An optimized spatial proximity model for fine particulate matter air pollution exposure assessment in areas of sparse monitoring

GIS-based proximity models are one of the key tools for the assessment of exposure to air pollution when the density of spatial monitoring stations is sparse. Central to exposure assessment that utilizes proximity models is the ‘exposure intensity–distance’ hypothesis. A major weakness in the application of this hypothesis is that it does not account for the Gaussian processes that are at the core of the physical mechanisms inherent in the dispersion of air pollutants.

Building upon the utility of spatial proximity models and the theoretical reliability of Gaussian dispersion processes of air pollutants, this study puts forward a novel Gaussian weighting function-aided proximity model (GWFPM). The study area and data set for this work consisted of transport-related emission sources of PM_2.5 in the Houston-Baytown-Sugar Land metropolitan area. Performance of the GWFPM was validated by comparing on-site observed PM_2.5 concentrations with results from classical ordinary kriging (OK) interpolation and a robust emission-weighted proximity model (EWPM). Results show that the fitting R² between possible exposure intensity calculated by GWFPM and observed PM_2.5 concentrations was 0.67. A variety of statistical evidence (i.e., bias, root mean square error [RMSE], mean absolute error [MAE], and correlation coefficient) confirmed that GWFPM outperformed OK and EWPM in estimating annual PM_2.5 concentrations for all monitoring sites. These results indicate that a GWFPM utilizing the physical dispersing mechanisms integrated may more effectively characterize annual-scale exposure than traditional models. Using GWFPM, receptors’ exposure to air pollution can be assessed with sufficient accuracy, even in those areas with a low density of monitoring sites. These results may be of use to public health and planning officials in a more accurate assessment of the annual exposure risk to a population, especially in areas where monitoring sites are sparse.     

Subduction factory processes beneath the Guguan cross-chain, Mariana Arc: no role for sediments, are serpentinites important?

We need to understand chemical recycling at convergent margins and how chemical interactions between subducted slab and the overlying mantle wedge affect mantle evolution and magmagenesis. This requires distinguishing contributions from recycled individual subducted components as well as those contributed by the mantle. We do this by examining magmatic products generated at different depths above a subduction zone, in an intra-oceanic arc setting. The Guguan cross-chain in the intra-oceanic Mariana arc overlies subducted Jurassic Pacific plate lithosphere at depths of ~125--230 km and erupts mostly basalt. Basalts from rear-arc volcanoes are more primitive than those from the magmatic front, in spite of being derived by lower degrees of melting of less-depleted mantle. Rear-arc magmas also show higher temperatures and pressures of equilibration. Coexisting mineral compositions become more MORB- or OIB-like with increasing height above the subduction zone. Trace element and isotopic variations indicate that the subduction component in cross-chain lavas diminishes with increasing depth to the subduction zone, except for water contents. There is little support for the idea that melting beneath the Mariana Trough back-arc basin depleted the source region of arc magmas, but melting to form rear-arc volcanoes may have depleted the source of magmatic front volcanoes. Enrichments in rear-arc lavas were not caused by sediment melting; the data instead favor an OIB-type mantle that has been modestly affected by subduction zone fluids. Our most important conclusion is that sediment fluids or melts are not responsible for the K--h relationship and other cross-chain chemical and isotopic variations. We speculate that an increasing role for supercritical fluids released from serpentinites interacting with modestly enriched mantle might be responsible for cross-chain geochemical and isotopic variations. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Coastal failures during the 1999 Kocaeli earthquake in Turkey

During the 1999 Kocaeli earthquake (M_w=7.4) in Turkey, coastal failures and sea inundation were observed and were particularly concentrated along the margins of Izmit Bay and Lake Sapanca, in pull-apart basins created by stepovers in the fault rupture. Geotechnical site characterization, geologic mapping, liquefaction evaluation, and slope stability analysis were carried out to identify the principal contributing factors of the coastal failures. Results from this study indicate that both liquefaction and tectonic subsidence contributed to the failures and sea inundation within the pull-apart basins. Most of the liquefaction sites were situated at the prograding nose of active delta fans, where the presence of steep slopes coupled with the loose sediments found within young active delta fan deposits resulted in liquefaction-induced slope failures and sea inundation. Liquefaction in other coastal deposits outside the actively prograding delta fans caused limited lateral spreading and only minor sea inundation. Outside the delta fans, where soils were not liquefiable, tectonic subsidence associated with normal faulting was the cause of the observed sea inundation. Generally, tectonic subsidence caused the most severe sea inundation. Based on these observations, the identification of regions susceptible to both tectonic subsidence and liquefaction are important when evaluating seismic hazards.     

Constraining diamond metasomatic growth using C- and N-stable isotopes: examples from Namibia

The present paper provides C- and N-stable isotope characteristics, N-contents and N-aggregation states for alluvial diamonds of known paragenesis from placers along the Namibian coast. The sample set includes diamonds with typical peridotitic and eclogitic inclusions and the recently reported “undetermined” suite of Leost et al. [Contrib. Mineral. Petrol. 145 (2003) 15] which resulted from infiltration of high temperature, carbonate-rich melts. δ¹³C-values range from −20.3‰ to −0.5‰ (n=48) for peridotitic diamonds and from −38.5‰ to −1.6‰ (n=45) for eclogitic diamonds. Diamonds belonging to the “undetermined” suite span a narrower range in δ¹³C from −8.5‰ to −2.7‰ (n=13). When compared with previous studies, diamonds from Namibia are characterised by unusually low proportions of N-free (i.e. Type II) peridotitic and eclogitic diamonds (3% and 2%, respectively) and an unprecedented high proportion of N-rich diamonds (15% and 73%, respectively, have N-contents >600 ppm). δ¹⁵N-values for diamonds of the peridotitic, eclogitic and “undetermined” suites range from −10‰ to +13‰ without correlations with either N-content or δ¹³C. The similarity in N-isotopic composition and the N-rich character of diamonds belonging to the eclogitic, peridotitic and “undetermined” suites is striking and suggests a close genetic relationship. We propose that a large part of the diamonds mined in Namibia formed during metasomatic events of similar style that introduced carbon and nitrogen into a range of different host lithologies.     

