Vertical Gradient of Aerosol Phase State over Stratified Alaskan-Arctic

NURUN NAHAR LATA, Zezhen Cheng, Susan Mathai, Darielle Dexheimer, Fan Mei, Swarup China, Pacific Northwest National Laboratory

     Abstract Number: 436
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
Particles’ phase state has a tremendous impact on several atmospheric processes such as heterogeneous reaction, cloud formation, heterogeneous ice nucleation, and secondary aerosol formation, which affects the Earth’s climate. The particles’ phase is governed by the characteristics of the particles (e.g., chemical composition) and atmospheric conditions (e.g., temperature and relative humidity). Due to the spatial and temporal variation of atmospheric conditions, ambient particles can exist in different phase states (e.g., liquid, semi-solid or solid). Additionally, the Arctic atmosphere is stratified, with different aerosol chemical compositions at different layers. However, our knowledge about the vertical profile of phase states is still not sufficient due to the lack of observation. It is essential to study the vertical profile of the phase state of submicron size ambient particles to understand the atmospheric processes over the Arctic.

The aerosol sampling was conducted via the tethered balloon system (TBS) at the U.S. Department of Energy Atmospheric Radiation Measurement Program’s facility at Oliktok Point, Alaska, to probe the vertical profile of the aerosol phase state. The TBS was loaded with an automated Size and Time-resolved Aerosol Collector (STAC) to collect particles at different altitudes for offline chemical analysis. The collected particles were characterized by using multimodal micro-spectroscopy techniques such as computer-controlled scanning electron microscopy with energy-dispersive X-ray spectroscopy scanning transmission X-ray microscopy with near-edge X-ray absorption fine structure spectroscopy. The chemical analysis indicates high altitude particles are dominated by carbonaceous particles and dust whereas low altitude particles are richer in carbonaceous and sulfate. We will probe the phase state of the ambient particles using an Environmental Scanning Electron Microscope (ESEM) with a tilted Peltier stage at atmospheric relevant temperature and relative humidity. Combining the chemical composition and direct observation of the phase state will improve our understanding of the vertical profile of the phase state.