534 research outputs found
Characterization of aerosol pollution events in France using ground-based and POLDER-2 satellite data
We analyze the relationship between daily fine particle mass concentration (PM2.5) and columnar aerosol optical thickness derived from the Polarization and Directionality of Earth's Reflectances (POLDER) satellite sensor. The study is focused over France during the POLDER-2 lifetime between April and October 2003. We have first compared the POLDER derived aerosol optical thickness (AOT) with integrated volume size distribution derived from ground-based Sun Photometer observations. The good correlation (R=0.72) with sub-micron volume fraction indicates that POLDER derived AOT is sensitive to the fine aerosol mass concentration. Considering 1974 match-up data points over 28 fine particle monitoring sites, the POLDER-2 derived AOT is fairly well correlated with collocated PM2.5 measurements, with a correlation coefficient of 0.55. The correlation coefficient reaches a maximum of 0.80 for particular sites. We have analyzed the probability to find an appropriate air quality category (AQC) as defined by U.S. Environmental Protection Agency (EPA) from POLDER-2 AOT measurements. The probability can be up to 88.8% (±3.7%) for the "Good" AQC and 89.1% (±3.6%) for the "Moderate" AQC
Absorption properties of Mediterranean aerosols obtained from multi-year ground-based remote sensing observations.
International audienceAerosol absorption properties are of high importance to assess aerosol impact on regional climate. This study presents an analysis of aerosol absorption products obtained over the Mediterranean basin or land stations in the region from multi-year ground-based AERONET observations with a focus on the Absorbing Aerosol Optical Depth (AAOD), Single Scattering Albedo (SSA) and their spectral dependence. The AAOD and Absorption Angström Exponent (AAE) dataset is composed of daily averaged AERONET level 2 data from a total of 22 Mediterranean stations having long time series, mainly under the influence of urban-industrial aerosols and/or soil dust. This dataset covers the 17-yr period 1996-2012 with most data being from 2003-2011 (~89% of level-2 AAOD data). Since AERONET level-2 absorption products require a high aerosol load (AOD at 440 nm > 0.4), which is most often related to the presence of desert dust, we also consider level-1.5 SSA data, despite their higher uncertainty, and filter out data with an Angström exponent < 1.0 in order to study absorption by carbonaceous aerosols. The SSA dataset includes AERONET level-2 products. Sun-photometer observations show that values of AAOD at 440 nm vary between 0.024 ± 0.01 (resp. 0.040 ± 0.01) and 0.050 ± 0.01 (0.055 ± 0.01) for urban (dusty) sites. Analysis shows that the Mediterranean urban-industrial aerosols appear "moderately" absorbing with values of SSA close to ~0.94-0.95 ± 0.04 (at 440 nm) in most cases except over the large cities of Rome and Athens, where aerosol appears more absorbing (SSA ~0.89-0.90 ± 0.04). The aerosol Absorption Angström Exponent (AAE, estimated using 440 and 870 nm) is found to be larger than 1 for most sites over the Mediterranean, a manifestation of mineral dust (iron) and/or brown carbon producing the observed absorption. AERONET level-2 sun-photometer data indicate a possible East-West gradient, with higher values over the eastern basin (AAEEast = 1.39/AAEWest = 1.33). The North-South AAE gradient is more pronounced, especially over the western basin. Our additional analysis of AERONET level-1.5 data also shows that organic absorbing aerosols significantly affect some Mediterranean sites. These results indicate that current climate models treating organics as nonabsorbing over the Mediterranean certainly underestimate the warming effect due to carbonaceous aerosols
Diffraction in low-energy electron scattering from DNA: bridging gas phase and solid state theory
Using high-quality gas phase electron scattering calculations and multiple
scattering theory, we attempt to gain insights on the radiation damage to DNA
induced by secondary low-energy electrons in the condensed phase, and to bridge
the existing gap with the gas phase theory and experiments. The origin of
different resonant features (arising from single molecules or diffraction) is
discussed and the calculations are compared to existing experiments in thin
films.Comment: 40 pages preprint, 12 figures, submitted to J. Chem. Phy
Vehicle taxes as a climate policy instrument: econometric evidence from Spain
