Mass distributions and morphological and chemical characterization of urban aerosols in the continental Balkan area (Belgrade)

This work presents characteristics of atmospheric aerosols of urban central Balkans area, using a size-segregated aerosol sampling method, calculation of mass distributions, SEM/EDX characterization, and ICP/MS analysis. Three types of mass distributions were observed: distribution with a pronounced domination of coarse mode, bimodal distribution, and distribution with minimum at 1 μm describing the urban aerosol. SEM/EDX analyses have shown morphological difference and variation in the content of elements in samples. EDX spectra demonstrate that particles generally contain the following elements: Al, Ca, K, Fe, Mg, Ni, K, Si, S. Additionally, the presence of As, Br, Sn, and Zn found in air masses from southeast segment points out the anthropogenic activities most probably from mining activities in southeastern part of Serbia. The ratio Al/Si equivalent to the ratio of desert dust was associated with air masses coming from southeastern and southwestern segments, pointing to influences from North Africa and Middle East desert areas whereas the Al/Si ratio in other samples is significantly lower. In several samples, we found high values of aluminum in the nucleation mode. Samples with low share of crustal elements in the coarse mode are collected when Mediterranean air masses prevailed, while high share in the coarse mode was associated with continental air masses that could be one of the approaches for identification of the aerosol origin. Graphical abstract ᅟ.This work presents characteristics of atmospheric aerosols of urban central Balkans area, using a size-segregated aerosol sampling method, calculation of mass distributions, SEM/EDX characterization, and ICP/MS analysis. Three types of mass distributions were observed: distribution with a pronounced domination of coarse mode, bimodal distribution, and distribution with minimum at 1 mu m describing the urban aerosol. SEM/EDX analyses have shown morphological difference and variation in the content of elements in samples. EDX spectra demonstrate that particles generally contain the following elements: Al, Ca, K, Fe, Mg, Ni, K, Si, S. Additionally, the presence of As, Br, Sn, and Zn found in air masses from southeast segment points out the anthropogenic activities most probably from mining activities in southeastern part of Serbia. The ratio Al/Si equivalent to the ratio of desert dust was associated with air masses coming from southeastern and southwestern segments, pointing to influences from North Africa and Middle East desert areas whereas the Al/Si ratio in other samples is significantly lower. In several samples, we found high values of aluminum in the nucleation mode. Samples with low share of crustal elements in the coarse mode are collected when Mediterranean air masses prevailed, while high share in the coarse mode was associated with continental air masses that could be one of the approaches for identification of the aerosol origin

ROBUST ESTIMATION WITH APPLICATION TO HIPPARCOS MINOR PLANET DATA M.L. Bougeard

Forty eight minor planets have been observed by the Hipparcos satellite. Pooling their precise position may allow to investigate a possible rotation between the dynamical reference frame and the ICRSHipparcos Reference system. Due to the repartition of the observations, ill-conditioning of the global system and outliers simultaneously occur. So, a direct least-squares fit is potentially misleading and we resort to the use of robust statistical alternatives. While it is now clear that no single robust regression is best, the L1 and Huber-M estimators are currently attracting attention under the occurence of contaminated Gaussian errors. Here, we present new algorithms based on the Spingarn Partial Inverse proximal decomposition method for L1 and HuberM estimation that take into account both primal and dual aspects of the optimization problem. The result is a family of highly parallel algorithms attractive for large scale problems. Implemented on the Connection Machine CM5, their comput..

Influence of the relative humidity on film formation by vapor induced phase separation

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Role of the fungus-growing termite Pseudacanthotermes spiniger (Isoptera, Macrotermitinae) in the dynamic of clay and soil organic matter content. An experimental analysis

This work focuses on the interactions between fungus-growing termites (Isoptera, Macrotermitinae), clay particles and soil organic matter (SOM). As major bioturbators in tropical ecosystems, termites create biogenic structures (galleries, sheetings, nests, mounds, fungus-comb chambers) that strongly influence the physical and chemical properties of soils. Different kinds of substrates were given to Pseudacanthotermes spiniger, one of the main famous Macrotermitinae termite species in West Africa: (i) clay (mainly illite), (ii) a mix of sand and clay, or (iii) sand. When we proposed both clay and sand, we observed a high selection of clay by termites. Observation of the properties of biogenic structures by Xray analysis showed that illite contained in the sheetings was strongly modified when compared to the bulk soil. We argue that the tennite's saliva and/or the action of stimulated associate microorganisms have extracted un-exchangeable potassium, then leading to the creation of smectite layers. Thus, the termites P spiniger, thanks to their building activity, can be seen as weathering agents of clay minerals. SOM content of the biogenic structures was found to be highly variable depending on the type of soil used (clay vs. sand) with enriched or impoverished C and N contents. Finally, we discuss how the auto-ecological requirements of termites (the balance between the cost of organic matter incorporation and the stability of the rehandled substrates) can affect soil and ecosystem functioning

Inter-annual variability of southerly winds in a coastal area of the Atacama Desert: implications for the export of aeolian sediments to the adjacent marine environment

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A simple model accounting for the uptake, transport, and deposition of wind-eroded mineral particles in the hyperarid coastal Atacama Desert of northern Chile

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Inter-annual variability of southerly winds in a coastal area of the Atacama Desert : implications for the export of aeolian sediments to the adjacent marine environment

The analysis of the aeolian content of marine cores collected off the coast of the Atacama Desert (Mejillones Bay, Chile) suggests that marine sediments can record inter-annual to inter-decadal variations in the regional southerly winds responsible for particle entrainment at the surface of the nearby desert. However, the establishment of a simple and direct correlation between the sediment and wind records is complicated by the difference of time scales between the erosion and accumulation processes. The aim of this work is to: (i) assess the inter-annual variability of the surface winds responsible for the sand movements; and (ii) determine whether the integration over periods of several months completely smoothes the rapid changes in characteristics of the transported and deposited aeolian material. To accomplish this aim, 14 years of 10 m hourly wind speed, measured at the Cerro Moreno (Antofagasta) Airport between 1991 and 2003 and at the Orica Station between 2000 and 2004, were analyzed. For each year, the wind speed statistical distribution can be represented by a combination of two to three Weibull functions. Winds of the lowest Weibull mode are too weak to move the sand grains at the surface of the pampa; this is not the case for the intermediate mode and especially for the highest speed mode which are able to erode the arid surface and transport particles to the bay. In each individual year of the period of study, the highest speed mode only accounted for a limited number of strong erosion events. Quantitative analysis of the distribution of the friction velocities and of their impact on erosion using a saltation model suggests that, although all wind speeds above threshold produce erosion events, values around 0.45 m sec-1 contribute less to the erosion flux. This gap allows separation of the erosion events into low and high saltation modes. The correlation (r = 0.997) between the importance of the third Weibull mode and the extent of higher rate saltation indicates that the inter-annual variability of the erosion at the surface of the pampa, as well as the transport of coarse particles (>100 mu m), are directly related to inter-annual variations in the prevalence of the strongest winds. Finally, a transport and deposition model is used to assess the possible impact of the wind inter-annual variability on the deposition flux of mineral particles in the bay. The results suggest that inter-annual differences in the wind speed distributions have a quantifiable effect on the intensity and size-distribution of this deposition flux. This observation suggests that a detailed analysis of the sediment cores collected from the bay could be used for reconstructing the inter-annual variability of past winds