Main Source Areas Research Articles

Detrital zircon U–Pb ages and whole-rock geochemistry of the Neoproterozoic Paulistana and Santa Filomena complexes, Borborema Province, northeastern Brazil: implications for source area composition, provenance, and tectonic setting

ABSTRACTThe Paulistana and Santa Filomena Complexes are situated in the southern part of the Borborema Province (northeastern Brazil), in the Riacho do Pontal Orogen, and represent meta-volcano-sedimentary sequences. We present compositional variations in the metasedimentary rocks and new U–Pb detrital zircon data. Major and trace elements indicate that the metasedimentary rocks from the Paulistana and Santa Filomena Complexes are composed mostly of immature to mature sediments derived from felsic-intermediate sources with moderate to slightly high chemical weathering. The geochemical signatures of the sediment protoliths for both complexes are characteristic of continental magmatic arc settings with minor contribution from recycled sediment sources. The source area for the Paulistana Complex rocks follow the compositional trend between calc-alkaline granites and granodiorites, whereas the Santa Filomena Complex rocks have a more restricted composition trending to more granodioritic sources. For the Paulistana Complex, two main source ages were identified: (1) Tonian (ca. 950 Ma – sample RPE-58) and Tonian–Stenian (ca. 1.0 Ga – sample RPE-103). These data coupled with geochemical information suggest that the Cariris Velhos arc system was the main source area for the Paulistana Complex. Regarding the Santa Filomena metasedimentary rocks, potential source-areas include: (1) Neoarchaean rocks (~2.6 Ga) represented by the adjacent basement rocks of the Riacho do Pontal Orogen; (2) Rhyacian–Orosirian rocks (2.2–2.0 Ga) of the Riacho do Pontal Orogen and the Pernambuco–Alagoas terrain, which include an augen-gneiss with arc-related geochemical signature; (3) Statherian granites (1.7–1.6 Ga); and (4) Cariris Velhos crust (1000–920 Ma). The metasedimentary rocks of the Paulistana Complex were deposited in a rift stage (ca. 900 Ma), which is related to the break-up of the Rodinia supercontinent. The metasedimentary rocks of the Santa Filomena Complex most probably were deposited in another rift stage (ca. 750–700 Ma) and could be correlatives of the rift formation of the Canindé Domain (Sergipano Orogen).

Chemical composition and source apportionment of PM2.5 – A case study from one year continuous sampling in the Chang-Zhu-Tan urban agglomeration

To understand the characteristics and source of atmospheric PM2.5 in Chang-Zhu-Tan urban agglomeration, PM2.5 samples were simultaneously collected at 11 monitoring sites within three cities of Changsha, Zhuzhou and Xiangtan from September 2013 to August 2014. Spatial and temporal variations of PM2.5 mass concentration and chemical compositions were analyzed based on the average values over the measurement sites in a specific urban area, including a comparison of PM2.5 at urban and urban background sites. Source apportionment was performed by PMF 5.0 (positive matrix factorization) model and potential source area affecting PM2.5 mass concentration was simulated using CWT (concentration-weighted trajectory analysis) analysis. The result showed the seasonal variation of PM2.5 mass concentration followed the order of winter > autumn > spring > summer. The OC/EC ratio in each season and each city were greater than 4.0, secondary inorganic ions accounted for at least 91% of the total water soluble inorganic ion concentration, presenting obvious secondary pollution characteristics. Coal combustion and vehicle emissions were two major sources of PM2.5 in all three cities, which accounted for about 35 percent and nearly 26 percent of contributions respectively. In addition, industrial emission and biomass burning were also significant sources in Changsha, while urban dust and biomass burning were significant sources in Zhuzhou and Xiangtan. Chang-zhu-tan urban agglomeration was the main source area of its PM2.5 and easy to form overlapping pollution areas. Meanwhile, northern neighboring city Yueyang and western bordering region Pingxiang also had a certain transmission influence on the formation of PM2.5.

