Cloud chemistry at the Puy de Dôme: variability and relationships with environmental factors

The chemical composition of cloud water was investigated during the winter-spring months of 2001 and 2002 at the Puy de D&#244;me station (1465 m above sea level, 45&deg;46&prime;22&prime;&prime; N, 2&deg;57&prime;43&prime;&prime; E) in an effort to characterize clouds in the continental free troposphere. Cloud droplets were sampled with single-stage cloud collectors (cut-off diameter approximately 7 &micro;m) and analyzed for inorganic and organic ions, as well as total dissolved organic carbon. Results show a very large variability in chemical composition and total solute concentration of cloud droplets, ranging from a few mg l^-1 to more than 150 mg l^-1. Samplings can be classified in three different categories with respect to their total ionic content and relative chemical composition: background continental (BG, total solute content lower than 18 mg l^-1), anthropogenic continental (ANT, total solute content from 18 to 50 mg l^-1), and special events (SpE, total solute content higher than 50 mg l^-1). The relative chemical composition shows an increase in anthropogenic-derived species (NO₃^-, SO₄^2- and NH₄⁺) from BG to SpE, and a decrease in dissolved organic compounds (ionic and non-ionic) that are associated with the anthropogenic character of air masses. <P style='line-height: 20px;'> We observed a high contribution of solute in cloud water derived from the dissolution of gas phase species in all cloud events. This was evident from large solute fractions of nitrate, ammonium and mono-carboxylic acids in cloud water, relative to their abundance in the aerosol phase. The comparison between droplet and aerosol composition clearly shows the limited ability of organic aerosols to act as cloud condensation nuclei. The strong contribution of gas-phase species limits the establishment of direct relationships between cloud water solute concentration and LWC that are expected from nucleation scavenging

Utilisation des outils numériques d'aide à la décision pour la gestion de l'eau

Le succès d'une gestion des écosystèmes naturels requiert une connaissance approfondie des différents processus qui interviennent et de leurs échelles de temps et d'espace particulières. Pour cette raison, les décideurs ont besoin d'analyser une vaste gamme de données et d'informations géographiques. Les modèles mathématiques, les systèmes d'informations géographi-ques et les systèmes experts sont capables de produire cette analyse, mais seule une minorité de gestionnaires les utilise actuellement. Cet article identifie quelques unes des raisons à l'origine de l'hésitation des gestionnaires à adopter de tels outils d'aide à la décision pour la gestion des ressources naturelles et propose une structure qui pourrait faciliter leur utilisation pour le processus de prise de décision. Cet exercice est réalisé à l'intérieur du contexte de la gestion intégrée par bassin. Une revue des systèmes d'aide à la décision est également présentée.Many methods of integrated or watershed management exist which account for the necessary biophysical and socio-economic factors at the watershed level. Some of these approaches are ecosystem oriented while others are socio-economically oriented. Whatever the definition, water management at the watershed level needs to account for a plenitude of variables related to the air, water, soil, biology, and economy. The successful management of natural ecosystems requires a thorough understanding of their characteristic time and spatial scales. Because of this, decision makers need to analyze a wide range of data and geographic information. Mathematical models, geographic information systems and expert systems are capable of performing this analysis, but only a minority of managers are currently using them. This paper identifies some of the reasons why ecosystem managers have been slow to adopt such decision support tools in natural resources management and proposes a framework to facilitate their use in the decision making process. This is done in an integrated watershed management context. A review of related decision support systems is also presented.Four types of decision-support tools are introduced : mathematical models, expert-systems, geographical information systems (GIS) and decision support systems (DSS). Mathematical models have long been used for simulation, prediction, and forecasting, however, they are often task specific and were rarely developed for management uses. GIS are more and more commonly being used for decision support as they become more affordable and user-friendly and are very well-suited for managing resources at a spatial scale. There exist many kinds of software ranging from a simple viewer used for cartographic purposes to complex GIS oriented toward spatial analysis and modelling. Expert systems are also interesting for decision support when specific goals are being considered. Finally, DSS are perhaps the digital tools most applicable to management purposes, often integrating one or more models, a GIS or expert system functionalities. There are two types of DSS : 1. Environmental Information Systems (EIS), and 2. Integrated Modelling Systems (IMS) EIS can be very user- friendly, relying heavily upon GIS and statistical functions.IMS also use GIS capabilities, but integrates several mathematical models as well. The level of integration between models varies considerably and the complexity of IMS are generally high.Two questions underlie the operational use of digital technologies for decision support. The first is whether or not such technology should be used at all, while the second is why such tools take time to be adopted by government and management agencies. The use of digital technologies is often required when the problem is complex and where there are a wide range of factors involved with different spatial and temporal scales. Three major constraints towards the implementation of decision support tools can be pinpointed :1. technology, 2. data, and 3. working organization. Technological constraints include cost, lack of user friendliness, and hardware problems, among other factors. Data constraints are mostly related to availability, cost, heterogeneity and volume. Finally, organization constraints pertain mostly to the manager's perception of the tool and the structural integration of the tool within the decision process.This paper proposes a 4-step approach to optimize the use of decision-support tools. The first step requires that managers and decision-makers clearly define their project, goals and budget, as well as, decide whether to use an integrated watershed management approach or a more discrete approach. This leads directly to the second step, which consists of choosing the most appropriate digital support tool. This requires communication between managers and scientists, and at this point, data gathering and integration should begin. The third phase consists of the development of a new tool or adaptation of an existing one within the context of the agency's management structure. The final step is the operational use of the decision support tool by the agency, following an initial trial period. The successful use of a decision support tool for management purposes depends on proper planning that accounts for all factors related to management needs, budget, data, ease of use, and organization integration

