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Large eddy simulation of reactive pollutants in a deep urban street canyon: Coupling dynamics with O3-NOx-VOC chemistry
2017
Zhong, Jian | Cai, Xiao-Ming | Bloss, William James
A large eddy simulation (LES) model coupled with O3-NOx-VOC chemistry is implemented to simulate the coupled effects of emissions, mixing and chemical pre-processing within an idealised deep (aspect ratio = 2) urban street canyon under a weak wind condition. Reactive pollutants exhibit significant spatial variations in the presence of two vertically aligned unsteady vortices formed in the canyon. Comparison of the LES results from two chemical schemes (simple NOx-O3 chemistry and a more comprehensive Reduced Chemical Scheme (RCS) chemical mechanism) shows that the concentrations of NO2 and Ox inside the street canyon are enhanced by approximately 30–40% via OH/HO2 chemistry. NO, NOx, O3, OH and HO2 are chemically consumed, while NO2 and Ox (total oxidant) are chemically produced within the canyon environment. Within-canyon pre-processing increases oxidant fluxes from the canyon to the overlying boundary layer, and this effect is greater for deeper street canyons (as found in many traditional European urban centres) than shallower (lower aspect ratio) streets. There is clear evidence of distinct behaviours for emitted chemical species and entrained chemical species, and positive (or negative) values of intensities of segregations are found between pairs of species with similar (or opposite) behaviour. The simplified two-box model underestimated NO and O3 levels, but overestimated NO2 levels for both the lower and upper canyon compared with the more realistic LES-chemistry model. This suggests that the segregation effect due to incomplete mixing reduces the chemical conversion rate of NO to NO2. This study reveals the impacts of nonlinear O3-NOx-VOC photochemical processes in the incomplete mixing environment and provides a better understanding of the pre-processing of emissions within canyons, prior to their release to the urban boundary layer, through the coupling of street canyon dynamics and chemistry.
Показать больше [+] Меньше [-]Transformation of PBDE mixtures during sediment transport and resuspension in marine environments (Gulf of Lion, NW Mediterranean Sea)
2012
Salvadó, Joan A. | Grimalt, Joan O. | López, Jordi F. | Durrieu de Madron, Xavier | Heussner, Serge | Canals, M. (Miquel)
Polybromodiphenyl ethers (PBDEs) in superficial sediments from the Gulf of Lion were studied. They were largely predominated by BDE 209 (98.7% of all PBDEs) indicating that the main source of these pollutants was the commercial mixture deca-BDE. This compound and the less brominated BDE exhibited a southwestward decreasing concentration gradient following the dominant marine currents and bottom relief, e.g. the Mud Belt, the submarine canyons and the Open Continental Slope. All PBDEs exhibited statistically significant correlations confirming the common origin. However, a progressive transformation of the dumped BDE 209 was identified showing a depletion paralleled by increases of the less brominated BDEs (from 8.6% to 22%). These less brominated compounds were accumulated at about 100–140km away from the Rhone prodelta, e.g. at the end of the submarine canyons, evidencing that these transformation compounds can be accumulated at long distances from the dumping sites in the marine system.
Показать больше [+] Меньше [-]Deposition patterns and transport mechanisms for the endocrine disruptor 4-nonylphenol across the Sierra Nevada Mountains, California
2014
Lyons, Rebecca | Van de Bittner, Kyle | Morgan-Jones, Sean
Dust and particulate distribution patterns are shifting as global climate change brings about longer drought periods. Particulates act as vehicles for long range transport of organic pollutants, depositing at locations far from their source. Nonylphenol, a biodegradation product of nonylphenol polyethoxylate, is a known endocrine disruptor. Nonylphenol polyethoxylate enters the environment as an inert ingredient in pesticide sprays, potentially traveling great distances from its application site. This is of concern when a highly agricultural region, California's Central Valley, lies adjacent to sensitive areas like the Eastern Sierra Nevada Mountains. The distribution and transport mechanisms for 4-nonylphenol were investigated in Eastern Sierra Nevada canyons. Regions close to canyon headwalls showed trace amounts of 4-nonylphenol in surface water, snow, and atmospheric deposition. Exposed areas had yearly average concentrations as high as 9 μg/L. Distribution patterns are consistent with particulate-bound transport. This suggests with increasing drought periods, higher levels of persistent organic pollutants are likely.