17 de Marzo (Santa Cruz, Argentina): A new distal source of Pampa del Asador type black obsidian and its implications for understanding hunter-gatherer behavior in Patagonia

Most obsidian artifacts from central and southern Patagonia were made of black obsidian from Pampa del Asador (PDA), an extended secondary source area centered at approximately 47°55′S and 71°08′W. Artifacts of obsidian from PDA have been found >600km to both the northeast and south and along the Atlantic coast 300km to the east of this major source area. Here we report a newly-discovered distal source of PDA-type black obsidian pebbles at 17 de Marzo (17M) located ~170km southeast of the main PDA source area. ICP-MS trace element data confirm that the relatively small (≤48mm) black obsidian pebbles from 17M are chemically similar to the four different types of PDA black obsidian. The dimensions of the pebbles compared to the sizes of PDA obsidian artifacts from archaeological sites in the vicinity of 17M, which date from as early as the late Pleistocene-Holocene transition, indicate that early hunter-gatherers could have used the pebbles from this distal secondary source of PDA obsidian to make tools. The pebbles appear to have been transported by fluvial-glacial processes along an ancient Chico River valley to their present site. 17M is part of the “Patagonian Gravel” deposits, which are widespread along the present Chico River valley suggesting that other distal PDA obsidian pebble sites along the river valley may possibly await discovery. The potential widespread availability of PDA obsidian pebbles along the Chico River drainage valley may help to explain why so many artifacts in this area were made of black PDA obsidian. Results obtained indicate that we can no longer assume that hunter-gatherers obtained raw PDA-type black obsidian only from PDA specific source. Black obsidian may have also been available, perhaps in pockets, over a considerable area east and up to ~170km distant southeast of PDA.

Provenance Signatures Recorded In Transgressive Sandstones of the Upper Cretaceous Iberian Seaway

Abstract: Maximum Mesozoic transgressions flooded many continental areas worldwide, forming a wide and shallow seaway on the Iberian Microplate during the Late Cretaceous. Several siliciclastic and mixed siliciclastic–carbonate units developed along the Iberian Massif (cratonic area) while, at the same time, epeiric carbonate platforms spanned Iberia. These siliciclastic deposits unconformably cover the Variscan basement, as well as the Permian and Triassic deposits. This study focuses on sandstone provenance in central Spain, in a transgressive, relatively quiet tectonic setting with a wide rock variety in the potential source areas. Results shown in this paper can be applied in analogue systems; transgressive sandstones often form important hydrocarbon reservoirs due to their high primary porosity. The Cretaceous siliciclastic deposits are included in four formations ranging in age from the Cenomanian to the early Coniacian. The deposits were initially of fluvial origin, followed by a coastal-tidal setting. Quantitative petrographic analysis of sandstones from these formations reveals compositional variations related to provenance and weathering degree. The oldest formation (Utrillas Fm.) was deposited on a paleorelief surface. Sandstone composition changes from arkosic sandstones in the depressed area (Petrofacies P1a) to younger quartzarenites when sediments were deposited on top of the paleotopographic high (Petrofacies P1b). Quartz grains in both sub-petrofacies are angular to subangular, and the framework is poorly sorted. Intense weathering conditions are deduced for Petrofacies P1b, manifested by grain infiltration, clay coatings, and the absence of plagioclase grains and alteration features on K-feldspars. All these observations have been related to wetter conditions during P1b deposition. Main source areas of the Utrillas Fm were Ordovician metasediments and orthogneisses, Permian volcanic rocks, and Triassic Buntsandstein facies. Petrofacies 2 encompasses the three coastal-tidal formations, constituted mainly by subarkoses generally showing a subangular and poorly sorted framework. The deduced source areas are mainly associated with Variscan granitoids, pre-Ordovician schists and paragneisses, and Ordovician metasediments. Glauconite and carbonate grains support intrabasinal inputs. The low degree of sorting of this petrofacies related to a low-energy sedimentary environment produced lower values of original porosity compared to transgressive sandstone hydrocarbon reservoirs. Also, intrabasinal inputs promoted carbonate cementation and contribute to almost occlude the porosity.

