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- ItemParticle characterization at the Cape Verde atmospheric observatory during the 2007 RHaMBLe intensive(München : European Geopyhsical Union, 2010) Müller, K.; Lehmann, S.; van Pinxteren, D.; Gnauk, T.; Niedermeier, N.; Wiedensohler, A.; Herrmann, H.The chemical characterization of filter high volume (HV) and Berner impactor (BI) samples PM during RHaMBLe (Reactive Halogens in the Marine Boundary Layer) 2007 shows that the Cape Verde aerosol particles are mainly composed of sea salt, mineral dust and associated water. Minor components are nss-salts, OC and EC. The influence from the African continent on the aerosol constitution was generally small but air masses which came from south-western Europe crossing the Canary Islands transported dust to the sampling site together with other loadings. The mean mass concentration was determined for PM10 to 17 μg/m3 from impactor samples and to 24.2 μg/m3 from HV filter samples. Non sea salt (nss) components of PM were found in the submicron fractions and nitrate in the coarse mode fraction. Bromide was found in all samples with much depleted concentrations in the range 1–8 ng/m3 compared to fresh sea salt aerosol indicating intense atmospheric halogen chemistry. Loss of bromide by ozone reaction during long sampling time is supposed and resulted totally in 82±12% in coarse mode impactor samples and in filter samples in 88±6% bromide deficits. A chloride deficit was determined to 8% and 1% for the coarse mode particles (3.5–10 μm; 1.2–3.5 μm) and to 21% for filter samples. During 14 May with high mineral dust loads also the maximum of OC (1.71μg/m3) and EC (1.25 μg/m3) was measured. The minimum of TC (0.25 μg/m3) was detected during the period 25 to 27 May when pure marine air masses arrived. The concentrations of carbonaceous material decrease with increasing particle size from 60% for the ultra fine particles to 2.5% in coarse mode PM. Total iron (dust vs. non-dust: 0.53 vs. 0.06 μg m3), calcium (0.22 vs. 0.03 μg m3) and potassium (0.33 vs. 0.02 μg m3) were found as good indicators for dust periods because of their heavily increased concentration in the 1.2 to 3.5 μm fraction as compared to their concentration during the non-dust periods. For the organic constituents, oxalate (78–151 ng/m3) and methanesulfonic acid (MSA, 25–100 ng/m3) are the major compounds identified. A good correlation between nss-sulphate and MSA was found for the majority of days indicating active DMS chemistry and low anthropogenic influences.
- ItemSpectral absorption coefficients and imaginary parts of refractive indices of Saharan dust during SAMUM-1(Milton Park : Taylor & Francis, 2017) Müller, T.; Schladitz, A.; Massling, A.; Kaaden, N.; Kandler, K.; Wiedensohler, A.During the SAMUM-1 experiment, absorption coefficients and imaginary parts of refractive indices of mineral dust particles were investigated in southern Morocco. Main absorbing constituents of airborne samples were identified to be iron oxide and soot. Spectral absorption coefficients were measured using a spectral optical absorption photometer (SOAP) in the wavelength range from 300 to 800 nm with a resolution of 50 nm. A new method that accounts for a loading-dependent correction of fibre filter based absorption photometers, was developed. The imaginary part of the refractive index was determined using Mie calculations from 350 to 800 nm. The spectral absorption coefficient allowed a separation between dust and soot absorption. A correlation analysis showed that the dust absorption coefficient is correlated (R2 up to 0.55) with the particle number concentration for particle diameters larger than 0.5 μm, whereas the coefficient of determination R2 for smaller particles is below 0.1. Refractive indices were derived for both the total aerosol and a dust aerosol that was corrected for soot absorption. Average imaginary parts of refractive indices of the entire aerosol are 7.4 × 10−3, 3.4 × 10−3 and 2.0 × 10−3 at wavelengths of 450, 550 and 650 nm. After a correction for the soot absorption, imaginary parts of refractive indices are 5.1 × 10−3, 1.6 × 10−3 and 4.5 × 10−4.