Показать больше [+] Меньше [-]Marine mercury-methylating microbial communities from coastal to Capbreton Canyon sediments (North Atlantic Ocean)
2020
Azaroff, Alyssa | Goñi Urriza, Marisol | Gassie, Claire | Monperrus, Mathilde | Guyoneaud, Rémy
Microbial mercury (Hg) methylation transforms inorganic mercury to neurotoxic methylmercury (MeHg) mainly in aquatic anoxic environments. Sampling challenges in marine ecosystems, particularly in submarine canyons, leads to a lack of knowledge about the Hg methylating microbia in marine sediments. A previous study showed an enrichment of mercury species in sediments from the Capbreton Canyon where both geochemical parameters and microbial activities constrained the net MeHg production. In order to characterize Hg-methylating microbial communities from coastal to deeper sediments, we analysed the diversity of microorganisms’ (16S rDNA-based sequencing) and Hg methylators (hgcA based cloning and sequencing). Both, 16S rDNA and hgcA gene analysis demonstrated that the putative Hg-methylating prokaryotes were likely within the Deltaproteobacteria, dominated by sulfur-compounds based reducing bacteria (mainly sulfate reducers). Additionally, others clades were also identified as carrying HgcA gene, such as, Chloroflexi, Spirochaetes, Elusimicrobia, PVC superphylum (Plantomycetes, Verrucomicrobia and Chlamydiae) and Euryarchaea. Nevertheless, 61% of the hgcA sequences were not assigned to specific clade, indicating that further studies are needed to understand the implication of new microorganisms carrying hgcA in the Hg methylation in marine environments. These first results suggest that sulfur cycle drives the Hg-methylation in marine ecosystem.
Показать больше [+] Меньше [-]Pelagic microplastics around an archipelago of the Equatorial Atlantic
2013
Ivar do Sul, Juliana A. | Costa, Monica F. | Barletta, Mario | Cysneiros, Francisco José A.
Plastic marine debris is presently widely recognised as an important environmental pollutant. Such debris is reported in every habitat of the oceans, from urban tourist beaches to remote islands and from the ocean surface to submarine canyons, and is found buried and deposited on sandy and cobble beaches. Plastic marine debris varies from micrometres to several metres in length and is potentially ingested by animals of every level of the marine food web. Here, we show that synthetic polymers are present in subsurface plankton samples around Saint Peter and Saint Paul Archipelago in the Equatorial Atlantic Ocean. To explain the distribution of microplastics around the Archipelago, we proposed a generalised linear model (GLM) that suggests the existence of an outward gradient of mean plastic-particle densities. Plastic items can be autochthonous or transported over large oceanic distances. One probable source is the small but persistent fishing fleet using the area.
Показать больше [+] Меньше [-]Large debris dumps in the northern South China Sea
2019
Peng, X. | Dasgupta, S. | Zhong, G. | Du, M. | Xu, H. | Chen, M. | Chen, S. | Ta, K. | Li, J.
Knowledge of the abundance, source, and fate of marine debris in the deep sea is largely constrained thus far. Here, we report the existence of large deep-sea debris dumps that have not been reported before on the seafloor worldwide. Marine debris remarkably accumulated at ~1700–1800 m in the tributary submarine canyons of the Xisha Trough, northern South China Sea (SCS). Although marine debris in Xisha Trough is patchy, the debris abundance was as high as 36,818 and 51,929 items/km² at locations SY78 and SY82, respectively, which is one order of magnitude higher than that in other submarine canyons. We propose that most of the debris came from fishery and navigation activities, as indicated by the categories of debris collected from the seafloor dumps. Seasonal surface ocean currents of the SCS and geomorphology of submarine canyons possibly influence the movement of the debris from coasts to the deep seafloor.
