Browsing by Autor "Francesco Zaratti"

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Análisis de correlación entre actividad solar y columna de ozono a latitudes tropicales
(2002) Flavio Ghezzi; Pablo Saavedra; Eduardo Palenque; Francesco Zaratti
Climatology of the ozone layer and the impact of uv radiation in the environment
(2010) Neusa Paes Leme; Damaris Kirsch Pinheiro; C. Casiccia; Eduardo Quel; Elian Wolfran; Francesco Zaratti
Measurements of UV
Comment on “Record solar UV irradiance in the tropical Andes, by Cabrol et al.”
(Frontiers Media, 2015) Richard McKenzie; G. Bernhard; S. Madronich; Francesco Zaratti
OPINION article Front. Environ. Sci., 08 April 2015Sec. Environmental Toxicology Volume 3 - 2015 | https://doi.org/10.3389/fenvs.2015.00026
CRISIS DEL OZONO Y CRISIS CLIMÁTICA: SIMILITUDES Y DIFERENCIAS
(2009) Francesco Zaratti
DNA damage and photosynthetic inhibition induced by solar ultraviolet radiation in tropical phytoplankton (Lake Titicaca, Bolivia)
(Taylor & Francis, 2001) E. Walter Helbling; Virginia E. Villafañe; Anita G. J. Buma; Marcos Andrade; Francesco Zaratti
Experiments were conducted during October 1998 in Lake Titicaca, Bolivia (16° S, 68° W, 3810 m a.s.l), to determine the effects of solar ultraviolet radiation (UVR) on phytoplankton photosynthetic rates and DNA damage. Water samples were taken daily and incubated in situ or in simulated in situ conditions using sharp cut-off filters to eliminate various portions of the UVR spectrum. The total inhibition of photosynthesis due to UVR in surface waters was 85%; the greatest part of this inhibition (65%) was due to UVAR (315–400 nm), the rest (20%) being due to UVBR (280–315 nm). The inhibition of photosynthesis decreased with depth so that there were no significant differences among treatments at 1.3 optical depths (K PAR). The loss of carbon assimilation in the integrated production over the euphotic zone (4.6 optical depths) was 17.4%, with 14% due to UVAR and an additional 3.4% due to UVBR. Lake Titicaca phytoplankton had a reshold for inhibition of photosynthesis at about 0.3 W m−2 for UVBR and 5 W m−2 for UVAR, below which no inhibition was detected. Above this threshold, photosynthetic inhibition increased steadily, with UVAR having the greatest effect. Analysis of biological weighting functions (BWFs) indicated that phytoplankton from Lake Titicaca was less sensitive to UVR than phytoplankton from other regions. DNA damage (evaluated through the formation of cyclobutane pyrimidine dimers, CPDs) was observed for a simulated worst-case situation (i.e. samples incubated in full sunlight) and significant CPD accumulation was found as a result of UVBR exposure, but not with UVAR. However, absolute levels of damage were relatively low when compared with results obtained at other locations, also suggesting the low sensitivity of Lake Titicaca phytoplankton to UVR. It seems that UVBR stress in these organisms acts via at least two cellular targets: the photosynthetic apparatus and nuclear DNA. Our results suggest that an eventual enhancement of UVBR, due to ozone depletion, would have little impact on the phytoplankton of Lake Titicaca.
DNA damage and photosynthetic inhibition induced by solar ultraviolet radiation in tropical phytoplankton (Lake Titicaca, Bolivia)
(Taylor & Francis, 2001) E. Walter Helbling; Virginia E. Villafañe; Anita G. J. Buma; Marcos Andrade; Francesco Zaratti
Experiments were conducted during October 1998 in Lake Titicaca, Bolivia (16° S, 68° W, 3810 m a.s.l), to determine the effects of solar ultraviolet radiation (UVR) on phytoplankton photosynthetic rates and DNA damage. Water samples were taken daily and incubated in situ or in simulated in situ conditions using sharp cut-off filters to eliminate various portions of the UVR spectrum. The total inhibition of photosynthesis due to UVR in surface waters was 85%; the greatest part of this inhibition (65%) was due to UVAR (315–400 nm), the rest (20%) being due to UVBR (280–315 nm). The inhibition of photosynthesis decreased with depth so that there were no significant differences among treatments at 1.3 optical depths (K PAR). The loss of carbon assimilation in the integrated production over the euphotic zone (4.6 optical depths) was 17.4%, with 14% due to UVAR and an additional 3.4% due to UVBR. Lake Titicaca phytoplankton had a reshold for inhibition of photosynthesis at about 0.3 W m−2 for UVBR and 5 W m−2 for UVAR, below which no inhibition was detected. Above this threshold, photosynthetic inhibition increased steadily, with UVAR having the greatest effect. Analysis of biological weighting functions (BWFs) indicated that phytoplankton from Lake Titicaca was less sensitive to UVR than phytoplankton from other regions. DNA damage (evaluated through the formation of cyclobutane pyrimidine dimers, CPDs) was observed for a simulated worst-case situation (i.e. samples incubated in full sunlight) and significant CPD accumulation was found as a result of UVBR exposure, but not with UVAR. However, absolute levels of damage were relatively low when compared with results obtained at other locations, also suggesting the low sensitivity of Lake Titicaca phytoplankton to UVR. It seems that UVBR stress in these organisms acts via at least two cellular targets: the photosynthetic apparatus and nuclear DNA. Our results suggest that an eventual enhancement of UVBR, due to ozone depletion, would have little impact on the phytoplankton of Lake Titicaca.
