In aquatic systems, fulvic acids (FAs) are expected to play key roles on the stability and aggregation behavior of manufactured nanoparticles (NPs). The exact conditions under which aggregation or dispersion occurs will depend on the nanoparticle surface charge properties, FAs concentration as well as solution conditions, such as pH and ionic strength. The systematic calculation of stability (aggregation versus disaggregation) diagrams is therefore a key aspect in the prediction of the environmental fate and behavior of manufactured nanoparticles in aquatic systems. In this study, the responses to changes in pH and FAs concentrations on the resulting surface charge of purified iron oxide nanoparticles (53 nm nominal diameter) is investigated. By adjusting the pH, different nanoparticle surface charge electrostatic regions are found, corresponding to positively, neutral, and negatively charged nanoparticle solutions. For each situation, the adsorption of negatively charged FAs at variable concentrations is considered by analyzing surface charge modifications and calculating experimental kinetics aggregation rates. Results show that, under the conditions used, and range of FAs environmental relevant conditions, the nanoparticle aggregation process is promoted only when the nanoparticle positive surface charge (solution pH less than the charge neutralization point) is compensated by the adsorption of FAs. In all the other cases, FAs adsorption and increase of FAs concentration are expected to promote not only the NPs stabilization but also the disaggregation of NPs aggregates. In addition, our study suggest that very low concentrations of FAs [0.1 mg/l are sufficient to rapidly stabilize iron hydroxide NPs solutions at concentration \5 mg/l.

The influence of aerosols on climate is highly dependent on the particle size distribution, concentration, and composition. In particular, the latter influences their ability to act as cloud condensation nuclei, whereby they impact cloud coverage and precipitation. Here, we simultaneously measured the concentration of aerosols from sea spray over the North Atlantic on board the exhaust-free solar-powered vessel “PlanetSolar”, and the sea surface physico-chemical parameters. We identified organic-bearing particles based on individual particle fluorescence spectra. Organic-bearing aerosols display specific spatio-temporal distributions as compared to total aerosols. We propose an empirical parameterization of the organic-bearing particle concentration, with a dependence on water salinity and sea-surface temperature only. We also show that a very rich mixture of organic aerosols is emitted from the sea surface. Such data will certainly contribute to providing further insight into the influence of aerosols on cloud formation, and be used as input for the improved modeling of aerosols and their role in global climate processes.

This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. Flocculation studies between cationic polymers and oppositely charged colloidal particles are reported in which both flocculation kinetics and floc structures are systematically investigated. The flocculation rate constant, stability ratio and kinetics laws are experimentally determined using particle counting for two polymer architectures; a cationic linear polymer and a two-branched polymer. Comparisons are also made using NaCl at different ionic concentrations for the destabilization of the colloidal particles. Detailed measurements of electrophoretic mobility and kinetics rate constants on varying the polymer dosage are reported. Results suggest that the polymer architecture plays important roles on the polymer dosage for the rapid destabilization of the colloidal suspension. The branched polymer at optimal dosage exhibits the highest flocculation rate constant, whereas on the other hand, the linear polymer concentration range of flocculation is larger. In both cases, polymer flocculation is more efficient by a factor of 5e6 than charge screening effects due to the presence of salt. Analysis of the stability ratio indicates that tele-bridging flocculation and electrostatic forces dictate the stability of the charged latex particle suspension. It is shown that the fractal concepts which are valid for aggregation processes are also applicable here and branched polymers as well as linear polymers yield to the formation of compact flocs in comparison to those obtained with salt.

Manufactured nanoparticles are now present in many daily use commercial products such as cosmetics, paints, food packaging, etc. One of the main consequences regarding the environment is their uncontrolled release and diffusion in the aquatic systems. To explore their environmental behavior in term of stability, coagulation and dissociation, it is important to perform investigation at the laboratory scale as a prerequisite for understanding their environmental behaviors. In this study, the stability of titanium dioxide (TiO 2 nanoparticles as a function of pH and fulvic acid concentration (one of the major organic component found in aquatic systems) is systematically examined by measuring the size and zeta potential variations of TiO 2 nanoparticles, fulvic acids mixtures and aggregates they can form. Experiments are also conducted at three different pH values corresponding to the three possible TiO 2 surface charge states: positive, neutral, and negative. The TiO 2 size and zeta potential evolution is then examined as a function of the concentration of negatively charged fulvic acids (FAs) by increasing successively the fulvic acids concentrations. Our results point out that in absence of fulvic acids, TiO 2 aggregation is achieved for pH values between 5 and 8 i.e., when the nanoparticle surface charge is close to the point of zero charge. At low and high pH values, nanoparticle surface charges result in strong electrostatic repulsions hence preventing aggregation. In presence of fulvic acids fast aggregation is achieved at low pH and with fulvic acids concentration comprised between 4 and 8 mg/L. In such conditions the nanoparticle surface charge neutralization is achieved via the adsorption of the negative fulvic acids on the positively charged nanoparticles. By increasing further the fulvic acids concentration, surface charge inversion is obtained then resulting in the restabilization of the nanoparticle solution via aggregate fragmentation (disaggregation). At high pH, the negatively charged fulvic acids are not found to adsorb significantly on the negatively charged nanoparticles. These results clearly pointed out the role of the pH, electrostatic interactions and FAs concentrations on the stability of NPs such as TiO 2 . It is shown that the environmental FAs concentrations are self-important to promote the dispersion of 50 mg/L TiO 2 nanoparticle solutions including aggregates.

The influence of the increase of the solution ionic strength on the flocculation of charged latex particles in the presence of cationic polymers is reported. Empirical flocculation rate constants are experimentally determined using particle counting and for two cationic polymers, one linear and the second with two branches. Comparisons are made with a solution containing monovalent salt only at different ionic concentrations in the absence of polymers. In all cases, polymer-induced flocculation is significantly more efficient than charge screening effects using salt only. Analysis of zeta potential measurements indicates that the charge neutralization and surface charge variations dictate the stability of the latex suspensions. Moreover, the addition of a small amount of salt in the polymer-particle mixtures results in a dramatic decrease of the polymer efficiency which is more pronounced for the linear polymeric flocculant. By increasing further the ionic strength, the rates of polymer flocculation are found to increase again but remain smaller than in the absence of salt.