During the SAMUM 2006 field campaign in southern Morocco, physical and chemical properties of desert aerosols were measured. Mass concentrations ranging from 30 μg m−3 for PM2.5 under desert background conditions up to 300 000 μg m−3 for total suspended particles (TSP) during moderate dust storms were measured. TSP dust concentrations are correlated with the local wind speed, whereas PM10 and PM2.5 concentrations are determined by advection from distant sources. Size distributions were measured for particles with diameter between 20 nm and 500 μm (parametrizations are given). Two major regimes of the size spectrum can be distinguished. For particles smaller than 500 nm diameter, the distributions show maxima around 80 nm, widely unaffected of varying meteorological and dust emission conditions. For particles larger than 500 nm, the range of variation may be up to one order of magnitude and up to three orders of magnitude for particles larger than 10 μm. The mineralogical composition of aerosol bulk samples was measured by X‐ray powder diffraction. Major constituents of the aerosol are quartz, potassium feldspar, plagioclase, calcite, hematite and the clay minerals illite, kaolinite and chlorite. A small temporal variability of the bulk mineralogical composition was encountered. The chemical composition of approximately 74 000 particles was determined by electron microscopic single particle analysis. Three size regimes are identified: for smaller than 500 nm in diameter, the aerosol consists of sulphates and mineral dust. For larger than 500 nm up to 50 μm, mineral dust dominates, consisting mainly of silicates, and—to a lesser extent—carbonates and quartz. For diameters larger than 50 μm, approximately half of the particles consist of quartz. Time series of the elemental composition show a moderate temporal variability of the major compounds. Calcium‐dominated particles are enhanced during advection from a prominent dust source in Northern Africa (Chott El Djerid and surroundings). The particle aspect ratio was measured for all analysed particles. Its size dependence reflects that of the chemical composition. For larger than 500 nm particle diameter, a median aspect ratio of 1.6 is measured. Towards smaller particles, it decreases to about 1.3 (parametrizations are given). From the chemical/mineralogical composition, the aerosol complex refractive index was determined for several wavelengths from ultraviolet to near‐infrared. Both real and imaginary parts show lower values for particles smaller than 500 nm in diameter (1.55–2.8 × 10−3i at 530 nm) and slightly higher values for larger particles (1.57–3.7 × 10−3i at 530 nm).

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This paper presents a review of recently acquired knowledge on the physico-chemical properties of mineral dust from Africa and Asia based on data presented and discussed during the Third International Dust Workshop, held in Leipzig (Germany) in September 2008. <br></br> Various regional field experiments have been conducted in the last few years, mostly close to source regions or after short-range transport. Although significant progress has been made in characterising the regional variability of dust properties close to source regions, in particular the mineralogy of iron and the description of particle shape and mixing state, difficulties remain in estimating the range of variability of those properties within one given source region. As consequence, the impact of these parameters on aerosol properties like optical properties, solubility, hygroscopicity, etc. – determining the dust impact on climate – is only partly understood. Long-term datasets in remote regions such as the dust source regions remain a major desideratum. <br></br> Future work should also focus on the evolution of dust properties during transport. In particular, the prediction of the mineral dust size distribution at emission and their evolution during transport should be considered as a high-priority. <br></br> From the methodological point of view, a critical assessment and standardisation of the experimental and analytical techniques is highly recommended. Techniques to characterize the internal state of mixing of dust particles, particularly with organic material, should be further developed

Abstract. Airborne lidar and in-situ measurements of aerosols and trace gases were performed in volcanic ash plumes over Europe between Southern Germany and Iceland with the Falcon aircraft during the eruption period of the Eyjafjalla 1 volcano between 19 April and 18 May 2010. Flight planning and measurement analyses were supported by a refined Meteosat ash product and trajectory model analysis. The volcanic ash plume was observed with lidar directly over the volcano and up to a distance of 2700 km downwind, and up to 120 h plume ages. Aged ash layers were between a few 100 m to 3 km deep, occurred between 1 and 7 km altitude, and were typically 100 to 300 km wide. Particles collected by impactors had diameters up to 20 µm diameter, with size and age dependent composition. Ash mass concentrations were derived from optical particle spectrometers for aCorrespondence to: U. Schumann (ulrich.schumann@dlr.de) 1 Also known as Eyjafjallajökull or Eyjafjöll volcano, http://www.britannica.com/EBchecked/topic/1683937/ Eyjafjallajokull-volcano particle density of 2.6 g cm −3 and various values of the refractive index (RI, real part: 1.59; 3 values for the imaginary part: 0, 0.004 and 0.008). The mass concentrations, effective diameters and related optical properties were compared with ground-based lidar observations. Theoretical considerations of particle sedimentation constrain the particle diameters to those obtained for the lower RI values. The ash mass concentration results have an uncertainty of a factor of two. The maximum ash mass concentration encountered during the 17 flights with 34 ash plume penetrations was below 1 mg m −3 . The Falcon flew in ash clouds up to about 0.8 mg m −3 for a few minutes and in an ash cloud with approximately 0.2 mg m −3 mean-concentration for about one hour without engine damage. The ash plumes were rather dry and correlated with considerable CO and SO 2 increases and O 3 decreases. To first order, ash concentration and SO 2 mixing ratio in the plumes decreased by a factor of two within less than a day. In fresh plumes, the SO 2 and CO concentration increases were correlated with the ash mass concentration. The ash plumes were often visible slantwise as faint dark layers, even for concentrations below 0.1 mg m −3 .Published by Copernicus Publications on behalf of the European Geosciences Union. U. Schumann et al.: Airborne observations of the Eyjafjalla volcano ash cloud over EuropeThe large abundance of volatile Aitken mode particles suggests previous nucleation of sulfuric acid droplets. The effective diameters range between 0.2 and 3 µm with considerable surface and volume contributions from the Aitken and coarse mode aerosol, respectively. The distal ash mass flux on 2 May was of the order of 500 (240-1600) kg s −1 . The volcano induced about 10 (2.5-50) Tg of distal ash mass and about 3 (0.6-23) Tg of SO 2 during the whole eruption period. The results of the Falcon flights were used to support the responsible agencies in their decisions concerning air traffic in the presence of v...

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