The role of ammonia in sulfuric acid ion induced nucleation

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Atmos. Chem. Phys., 8, 2859–2867, 2008 © Author(s) 2008. This work is distributed under the Creative Commons Attribution 3.0 License. Atmospheric Chemistry and Physics The role of ammonia in sulfuric acid ion induced nucleation I. K. Ortega, T. Kurtén, H. Vehkamäki, and M. Kulmala Division of Atmospheric Sciences, Department of Physical Sciences, P.O. Box 64, FI-00014 University of Helsinki, Finland Received: 9 January 2008 – Published in Atmos. Chem. Phys. Discuss.: 17 March 2008 Revised: 20 May 2008 – Accepted: 20 May 2008 – Published: 5 June 2008 Abstract. We have developed a new multi-step strategy for quantum chemical calculations on atmospherically relevant cluster structures that makes calculation for large clusters affordable with a good accuracy-to-computational effort ratio. We have applied this strategy to evaluate the relevance of ternary ion induced nucleation; we have also performed calculations for neutral ternary nucleation for comparison. The results for neutral ternary nucleation agree with previous results, and confirm the important role of ammonia in enhancing the growth of sulfuric acid clusters. On the other hand, we have found that ammonia does not enhance the growth of ionic sulfuric acid clusters. The results also confirm that ioninduced nucleation is a barrierless process at high altitudes, but at ground level there exists a barrier due to the presence of a local minimum on the free energy surface. 1 Introduction Aerosols are ubiquitous in the Earth’s lower atmosphere. They affect human health, visibility, atmospheric chemistry, and climate. Aerosols influence climate directly by scattering and absorbing radiation, and indirectly by acting as cloud condensation nuclei and affecting cloud properties. Gas-toparticle nucleation is an important source of new aerosol particles in the Earth’s atmosphere (Kulmala et al., 2004). A strong correlation has been observed between new-particle formation and sulfuric acid concentrations (Weber et al., 1996, Weber et al., 1997, Kulmala et al., 2006, Sihto et al., 2006, Riipinen et al., 2007). Water is also implicated in the formation of new particles because it is abundant, and because it significantly lowers the saturation vapor pressure of sulfuric acid. However, in many cases the observed rates of particle formation greatly exceed those expected on the Correspondence to: I. K. Ortega ( basis of binary homogeneous sulfuric acid-water nucleation. Although several alternative processes have been proposed, the most realistic candidates are (a) homogeneous ternary water-sulfuric acid-ammonia nucleation, (b) ion-induced nucleation of binary or ternary inorganic vapours or of organic vapours and (c) barrierless homogeneous nucleation of, for example, iodine species (Kulmala et al., 2000; Kulmala 2003; Lovejoy et al., 2004). Atmospheric new-particle formation might actually be a two-step process (Kulmala et al., 2000). The first step would be the nucleation process itself, producing atmospheric (neutral or ion) clusters. The second step would be the activation of clusters for growth (Kulmala et al., 2006). The first step could also include the recombination of atmospheric ion clusters. In the first step, ternary homogenous nucleation seems to be thermodynamically possible in many atmospheric conditions (Anttila et al., 2005). Also ion-induced nucleation has been shown to contribute to observed particle formation events, for example in boreal forest regions (Laakso et al., 2006), though its total contribution to new-particle formation events on the annual scale is very likely to be less than 10% even if ion recombination is included (Kulmala et al., 2007) The precise identities of the participating ionic and neutral molecular species are as yet unknown. Cluster properties predicted by bulk thermodynamics are not valid during the atmospheric nucleation processes. Therefore, quantum chemical studies are needed to find reliable formation pathways for small clusters. Among the proposed mechanisms, one of the less studied is ion-induced ternary nucleation. As far as we know, there is only one work by Kurtén et al. (2007a) dealing with the hydrogensulfate ion – ammonia system; in their work the authors have performed quantum chemical calculations at the MP2/aug-cc-pV(T+d)Z level (with corrections at the MP4/aug-cc-pV(D+d)Z level) on clusters with one sulfuric acid or hydrogensulfate ion and one ammonia. Published by Copernicus Publications on behalf of the European Geosciences Union. 