Trajectory-Based Models and Remote Sensing for Biomass Burning Assessment in Bangladesh

ABSTRACTBiomass burning is a major global source of fine primary carbonaceous particles including strongly light absorbing compounds and marker compounds. In a prior study, particulate matter (PM) sampling was conducted during 2010–2012 period at sites in Rajshahi, Dhaka, Khulna, and Chittagong. PM samples were collected using dichotomous samplers in the PM2.5 and PM2.5–10 size fractions. The samples were analyzed for mass, black carbon at 370 nm (UVBC) and 880 nm (BC), Delta-C (UVBC-BC), and elemental compositions with X-ray fluorescence. Source apportionment using PMF was performed to identify and quantify the PM sources. Results showed that biomass burning contributions during winters in Rajshahi were substantially higher than in Dhaka, Khulna, or Chittagong. Agricultural burning areas of the Indo-Gangetic Plain were hypnotized as the primary source region. The present study explores the relationships between the source regions using trajectory ensemble models and determines if transported biomass PM has disproportionately affected air quality in Rajshahi. The probable source locations that were identified included Pakistan, northern India, Nepal, Bangladesh, Northeastern India, and Myanmar. To assess the model results, satellite measurements of fire radiative power (FRP) were calculated based on fire data acquired by the MODerate-resolution Imaging Spectro-radiometer (MODIS) sensor in six defined areas. High fire occurrences from MODIS coincident with the source regions identified in Nepal, Northeastern India and Myanmar in winter. The instantaneous FRP values ranged between 4.4 MW and 2449 MW. The mean winter FRP values for Nepal and Northeastern India were higher than for the other regions with Nepal having the overall highest value. Fire locations with their mean power, NASA Satellite pictures and particles speed along trajectories have been analyzed. In summary, the integrated outcome of the different techniques has identified Northern India and Nepal as the main source area responsible for the increased biomass burning concentration difference at Rajshahi.

Detrital zircon U‐Pb ages and Hf isotopic constraints on the terrigenous sediments of the Western Alps and their paleogeographic implications

AbstractDetrital zircons from Cretaceous micaschist, late Eocene‐earliest Oligocene sandstone and early Oligocene siltstone of the Western Alps fall into three main separable age clusters at 610–540 Ma, 490–430 Ma, and 340–280 Ma that correspond to the Cadomian (Neoproterozoic), Ordovician, and Variscan (Carboniferous) events widespread in western and central Europe. Hf isotopic results indicate that these three magmatic and tectonic episodes did not give rise to significant production of juvenile crust. A distinguishable group of Triassic zircons, around 250–200 Ma which is considered to derive from the Southern Alps, has been detected in the early Oligocene “Schistes à Blocs” formation and the Briançonnais “Flysch Noir”. In contrast, this age group is absent in late Eocene to earliest Oligocene sandstones. In agreement with sedimentological studies, our results show that the main source areas of the Eocene sandstone were probably located in the European continent. The arrival of detritus from the Internal Zone occurred in early Oligocene, coeval with the tectonic rotation from northwestward to westward in the propagation of allochthonous units. Based on previous studies and our new data, we argue that the Briançonnais Zone was likely a paleorelief since the middle Eocene that accounts for the lack of detritus from the Adriatic units. Contemporary sediments were accumulated in the foredeep of the Adriatic plate. From Oligocene time onward, the blockage was cut through after a regional uplifting, and thus, the Internal Zone started to provide detritus into the western flexural basins.

Sediment and Phosphorus Loads from a Stream Draining Agricultural and Forest Lands in Northwest Spain

ABSTRACTTransport of suspended sediment (SS) and phosphorus (P) via surface runoff from soils to surface waters is a major problem of water quality degradation in many European rivers and in other parts of the world. This problem is especially serious during wet periods, which can produce twice the P loads of dry periods. In this study, the SS load and particulate phosphorus (PP) exported from a small catchment located in NW Spain (in which cultivated soils had different degrees of vegetation cover) were analyzed during two rainy periods of February 2006 and February 2007. The SS and PP loads were calculated from the data of discharge, and SS and PP concentrations were measured in water samples collected at the catchment outlet. SS and PP loads were higher in 2006 than in 2007, while there was higher rainfall and stream flow in 2007. Differences in the degree of vegetation cover in the cultivated fields with good connectivity with the stream, which was the main source area of sediment in this catchment, explain the differences in SS and PP loads between the two periods. Soil losses caused during both rainy periods were low (0.02 Mg ha−1); however, they may be detrimental to quality of the stream water due to the P linked to soil particles. PP concentrations were above the critical values of P for eutrophication during the study periods, highlighting the need to take conservation measures to reduce soil erosion and sediment delivery to watercourse.

