Characterization of distinct Arctic Aerosol Accumulation Modes and their Sources

Measurements of aerosol number size distributions (9-915 nm), as well as aerosol chemistry and cloud condensation nuclei (CCN) activity, were undertaken at Villum Research Station, Station Nord (VRS) in North Greenland during a 7 year record (2010-2016). Clustering analysis on daily size distributions identified several k-means SMPS clusters. K-means clusters of accumulation aerosols (with main size modes >100 nm) accounted for 56% of the total aerosol time sampling period (89-91% during February-April, 1-3% during June-August). By air trajectory association, diurnal variation patterns, and relationship to meteorological and pollution variables, three typical accumulation-mode aerosol categories were identified: Haze (32% of the time), Bimodal (14%) and Aged (6%). In brief: (1) Haze accumulation aerosol shows a single mode at 150 nm, peaking in February-April, with highest loadings of sulfate and black carbon concentrations; (2) Aged accumulation aerosol shows a single mode at 213 nm, peaking in September-October and is associated with cloudy and humid weather conditions during autumn; and (3) Accumulation Bimodal aerosol shows two modes at 38 nm and 150 nm, peaking in June-August, with the highest ratio of organics to sulfate concentrations. The three aerosol categories were considered alongside Cloud Condensation Nuclei (CCN) concentrations. We suggest that organic compounds - likely biogenic in nature and responsible for the smaller mode in the Bimodal category - contribute significantly to the CCN activity. It is concluded that - at least during summer - an Aitken mode, biogenic in origin always coexists with an accumulation mode, stressing the importance of better characterizing the marine ecosystem and the aerosol-mediated climate effects in the Arctic.