2860 I. K. Ortega et al.: Ammonia in sulfuric acid ion induced nucleation In the present work, we have studied clusters containing one hydrogensulfate ion, one ammonia and up to three sulfuric acid molecules. To evaluate the role of ammonia in the clusters, we also have performed calculation for neutral clusters containing up to four sulfuric acid molecules with and without ammonia, and for charged clusters without ammonia. In order to make affordable the calculation for the largest clusters investigated in this study, a new theoretical strategy has been developed. 2 alytical formulae are available (Jensen, 1998) for the different contributions to the thermal entropies and enthalpies: Hrot = Strans 2.1 Thermodynamics calculation We can approximate the total free energy of these systems as a sum of terms involving translational, rotational, vibrational and electronic states. We have used the rigid-rotor harmonicoscillator (RRHO) approximation, within which standard anAtmos. Chem. Phys., 8, 2859–2867, 2008 Srot (1) 3 RT 2 Hvib = R Computational details Our calculations were performed using a systematic multistep method. The initial guess geometries were chosen using chemical intuition and, when possible, geometries from earlier studies (Kurtén et al., 2007a, b, c; Torpo et al., 2007; Lovejoy et al., 2004). The SPARTAN program (Wavefunction Inc., 2006) was then used to pre-optimize these structures. Once a large enough set of geometries was sampled, the more stable isomers (usually between 6 and 10) were optimized using the SIESTA program (Soler et al., 2002), which is based on DFT, uses linear combinations of atomic orbitals as wave functions, and norm conserving pseudopotentials for the core electrons. Preliminary calculations were performed to choose the best functional and basis set for this system. The gradient corrected BLYP functional (Miehlich et al., 1989) gave the best agreement with experimental molecular geometries, and the double-ζ polarized (DZP) functions were found to be the best compromise between accuracy and computational effort. Vibrational harmonic frequencies were also calculated using this program, and were used to estimate the entropy and thermal contributions to the enthalpy and Gibbs free energy of the clusters. Finally, the optimized structures from the SIESTA program were used to perform single point energy calculations using the TURBOMOLE program (Ahlrichs et al., 1989) with the Resolution of Identity- Coupled Cluster Single and Doubles method (RI-CC2) (Hättig et al., 2000). The chosen basis set was aug-cc-pV(T+d)Z (Dunning Jr., et al., 2001), which is identical to aug-cc-pVTZ for hydrogen, oxygen and nitrogen atoms, and contains one extra set of d-orbitals for the sulfur atoms. The choice of basis set was based on previous results (Kurtén et al., 2007c) which indicate that basis-set effects beyond the aug-cc-pV(T+d)Z level are, at least with the MP2 method, too small (under 0.5 kcal/mol in terms of binding energy per molecule) to justify the computational effort of using e.g. a quadruple-ζ basis. 5 RT 2 Htrans = (2) 3N −6  X i=1 hvi hvi 1 + 2k k ehvi /kT − 1 V 5 = R + R ln 2 NA   √ 3 π = R  + ln  2 σ Svib = R 3N −6  X i=1  2π MkT h2 8π 2 kT h2  3/2 ! !3/2  p I1 I2 I3  (3) (4) (5)   hvi 1 −hvi /kT − ln 1 − e (6) kT ehvi /kT − 1 Gtherm (T , P ) = Htherm (T ) − T S(T , P ) (7) G(T , P ) = Gtherm (T , P ) + E0 (8) In these equations H , S and G are the enthalpy, entropy and free energy respectively, and the subscripts correspond to translational, rotational, vibrational and thermal, R is the ideal gas constant, T is the temperature, h is the Planck constant, k is the Boltzmann constant, ν i are the harmonic frequencies calculated by SIESTA( where the notation index i runs from 1 to total number of frequencies, 3N-6, where N is the number of atoms), M is the molecule mass, V is the molar volume, NA is the Avogadro number, I1,2,3 are the moments of inertia, calculated from SIESTA optimized geometries, σ is the order of the rotational subgroup in the molecular point group (i.e. the number of proper symmetry operations) and E0 is the electronic energy, which is calculated by TURBOMOLE. It should be noted that though the free energies