Very coarse-grained beaches as a response to generalized sea level drops in a complex active tectonic setting: Pleistocene marine terraces at the Cadiz coast, SW Spain

The studied Pleistocene deposits at the Cadiz coast are located on the current intertidal zone or at cliffs parallel to the actual coast (6.50ma.s.l.) from the localities of El Puerto de Santa María to Chiclana. Five sequences of very coarse-grained beaches have been recognized and dated. They unconformably overlie Pliocene units and are formed by clast-supported conglomerate and coarse-grained sandstone. Chronological ages (87Sr/86Sr and AMS 14C analysis) and stratigraphic correlation stand that the oldest marine terrace is the one placed topographically higher and towards the SE of Cadiz city, dated as Early Pleistocene (1.3Ma). After it, the sea retreatment produces subaerial exposure of Sequence 1 and the development of several calcrete profiles and a paleokarst. Subsequent sea-level rises allow the sedimentation of Sequences 2, 3 and 4 during Early-Middle Pleistocene (1 to 0.8Ma) in areas close to Cadiz city, with subaerial exposure recorded at the top of Sequences 3 and 4. During the very Upper Pleistocene, sedimentation of Sequence 5 occurs towards the SE of Cadiz city. Based on the spatial position of Sequence 5 we can conclude that this area constituted a downthrown block during the Latest Pleistocene, in relation to neotectonic processes and diapirism.Sandstone framework (hybrid arenites) reveals that main source areas for these marine terraces include units from the Betic Orogene (Betic external zones -Triassic and Jurassic rocks-and the Gibraltar arc), the Guadalquivir basin passive margin (Iberian Massif), the Guadalquivir foreland basin (marine Miocene and Pliocene record) and local inputs of Pleistocene units. The siliciclastic supplies from sources were mainly constant during the sedimentation of all set of sequences, suggesting maturation processes as reworking and recycling of homogenized sediments during transport. Early diagenetic processes have been identified as carbonate cementation, neomorphism and dissolution, outlining the deduced sea-level fluctuations during deposition of Pleistocene sequences.The marine terraces arrangement and its comparison with regionally adjacent areas allows to deduce that the southern and central Portuguese coast (Iberian Massif) and of the southern and southeastern Spanish coast (Betic Orogene) were predominantly tectonically raising during Pleistocene. However, the Cadiz Gulf coast (formerly Guadalquivir foreland basin) was mainly sinking during the same time interval.

Late Pleistocene and Holocene tephrostratigraphy of interior Alaska and Yukon: Key beds and chronologies over the past 30,000 years

Abstract The Aleutian Arc-Alaska Peninsula and Wrangell volcanic field are the main source areas for tephra deposits found across Alaska and northern Canada, and increasingly, tephra from these eruptions have been found further afield in North America, Greenland, and Europe. However, there have been no broad scale reviews of the Late Pleistocene and Holocene tephrostratigraphy for this region since the 1980s, and this lack of data is hindering progress in identifying these tephra both locally and regionally. To address this gap and the variable quality of associated geochemical and chronological data, we undertake a detailed review of the latest Pleistocene to Holocene tephra found in interior Alaska and Yukon. This paper discusses nineteen tephra that have distributions beyond southwest Alaska and that have the potential to become, or already are, important regional markers. This includes three ‘modern’ events from the 20th century, ten with limited data availability but potentially broad distributions, and six that are widely reported in interior Alaska and Yukon. Each tephra is assessed in terms of chronology, geochemistry and distribution, with new Bayesian age estimates and geochemical data when possible. This includes new major-element geochemical data for Crater Peak 1992, Redoubt 1989–90, and two andesitic tephra from St Michael Island (Tephra D), as well as revised age estimates for Dawson tephra, Oshetna, Hayes set H, Aniakchak CFE II, and the White River Ashes, northern and eastern lobes.

