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In this paper a study of the electrocatalytic oxidation of salicylic acid (SA) at a Pt electrode coated with a Co/Al hydrotalcite-like compound (Co/Al HTLC coated-Pt) film is presented. The voltammetric behaviour of the modified electrode in 0.1M NaOH shows two different redox couples: Co(II)/Co(III) and Co(III)/Co(IV). The electrocatalysis occurs at the same potential of the latter couple, showing that Co(IV) centers act as the oxidant. The CV investigation demonstrates that the process is controlled both by mass and charge transfer and that the Co(IV) centers involved in the oxidation are two for each SA molecule. The estimated value of the catalytic constant is 4×10(4) M(-1) s(-1). The determination of salicylic acid was performed both by DPV and chronoamperometry. The linearity ranges and the LOD values resulted 1×10(-5) to 5×10(-4), 5×10(-7) to 1×10(-4), 6×10(-6) and 2×10(-7) M, respectively. The Co/Al HTLC electrode has been used for SA determination in BAYER Aspirina® and the obtained results are consistent with an independent HPLC analysis.

L'analisi dei bromati nelle acque potabili pone dei problemi analitici sia dal punto di vista dei limiti di rilevabilità che dall'interferenza che può essere causata dalla matrice

Iron is the most abundant transition metal in the atmosphere and can play a significant role in cloudwater chemistry where its reactivity is closely related to the partitioning between Fe(II) and Fe(III). The objective of this work is to determine the total iron content and the iron speciation in a free tropospheric site, and to understand which factors influence these parameters. We collected 147 samples of cloudwater during 34 cloud events over a period of four years at the puy de Dˆome summit. Besides iron we measured other chemical compounds, solar radiation, physico-chemical and meteorological parameters potentially connected with iron reactivity. The total iron concentrations ranged from 0.1 to 9.1 μMwith the major frequency occurring at low levels. The pH and presence of organic complexants seem to be the most significant factors connected with total dissolved iron; while the iron oxidation state seems to be an independent factor. Light intensity, presence of complexants or oxidants (H2O2) do not influence the Fe(II)/Fe(Total) ratio, that was quite constant at about 0.75. This could be due to the potential redox that forces the Fe(II)-Fe(III) couple to the reduced form or, more probably to the complexation by Natural Organic Matter, that can stabilize iron in its reduced form and prevent further oxidation. Our field measurements did not show the diurnal cycle observed in surface water and predicted by models of atmospheric chemistry. This result prompts a more careful review of the role of iron and, by analogy, all the transition metals in atmospheric liquid phase, often over-estimated in the literature.

Formaldehyde and hydrogen peroxide are key constituents of atmospheric photochemical processes, in particular those involved in the HOx and NOx cycles. Direct photolysis of hydrogen peroxide is a source of radicals in both gas and aqueous phases and could therefore be used as an indicator of photochemical activity. Formaldehyde is both a primary pollutant and is produced by oxidation of organic compounds by reactions that can take place both in gas and liquid phases. As such, it can be considered an indicator of organic matter state of oxidation. Quantifying the behaviour of these 2 species in clouds is therefore of importance to better constraining the relative importance of gaseous versus liquid phase processes and to check the validity of current cloud chemistry models. In this study, we have used four years of cloud samples collected at the puy de Dôme atmospheric station to investigate the seasonal and diurnal dependence of both H2O2 and HCHO concentrations. A significant seasonal and diurnal dependence of H2O2 concentration in cloud droplets is found with maxima during summer time and round noon time. This shows that solar radiation is one of the most important factors that drive the cloud aqueous hydrogen peroxide concentration. On the contrary, the aqueous concentrations of HCHO do not appear to be linked to solar intensity. In addition, cloud samples collected at puy de Dôme have been used in laboratory experiments to better understand chemical phase processes. Both natural cloud samples and artificial cloud solutions were irradiated in a photo-reactor and the variations of pH, redox potential and key atmospheric substances (HCHO, H2O2, dissolved organic carbon (DOC), and carboxylic acids) were continuously monitored during the experiments. The behaviour of cloud samples differs significantly from that of artificial solutions. H2O2 concentration during the irradiations shows a decrease of about 15% h−1 while it usually increases for artificial solutions. DOC is not varying, while the behaviour of carboxylic acids and formaldehyde appears to depend on the cloud pH. These results lead to the conclusion that H2O2 in cloud is mainly produced by gas-to liquid transfer and subsequently photo-chemically consumed in the cloud water. Instead, the processes controlling the concentration of HCHO are more complex and clearly change with cloud pH, and hence the degree of anthropogenic influence of the air mass.