computed using the RRHO approximation are not quantitatively accurate (Kurtén et al., 2007a, Kathmann et al., 2007), they can be used quite reliably to qualitatively compare, e.g., different nucleation pathways, as the effects of anharmonicity tend to cancel out when differences in free energies are calculated. Using as input for these equations the frequencies and moments of inertia obtained from the SIESTA program and the electronic energy calculated with TURBOMOLE, we can calculate enthalpy H , entropy S and Gibbs free energy G for a given temperature T and pressure P . Using this data we can then calculate the clusters’ formation free energies from the isolated molecules using the general expression: 1G(T , P )for = G(T , P )cluster − (nSA G(T , P )SA +nAm G(T , P )Am + nion G(T , P )ion ) (9) I. K. Ortega et al.: Ammonia in sulfuric acid ion induced nucleation 2861 Table 1. Enthalpy change 1H (in units of kcal/mol) comparison between experimental and calculated values. Reaction 1H 295K (Lovejoy et al., 2004) 1H 295K Calculated − H2 SO4 + HSO− 4 → H2 SO4 · HSO4 − H2 SO4 + H2 SO4 ·HSO4 → (H2 SO4 )2 · HSO− 4 − H2 SO4 + (H2 SO4 )2 · HSO− 4 → (H2 SO4 )3 · HSO4 –41.8 –27.4 –23.8 –49.2 –26.8 –23.2 Table 2. The Gibbs formation free energies (relative to molecules with partial pressure 1 atm) in units of kcal/mol at 298, 265 and 242 K are listed as a function of the number of total sulfuric acid molecules and hydrogensulfate ions in the clusters. n SA (H2 SO4 )n (H2 SO4 )n ·NH3 (H2 SO4 )n−1 ·(HSO− 4) (H2 SO4 )n−1 ·(HSO− 4 )·NH3 298 K 2 3 4 –8.84 –9.66 –17.73 –19.15 –28.07 –39.23 –34.52 –52.71 –60.57 –33.05 –66.52 –70.20 265 K 2 3 4 –9.65 –12.54 –21.50 –21.82 –32.11 –43.51 –36.14 –55.28 –62.62 –35.78 –69.79 –75.89 242 K 2 3 4 –10.21 –14.55 –24.12 –23.67 –34.93 –46.50 –37.26 –57.07 –67.78 Where n is the number of molecules of each species in the cluster (subscript SA corresponds to sulfuric acid, Am to ammonia and ion to hydrogensulfate ion). Equation (9) gives the formation free energies at some standard conditions (usually P0 =1 atm and T =298 K), but to obtain a realistic picture of the free energies in atmospheric conditions, we have to take into account the relative concentration of each molecular species in atmosphere. This is done via the law of mass action, with which the calculated free energies can be converted to ambient conditions in terms of the partial pressures of each compound:   P0 1G(PSA, , PAm , Pion ) = 1G(P0 ) + nSA RT ln Psa     P0 P0 + nion RT ln (10) +nAm RT ln PAm Pion Where 1G(P0 ) is the free energy at standard pressure, nSA , nAm and nion , are the number of sulfuric acid, ammonia and hydrogensulfate ion molecules in the cluster andPSA , PAm and Pion are the actual partial pressures of sulfuric acid, ammonia and hydrogensulfate ion at atmospheric conditions. –37.68 –72.07 –79.86 2.2 Methodology performance In order to check the performance of our methodology we have calculated enthalpy changes 1H at 295K for the reac− tions (H2 SO4 )a ·HSO− 4 + H2 SO4 → (H2 SO4 )a+1 ·HSO4 with a=0–2, and compared the results with experimental values given by Lovejoy et al. (2004). The results of the comparison are shown in Table 1. As we can see in the table, our multi-step method overestimates the value of 1H for the first sulfuric acid addition by 7.4 kcal/mol. This difference is mainly due to the high anharmonicity of the HSO− 4 ion, and specifically to the presence of one internal rotation which is incorrectly modeled as a lowfrequency vibration, see, e.g., Kurtén et al. (2007a) for details. As mentioned in the previous section, we are using the harmonic oscillator approximation to obtain the thermodynamic properties of the system, and this particular molecule is not well described with this approximation. We also can see in the table that the difference between calculated and experimental 1H values is much lower (–0.6 kcal/mol) for the reactions not involving the isolated ion, where the participating species are less anharmonic. It should be noted that the error due to the anharmonicity of the hydrogensulfate ion is Atmos. Chem. Phys., 8, 2859–2867, 2008 2862 I. K. Ortega et al.: Ammonia in sulfuric acid ion induced nucleation 2.3 A B C D E F G H I J K L Fig. 1. The most stable clusters: (A) (H2 SO4 )2 , (B) (H2 SO4 )3 , (C) (H2 SO4 )4 , (D) (H2 SO4 )·(HSO− 4 ), (E) (H2 SO4 )2 · (HSO− 4 ), (F) (H2 SO4 )3 ·(HSO− 4 ), (G) (H2 SO4 )2 ·NH3 , (H) (H2 