16 research outputs found
Effects of mixing state on optical and radiative properties of black carbon in the European Arctic
Atmospheric aging promotes internal mixing of black carbon
(BC), leading to an enhancement of light absorption and radiative forcing.
The relationship between BC mixing state and consequent absorption
enhancement was never estimated for BC found in the
Arctic region. In the present work, we
aim to quantify the absorption enhancement and its impact on radiative
forcing as a function of microphysical properties and mixing state of BC
observed in situ at the Zeppelin Arctic station (78° N) in the
spring of 2012 during the CLIMSLIP (Climate impacts of short-lived pollutants
in the polar region) project.Single-particle soot photometer (SP2) measurements showed a mean mass
concentration of refractory black carbon (rBC) of 39 ng mâ3, while the
rBC mass size distribution was of lognormal shape, peaking at an rBC mass-equivalent diameter (DrBC) of around 240 nm. On average, the
number fraction of particles containing a BC core with
DrBC>80 nm was less than 5 % in the size range (overall
optical particle diameter) from 150 to 500 nm. The BC cores were internally
mixed with other particulate matter. The median coating thickness of BC cores
with 220 nm < DrBC<â260 nm was 52 nm, resulting
in a coreâshell diameter ratio of 1.4, assuming a coated sphere morphology.
Combining the aerosol absorption coefficient observed with an Aethalometer
and the rBC mass concentration from the SP2, a mass absorption cross section
(MAC) of 9.8 m2 gâ1 was inferred at a wavelength of 550 nm.
Consistent with direct observation, a similar MAC value (8.4 m2 gâ1
at 550 nm) was obtained indirectly by using Mie theory and assuming a
coated-sphere morphology with the BC mixing state constrained from the SP2
measurements. According to these calculations, the lensing effect is
estimated to cause a 54 % enhancement of the MAC compared to that of bare
BC particles with equal BC core size distribution. Finally, the ARTDECO
radiative transfer model was used to estimate the sensitivity of the
radiative balance to changes in light absorption by BC as a result of a varying
degree of internal mixing at constant total BC mass. The clear-sky noontime
aerosol radiative forcing over a surface with an assumed wavelength-dependent
albedo of 0.76â0.89 decreased, when ignoring the absorption enhancement, by
â0.12 W mâ2 compared to the base case scenario, which was constrained
with mean observed aerosol properties for the Zeppelin site in Arctic spring.
The exact magnitude of this forcing difference scales with environmental
conditions such as the aerosol optical depth, solar zenith angle and surface
albedo. Nevertheless, our investigation suggests that the absorption
enhancement due to internal mixing of BC, which is a systematic effect,
should be considered for quantifying the aerosol radiative forcing in the
Arctic region.</p
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.
<br><br>
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
Hyperparameter estimation for uncertainty quantification in mesoscale carbon dioxide inversions
Uncertainty quantification is critical in the inversion of CO2 surface fluxes from atmospheric concentration measurements. Here, we estimate the main hyperparameters of the error covariance matrices for a priori fluxes and CO2 concentrations, that is, the variances and the correlation lengths, using real, continuous hourly CO2 concentration data in the context of the Ring 2 experiment of the North American Carbon Program Mid Continent Intensive. Several criteria, namely maximum likelihood (ML), general cross-validation (GCV) and χ 2 test are compared for the first time under a realistic setting in a mesoscale CO2 inversion. It is shown that the optimal hyperparameters under the ML criterion assure perfect χ 2 consistency of the inverted fluxes. Inversions using the ML error variances estimates rather than the prescribed default values are less weighted by the observations, because the default values underestimate the model-data mismatch error, which is assumed to be dominated by the atmospheric transport error. As for the spatial correlation length in prior flux errors, the Ring 2 network is sparse for GCV, and this method fails to reach an optimum. In contrast, the ML estimate (e.g. an optimum of 20 km for the first week of June 2007) does not support long spatial correlations that are usually assumed in the default values
Southward spreading of the Fukushima-derived radiocesium across the Kuroshio Extension in the North Pacific
The accident of the Fukushima Dai-ichi nuclear power plant in March 2011 released a large amount of radiocesium into the North Pacific Ocean. Vertical distributions of Fukushima-derived radiocesium were measured at stations along the 149°E meridian in the western North Pacific during the winter of 2012. In the subtropical region, to the south of the Kuroshio Extension, we found a subsurface radiocesium maximum at a depth of about 300â
m. It is concluded that atmospheric-deposited radiocesium south of the Kuroshio Extension just after the accident had been transported not only eastward along with surface currents but also southward due to formation/subduction of subtropical mode waters within about 10 months after the accident. The total amount of decay-corrected 134Cs in the mode water was an estimated about 6 PBq corresponding to 10â60% of the total inventory of Fukushima-derived 134Cs in the North Pacific Ocean
Induction of miR-155 after Brain Injury Promotes Type 1 Interferon and has a Neuroprotective Effect
Traumatic brain injury (TBI) produces profound and lasting neuroinflammation that has both beneficial and detrimental effects. Recent evidence has implicated microRNAs (miRNAs) in the regulation of inflammation both in the periphery and the CNS. We examined the expression of inflammation associated miRNAs in the context of TBI using a mouse controlled cortical impact (CCI) model and found increased levels of miR-21, miR-223 and miR-155 in the hippocampus after CCI. The expression of miR-155 was elevated 9-fold after CCI, an increase confirmed by in situ hybridization (ISH). Interestingly, expression of miR-155 was largely found in neuronal nuclei as evidenced by co-localization with DAPI in MAP2 positive neurons. In miR-155 knock out (KO) mice expression of type I interferons IFNα and IFNÎČ, as well as IFN regulatory factor 1 and IFN-induced chemokine CXCL10 was decreased after TBI relative to wild type (WT) mice. Unexpectedly, miR-155 KO mice had increased levels of microglial marker Iba1 and increased neuronal degeneration as measured by fluoro-jade C (FJC) staining, suggesting a neuroprotective role for miR-155 in the context of TBI. This work demonstrates a role for miR-155 in regulation of the IFN response and neurodegeneration in the aftermath of TBI. While the presence of neuronal nuclear miRNAs has been described previously, their importance in disease states is relatively unknown. Here, we show evidence of dynamic regulation and pathological function of a nuclear miRNA in TBI