El eclipse solar en Bolivia
(1995) Francesco Zaratti; Carmen Rosa Serrano
Erythemally weighted UV variations at two high‐altitude locations
(American Geophysical Union, 2003) Francesco Zaratti; Ricardo Forno; J. García Fuentes; Marcos Andrade
A field campaign, with the purpose of measuring the rate of integrated erythemally weighted ultraviolet radiation (UVR) with altitude, was carried out at two high‐altitude locations near La Paz, Bolivia. The horizontal distance between the two sites is 25 km and they differ in height by 2 km. Irradiance data were obtained only on clear days and were analyzed using three different methods: (1) by comparison of integrated erythemal solar UV irradiances (daily doses) at both locations; (2) by calculation of the slope of the plot of the irradiance at the higher location against the irradiance at the lower location at the same time; and (3) by the asymptotic ratio, based on Beer's law, of the irradiances. The results show that erythemally weighted UV irradiance increases with altitude at an approximate rate of 7% per kilometer. The experimental data were compared with the output of a well‐known radiative model for local conditions. A sensitivity study of the nonmeasured input parameters indicated that the modeled rates of increase are slightly lower than the measured ones. Even more, these rates are not very sensitive to reasonable variations of the unknown parameters.
Estudio de estabilidad del Brewer #110 y de desgaste de las lámparas de calibración portátiles
(2001) Ricardo Forno; Francesco Zaratti
Fixed scale transformation applied to fractal aggregation with levy flight particle trajectories
(Elsevier BV, 1995) Francesco Zaratti; Ignacio Ruiz; L. Pietronero; Alessandro Vespignani
Inhibition of phytoplankton photosynthesis by solar ultraviolet radiation: studies in Lake Titicaca, Bolivia
(Wiley, 1999) VirginiaE. Villafa�e; Marcos Andrade; V. Lairana; Francesco Zaratti; E. Walter Helbling
1. Lake Titicaca is a large, high altitude (3810 m a.s.l.) tropical lake (16°S, 68°W) that lies on the border of Bolivia and Perú, receiving high fluxes of ultraviolet radiation (UVR) throughout the year. Our studies were conducted during September of 1997 with the main objective of studying the impact of solar UVR upon phytoplankton photosynthesis. 2. Water samples were taken daily and incubated in situ (down to 14 m depth) under three radiation treatments to study the relative responses to PAR (Photosynthetic Available Radiation, 400–700 nm), UV‐A (320–400 nm), and UV‐B (280–320 nm) radiation. 3. Photosynthetic inhibition by UVR in surface waters was about 80%, with UV‐A accounting for 60% and UV‐B for 20%; the inhibition by high levels of PAR was less than 20%. The inhibition due to UVR decreased with depth so that there were no significant differences between treatments at 8.5 m depth. 4. The amount of inhibition per unit energy received by phytoplankton indicates that even though there was a significant inhibition of photosynthesis due to UVR, species in Lake Titicaca seem to be better adapted than species in high latitude environments. 5. The cellular concentration of UV‐absorbing compounds, a possible mechanism of photoadaptation, was low in phytoplanktonic species. However, they were abundant in zooplankton, suggesting a high rate of bioaccumulation through the diet.
Investigations on the effect of high surface albedo on erythemally effective UV irradiance: Results of a campaign at the Salar de Uyuni, Bolivia
(Elsevier BV, 2007) Joachim Reuder; Flavio Ghezzi; Eduardo Palenque; Rene Torrez; Marcos Andrade; Francesco Zaratti
LALINET: The First Latin American–Born Regional Atmospheric Observational Network
(American Meteorological Society, 2016) Juan Carlos Antuña; Eduardo Landulfo; René Estevan; Boris Barja; Alan Robock; Elián Wolfram; P. Ristori; B. R. Clemesha; Francesco Zaratti; Ricardo Forno
Abstract Sustained and coordinated efforts of lidar teams in Latin America at the beginning of the twenty-first century have built the Latin American Lidar Network (LALINET), the only observational network in Latin America created by the agreement and commitment of Latin American scientists. They worked with limited funding but an abundance of enthusiasm and commitment toward their joint goal. Before LALINET, there were a few pioneering lidar stations operating in Latin America, described briefly here. Biannual Latin American lidar workshops, held from 2001 to the present, supported both the development of the regional lidar community and LALINET. At those meetings, lidar researchers from Latin America met to conduct regular scientific and technical exchanges among themselves and with experts from the rest of the world. Regional and international scientific cooperation has played an important role in the development of both the individual teams and the network. The current LALINET status and activities are described, emphasizing the processes of standardization of the measurements, methodologies, calibration protocols, and retrieval algorithms. Failures and successes achieved in the buildup of LALINET are presented. In addition, the first LALINET joint measurement campaign and a set of aerosol extinction profile measurements obtained from the aerosol plume produced by the Calbuco volcano eruption on 22 April 2015 are described and discussed.
