Vertical gradient in atmospheric particle phase state: a case study over the alaskan arctic oil fields†

The phase state of atmospheric particles impacts atmospheric processes like heterogeneous reactions, cloud droplet activation, and ice nucleation, influencing Earth's climate. Factors like chemical composition, temperature, and relative humidity govern particle phase states. The Arctic atmosphere is stratified, with varying particle compositions, but vertical profiles of submicron phase states remain poorly understood due to limited aloft measurements. To address this, particle samples were collected via a tethered balloon system (TBS) at the U.S. Department of Energy Atmospheric Radiation Measurement Program's facility at Oliktok Point, Alaska, on November 19, 2020. Using an environmental scanning electron microscope with a tilted Peltier stage to simulate atmospheric conditions, we probed particle phase states, observing near-spherical, dome-like, and flat shapes upon substrate impact. Particles at an altitude of 300 m contained similar, high fractions of viscous particles (79 ± 9%) compared to ground-level (74 ± 5%). Chemical characterization revealed that carbonaceous-rich and carbonaceous sulfate-rich particles dominate ground-level samples, while 300 m samples included more carbonaceous-rich and carbonaceous-coated dust particles. STXM-NEXAFS further highlighted differences in particle mixing states, with a higher abundance of organic and mixed organic–inorganic particles at both altitudes. Integrating chemical composition and phase state measurements demonstrated that carbonaceous-rich and organic-dominated particles exhibited higher viscosities, while inorganic-rich particles displayed lower viscosities. This finding establishes an association between composition and phase state, offering critical insights into the vertical stratification of Arctic particles.