Online single-particle characterization of ice-nucleating particles (INPs) at the High Altitude Research Station Jungfraujoch (3580 m a.s.l.), Switzerland

Abstract. Ice-nucleating particles (INPs) modulate the phase, radiative properties, and lifetime of clouds, yet direct observational evidence linking single aerosol particles to atmospheric ice nucleation (IN) remains challenging because of the low abundance of INPs. We sampled ambient aerosols by coupling an INP counter to a single-particle mass spectrometry (SPMS) via a pumped counter-flow virtual impactor at Jungfraujoch during wintertime. Ice crystal residuals (ICRs) sampled under conditions representative of mixed-phase and cirrus cloud formation and total aerosol sampled directly by the SPMS were chemically characterized. Mineral dust (MD) dominated the ICR population under both cloud regimes despite its minor contribution to ambient aerosol particles by number. Two distinct MD subclasses associated with local construction activities (MD-K/Al/Fe) and transported sources (MD-Ca) were identified. MD-K/Al/Fe contributed substantially to the INP population in the cirrus cloud regime, demonstrating that local anthropogenic activity can influence atmospheric INPs populations. In contrast, sulfate, organics, nitrate, and biomass burning aerosol (BBA) particles contributed only a minor fraction of ICRs despite dominating the ambient aerosol population, indicating low IN activity under the investigated conditions. However, Pb signatures were enriched in BBA ICRs, suggesting enhanced IN activity of Pb-containing BBA particles, whereas no corresponding enrichment was observed for Pb-containing MD-K/Al/Fe particles. Sporadic meteoric particles detected during stratospheric-intrusion events indicate a potential contribution of stratospheric aerosols to tropospheric primary IN. Limited in-cloud observations suggest that natural cloud processing may modify the IN activity of MD-K/Al/Fe and BBA particles.