Tricritical behavior of the frustrated XY antiferromagnet

Extensive histogram Monte-Carlo simulations of the XY antiferromagnet on a stacked triangular lattice reveal exponent estimates which strongly favor a scenario of mean-field tricritical behavior for the spin-order transition. The corresponding chiral-order transition occurs at the same temperature but appears to be decoupled from the spin-order. These results are relevant to a wide class of frustrated systems with planar-type order and serve to resolve a long-standing controversy regarding their criticality.Comment: J1K 2R1 4 pages (RevTex 3.0), 4 figures available upon request, Report# CRPS-94-0

Formation of hydroxyl radicals by irradiated 1-nitronaphthalene (1NN): oxidation of hydroxyl ions and water by the 1NN triplet state

International audienceThe excited triplet state of 1-nitronaphthalene (31NN*) reacts with OH- with a second-order reaction rate constant of (1.66 ± 0.8)¥107 M-1 s-1 (m ± s). The reaction yields the ∑OH radical and the radical anion 1NN-∑. In aerated solution, the radical 1NN-∑ would react with O2 to finally produce H2O2 upon hydroperoxide/superoxide disproportionation. The photolysis of H2O2 is another potential source of ∑OH, but such a pathway would be a minor one in circumneutral (pH 6.5) or in basic solution ([OH-] = 0.3-0.5 M). The oxidation of H2O by 31NN*, with rate constant 3.8 ± 0.3 M-1 s-1, could be the main ∑OH source at pH 6.5

Simultaneously enhanced photocatalytic and antibacterial activities of TiO2/Ag composite nanofibers for wastewater purification