SO4 )3 ·NH3 , (I) (H2 SO4 )4 ·NH3 , (J) (H2 SO4 )·(HSO− 4 )·NH3 , (K) (H2 SO4 )2 ·(HSO− 4 )·NH3 , − (L) (H2 SO4 )3 ·(HSO4 )·NH3 . White atoms are hydrogen, the red ones are oxygen, the yellow ones sulfurs and the blue atoms nitrogen. a constant factor, and does not affect the intercomparison of different ion-induced nucleation mechanisms. It does, however, somewhat decrease the reliability of the comparison of neutral and ion-induced mechanisms to each other. It can be seen that the methodology applied in this paper yields, in general, values that are in good agreement with experimental results. In the case of highly anharmonic molecules the results deviate more form the experimental values, but the difference is comparable to other quantum chemistry methods used to study these systems. Atmos. Chem. Phys., 8, 2859–2867, 2008 Results and discussion Modeling the hydration of sulfuric acid – ammonia clusters is problematic. In typical atmospheric conditions, two-acid clusters can be bound to seven or eight water molecules according to previous results (Kurtén et al., 2007c). The addition of water molecules to the cluster increases the computational effort in two ways. First, increasing the size of the system results in an increment in the CPU time and memory needed for the calculations, and second, the number of possible conformers increases combinatorially with the number of molecules present in the cluster. Also, as the degree of water-water bonding grows, the harmonic oscillator and rigid rotor approximation that we have assumed become less reliable. Previous results (Kurtén et al., 2007b, c; Ianni and Bandy, 1999) indicates that the binding of ammonia to the clusters is only weakly dependent on the water content. The effect is also to some extent systematic: the addition of water molecules tends to somewhat decrease the binding of ammonia to the cluster. Thus, the binding of a few water molecules to the cluster is unlikely to significantly disrupt the bonding pattern of the sulfuric acid – ammonia cluster. As the objective of this work was to study large clusters like (H2 SO4 )4 ·NH3 , which already requires a quite significant computational effort, we have only considered dehydrated clusters. Hydration will certainly change the quantitative results (e.g., the free energy curves), but the qualitative conclusions regarding, e.g., the role of ammonia or the existence of a barrier for ion-induced nucleation are expected to be reliable despite the absence of water molecules in our simulations. Figure 1 shows the structure of the most stable configuration for each cluster, obtained using the SIESTA program with the BLYP functional and the DZP basis set, sometimes the energy difference between the two most stable clusters was below 1 kcal/mol. The structures have been drawn using the MOLDEN 3.8 visualization package (Schaftenaar et al., 2000). Table 2 list the obtained 1Gcluster values (with respect to formation from free molecules) at 298, 265 and 242 K and monomer pressures of 1 atm, as a function of total number of sulfuric acid molecules and HSO− 4 ions in the cluster. The calculation of the thermal contributions to the free energies has been described in the previous section. It can be seen from Table 2 that, as expected from previous studies (Torpo et al., 2007; Nadykto and Yu, 2007), the presence of ammonia in the neutral clusters is favored thermodynamically in comparison with pure sulfuric acid clusters: the free energy for complexation is more negative in clusters with ammonia. From the table we can also see that this free energy lowering at first becomes more important as the number of sulfuric acids increases. However, the magnitude of the effect for the (H2 SO4 )3 ·NH3 +H2 SO4 → (H2 SO4 )4 ·NH3 reaction is less than that for the (H2 SO4 )2 ·NH3 +H2 SO4 → (H2 SO4 )3 ·NH3 reaction. By comparing the ionic and neutral clusters, we can see that the presence of the hydrogensulfate I. K. Ortega et al.: Ammonia in sulfuric acid ion induced nucleation 2863 Table 3. The temperature and vapor pressure values chosen to represent different conditions. 