The A-LIFE aircraft field experiment in the Eastern Mediterranean: what have we learned about mineral dust mixtures?

Mineral dust is a key component of the globally-emitted aerosol mass. Although, mineral dust mixes with anthropogenic pollution during its atmospheric lifetime, data on polluted mineral dust layers have been scarce.

In April 2017, the A-LIFE aircraft field experiment (www.a-life.at) was carried out in the Eastern Mediterranean. A-LIFE combined ground-based, airborne, satellite, and modelling efforts to characterize mineral dust mixtures with unprecedented detail. In 22 research flights (~80 flight hours), outbreaks of Saharan and Arabian dust, as well as pollution, biomass burning, and dust-impacted clouds were studied, and a unique aerosol and cloud data set was collected. Aerosol source apportionment was achieved with the Lagrangian transport and dispersion model FLEXPART version 8.2. Based on FLEXPART model results and aerosol measurements, the observations were classified into 12 aerosol types consisting of four main aerosol types (Saharan dust, Arabian dust, mixtures with and without coarse mode). Each of the four main aerosol types was further separated into three sub-classes (clean, moderately-polluted and polluted). For each of the 12 aerosol classes, microphysical and optical aerosol properties were derived.

For the first time, the effect of pollution on the microphysical and optical properties of Saharan and Arabian dust was investigated systematically, revealing significant changes as a function of pollution content. The particle size distribution changes as a function of pollution content with effective diameters systematically decreasing for increasing pollution content. The collected data also provide new insights into the impact of Saharan and Arabian dust on cloud evolution processes, atmospheric radiation budget, and local meteorology. One outstanding finding of A-LIFE is that scattering properties of polluted dust mixtures do not show the typical dust signature, but rather show a wavelength-dependency of the scattering coefficient which is typical for pollution. This means that optical properties of mineral mixtures are frequently dominated by the pollution.

In this presentation, we will show the results of the A-LIFE project including its mission objectives, experimental design, and meteorological conditions; highlight major A-LIFE findings; and feature the available data products on the optical, microphysical, and hygroscopic properties of pure and polluted mineral dust.