Saharan dust in the Finnish atmosphere and on the ground: Citizen science to verify transport and deposition modeling

Long-range transported mineral dust has a wide range of direct and indirect effects as a pollutant, nutrient and climate-forcer.On 2123 February 2021, dust from a sand and dust storm in northern Africa was transported to Finland, north of 60N. The episode was predicted 5 days in advance by the global operational SILAM forecast (silam.fmi.fi). The scavenging of dust by snowfall and freezing rain in Finland resulted in a rare case of substantial mineral dust contamination of snow surfaces over a large area in the southern part of the country. A citizen science campaign was set up to collect contaminated snow samples prepared according to the scientists instructions. The campaign gained wide national interest in television, radio, newspapers and social media, and dust samples were received from 525 locations in Finland, up to 64.3N. The samples were utilised in investigating the ability of an atmospheric dispersion model to simulate the dust episode. The magnetic properties and mineralogy of the particles combined with modeling confirmed that dust came from a wide Sahara and Sahel area from 5000 km away. The modeled deposition area agreed well with the citizen observations and measured particle size distributions. Overall, our results revealed the features of this rare event and demonstrate how deposition samples can be used to evaluate the skills and limitations of current atmospheric models. Previously, a strong Saharan dust deposition in Finland has been documented for northern Finland in 1991. It is estimated that Saharan dust reaches Finland every year, but most often the dust remains in the atmosphere and deposits on the ground only seldom in Finland.ReferencesMeinander, O., Kouznetsov, R., Uppstu, A.et al.African dust transport and deposition modelling verified through a citizen science campaign in Finland.Sci Rep13, 21379 (2023). https://doi.org/10.1038/s41598-023-46321-7