On the energy balance closure and net radiation in complex terrain

In complex, sloping terrain, horizontal measurements of net radiation are not reflective of the radiative energy available for the conductive and convective heat exchange of the underlying surface. Using data from a grassland site on a mountain slope characterised by spatial heterogeneity in inclination and aspect, we tested the hypothesis that a correction of the horizontal net radiation measurements which accounts for the individual footprint contributions of the various surfaces to the measured sensible and latent heat eddy covariance fluxes will yield more realistic slope-parallel net radiation estimates compared to a correction based on the average inclination and aspect of the footprint. Our main result is that both approaches led to clear, but very similar improvements in the phase between available energy and the sum of the latent and sensible heat fluxes. As a consequence the variance in the sum of latent and sensible heat flux explained by available radiation improved by>10%, while energy balance closure improved only slightly. This is shown to be mainly due to the average inclination and aspect corresponding largely with the inclination and aspect of the main flux source area in combination with a limited sensitivity of the slope correction to small angular differences in, particularly, inclination and aspect. We conclude with a discussion of limitations of the present approach and future research directions.

Age, provenance and tectonic setting of the high-grade Jequitinhonha Complex, Araçuaí Orogen, eastern Brazil

ABSTRACT: The Jequitinhonha Complex of the northeastern Araçuaí orogen is an extensive sedimentary unit metamorphosed in the amphibolite-granulite facies transition around 580-545 Ma. The unit consists of Al-rich (kinzigitic) paragneisses with decametric intercalations of graphite gneisses and quartzites, and centimetric to metric lenses of calcsilicate rocks. A new detrital zircon U-Pb age spectrum is reported for a sample of quartzite, and whole-rock geochemical (major and trace elements, 9 samples) and Sm-Nd isotope data (10 samples) for Jequitinhonha Complex paragneiss. Together with published data these show that: (1) the geochemistry of paragneiss samples of the Jequitinhonha Complex are similar to those of passive margin sedimentary protoliths; (2) detrital zircon data yield U-Pb age populations between ca. 0.9 and 2.5 Ga; and (3) Sm-Nd TDM model ages range from 1.6 to 1.8 Ga and εNd(575 Ma) around -7.5. The data reveal a mixture of Cryogenian to Mesoproterozoic rift-related igneous rocks with the Palaeoproterozoic-Archaean basement rocks of the São Francisco-Congo palaeocontinent as the main source areas, and also support the correlation between the Jequitinhonha Complex and the passive margin units of the upper Macaúbas Group, constituting the precursor basin of the orogen. Our results, with the absence of ophiolites in the Jequitinhonha Complex, reinforce the interpretation that the São Francisco-Congo palaeocontinent was not divided to the north of the focused region, suggesting an ensialic termination of a gulf during the Neoproterozoic.

Back-trajectory analysis of African dust outbreaks at a coastal city in southern Spain: Selection of starting heights and assessment of African and concurrent Mediterranean contributions

The present study uses a back-trajectory analysis at multiple heights for better interpretation of the impact of the African dust outbreaks in the coastal Mediterranean city of Málaga (Spain), the southernmost large city in Europe. Throughout a 3-year period, 363 days were identified as dusty days by atmospheric transport models. During these events, PM10, SO2, O3, temperature, AOD and Ångström exponent showed statistically significant differences compared to days with no African dust. It was found that under African dust events, the study site was influenced by Mediterranean air masses at the lowermost heights and by Atlantic advections at high altitudes, while African air masses mostly reached Málaga at intermediate levels. Specifically, the lowest heights at which air masses reached the study site after having resided over Africa are confined into the 1000–2000 m range. The decoupling between the lowest heights and the ones for dust transport may explain the presence of aged air masses at the time of the African outbreak. Additionally, with the aim of studying the influence of the air mass origin and history on air quality, a new procedure based on Principal component analysis (PCA) is proposed to determine which altitudes are best suited as starting points for back-trajectory calculations, as they maximize the differences in residence time over different areas. Its application to Málaga identifies three altitudes (750, 2250 and 4500 m) and a subsequent analysis of back-trajectories for African dust days provided the main source areas over Africa as well as further insight on the Mediterranean contribution.

