14 research outputs found
Technical Note: The air quality modeling system Polyphemus
International audiencePolyphemus is an air quality modeling platform which aims at covering the scope and the abilities of modern air quality systems. It deals with applications from local scale to continental scale, using two Gaussian models and two Eulerian models. It manages passive tracers, radioactive decay, photochemistry and aerosol dynamics. The structure of the system includes four independent levels with data management, physical parameterizations, numerical solvers and high-level methods such as data assimilation. This enables sensitivity and uncertainty analysis, primarily through multimodel approaches. On top of the models, drivers implement advanced methods such as model coupling or data assimilation
Simulation of aerosol optical properties over Europe with a 3-D size-resolved aerosol model: comparisons with AERONET data
International audienceThis paper aims at presenting a model-to-data comparison of the Aerosol Optical Thickness (AOT) and of a few sparse data for Single Scattering Albedo (SSA) over Europe for one year. The main contribution of this paper is the sensitivity study to a large number of parameters, including physical and numerical parameters of the aerosol model itself. The optical parameters are computed from a size-resolved aerosol model embedded in the POLYPHEMUS system. The methodology is first described, showing that several hypothesis can be made for micro-physical aerosol properties. The simulation is made over one year (2001); statistics and monthly time series for the simulation and AERONET data are used to evaluate the ability of the model to reproduce AOT and vertically averaged SSA fields and their variability. The relation with the uncertainties of measurements is discussed. Then a sensitivity study with respect to the mixing state of the particle, the way to take into account water uptake, numerical parameters and physical parameteriza-tions of the model is carried out. The results indicate that the mixing state of particles has an influence on optical parameters , as well as the computation of the wet diameter. But some physical and numerical parameters associated with the aerosol model itself have even more influence under certain conditions, through the uncertainties on the aerosol chemical composition, and their size distribution
Technical Note: A new SIze REsolved Aerosol Model (SIREAM)
We briefly present in this short paper a new SIze REsolved Aerosol Model (S<small>IREAM</small>) which simulates the evolution of atmospheric aerosol by solving the General Dynamic Equation (GDE). S<small>IREAM</small> segregates the aerosol size distribution into sections and solves the GDE by splitting coagulation and condensation/evaporation-nucleation. A quasi-stationary sectional approach is used to describe the size distribution change due to condensation/evaporation, and a hybrid equilibrium/dynamical mass-transfer method has been developed to lower the computational burden. S<small>IREAM</small> uses the same physical parameterizations as those used in the Modal Aerosol Model, M<small>AM</small> Sartelet et al. (2006). It is hosted in the modeling system P<small>olyphemus</small> Mallet et al., 2007, but can be linked to any other three-dimensional Chemistry-Transport Model
An inverse modeling method to assess the source term of the Fukushima Nuclear Power Plant accident using gamma dose rate observations
The Chernobyl nuclear accident, and more recently the Fukushima accident,
highlighted that the largest source of error on consequences assessment is
the source term, including the time evolution of the release rate and its
distribution between radioisotopes. Inverse modeling methods, which combine
environmental measurements and atmospheric dispersion models, have proven
efficient in assessing source term due to an accidental situation (Gudiksen,
1989; Krysta and Bocquet, 2007; Stohl et al., 2012a; Winiarek et al.,
2012). Most existing approaches are designed to use air sampling
measurements (Winiarek et al., 2012) and some of them also use deposition
measurements (Stohl et al., 2012a; Winiarek et al., 2014). Some studies
have been performed to use dose rate measurements (Duranova et al., 1999;
Astrup et al., 2004; Drews et al., 2004; Tsiouri et al., 2012) but none
of the developed methods were carried out to assess the complex source term
of a real accident situation like the Fukushima accident. However, dose rate
measurements are generated by the most widespread measurement system, and in
the event of a nuclear accident, these data constitute the main source of
measurements of the plume and radioactive fallout during releases. This
paper proposes a method to use dose rate measurements as part of an inverse
modeling approach to assess source terms.
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The method is proven efficient and reliable when applied to the accident at
the Fukushima Daiichi Nuclear Power Plant (FD-NPP). The emissions for the
eight main isotopes <sup>133</sup>Xe, <sup>134</sup>Cs, <sup>136</sup>Cs, <sup>137</sup>Cs,
<sup>137m</sup>Ba, <sup>131</sup>I, <sup>132</sup>I and <sup>132</sup>Te have been assessed.
Accordingly, 105.9 PBq of <sup>131</sup>I, 35.8 PBq of <sup>132</sup>I, 15.5 PBq of
<sup>137</sup>Cs and 12 134 PBq of noble gases were released. The events
at FD-NPP (such as venting, explosions, etc.) known to have caused
atmospheric releases are well identified in the retrieved source term. The
estimated source term is validated by comparing simulations of atmospheric
dispersion and deposition with environmental observations. In total, it was
found that for 80% of the measurements, simulated and observed dose
rates agreed within a factor of 2. Changes in dose rates over time have been
overall properly reconstructed, especially in the most contaminated areas to
the northwest and south of the FD-NPP. A comparison with observed atmospheric
activity concentration and surface deposition shows that the emissions of
caesiums and <sup>131</sup>I are realistic but that <sup>132</sup>I and <sup>132</sup>Te are
probably underestimated and noble gases are likely overestimated. Finally, an
important outcome of this study is that the method proved to be perfectly
suited to emergency management and could contribute to improve emergency
response in the event of a nuclear accident
Integration of Neural Network Preprocessing Model for OMI Aerosol Optical Depth Data Assimilation
The IRSN’s earliest assessments of the Fukushima accident's consequences for the terrestrial environment in Japan
In 2011 the IRSN conducted several assessments of atmospheric
radioactive releases due to the Fukushima Daiichi NPP accident (March
11, 2011) and of their impact on Japan’s terrestrial environment.
They were based on the IRSN’s emergency management tools and on
the abundant information and technical data gradually published
in Japan. According to these assessments, the main release phase
lasted from March 12 to 25, 2011 and impacted Japanese land in two
events, the first on 15 and 16 March, in which the main radioactive
deposits were formed, and the second from March 20 to 23, which
was less significant. The highest amounts of radioactive deposits were
found in an area extending upwards of several tens of kilometers
northwest of the plant. Lower amounts were discontinuously scattered
in an area extending up to over 250 km away. Initially composed
mainly of short-lived radionuclides, the deposits’ activity sharply
decreased in the subsequent weeks. Since the summer of 2011, cesium-134
and cesium-137 have become the residual deposits’ main components.
According to IRSN estimates, in the absence of protection, the doses
due to exposure to the radioactive plume during the atmospheric
release phase may have been potentially higher for people who remained
in coastal areas up to several tens of kilometers north and south
of the damaged plant. Thereafter, people living up to 50 km northwest
of the plant, outside the 20-km emergency evacuation zone, were potentially
most vulnerable to residual radioactive deposits over time