Chemical and physical processes in the atmospheric multiphase systems significantly influence the transport, vertical redistribution, chemical transformation, and removal of chemical species from the atmosphere, and hence impact on the lifetime of both aerosols and gases. The chemical composition of cloud droplets is an important indicator of the oxidative properties of the atmospheric liquid phase. At present, most of the available knowledge in cloud chemical composition is derived from experimental field campaigns and, hence, only provides limited information on the temporal evolution of cloud chemistry. In this study, we compiled 5 years of measurements performed at the puy de Dôme atmospheric station (1465m a.s.l., Central France) and corresponding to more than 40 cloud events and 175 collected samples. Samples have been collected throughout the year for several seasons and at different time of nights and days. Because air masses reaching the sampling site have different origins (Marine/Atlantic Ocean, Continental, Saharan) and degree of anthropogenic influence, the data base offers a very complete view of cloud composition variability. To our knowledge, this corresponds to one of the largest data base available from a free tropospheric site. A set of parameters has been measured in each cloud sample and includes pH, conductivity, redox potential, dissolved organic carbon, cations and anions. In some cases, the measurements are completed by the determination of liquid phase concentrations of Fe(II)/Fe(III), HCHO, H2O2 as well as of the cloud liquid water content (LWC). In addition, the data base is completed by measurements performed in a continuous basis at the station, including reactive gases and aerosol physical, chemical and optical properties. Meteorological and radiative measurements are also available at the station. Back-trajectory analyses are regularly computed to establish a climatology of the different air masses advected to the sampling site. Our results show no significant seasonal dependence of the cloud chemical composition that appears to be rather driven by the air mass origin. Clearly, we can distinguish a significant human impact on cloud chemical composition identified with very low pH and increased redox potential, DOC and NO−3 concentrations. On a climatological basis, the LWC does not appear to be driving the total ionic content (TIC) that is mostly controlled by the concentration of cloud condensation nuclei and soluble gas phase species concentrations.

Atmospheric aerosol impact on climate is one of the most uncertain aspects of the climate change. The need for a better knowledge of its physical, chemical and optical properties, as well as there seasonal and inter-annual variations, was clearly expressed by the scientific community. In particular, long term measurements series available for the free troposphere are scarce, although it is crucial to better understand the origin, the different properties, and the role of aerosol particles on climate processes in the Troposphere. The site of the puy de Dôme (Central France, 1465 m.a.s.l.) lies in the free troposphere most of the time. Continuous measurements of aerosols properties (number size distribution, optical properties and chemical composition), combined with in-situ meteorological instrumentation and continuous measurements of reactive gaseous species (O3, NOx, NOy, HCHO, CO and SO2) have been performed over the past years. We will present the evolution over a 3-year period of aerosol chemical, optical and physical properties at this site. The puy de Dôme site is dominantly under the influence of westerly winds although advection of air masses from Northern and Eastern Europe as well as episodes of Saharan dust occurs frequently. Weekly filter samples have been collected and analyzed for their inorganic and organic contents. The variations of both carbonaceous matter (Elemental and Organic Carbon, (EC and OC), divided into water soluble and insoluble organic carbon (WSOC and WISOC and organic acids)) and inorganic species show significant seasonal variability The variations of the chemical properties are analyzed as a function of the air mass trajectory and linked to the optical (black carbon concentrations and diffusion coefficient) and physical (Number concentration and, for some periods, size distribution) properties. This analysis permits a classification of aerosol properties associated to the different air masses encountered at the puy de Dôme. This data set will be of interest model validation in an area (free troposphere, Western Europe) that is still poorly documented.