Isotopic Evidence for Long‐Distance Mammal Procurement, Chaco Canyon, New Mexico, USA

Previous research on the prehistoric communities of Chaco Canyon, New Mexico (ca. A.D. 800–1250) provides evidence of an extensive procurement system of nonlocal food and economic goods. In this paper, we use oxygen and strontium isotope analyses to establish whether animal protein followed a similar pattern. We contextualized our isotopic analyses of the archaeofaunas from recent excavations at Pueblo Bonito with data on modern faunas across an area of approximately 100,000 km2 around the site. Our results show that most archaeological deer, rabbits, and prairie dogs were obtained from >40 km away from Pueblo Bonito with the latter two likely being garden hunted. The Chuska Mountains west of Chaco Canyon and more distant San Juan Mountains to the north were the main source areas. These results closely align with previous results on architectural wood, corn, and other key resources. The importation of small game animals suggests that the local supplies could not meet the needs of the community. Long‐distance meat procurement may have been embedded within a more complex network of ritual‐goods exchange or tribute that helped to offset the transport costs. Resource depletion may have contributed to the eventual abandonment of the region during the Medieval Warm Period.

Geochemistry of fine-grained clastic rocks in the Mesoproterozoic Kawabulake Group: implications for provenance and the tectonic model of the Eastern Tianshan, Xinjiang, NW China

The Mesoproterozoic Kawabulake Group, which is unconformably overlain by the Lower Cambrian Huangshan Formation and conformably overlies the Mesoproterozoic Xingxingxia Group in the Eastern Tianshan area, NW China, is comprised mainly of siltstone, slate, sandstone and phyllite. New geochemical data for the clastic rocks from the Kawabulake Group were investigated to constrain the provenance and weathering history of the source rocks, in order to evaluate the tectonic evolution of the Eastern Tianshan area. Kawabulake Group rocks are compositionally similar to PAAS (average Post-Archean Australian Shale), indicating derivation from a felsic source that is characterized by depletion in some HFSEs such as Nb, Ta and Ti. The Chemical Index of Alteration (CIA) for the sandstone, siltstone and slate samples (CIA = 60 on average) suggests intensely weathered sources. Light REE-enrichment patterns ((La/Yb)CN = 4–20) coupled with negative Eu anomalies (Eu/Eu* between 0.44 and 0.89 with an average of 0.62) are similar to those of PAAS, consistent with cratonic sources. The major and trace element compositions imply a dominantly Precambrian felsic source region with a minor contribution from mafic materials. The Sr–Nd isotopic compositions and the ages of T DM2 (~3.4, 2.5–1.8, 1.2 and 1.0 Ga) are consistent with the evolutionary history of Kuluketage in the northern Tarim, suggesting that the Tarim Craton was the main source area for the Kawabulake Group.

Water sources and mixing in riparian wetlands revealed by tracers and geospatial analysis.

Mixing of waters within riparian zones has been identified as an important influence on runoff generation and water quality. Improved understanding of the controls on the spatial and temporal variability of water sources and how they mix in riparian zones is therefore of both fundamental and applied interest. In this study, we have combined topographic indices derived from a high‐resolution Digital Elevation Model (DEM) with repeated spatially high‐resolution synoptic sampling of multiple tracers to investigate such dynamics of source water mixing. We use geostatistics to estimate concentrations of three different tracers (deuterium, alkalinity, and dissolved organic carbon) across an extended riparian zone in a headwater catchment in NE Scotland, to identify spatial and temporal influences on mixing of source waters. The various biogeochemical tracers and stable isotopes helped constrain the sources of runoff and their temporal dynamics. Results show that spatial variability in all three tracers was evident in all sampling campaigns, but more pronounced in warmer dryer periods. The extent of mixing areas within the riparian area reflected strong hydroclimatic controls and showed large degrees of expansion and contraction that was not strongly related to topographic indices. The integrated approach of using multiple tracers, geospatial statistics, and topographic analysis allowed us to classify three main riparian source areas and mixing zones. This study underlines the importance of the riparian zones for mixing soil water and groundwater and introduces a novel approach how this mixing can be quantified and the effect on the downstream chemistry be assessed.