30 Variable 1G1 conditions 1G2 conditions 1G3 conditions Temperature (K) PAM (cm−3 ) PSA (cm−3 ) Pion (cm−3 ) Upper troposphere 242 4.246·108 2.000·107 1.000·103 Mid-troposphere 265 2.769·1010 1.000·107 1.000·103 Ground level 298 2.769·1010 1.000·106 1.000·102 40 242K 25 30 20 25 G (Kcal/mol) 15 G (Kcal/mol) 265K 35 10 5 0 20 15 10 5 -5 0 equilibrium value of MeCpG steps (,+14 deg.) [31,44]. In comparison, methylation has a significantly lower stability cost when happening at major groove positions, such as 211 and 21 base pair from dyad (mutations 9 and 12), where the roll of the nucleosome bound conformation (+10 deg.) is more compatible with the equilibrium geometry of MeCpG steps. The nucleosome destabilizing effect of cytosine methylation increases with the number of methylated cytosines, following the same position dependence as the single methylations. The multiple-methylation case reveals that each major groove meth- PLOS Computational Biology | 3 November 2013 | Volume 9 | Issue 11 | e1003354 DNA Methylation and Nucleosome Positioning ylation destabilizes the nucleosome by around 1 kJ/mol (close to the average estimate of 2 kJ/mol obtained for from individual methylation studies), while each minor groove methylation destabilizes it by up to 5 kJ/mol (average free energy as single mutation is around 6 kJ/mol). This energetic position-dependence is the reverse of what was observed in a recent FRET/SAXS study [30]. The differences can be attributed to the use of different ionic conditions and different sequences: a modified Widom-601 sequence of 157 bp, which already contains multiple CpG steps in mixed orientations, and which could assume different positioning due to the introduction of new CpG steps and by effect of the methylation. The analysis of our trajectories reveals a larger root mean square deviation (RMSD) and fluctuation (RMSF; see Figures S2– S3 in Text S1) for the methylated nucleosomes, but failed to detect any systematic change in DNA geometry or in intermolecular DNA-histone energy related to methylation (Fig. S1B, S1C, S4–S6 in Text S1). The hydrophobic effect should favor orientation of the methyl group out from the solvent but this effect alone is not likely to justify the positional dependent stability changes in Figure 2, as the differential solvation of the methyl groups in the bound and unbound states is only in the order of a fraction of a water molecule (Figure S5 in Text S1). We find however, a reasonable correlation between methylation-induced changes in hydrogen bond and stacking interactions of the bases and the change in nucleosome stability (see Figure S6 in Text S1). This finding suggests that methylation-induced nucleosome destabilization is related to the poorer ability of methylated DNA to fit into the required conformation for DNA in a nucleosome. Changes in the elastic deformation energy between methylated and un-methylated DNA correlate with nucleosomal differential binding free energies To further analyze the idea that methylation-induced nucleosome destabilization is connected to a worse fit of methylated DNA into the required nucleosome-bound conformation, we computed the elastic energy of the nucleosomal DNA using a harmonic deformation method [36,37,44]. This method provides a rough estimate of the energy required to deform a DNA fiber to adopt the super helical conformation in the nucleosome (full details in Suppl. Information Text S1). As shown in Figure 2, there is an evident correlation between the increase that methylation produces in the elastic deformation energy (DDE def.) and the free energy variation (DDG bind.) computed from MD/TI calculations. Clearly, methylation increases the stiffness of the CpG step [31], raising the energy cost required to wrap DNA around the histone octamers. This extra energy cost will be smaller in regions of high positive roll (naked DNA MeCpG steps have a higher roll than CpG steps [31]) than in regions of high negative roll. Thus, simple elastic considerations explain why methylation is better tolerated when the DNA faces the histones through the major groove (where positive roll is required) that when it faces histones through the minor groove (where negative roll is required). Nucleosome methylation can give rise to nucleosome repositioning We have established that methylation affects the wrapping of DNA in nucleosomes, but how does this translate into chromatin structure? As noted above, accumulation of minor groove methylations strongly destabilizes the nucleosome, and could trigger nucleosome unfolding, or notable changes in positioning or phasing of DNA around the histone core. While accumulation of methylations might be well tolerated if placed in favorable