_____________________________________________________________________________________________________________________________ The Arctic is warming rapidly – faster than the rest of the world. A number of processes have been proposed for this so-called Arctic polar amplification. While sea ice is known to play an important role on reflecting solar radiation and altering the Earth’s surface temperature, the roles of other processes are difficult to quantify. Especially, contributions from atmospheric mechanisms associated with ice-nucleating particles (INP; a few in a million aerosol particles below -20 °C) and ice-involved clouds remain uncertain in the Arctic. This project aims to fill the gap by investigating the sources (natural/manmade), atmospheric abundance/budget, chemical composition and physical properties of INPs in the Atlantic sector of the Arctic. Moreover, the large measurement uncertainties in number concentrations, chemical composition and sources of INPs are problematic for modeling real-life phenomena. This research targets minimizing the measurement uncertainties and addresses this critical deficiency through a series of studies that involve direct collection of ice-nucleating particles and their residuals. To characterize Arctic ice-nucleating particles, a novel portable ice nucleation experiment chamber and a cold stage-supported droplet freezing assay will be used to obtain freezing temperature spectra of airborne particle samples. A new inertial ice