Variability in Transport Pathways and Source Areas of PM10 in Beijing during 2009-2012

ABSTRACTThe transport pathways and source areas of PM10 in Beijing were examined on the basis of a model-assisted analysis. Computed back trajectories were used to trace the air history. The aim of this work was to study the main source areas of PM10, the variability of transport pathways, and potential source areas in Beijing. The results reveal that the major potential source areas of PM10 in Beijing were Hebei, Shandong, Tianjin, northwest of Inner Mongolia, and Outer Mongolia. The main source areas of PM10 have changed from the northwest to the south and southeast of Beijing during 2009–2012. During the study period, the regional contributions of PM10 from Shandong, Tianjin and Henan increased, whereas those from Inner Mongolia and Mongolia decreased compared with 2003–2009. The northwest airflow is a key factor in extreme pollution episodes. Sand storm partly contributed to the PM10 concentration in fast northwesterly transport paths. PM10 concentrations in winter and spring were higher than autumn and summer. In spring and summer, Beijing was strongly affected by long-range transport. Long-range transport had a weaker effect on PM10 concentrations during autumn and winter. The clustering of back-trajectories and PSCF results indicate the need to reduce PM10 transport from areas surrounding Beijing, particularly from the south of Beijing.

Composition and origin of PM 10 in Cape Verde: Characterization of long-range transport episodes

Abstract A receptor modelling study was performed to identify source categories and their contributions to the PM10 total mass at the Cape Verde archipelago. Trajectory statistical methods were also used to characterize the main atmospheric circulation patterns causing the transport of air masses and to geographically identify the main potential source areas of each PM10 source category. Our findings point out that the variability of the PM10 levels at Cape Verde was prompted by the advections of African mineral dust. The mineral dust load was mainly composed by clay-silicates mineral derived elements (22% of the PM10 total mass on average) with lower amounts of carbonates (9%). A clear northward gradient was observed in carbonates concentration that illustrates the differences in the composition according to the source regions of mineral dust. Mineral dust was frequently linked to industrial emissions from crude oil refineries, fertilizer industries as well as oil and coal power plants, located in the northern and north-western coast of the African continent (29%). Sea salt was also registered in the PM10 mass during most part of the sampling period, with a lower impact in the PM10 levels than the mineral dust one (26%). Combustion aerosols (6%) reached the highest mean values in summer as a consequence of the emissions from local-regional sources. Biomass burning aerosols produced from October to November in sub-sahelian latitudes, had a clear influence in the content of elemental carbon (EC) recorded at Cape Verde but a small impact in the PM10 total mass levels. A minor contribution to the PM10 mass has been associated to secondary inorganic compounds-SIC. Namely, ammonium sulfate and nitrate (SIC 1–5%) and calcium sulfate and nitrate (SIC 2–3%). The main origin of SIC 1 was attributed to emissions of SO2 and NOx from industrial sources located in the northern and north-western African coast and from wildfires produced in the continent. SIC 2 had a clear regional origin in the summer period. However, in the winter period there were probably contributions of soil emissions of evaporate minerals from regions of eastern Algeria. The location of Cape Verde in the Atlantic Ocean at subtropical latitudes, and the absence of relevant local sources of anthropogenic atmospheric pollutants, becomes this archipelago, a perfect site to study the impact of external contributions on the background levels of PM10 registered over the north-eastern tropical Atlantic.