High throughput of polyacylonitile (PAN)-based Ag/TiO2 composite nanofibers were prepared by using needleless electrospinning method. The morphology and crystallinity characterization revealed uniform and smooth nanofibers with an average diameter ranged from 160 to 260 nm. The enhanced photocatalytic activity of PAN/Ag/TiO2 compared with PAN/TiO2 nanofibers under visible light irradiation was linked with high interfacial charge transfer and low bandgap due to Ag entity. High photodegradation efficiency for methyl orange, rhodamine B and methylene blue were achieved as 99.5%, 92% and 99% respectively during the 4 h experiment. Effect of key parameters (i.e. pH, oxygen and Ag/TiO2 loading dosage) on photodegradation efficiency of dyes were also investigated. Active species trapping experiments demonstrated that •O2- and •OH were dominant active species in the photocatalytic degradation of dyes. These composite nanofibers have also exhibited excellent antibacterial activity, e.g. 95% of E. coli and 99% of S. aureus were killed in 2 h. Bifunctional nanofibers can be easily recovered from the aqueous solution as compared with the TiO2 nanoparticles. Moreover, the daily production rate of nanofibers has reached over 1.4 kg in the laboratory test, which is 60 times higher than that using the single needle electrospinning method. This production rate may be further optimized in the pilot scale studies. High productivity and strong catalytic properties of nanofibers propose their potential applications in environmental remediation for economically and eco-friendly wastewater and air treatment materials

Microcystis aeruginosa synergistically facilitate the photocatalytic degradation of tetracycline hydrochloride and Cr(VI) on PAN/TiO2/Ag nanofiber mats

Cyanobacterial blooms can cause serious damage to aquatic ecosystems. However, we have demonstrated that typical algae-blooming species Microcystis aeruginosa (M. aeruginosa) combined with photocatalysts could synergistically facilitate the photodecontamination of tetracycline hydrochloride (TC) and Cr(VI). In this study, for the first time, harmful algae were successfully converted into photoreactive bionano hybrid materials by immobilizing M. aeruginosa cells onto polyacrylonitrile (PAN)-TiO2/Ag hybrid nanofibers, and their photocatalytic activity was evaluated. The addition of M. aeruginosa significantly improved the photodecontamination, and the reaction rate constant (k) values of TC and Cr(VI) degradation by M. aeruginosa-PAN/TiO2/Ag nanofiber mats were 2.4 and 1.5-fold higher than that of bare PAN/TiO2/Ag nanofiber. Photoreaction caused damage to algae cells, but no microcystin was found that had been photodegraded simultaneously. The effects of various active species were also investigated, and the photodegradation mechanism was proposed. Recycling tests revealed that this flexible M. aeruginosa-PAN/TiO2/Ag hybrid mat had potential application in the removal of mixed organic and inorganic pollutants with high efficiency and without secondary pollutants. Thus, harmful algae blooms could serve as an efficient materials to remove toxic pollutants in a sustainable way under visible light irradiation

Oxygen nanobubbles enhanced photodegradation of oxytetracycline under visible light: synergistic effect and mechanism

International audienceNanobubbles have gained much attention due to their unusual properties such as large specific surface area, surface energy and internal energy, thereby, increase the surface reaction and improve the mass transfer efficiency. The long term stability of nanobubbles and generation of reactive oxygen species enables them to address various environmental issues for water purification without secondary pollution. However, there are few studies concerning the application of oxygen nanobubbles in the advanced oxidation processes (AOPs). In this study, first time, oxygen nanobubbles were introduced into the photoreaction system under visible light irradiation for enhanced photodegradation of oxytetracycline (OTC). Results indicated that oxygen nanobubbles significantly improved the photodegradation of OTC through high mass transfer and generation of reactive radicals during the nanobubble collapse. The oxygen nanobubble stability was confirmed to be pH dependent. The nanobubbles concentration increased from 0.76 to 3.78 × 108 particles/mL, while the mean size decreased from 205 nm to 138 nm as the pH value increased (3.2–11.0). The photodegradation efficiency of OTC was improved from 45% to 98% with the increase of pH (4.0–11.0). Oxygen nanobubbles hold promise to improve the AOPs, such as reducing catalysts and chemicals usage and costs. Quenching experiments demonstrated that OH was the predominant active species induced the photodegradation of OTC. With the development of nanobubbles technology, it is anticipated to realize totally chemicals free green technology. This study provides a novel nanobubble/AOPs technology, which will be more efficient and environmental friendly and will have broad application in waste water treatment and drinking water purification