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Vertical distribution of aerosols in dust storms during the Arctic winter

Abstract : High Latitude Dust (HLD) contributes 5% to the global dust budget, but HLD measurements are sparse. Dust observations from Iceland provide dust aerosol distributions during the Arctic winter for the first time, profiling dust storms as well as clean air conditions. Five winter dust storms were captured during harsh conditions. Mean number concentrations during the non-dust flights were <5 particles cm −3 for the particles 0.2-100 µm in diameter and >40 particles cm −3 during dust storms. A moderate dust storm with >250 particles cm −3 (2 km altitude) was captured on 10 th January 2016 as a result of sediments suspended from glacial outburst flood Skaftahlaup in 2015. Similar concentrations were reported previously in the Saharan air layer. Detected particle sizes were up to 20 µm close to the surface, up to 10 µm at 900 m altitude, up to 5 µm at 5 km altitude, and submicron at altitudes >6 km. Dust sources in the Arctic are active during the winter and produce large amounts of particulate matter dispersed over long distances and high altitudes. HLD contributes to Arctic air pollution and has the potential to influence ice nucleation in mixed-phase clouds and Arctic amplification. The Arctic surface atmosphere has undergone radical changes in past decades resulting in at least two times larger warming (~1.5 °C) than the global mean temperature change. Such Arctic warming, often referred to as Arctic amplification, is attributed to greenhouse gas feedback while short-lived aerosols act as important forcing agents as well 1-4. The most radiation absorbing aerosols known in the Arctic atmosphere are black carbon and dark-coloured dust, but they have been also identified as strong light absorbing impurities when deposited on snow or ice 1,5-11. Although the direct radiative forcing of aerosols in the Arctic atmosphere is estimated to be larger than indirect radiative forcing via snow feedback, early snow cover removal can result in comparatively larger climate effects 12. The seasonality of high aerosol loadings in the Arctic is typically bimodal, with one major peak in late winter/spring and the secondary peak in autumn 3,13. The origin of absorbing particles is mostly attributed to long-range transport from outside of the Arctic. However, within the Arctic region there are large areas where the terrain serves as sources of dust that impact high latitudes 14,15. We refer to these as High Latitude Dust sources (HLD). The first estimates are that all HLD sources cover >500,000 km 2 and contribute to at least 5% of the global dust budget 14. Iceland is the largest Arctic as well as European desert, comprised of volcanic and glacio-volcanic sediments, with high dust event frequency (>135 dust days annually) and year round occurrence 14,16-19. Icelandic volcanic dust can be transported distances over 1000 km and it can affect large Arctic glaciated and sea areas due to its deposition on snow, ice and sea ice 9,17,20-25. Direct aerosol measurements in Iceland have shown high Particulate Matter (PM) mass and number concentrations during dust storms in situ 22,26-28 and on board of the aircraft 29. Snow-dust storms (when dust is mixed with snow during a dust storm or deposited on snow) and some of the most extreme wind erosion events recorded on Earth have been observed and measured in Iceland, the most active HLD source in the Arctic 14,17,28,30,31. Measurement of the vertical distribution of aerosols is crucial for understanding the physical properties of tropospheric Arctic aerosols. However, scientific studies of airborne measurements of aerosol distribution in the Arctic are rare. Reported direct aerosol concentration measurements in vertical atmospheric profiles in the Arctic are limited to spring/summer season and low altitude of atmospheric profile (altitude ~2 km in Laakso et al. 32 , <3 km in Bates et al. 33 , <1 km in Moroni et al. 34 , and ~1 km in Ferrero et al. 35). Winter direct measurements of Arctic aerosol profiles for the whole troposphere column in addition to the presence of the polar vortex are scarce due to
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Pavla Dagsson-Waldhauserova, Jean-Baptiste Renard, Haraldur Olafsson, Damien Vignelles, Gwenaël Berthet, et al.. Vertical distribution of aerosols in dust storms during the Arctic winter. Scientific Reports, Nature Publishing Group, 2019, 9 (1), 11 p. ⟨10.1038/s41598-019-51764-y⟩. ⟨insu-02483471⟩

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