Sources of long-lived atmospheric VOCs at the rural boreal forest site, SMEAR II

Abstract. In this study a long-term volatile organic compound (VOCs) concentration data set, measured at the SMEAR II (Station for Measuring Ecosystem–Atmosphere Relations) boreal forest site in Hyytiälä, Finland during the years 2006–2011, was analyzed in order to identify source areas and profiles of the observed VOCs. VOC mixing ratios were measured using proton transfer reaction mass spectrometry. Four-day HYSPLIT 4 (Hybrid Single Particle Lagrangian Integrated Trajectory) backward trajectories and the Unmix 6.0 receptor model were used for source area and source composition analysis. Two major forest fire events in Russia took place during the measurement period. The effect of these fires was clearly visible in the trajectory analysis, lending confidence to the method employed with this data set. Elevated volume mixing ratios (VMRs) of non-biogenic VOCs related to forest fires, e.g. acetonitrile and aromatic VOCs, were observed. Ten major source areas for long-lived VOCs (methanol, acetonitrile, acetaldehyde, acetone, benzene, and toluene) observed at the SMEAR II site were identified. The main source areas for all the targeted VOCs were western Russia, northern Poland, Kaliningrad, and the Baltic countries. Industrial areas in northern continental Europe were also found to be source areas for certain VOCs. Both trajectory and receptor analysis showed that air masses from northern Fennoscandia were less polluted with respect to both the VOCs studied and other trace gases (CO, SO2 and NOx), compared to areas of eastern and western continental Europe, western Russia, and southern Fennoscandia.

Evaporation of traffic-generated nanoparticles during advection from source

Abstract Earlier work has demonstrated the potential for volatilisation of nanoparticles emitted by road traffic as these are advected downwind from the source of emissions, but there have been few studies and the processes have yet to be elucidated in detail. Using a dataset collected at paired sampling sites located respectively in a street canyon and in a nearby park, an in depth analysis of particle number size distributions has been conducted in order to better understand the size reduction of the semi-volatile nanoparticles. By sorting the size distributions according to wind direction and fitting log normal modes, it can be seen that the mode peaking at around 22 nm at the street canyon site is on average shrinking to 6.2 nm diameter at the park site which indicates a mean shrinkage rate for these particles of 0.13 nm s−1 with temperatures within the range 12–18 °C. The diurnal variation of the shrunken mode in the park reflects the diurnal pattern of particle concentrations at the street canyon site taken as the main source area. An analysis of peak diameter for the smallest mode at the downwind park site shows an inverse relationship to wind speed suggesting that dilution rather than travel time is the main determinant of the particle shrinkage rate. An evaluation of previously collected C10 to C35 n-alkane data from a different urban location shows a good fit to Pankow partitioning theory reflecting the semi-volatility of compounds believed to be representative of the composition of diesel exhaust nanoparticles, hence confirming the feasibility of an evaporative mechanism for particle shrinkage.

The interplay between tectonics, sediment dynamics and gateways evolution in the Danube system from the Pannonian Basin to the western Black Sea

Understanding the natural evolution of a river–delta–sea system is important to develop a strong scientific basis for efficient integrated management plans. The distribution of sediment fluxes is linked with the natural connection between sediment source areas situated in uplifting mountain chains and deposition in plains, deltas and, ultimately, in the capturing oceans and seas. The Danube River–western Black Sea is one of the most active European systems in terms of sediment re-distribution that poses significant societal challenges. We aim to derive the tectonic and sedimentological background of human-induced changes in this system and discuss their interplay. This is obtained by analysing the tectonic and associated vertical movements, the evolution of relevant basins and the key events affecting sediment routing and deposition. The analysis of the main source and sink areas is focused in particular on the Miocene evolution of the Carpatho-Balkanides, Dinarides and their sedimentary basins including the western Black Sea. The vertical movements of mountains chains created the main moments of basin connectivity observed in the Danube system. Their timing and effects are observed in sediments deposited in the vicinity of gateways, such as the transition between the Pannonian/Transylvanian and Dacian basins and between the Dacian Basin and western Black Sea. The results demonstrate the importance of understanding threshold conditions driving rapid basins connectivity changes superposed over the longer time scale of tectonic-induced vertical movements associated with background erosion and sedimentation. The spatial and temporal scale of such processes is contrastingly different and challenging. The long-term patterns interact with recent or anthropogenic induced modifications in the natural system and may result in rapid changes at threshold conditions that can be quantified and predicted. Their understanding is critical because of frequent occurrence during orogenic evolution, as commonly observed in the Mediterranean area and discussed elsewhere.