Abstract
Abstract. Aerosols are an integral part of the Arctic climate system due to their direct interaction with radiation and indirect interaction through cloud formation. Understanding aerosol size distributions and their dynamics is crucial for the ability to predict these climate relevant effects. When of favourable size and composition, both long-range-transported – and locally formed particles – may serve as cloud condensation nuclei (CCN). Small changes of composition or size may have a large impact on the low CCN concentrations currently characteristic of the Arctic environment. We present a cluster analysis of particle size distributions (PSDs; size range 8–500 nm) simultaneously collected from three high Arctic sites during a 3-year period (2013–2015). Two sites are located in the Svalbard archipelago: Zeppelin research station (ZEP; 474 m above ground) and the nearby Gruvebadet Observatory (GRU; about 2 km distance from Zeppelin, 67 m above ground). The third site (Villum Research Station at Station Nord, VRS; 30 m above ground) is 600 km west-northwest of Zeppelin, at the tip of north-eastern Greenland. The GRU site is included in an inter-site comparison for the first time. K-means cluster analysis provided eight specific aerosol categories, further combined into broad PSD classes with similar characteristics, namely pristine low concentrations (12 %–14 % occurrence), new particle formation (16 %–32 %), Aitken (21 %–35 %) and accumulation (20 %–50 %). Confined for longer time periods by consolidated pack sea ice regions, the Greenland site GRU shows PSDs with lower ultrafine-mode aerosol concentrations during summer but higher accumulation-mode aerosol concentrations during winter, relative to the Svalbard sites. By association with chemical composition and cloud condensation nuclei properties, further conclusions can be derived. Three distinct types of accumulation-mode aerosol are observed during winter months. These are associated with sea spray (largest detectable sizes, >400 nm), Arctic haze (main mode at 150 nm) and aged accumulation-mode (main mode at 220 nm) aerosols. In contrast, locally produced particles, most likely of marine biogenic origin, exhibit size distributions dominated by the nucleation and Aitken mode during summer months. The obtained data and analysis point towards future studies, including apportioning the relative contribution of primary and secondary aerosol formation processes and elucidating anthropogenic aerosol dynamics and transport and removal processes across the Greenland Sea. In order to address important research questions in the Arctic on scales beyond a singular station or measurement events, it is imperative to continue strengthening international scientific cooperation.
Highlights
The Arctic is a region sensitive to perturbations of the radiation budget, with complex feedback mechanisms
The average size distributions at ZEP and Villum Research Station at Station Nord (VRS) are broadly similar during the months of January and February (Fig. 2a–b), with low particle number concentrations and a broad accumulation mode, though larger at the ZEP site than at the VRS one
The increased occurrence of new particle formation (NPF) events in May was found to correspond with the increasing concentration of biogenic aerosol in the Svalbard sites (Becagli et al, 2016; Dall’Osto et al, 2017a)
Summary
The Arctic is a region sensitive to perturbations of the radiation budget, with complex feedback mechanisms. In order to improve the ability to estimate direct and indirect climate effects, a better knowledge of aerosols is an essential requisite. This includes aerosol properties and seasonal variability, their sources and the associated atmospheric reactions and transport processes. Tunved et al (2013) subsequently reported a qualitative and quantitative assessment of more than 10 years of aerosol number size distribution data from the same location. They reported that seasonal variation seems to be controlled by both dominant sources as well as meteorological conditions. Additional results from multi-year measurements reported similar conclusions using aerosol number size distributions collected at Tiksi (Asmi et al, 2016), Alert (Croft et al, 2016), Utqiagvik (formerly Barrow; Lathem et al, 2013; Sharma et al, 2006; Polissar et al, 2001) and Villum Research Station at Station Nord (Nguyen et al, 2016)
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