positions, accumulation in unfavorable positions would destabilize the nucleosome, which might trigger changes in chromatin structure. Chromatin could in fact react in two different ways in response to significant levels of methylation in unfavorable positions: i) the DNA could either detach from the histone core, leading to nucleosome eviction or nucleosome repositioning, or ii) the DNA could rotate around the histone core, changing its phase to place MeCpG steps in favorable positions. Both effects are anticipated to alter DNA accessibility and impact gene expression regulation. The sub-microsecond time scale of our MD trajectories of methylated DNAs bound to nucleosomes is not large enough to capture these effects, but clear trends are visible in cases of multiple mutations occurring in unfavorable positions, where unmethylated and methylated DNA sequences are out of phase by around 28 degrees (Figure S7 in Text S1). Due to this repositioning, large or small, DNA could move and the nucleosome structure could assume a more compact and distorted conformation, as detected by Lee and Lee [29], or a slightly open conformation as found in Jimenez-Useche et al. [30]. Using the harmonic deformation method, we additionally predicted the change in stability induced by cytosine methylation for millions of different nucleosomal DNA sequences. Consistently with our calculations, we used two extreme scenarios to prepare our DNA sequences (see Fig. 3): i) all positions where the minor grooves contact the histone core are occupied by CpG steps, and ii) all positions where the major grooves contact the histone core are occupied by CpG steps. We then computed the elastic energy required to wrap the DNA around the histone proteins in unmethylated and methylated states, and, as expected, observed that methylation disfavors DNA wrapping (Figure 3A). We have rescaled the elastic energy differences with a factor of 0.23 to match the DDG prediction in figure 2B. In agreement with the rest of our results, our analysis confirms that the effect of methylation is position-dependent. In fact, the overall difference between the two extreme methylation scenarios (all-in-minor vs all-in-major) is larger than 60 kJ/mol, the average difference being around 15 kJ/ mol. We have also computed the elastic energy differences for a million sequences with CpG/MeCpG steps positioned at all possible intermediate locations with respect to the position (figure 3B). The large differences between the extreme cases can induce rotations of DNA around the histone core, shifting its phase to allow the placement of the methylated CpG steps facing the histones through the major groove. It is illustrative to compare the magnitude of CpG methylation penalty with sequence dependent differences. Since there are roughly 1.5e88 possible 147 base pairs long sequence combinations (i.e., (4n+4(n/2))/2, n = 147), it is unfeasible to calculate all the possible sequence effects. However, using our elastic model we can provide a range of values based on a reasonably large number of samples. If we consider all possible nucleosomal sequences in the yeast genome (around 12 Mbp), the energy difference between the best and the worst sequence that could form a nucleosome is 0.7 kj/mol per base (a minimum of 1 kJ/mol and maximum of around 1.7 kJ/mol per base, the first best and the last worst sequences are displayed in Table S3 in Text S1). We repeated the same calculation for one million random sequences and we obtained equivalent results. Placing one CpG step every helical turn gives an average energetic difference between minor groove and major groove methylation of 15 kJ/ mol, which translates into ,0.5 kJ/mol per methyl group, 2 kJ/ mol per base for the largest effects. Considering that not all nucleosome base pair steps are likely to be CpG steps, we can conclude that the balance between the destabilization due to CpG methylation and sequence repositioning will depend on the PLOS Computational Biology | 4 November 2013 | Volume 9 | Issue 11 | e1003354 DNA Methylation and Nucleosome Positioning Figure 3. Methylated and non-methylated DNA elastic deformation energies. (A) Distribution of deformation energies for 147 bplong random DNA sequences with CpG steps positioned every 10 base steps (one helical turn) in minor (red and dark red) and major (light and dark blue) grooves respectively. The energy values were