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).

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...

Airborne measurements of Lidar backscatter, aerosol concentrations (particle diameters of 4 nm to 50 μm), trace gas mixing ratios (SO₂, CO, O₃, H₂O), single particle properties, and meteorological parameters have been performed in volcanic ash plumes with the Falcon aircraft operated by Deutsches Zentrum für Luft- und Raumfahrt (DLR). A series of 17 flights was performed over Europe between Southern Germany and Iceland during the eruption period of the Eyjafjalla¹ 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. Lidar and in-situ measurements covered plume ages of 7 h to 120 h. 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 concentration was evaluated for a material density of 2.6 g cm^&minus;3 and for either weakly or moderately absorbing coarse mode particles (refractive index 1.59+0<i>i</i> or 1.59+0.004<i>i</i>). In the absorbing case, the ash concentration is about a factor of four larger than in the non-absorbing limit. Because of sedimentation constraints, the smaller results are the more realistic ones for aged plumes. The Falcon flew in ash clouds up to about 1 mg m^&minus;3 for a few minutes and in an ash cloud with more than 0.2 mg m^&minus;3 mean-concentration for about one hour without engine damages. In fresh plumes, the SO₂ concentration was correlated with the ash mass concentration. Typically, 0.5 mg m^&minus;3 ash concentration was related to about 100 nmol mol^&minus;31 SO₂ mixing ratio and 70 nmol mol^&minus;1 CO mixing ratio increases for this volcano period. In aged plumes, layers with enhanced coarse mode particle concentration but without SO₂ enhancements occurred. To first order, ash concentration and SO₂ mixing ratio in the plumes decreased by a factor of two within less than a day. The ash plumes were often visible as faint dark layers even for concentrations below 0.1 mg m^&minus;3. The ozone concentrations and the humidity inside the plumes were often reduced compared to ambient values. The large abundance of volatile Aitken mode particles suggests nucleation of sulfuric acid droplets. Ammonium sulfate particles were also found on the impactors. The effective diameters decreased from about 5 μm in the fresh plume to about 1 μm for plume ...

Abstract.We have retrieved the wavelength-dependent imaginary parts of the complex refractive index for five different Saharan dust aerosol particles of variable mineralogical composition at wavelengths between 305 and 955 nm. The dust particles were generated by dispersing soil samples into a laboratory aerosol chamber, typically yielding particle sizes with mean diameters ranging from 0.3 to 0.4 µm and maximum diameters from 2 to 4 µm. The extinction and absorption coefficients as well as the number size distribution of the dust particles were simultaneously measured by various established techniques. An inversion scheme based on a spheroidal dust model was employed to deduce the refractive indices. The retrieved imaginary parts of the complex refractive index were in the range from 0.003 to 0.005, 0.005 to 0.011, and 0.016 to 0.050 at the wavelengths 955, 505, and 305 nm. The hematite content of the dust particles was determined by electron-microscopical single particle analysis. Hematite volume fractions in the range from 1.1 to 2.7 % were found for the different dusts, a range typical for atmospheric mineral dust. We have performed a sensitivity study to assess how accurately the retrieved imaginary refractive indices could be reproduced by calculations with mixing rule approximations using the experimentally determined hematite contents as input.

A B S T R A C TA large field experiment of the Saharan Mineral Dust Experiment (SAMUM) was performed in Praia, Cape Verde, in January and February 2008. The aerosol at Praia is a superposition of mineral dust, sea-salt, sulphates and soot. Particles smaller than 500 nm are mainly mineral dust, mineral dust-sulphate mixtures, sulphates and soot-sulphate mixtures. Particles larger then 2.5 µm consist of mineral dust, sea-salt and few mineral dust-sulphate mixtures. A transition range exists in between. The major internal mixtures are mineral dust-sulphate and soot-sulphate. Mineral dust-sea-salt mixtures occur occasionally, mineral dust-soot mixtures were not observed. The aspect ratio was 1.3-1.4 for dry particles smaller than 500 nm and 1.6-1.7 for larger ones. Parameterizations are given for dry and humid state. Although the real part of the refractive index showed low variation (1.55-1.58 at 532 nm), a multi-modal imaginary part was detected as function of particle size, reflecting the complex composition. Soot mainly influences the absorption for wavelengths longer than the haematite absorption edge, whereas for shorter wavelengths dust is dominating. The refractive index of the aerosol depends on the source region of the mineral dust and on the presence/absence of a marine component.

Sea spray particles ejected as a result of bubbles bursting from artificial seawater containing salt and organic matter in a stainless steel tank were sampled for size distribution, morphology, and cloud condensation nucleus (CCN) activity. Bubbles were generated either by aeration through a diffuser or by water jet impingement on the seawater surface. Three objectives were addressed in this study. First, CCN activities of NaCl and two types of artificial sea salt containing only inorganic components were measured to establish a baseline for further measurements of mixed organic–inorganic particles. Second, the effect of varying bubble residence time in the bulk seawater solution on particle size and CCN activity was investigated and was found to be insignificant for the organic compounds studied. Finally, CCN activities of particles produced from jet impingement were compared with those produced from diffuser aeration. Analyses indicate a considerable amount of organic enrichment in the jet-produced particles relative to the bulk seawater composition when sodium laurate, an organic surfactant, is present in the seawater. In this case, the production of a thick foam layer during impingement may explain the difference in activation and supports hypotheses that particle production from the two methods of generating bubbles is not equal.

A B S T R A C T During the second Saharan Mineral Dust Experiment (SAMUM-2) field campaign, particles with geometric diameters (d) between ∼0.1 and 25 μm were collected on board of the Deutsches Zentrum für Luft-und Raumfahrt (German Aerospace Center, DLR) Falcon aircraft. Size, chemical composition and mixing state of aerosols sampled (spatially and vertically resolved) along the West African coastline and in the Cape Verde Islands region were determined by electron microscopy. A pronounced layer structure of biomass-burning aerosol and desert dust was present for all days during the sampling period from 23 January to 6 February. The aerosol composition of the small particles (d < 0.5 μm) was highly variable and in cases of biomass burning strongly dominated by soot with up to 90% relative number abundance. Internal mixtures of soot particles with mineral dust were not detected. Soot was only observed to mix with secondary sulphate. The coarse particles (d > 0.5 μm) were dominated by silicates. In the Cape Verde Islands region mineral dust is well mixed. The determination of source regions by elemental or mineralogical composition was generally not possible, except for air masses which were transported over the Gulf of Guinea. The real part of the refractive index showed little variation. In contrast, the imaginary part strongly depended on the abundance of soot (biomass-burning aerosol) and haematite (mineral dust).

No abstract