Medidas de albedo en UV-b en el salar de Uyuni
(2010) Francesco Zaratti; Ricardo Forno; Gonzalo Gutiérrez; Roger Apaza; Fernando Velarde
Se reportan los resultados finales del proyecto bianual, centrado en dos campa ˜nas de medici ´on de la Radiaci´on Ultravioleta (RUV) en el Salar de Uyuni: la primera en mayo de 2008 y la otra en noviembre de 2008. Los datos recogidos en ambas campa ˜nas y el an´alisis respectivo han permitido llegar a importantes resultados en los dos objetivos principales del proyecto: medida del albedo superficial en la banda UV y cuantificaci ´on del alcance del mismo en la regi´on circundante al Salar. En el primer objetivo, se han encontrado indicios s´olidos de que el albedo depende no s´olo de la estaci´on del a ˜no, como se podr´ia esperar debido al r´egimen de lluvias localizado en los meses de enero a marzo, sino tambi´en de los cambios clim´aticos que se est ´an dando en la regi´on, lo que podr´ia conllevar una disminuci ´on del albedo, se ˜nal del “ensuciamiento” del Salar. Adicionalmente se ha medido el alcance de los efectos de albedo en el Salar, pero el an´alisis no muestra a ´un resultados concluyentes
Medidas de RUV-B en una localidad en altura: El caso de La Paz, Bolivia
(1997) Marcos Andrade; R.N Forno; Eduardo Palenque; Francesco Zaratti
Proposal for a modification of the UVI risk scale
(Springer Science+Business Media, 2014) Francesco Zaratti; Rubén D. Piacentini; Héctor A. Guillén; Sergio Cabrera; Ben Liley; Richard McKenzie
Resultados preliminares de la campaña de ozonosondeo en La Paz, Bolivia
(1999) Francesco Zaratti; M Andrade; Rodrigo Lavalhos Dal Forno
Seis años de medidas de ozono y radiación ultravioleta en La Paz, Bolivia
(2003) Francesco Zaratti; Ricardo Forno; Pablo Saavedra; Lucy Cuarita
UV-B measurements in a high altitude location: the case for La Paz, Bolivia
(1997) Marcos Andrade; Ricardo Forno; Eduardo Palenque; Francesco Zaratti
UV‐B optical thickness observations of the atmosphere
(American Geophysical Union, 2001) V. W. J. H. Kirchhoff; A. A. Silva; Camilla Costa; Neusa Paes Leme; Hamilton Germano Pavão; Francesco Zaratti
The optical thickness of the atmosphere, τ, was deduced from measurements of narrowband direct solar UV‐B radiation. A measurement campaign was organized to obtain the radiation at three different sites, during the month of August 1999, using the same methods and instruments, in order to deduce the atmospheric optical thickness in the spectral UV‐B range (280–320 nm). The three observation sites were chosen to cover a wide range of measurement conditions; located near the tropical Atlantic Ocean (Natal, 5.8°S, 35.2°W), on the Andes mountains (La Paz, 16.5°S, 68.1°W), and in the biomass burning area of central Brazil (Campo Grande, 19.2°S, 54.3°W). The UV‐B measurements were made with a Brewer spectrophotometer at each site. Since the instrument measures atmospheric ozone and SO 2 simultaneously, it is possible, from the total atmospheric optical thickness τ, to deduce the aerosol optical thickness τ aerosol . The results have been combined in different ways to compare with satellite data, showing good performance. Time variations as short as about 10 min can be seen. On clear days the time variations are relatively small, as expected. On the other hand, for the biomass burning site, for conditions of mixed air masses (the instrument is not looking directly at plumes) one can see very large variations in τ in relatively short time intervals, for example, for one case, from 3.5 to 7.0 in about 30 min. Absolute values for τ at Natal and La Paz were near 2.0 and at Campo Grande, between 2.5 and 3.0, but with occasional highs of about 4.5. For τ aerosol , Natal and La Paz had values between 0.0 and 0.4, whereas Campo Grande had most values near 0.4, with occasional highs near 1.0, 1.2, and 2.2.