Pliocene sedimentation in a shallow, cool-water, estuarine gulf, Murray Basin, South Australia

The Pliocene Norwest Bend Formation is a well‐preserved succession of terrestrial and shallow‐marine deposits in the Murray Basin, South Australia. Sediments in this unit consist of two discrete terrigenous clastic‐rich, decametre‐scale sequences, or informal members, which record episodes of marine incursion during the Early and Late Pliocene respectively. The base of each sequence is a transgressive lag and/or strandline deposit that is transitional upwards into a highstand, subtidal, terrigenous clastic and cool‐water carbonate sediment accumulation. The top of each sequence is incised by fluvial channels that are filled by river deposits which formed as relative sea‐level fell and terrestrial environments prograded basinward. Sedimentological data suggest that gross stratigraphic architecture was primarily determined by glacioeustasy. Differences in sedimentary style between these two sequences, however, reflect a major climatic change that took place in southern Australia during the mid‐Pliocene. The lower quartzose sand member is formed of siliciclastic sediment derived from prolonged, deep, subaerial weathering and contains a bivalve‐dominated, cool‐temperate, open‐marine mollusc assemblage. These sediments accumulated under an equitable, relatively warm, humid climate. The Murray Basin during this time, because of high fluvial discharge, was a salt‐wedge estuary with typical estuarine circulation. In contrast, the upper, oyster‐rich member is typified by large monospecific oyster buildups that grew in restricted coastal environments. Strandline deposits contain a warm‐temperate skeletal assemblage. Contemporaneous aeolian sediments accumulated under warm, semi‐arid climatic conditions. Well‐developed ferricrete, silcrete and calcrete horizons reflect cyclic conditions of rainwater infiltration and evaporation in the seasonally dry climate that typifies southern Australia today. Highly seasonal rainfall produced an estuary that fluctuated annually from being well to partially mixed. These Pliocene sediments support the notion that mollusc‐rich facies are the signature of cool‐water carbonate accumulations in inboard neritic environments. Unlike bryozoans that dominate the outer parts of Cenozoic cool‐water carbonate shelves, molluscs evolved to exploit an array of coastal ecosystems with wide salinity variations and variable sedimentation rates.     

Peridotitic diamonds from Namibia: constraints on the composition and evolution of their mantle source

About half the diamonds studied from the Cenozoic placer deposits along the Namibian coast belong to the peridotitic suite. The peridotitic mantle source is heterogeneous ranging from lherzolitic to strongly Ca depleted (down to 0.24 wt.% CaO in garnet) and shows large variations in Cr/Al ratio, illustrated by very low to very high Cr₂O₃ contents in garnet (2.6–17.3 wt.%). The Cr-rich end of this range includes exceptionally high Cr₂O₃ contents in Mg-chromite (70.7 wt.%) and clinopyroxene (3.6 wt.%). Garnet-olivine thermometry appears to indicate two groups, one that equilibrated at temperatures between 1200 and 1220°C and a second between 960 and 1100°C. Combined estimates of pressure and temperature based on garnet-orthopyroxene pairs indicate a large variance in geothermal gradients, corresponding to 38–42 mW/m² surface heat flow.

The trace-element composition of peridotitic garnet inclusions (determined by SIMS) also indicates large diversity. Two principal groups, corresponding to different styles of metasomatic source enrichment, are recognized. The first group ranges from extremely LREE_N-depleted patterns, through trough-shaped REE_N to sinusoidal patterns with the position of the first peak gradually moving from the LREE_N to the MREE_N. This series of REE patterns is interpreted to reflect a range of metasomatic agents with decreasing LREE/HREE. Only in the case of the two garnets with REE_N peaking at Sm–Eu is this process connected with enrichment in Zr, without significant introduction of Y and Ti. The metasomatism responsible is interpreted as reflecting percolation of CHO-fluids through harzburgite under sub-solidus conditions. A second group of garnets shows an increase from LREE_N–MREE_N and almost flat (lherzolitic garnet) to moderately declining MREE_N–HREE_N at super-chondritic levels. This second style of metasomatism is caused by an agent carrying HFSE and showing only moderate enrichment in LREE over HREE, which points towards silicate melts.     

Late Paleozoic deformation and exhumation in the Sierras Pampeanas (Argentina): 40Ar/39Ar-feldspar dating constraints

International Journal of Earth Sciences - Systematic 40Ar/39Ar feldspar data obtained from the Sierras Pampeanas are presented, filling the gap between available high-...     

Temporal observations of rip current circulation on a macro-tidal beach

A field experiment was conducted on a high energy macro-tidal beach (Perranporth, UK) to examine rip current dynamics over a low-tide transverse bar/rip system in response to changing tide and wave conditions. Hydrodynamic data were collected using an array of in situ acoustic doppler current meters and pressure transducers, as well as 12 GPS-tracked Lagrangian surf zone drifters. Inter-tidal and sub-tidal morphology were measured through RTK-GPS and echo-sounder surveys. Data were collected for eight consecutive days (15 tides) over a spring-neap tidal cycle with tidal ranges of 4–6.5 m and offshore significant wave heights of 1–2 m and peak periods of 5–12 s.