C and − 18 °C, and at Sw = 1.02, i.e. in the condensation freezing mode. The percentage of repeatability was higher for ATD with respect to the Artic-sampled aerosol processed in the condensation mode. This may depend on greater particle morphology variation of the mixed organic-inorganic aerosol due to the hydration and dehydration cycle.