Показать больше [+] Меньше [-]Marine litter in the upper São Vicente submarine canyon (SW Portugal): Abundance, distribution, composition and fauna interactions
2015
Oliveira, Frederico César Barbosa de | Monteiro, Pedro | Bentes, Luis | Henriques, Nuno Sales | Aguilar Melantzón, Ricardo | Gonçalves, Jorge M.S.
Marine litter has become a worldwide environmental problem, tainting all ocean habitats. The abundance, distribution and composition of litter and its interactions with fauna were evaluated in the upper S. Vicente canyon using video images from 3 remote operated vehicle exploratory dives. Litter was present in all dives and the abundance was as high as 3.31 items100m−1. Mean abundance of litter over rock bottom was higher than on soft substrate. Mean litter abundance was slightly higher than reported for other canyons on the Portuguese margin, but lower in comparison to more urbanized coastal areas of the world. Lost fishing gear was the prevalent type of litter, indicating that the majority of litter originates from maritime sources, mainly fishing activity. Physical contact with sessile fauna and entanglement of specimens were the major impacts of lost fishing gear. Based on the importance of this region for the local fishermen, litter abundance is expected to increase.
Показать больше [+] Меньше [-]Temporal evolution of lead isotope ratios in sediments of the Central Portuguese Margin: A fingerprint of human activities
2013
Stable Pb isotope ratios (206Pb/207Pb, 208Pb/206Pb), 210Pb, Pb, Al, Ca, Fe, Mn and Si concentrations were measured in 7 sediment cores from the west coast of the Iberian Peninsula to assess the Pb contamination throughout the last 200years. Independently of their locations, all cores are characterized by increasing Pb/Al rends not related to grain-size changes. Conversely, decreasing trends of 206Pb/207Pb were found towards the present. This tendency suggest a change in Pb sources reflecting an increased proportion derived from anthropogenic activities. The highest anthropogenic Pb inventories for sediments younger than 1950s were found in the two shallowest cores of Cascais and Lisboa submarine canyons, reflecting the proximity of the Tagus estuary. Lead isotope signatures also help demonstrate that sediments contaminated with Pb are not constrained to estuarine–coastal areas and upper parts of submarine canyons, but are also to transferred to a lesser extent to deeper parts of the Portuguese Margin.
Показать больше [+] Меньше [-]Photocatalytic abatement results from a model street canyon
2015
Gallus, M. | Ciuraru, R. | Mothes, F. | Akylas, V. | Barmpas, F. | Beeldens, A. | Bernard, F. | Boonen, E. | Boréave, A. | Cazaunau, M. | Charbonnel, N. | Chen, H. | Daële, V. | Dupart, Y. | Gaimoz, C. | Grosselin, B. | Herrmann, H. | Ifang, S. | Kurtenbach, R. | Maille, M. | Marjanovic, I. | Michoud, V. | Mellouki, A. | Miet, K. | Moussiopoulos, N. | Poulain, L. | Zapf, P. | George, C. | Doussin, J. F. | Kleffmann, J.
During the European Life+ project PhotoPAQ (Demonstration of Photocatalytic remediation Processes on Air Quality), photocatalytic remediation of nitrogen oxides (NOₓ), ozone (O₃), volatile organic compounds (VOCs), and airborne particles on photocatalytic cementitious coating materials was studied in an artificial street canyon setup by comparing with a colocated nonactive reference canyon of the same dimension (5 × 5 × 53 m). Although the photocatalytic material showed reasonably high activity in laboratory studies, no significant reduction of NOₓ, O₃, and VOCs and no impact on particle mass, size distribution, and chemical composition were observed in the field campaign. When comparing nighttime and daytime correlation plots of the two canyons, an average upper limit NOₓ remediation of ≤2 % was derived. This result is consistent only with three recent field studies on photocatalytic NOₓ remediation in the urban atmosphere, whereas much higher reductions were obtained in most other field investigations. Reasons for the controversial results are discussed, and a more consistent picture of the quantitative remediation is obtained after extrapolation of the results from the various field campaigns to realistic main urban street canyon conditions.
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