In order to studying the concentration and the chemical characterization of atmospheric particulate in the different season in all the Italian territory, inside the SITECOS project (PRIN 2004), a gravimetric sampling campaigns have been conducted. The PM10 and PM2.5 samplings were placed at the same time in different sites along the Italian peninsula. The sampling sites were: Bari, Taranto, Pollino (m.1800, remote site), Catania, Sesto Fiorentino, Florence, Arezzo, Grosseto, Capannori-LU, Prato, Montale-PT (rural site), Bologna and Monte Cimone (m.2100, remote site on Italian Apennines), Padua, Milan, San Colombano (m.2300, remote site on Italian Alps), Trieste and San Rocco a Muggia (TS). Daily PM2.5 and PM10 samples have been collected, to do a “sampling bank “, available for a further chemical / physical / toxicological characterization of atmospheric particulate Samples have been chemically characterized according to their main species: PAHs, inorganic ions and EC/OC in the PM2.5 samples; elements in the PM10 samples. In the Padana plain (Milan, Bologna, Padua) the PM concentration is uniform and a strong seasonal trend is observed, with the highest values in winter time and the lowest values in summer while PM concentration in S. Colombano and Monte Cimone sites show an opposite seasonality, with the highest values in summer and the lowest ones in winter. These data show a slight evolution during the winter’s day because of the height of the dispersion layer, in connection with microclimatic parameters; for example in Milan city during acute cases of pollution, the height is no more that 300m (Ferrero et al., 2006). Remote sites of S. Colombano and Monte Cimone in the winter time are above the boundary layer while during summer period they are on it. In the center of Italy PM seasonality concentration is less important while in the South Italy and in Sicily there is any seasonal trend. The reasons are, in part, linked to the different meteoclimatic features present in the Italian peninsula. Chemical composition data show a significant differences. In the North of Italy there is a strong seasonality of ionic component; in particular, during the winter, the Nitrate concentration is higher than the Sulfate one while the situation is opposed in summer. Ammonium does not show a strong seasonality, but it remains pretty constant; the same applies to Carbon. In the South of Italy cities, SO , NO 3 - and NH 4 + , primary component of inorganic ions, they do not show a seasonality with a Sulfate concentration that is always higher than Nitrates. In the center of Italy the seasonality is less marked thanks to the inorganic ions. Sulfate and Nitrate are similar from a percentage point of view. Also PAHs (expressed in weight/weight, quality of particulate), in the Padana plain, shows a strong seasonality, with a high percentage in the winter season and a lower one in summer (Ravindra et al., 2006). Over the year concentrations are constant in South of Italy, while in the center area, the seasonality is less strong. The vehicles traffic source is estimated to be one of the main PM source in the Padana plain, while in the South of Italy there are other sources like photochemistry reactivity, Saharan Dust events, etc. These results show a different role of PM sources along the Italian peninsula and they carry fundamental information for a correct management of the complex problem on a national scale. Ferrero, L., Lazzati, Z., Lo Porto, C., Perrone, M.G., Petraccone, S., Sangiorgi, G., Bolzacchini, E., (2006) Vertical distribution of particulate matter in the urban atmosphere of Milan. Poster. International Aerosol Conference 2006. Ravindra, K., Bencs, L., Wauters, E., Hoog, J., Deutsch, F., Roekens, E., Bleux, N., Berghmans, P., Van Grieken, R., (2006) Seasonal and sitespecific variation in vapour and aerosol phase PAHs over Flanders (Belgium) and their relation with anthropogenic activities. Atmospheric Environment 40 (2006) 771-785.