Large Summer Contribution of Organic Biogenic Aerosols to Arctic Cloud Condensation Nuclei

Lange, R.; Dall'Osto, M.; Wex, H.; Skov, H.; Massling, A.
Geophysical Research Letters
A k-means cluster analysis of a 5-year aerosol particle size distribution data set from northeast Greenland is combined with measurements of coincident shorter field studies of aerosol equivalent black carbon (eBC) content, hygroscopic growth factor (HGF), and cloud condensation nuclei (CCN) concentrations. This led to five clusters strongly controlled by natural emissions (eBC 8-15 ng/m(3)) and three anthropogenic clusters with larger particle concentrations in the accumulation mode (eBC 29-77 ng/m(3)). The HGF and CCN properties of the eight aerosol clusters differ drastically. Anthropogenic clusters feature high growth factors (1.62-1.81) and low CCN. values (0.10-0.46), while natural clusters show lower HGF (1.38-1.70) but remarkably higher. values (0.35-0.51). Extrapolating the CCN properties on the basis of the cluster analysis to annual timescales suggests that biogenic organic aerosol may drive Arctic aerosol production during summer. Plain Language Summary The variability of the warming Arctic-particularly the decreasing sea ice extent-is likely to boost the control of the ocean on the atmospheric composition. Key factors controlling Arctic aerosol-climate interactions are sources, chemical transformations, and removal mechanisms of aerosols and their precursor gases. However, knowledge on the composition and sources of summer aerosols is insufficient. To tackle this problem, we use an approach where aerosol particle size distributions, aerosol equivalent black carbon, hygroscopic growth factor, and cloud condensation nuclei measurements at Villum Research Station within the period 2012-2016 are synergistically combined. Our results suggest that marine sources of new particle formation and growth dominate summer Arctic background conditions. These aerosols are organic rich in nature. Elevated cloud condensation nuclei concentrations occurred when secondary Arctic biogenic organic aerosols were detected.
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