High time resolution mineral dust deposition characterization with respect to particle size, composition and atmospheric ageing at locations relevant for the atmospheric-oceanic dust budget

• Applicant: Professor Dr. Konrad Kandler
• Subject Area: Atmospheric Science ; Oceanography
• Term: from 2015 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 264912134

Wet and dry deposition are the major processes removing mineral dust, one of the major aerosol types, from the atmospheric system. Providing suitable conditions, teragrams of dust per year are transported on intercontinental scales. When mineral dust reaches the earth surface far away from its source, it may significantly influence ecosystems. In particular ocean ecosystems are limited in their productivity by lack of nutrients, which can be supplied by dust. Also, geo-engineering ideas exist by artificial ocean fertilization. Despite of this high impact, measurements of dust deposition are rare and model performance as validated by the few available data sets is poor. Mainly lack of detailed data is currently limiting our understanding of the global dust cycle. Moreover, deficits in dry deposition measurement techniques hamper acquisition of proper data.In the proposed project, a new automated wet and dry deposition sampling system will be developed and thoroughly characterized. The system will collect samples on meteorological relevant time scales (hours to days), overcoming the problem of past deposition measurements, which usually provided time resolution of weeks or months. By using automated scanning electron microscopy for particle analysis, the method will provide data sets of unprecedented detail richness. Data will include particle size distribution, elemental composition, and particle mixing state in the particle size range between 700 nm and 100 µm in diameter. Special attention will be given to the potential nutrients, iron, phosphorus, potassium, magnesium, and calcium. Particle hygroscopicity will be measured for selected samples.After the test phase on Frioul island, where the samplers will be validated with existing time series, three instruments will be deployed on locations relevant for dust input into the ocean: on the island of Sao Vicente, Cape Verde; Barbados, capturing Saharan outflow; and on Heimaey island, Iceland, capturing Arctic dust. A second project phase is planned (after present project), in which the network will be extended to New Island, Falkland, in the South American plume; to at Araoteke, Amakusa island Japan, Asian outflow; and to Amsterdam island, located between the South African west-east and Australian east-west outflow. The project will provide for the first time continuous series of mineral dust wet and dry deposition with daily (dry) or event-based (wet) time resolution and particle size resolution. Atmospheric key factors leading to deposition events will be characterized. We will assess the partitioning of nutrients - in particular of iron and phosphorus - between wet and dry deposition and will determine the according size distributions. Particle mixing state and particle shape will be assessed by mixing models and image analysis. A public database will be provided for model validation. It is planned that the stations will continue operation after the DFG funding phase.

• DFG Programme: Research Grants