rescaled by the slope of a best-fit straight line of figure 2, which is 0.23, to por la lectura a través de la lectura de la prensa. La educación en los medios las fuerzas dispersas en función de los soportes mediáticos y orientarse más hacia la educación en medios que al dominio adquiere pleno derecho y entidad en la sección sexta titulada «competencias sociales y cívi- técnico de los aparatos. cas» que indica que «los alum- nos deberán ser capaces de juz- gar y tendrán espíritu crítico, lo que supone ser educados en los las programaciones oficiales, ya que, a lo largo de un medios y tener conciencia de su lugar y de su influencia estudio de los textos, los documentalistas del CLEMI en la sociedad». han podido señalar más de una centena de referencias a la educación de los medios en el seno de disciplinas 4. Un entorno positivo como el francés, la historia, la geografía, las lenguas, Si nos atenemos a las cifras, el panorama de la las artes plásticas : trabajos sobre las portadas de educación en medios es muy positivo. Una gran ope- prensa, reflexiones sobre temas mediáticos, análisis de ración de visibilidad como la «Semana de la prensa y publicidad, análisis de imágenes desde todos los ángu- de los medios en la escuela», coordinada por el CLE- los, reflexión sobre las noticias en los países europeos, MI, confirma año tras año, después de 17 convocato- información y opinión rias, el atractivo que ejerce sobre los profesores y los Esta presencia se constata desde la escuela mater- alumnos. Concebida como una gran operación de nal (2 a 6 años) donde, por ejemplo, se le pregunta a complementariedad entre la escuela y los profesiona- los niños más pequeños si saben diferenciar entre un les de los medios, alrededor del aprendizaje ciudada- periódico, un libro, un catálogo, a través de activida- no de la comunicación mediática, este evento moviliza des sensoriales, si saben para qué sirve un cartel, un durante toda una semana un porcentaje elevado de periódico, un cuaderno, un ordenador si son capa- centros escolares que representan un potencial de 4,3 ces de reconocer y distinguir imágenes de origen y de millones de alumnos (cifras de 2006). Basada en el naturaleza distintas. Podríamos continuar con más voluntariado, la semana permite desarrollar activida- ejemplos en todos los niveles de enseñanza y práctica- des más o menos ambiciosas centradas en la introduc- Páginas 43-48 ción de los medios en la vida de la escuela a través de la instalación de kioscos, organización de debates con profesionales y la confección por parte de los alumnos de documentos difundidos en los medios profesionales. Es la ocasión de dar un empujón a la educación en medios y de disfrutarlos. Los medios –un millar en 2006– se asocian de maneras diversas ofreciendo ejemplares de periódicos, acceso a noticias o a imágenes, proponiendo encuentros, permitiendo intervenir a los jóvenes en sus ondas o en sus columnas Esta operación da luz al trabajo de la educación en medios y moviliza a los diferentes participantes en el proyecto. 5. La formación de los docentes La formación es uno de los pilares principales de la educación en los medios. Su función es indispensable ya que no se trata de una disciplina, sino de una enseñanza que se hace sobre la base del voluntariado y del compromiso personal. Se trata de convencer, de mostrar, de interactuar. En primer lugar es necesario incluirla en la formación continua de los docentes, cuyo volumen se ha incrementado desde 1981 con la aparición de una verdadera política de formación continua de personal. Es difícil dar una imagen completa del volumen y del público, pero si nos atenemos a las cifras del CLEMI, hay más de 24.000 profesores que han asistido y se han involucrado durante 2004-05. 5.1. La formación continua En la mayoría de los casos, los profesores reciben su formación en contextos cercanos a su centro de trabajo, o incluso en este mismo. Después de una política centrada en la oferta que hacían los formadores, se valora más positivamente la demanda por parte del profesorado, ya que sólo así será verdaderamente fructífera. Los cursos de formación se repartieron en varias categorías: desde los formatos más tradicionales (cursos, debates, animaciones), hasta actividades de asesoramiento y de acompañamiento, y por supuesto los coloquios que permiten un trabajo en profundidad ya que van acompañados de expertos investigadores y profesionales. Citemos, por