An Arctic climatology of particle number size distributions and cloud condensation nuclei during warm and moist intrusions

Abstract Recent studies indicate that warm and moist intrusions are significant sources of aerosols in the Arctic. Yet their contribution to different aerosol particle size modes, cloud condensation nuclei (CCN), and droplet number concentrations ( N d ) remains largely unconstrained. Here, we use long-term aerosol observations from five Arctic observatories and show that intrusions are a major driver of CCN perturbations, particularly in summer, significantly increasing accumulation mode particle, CCN and N d number concentrations at all sites. In winter and spring, intrusions decrease concentrations at sites near 0° longitude (Zeppelin, Villum, Alert) but increase them at sites near 180° (Tiksi, Utqiaġvik/Barrow). These contrasting patterns reflect the interplay between emission sources and wet scavenging along air mass trajectories. Our findings highlight that intrusions have a strong impact on Arctic aerosol and cloud properties and are a key component of the Arctic climate system.