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.

Figure 1

Vertical particle size distributions of the typologies for the flights on 7th November 2013, 28^th January 2015, 9^th January 2016, 10^th January 2016, 12^th January 2016, and 13^th January 2016. Liquid refers to transparent droplets (fog, cloud, liquid marine droplets with salt).

Figure 2

Size distribution for all the flights at an altitude of 3 km.

Figure 3

LOAC speciation index for 10^th January 2016 flight. Left: Inside a volcanic dust layer; right: Above the dust layer, where no identification of the particles can be done, probably because of the presence of various types of aerosols.

Figure 4

MODIS Aqua true-colour satellite images of southern Iceland from 10^th, 12^th and 13^th January 2016 with no cloud obstruction of the dust plumes (marked red). Active dust sources are in italic. Image courtesy of the NASA Worldview (https://worldview.earthdata.nasa.gov/).

Figure 5

CALIPSO cross sections of 532 nm total attenuated backscatter and the vertical feature mask for the overpass of Iceland on 13^th January 2016. LOAC flight marked with red circle. The relationship between the dust column marked with red arrow and the dust plume captured in Fig. 4 is questionable (image from courtesy of the NASA/CALIPSO system, https://www-calipso.larc.nasa.gov/).

Figure 6

Launch of LOAC during strong winds in Hvalfjordur bay, West Iceland, on 12^th January 2016 (Photo by RAX, Ragnar Axelsson).

Figure 7

Particle size distributions at different altitudes for the flights on 7th November 2013, 28^th January 2015, 9^th January 2016, 10^th January 2016, 12^th January 2016, and 13^th January 2016.