ejemplo en 2005, los coloquios del CLEMI-Toulouse sobre el cine documental o el del CLEMI-Dijon sobre «Políticos y medios: ¿connivencia?». Estos coloquios, que forman parte de un trabajo pedagógico regular, reagrupan a los diferentes participantes regionales y nacionales alrededor de grandes temas de la educación en medios y permiten generar nuevos conocimientos de aproximación y una profundización. Páginas 43-48 Hay otro tipo de formación original que se viene desarrollando desde hace menos tiempo, a través de cursos profesionales, como por ejemplo, en el Festival Internacional de Foto-periodismo «Visa para la imagen», en Perpignan. La formación se consolida en el curso, da acceso a las exposiciones, a las conferencias de profesionales y a los grandes debates, pero añade además propuestas pedagógicas y reflexiones didácticas destinadas a los docentes. Estas nuevas modalidades de formación son también consecuencia del agotamiento de la formación tradicional en las regiones. Los contenidos más frecuentes en formación continua conciernen tanto a los temas más clásicos como a los cambios que se están llevando a cabo en las prácticas mediáticas. Así encontramos distintas tendencias para 2004-05: La imagen desde el ángulo de la producción de imágenes animadas, el análisis de la imagen de la información o las imágenes del J.T. La prensa escrita y el periódico escolar. Internet y la información en línea. Medios y educación de los medios. 5.2 La formación inicial La formación inicial está aun en un grado muy ini- cial. El hecho de que la educación en medios no sea una disciplina impide su presencia en los IUFM (Institutos Universitarios de Formación de Maestros) que dan una prioridad absoluta a la didáctica de las disciplinas. En 2003, alrededor de 1.400 cursillistas sobre un total de 30.000 participaron en un momento u otro de un módulo de educación en medios. Estos módulos se ofrecen en función del interés que ese formador encuentra puntualmente y forman parte a menudo de varias disciplinas: documentación, letras, historia-geografía Estamos aún lejos de una política concertada en este dominio. La optativa «Cine-audiovisual» ha entrado desde hace muy poco tiempo en algunos IUFM destinada a obtener un certificado de enseñanza de la opción audiovisual y cine. Internet tiene cabida también en los cursos de formación inicial, recientemente con la aparición de un certificado informático y de Internet para los docentes, dirigido más a constatar competencias personales que a valorar una aptitud para enseñarlos. 6. ¿Y el futuro? El problema del futuro se plantea una vez más por la irrupción de nuevas técnicas y nuevos soportes. La difusión acelerada de lo digital replantea hoy muchas cuestiones relativas a prácticas mediáticas. Muchos Comunicar, 28, 2007 47 Comunicar, 28, 2007 Enrique Martínez-Salanova '2007 para Comunicar 48 trabajos que llevan el rótulo de la educación en medios solicitan una revisión ya que los conceptos cambian. La metodología elaborada en el marco de la educación en medios parece incluso permitir la inclinación de la sociedad de la información hacia una sociedad del conocimiento, como defiende la UNESCO. En Francia, se necesitaría unir las fuerzas dispersas en función de los soportes mediáticos y orientarse más hacia la educación en medios que al dominio técnico de los aparatos. Los avances recientes en el reconocimiento de estos contenidos y las competencias que supondrían podrían permitirlo. Referencias CLEMI/ACADEMIE DE BORDEAUX (Ed.) (2003): Parcours médias au collège: approches disciplinaires et transdisciplinaires. Aquitaine, Sceren-CRDP. GONNET, J. (2001): Education aux médias. Les controverses fécondes. Paris, Hachette Education/CNDP. SAVINO, J.; MARMIESSE, C. et BENSA, F. (2005): L’éducation aux médias de la maternelle au lycée. Direction de l’Enseignement Scolaire. Paris, Ministère de l’Education Nationale, Sceren/CNDP, Témoigner. BEVORT, E. et FREMONT, P. (2001): Médias, violence et education. Paris, CNDP, Actes et rapports pour l’éducation. – fiches pédagogiques, rapports et liens avec les pages régionales/académiques. – Le site «Quai des images» est dédié à l’enseignement du cinéma et de l’audiovisuel. – la rubrique «Côté profs» a une entrée «education aux médias». – Programme européen d’éducation aux risques liés à Internet. dResedfeleexliobnuetsacón Páginas 43-48
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