Size-Resolved Aerosol Composition over the Arctic Reveals Cloud Processed Aerosol In-Cloud and above Cloud

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

     Abstract Number: 442
     Working Group: Aerosols, Clouds and Climate

Abstract
Aerosol physicochemical properties have a significant impact on Arctic climate via both aerosol-radiation and aerosol-cloud interactions. Several previous ground-based aerosol measurements indicate the relevance of aerosol composition for Arctic cloud formation. However, the morphology and chemical composition of the aerosols from ground-based measurement might be different from those of the particles at high altitudes due to oxidation and cloud processing, which is poorly understood due to limited observation of size-resolved aerosol chemistry in the cloud. This study investigated the vertical variability of aerosol particle composition in August 2019 using a tethered balloon system (TBS) at the US Department of Energy's Atmospheric Radiation Measurement Program's mobile facility at Oliktok Point, Alaska. This study focused on different cloud layers under two typical conditions, background aerosol and polluted conditions. A total of ~19600 particles from two case studies were characterized using single-particle multimodal micro-spectroscopy techniques. The chemical analysis shows a clear difference in vertical aerosol chemical compositions. The background case indicates a broadening of chemically specific size distribution with a high abundance of sulfate aerosols at the high altitude (1000m, which was above the cloud) with core-shell morphology, suggesting possible cloud processing of particles. The low altitude (500m, in the cloud) aerosol is dominated by carbonaceous aerosol with narrow size distribution. The pollution case also indicates a broadening of size distribution at high altitude (1125m, which was in the cloud) with the dominance of carbonaceous and sulfate coated aerosol particles, whereas the low altitude (725m) particle population is richer in carbonaceous, carbonaceous coated dust particles with narrow size distribution. The broadened carbonaceous aerosol population from high altitude can serve as cloud condensation nuclei and participate in Arctic cloud formation. Findings from this study will improve the understanding of the implication of Arctic aerosol physicochemical properties on Arctic cloud formation and radiative properties.