Abstract
In this work, we analysed aerosol measurements from lidar and PM10 samples around the European Arctic site of Ny-Ålesund during late winter–early spring 2019. Lidar observations above 700 m revealed time-independent values for the aerosol backscatter coefficient (ββ), colour ratio (CR), linear particle depolarisation ratio (δδ) and lidar ratio (LR) from January to April. In contrast to previous years, in 2019 the early springtime backscatter increase in the troposphere, linked to Arctic haze, was not observed. In situ nss-sulphate (nss-SO42−) concentration was measured both at a coastal (Gruvebadet) and a mountain (Zeppelin) station, a few kilometres apart. As we employed different measurement techniques at sites embedded in complex orography, we investigated their agreement. From the lidar perspective, the aerosol load (indicated by ββ) above 700 m changed by less than a factor of 3.5. On the contrary, the daily nss-SO42− concentration erratically changed by a factor of 25 (from 0.1 to 2.5 ng m−3) both at Gruvebadet and Zeppelin station, with the latter mostly lying above the boundary layer. Moreover, daily nss-SO42− concentration was remarkably variable (correlation about 0.7 between the sites), despite its long-range origin. However, on a seasonal average basis the in situ sites agreed very well. Therefore, it can be argued that nss-SO42− advection mainly takes place in the lowest free troposphere, while under complex orography it is mixed downwards by local boundary layer processes. Our study suggests that at Arctic sites with complex orography ground-based aerosol properties show higher temporal variability compared to the free troposphere. This implies that the comparison between remote sensing and in situ observations might be more reasonable on longer time scales, i.e., monthly and seasonal basis even for nearby sites.
Highlights
The Arctic is known to be a meteorologically sensitive region as its near-surface temperature increases at least twice as fast as in the rest of the globe
Regarding the measurements at Zeppelin site, sampling and analytical determination were accomplished by using the methods described in the EMEP Manual v1996 as reported in the EBAS NILU website and data were obtained from the same website
Our observations support the following mechanism: in late winter–early spring aerosol is advected into the Arctic in the lower free troposphere
Summary
The Arctic is known to be a meteorologically sensitive region as its near-surface temperature increases at least twice as fast as in the rest of the globe. While the assessment of Arctic aerosol radiative properties in terms of case studies [7], regional [8] and global [9] models makes progress, a systematic comparison between modelled and quality-assured observational aerosol data is still missing. In a follow-up study (Ferrero et al [30]), aerosol measurements over Gruvebadet (in situ obtained from tethered balloon) and NyÅlesund (lidar-based) were combined. Despite all efforts so far, there are open research questions: Given the mentioned climate change in Spitsbergen, what are long-term changes in properties of Arctic aerosol, both from remote sensing and ground-based in situ perspective? As an aerosol closure in terms of chemical and optical properties typically does not provide a clear match for case studies, how do aerosol properties from two nearby in situ stations and a lidar compare on a seasonal scale?. We thoroughly investigate the effect of hygroscopicity on the derived aerosol properties
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