We study the local distortionary effects of notches in Spainâs CO2-based vehicle registration tax on the distribution of new car CO2 performance. These effects are the smoking gun of carmaker strategic behaviour and affect in turn tax revenue and CO2 emissions. Using model-level data on all car registrations in Spain 2010-2020, we apply the bunching approach to the three thresholds of the tax scheme: 120, 160, and 200 gCO2/km. We find that the tax notches strongly affected market outcomes, resulting in the sale of about 388,000 more cars (overall) at or just below the thresholds compared to the respective counterfactuals without the thresholds. This translates into about âŹ335 million of foregone tax revenue and only very limited extra abatement of CO2 emissions. Over 90-95% of all estimated bunching took place at the first threshold (120 gCO2/km). Over 60% of all estimated bunching took place before 2015. Bunching diminished over time, which reflects diminished effectiveness of the tax in both reducing CO2 emissions and generating revenue. Taking the interactions with both EU vehicle emission standards and similar CO2-related policies in other Member States into consideration is important for interpreting these results
Evaluation and Selection of the MEUST Submarine Site
http://meust.cnrs.fr/MEUST_site_choice_report.pdfThis report summarizes the results of the investiga tions performed to select the MEUST submarine site. Measurement campaigns have been conducted during 2012 on several locations off shore of Toulon. During this period the most distant site has s hown a higher sensitivity to bioluminescence seasonal variations, whereas the more coastal sites had simila r conditions as Antares. This observation combined with logistic constraints leads to select a site located at similar latitude as Antares but more western on the other side of the CC5 telecommunication cable to Cors ica. The route of the MEUST Main Electro-Optical Cable has been defined accordingly, with some flexib ility to allow fine tuning of its end point as function of the outcome of the final site characterizations scheduled in 2013
The Sloan Lens ACS Survey. VII. Elliptical Galaxy Scaling Laws from Direct Observational Mass Measurements
We use a sample of 53 massive early-type strong gravitational lens galaxies
with well-measured redshifts (ranging from z=0.06 to 0.36) and stellar velocity
dispersions (between 175 and 400 km/s) from the Sloan Lens ACS (SLACS) Survey
to derive numerous empirical scaling relations. The ratio between central
stellar velocity dispersion and isothermal lens-model velocity dispersion is
nearly unity within errors. The SLACS lenses define a fundamental plane (FP)
that is consistent with the FP of the general population of early-type
galaxies. We measure the relationship between strong-lensing mass M_lens within
one-half effective radius (R_e/2) and the dimensional mass variable M_dim =
G^-1 sigma_e2^2 R_e/2 to be log_10 [M_lens/10^11 M_Sun] = (1.03 +/- 0.04)
log_10 [M_dim/10^11 M_Sun] + (0.54 +/- 0.02) (where sigma_e2 is the projected
stellar velocity dispersion within R_e/2). The near-unity slope indicates that
the mass-dynamical structure of massive elliptical galaxies is independent of
mass, and that the "tilt" of the SLACS FP is due entirely to variation in total
(luminous plus dark) mass-to-light ratio with mass. Our results imply that
dynamical masses serve as a good proxies for true masses in massive elliptical
galaxies. Regarding the SLACS lenses as a homologous population, we find that
the average enclosed 2D mass profile goes as log_10 [M(<R)/M_dim] = (1.10 +/-
0.09) log_10 [R/R_e] + (0.85 +/- 0.03), consistent with an isothermal (flat
rotation curve) model when de-projected into 3D. This measurement is
inconsistent with the slope of the average projected aperture luminosity
profile at a confidence level greater than 99.9%, implying a minimum
dark-matter fraction of f_DM = 0.38 +/- 0.07 within one effective radius.
(abridged)Comment: 13 pages emulateapj; accepted for publication in the Ap
Molecular gas in NUclei of GAlaxies (NUGA) VII. NGC4569, a large scale bar funnelling gas into the nuclear region
This work is part of the NUGA survey of CO emission in nearby active
galaxies. We present observations of NGC4569, a member of the Virgo Cluster. We
analyse the molecular gas distribution and kinematics in the central region and
we investigate a possible link to the strong starburst present at the nucleus.
70% of the 1.1x10^9 Msolar of molecular gas detected in the inner 20" is found
to be concentrated within the inner 800 pc and is distributed along the large
scale stellar bar seen in near-infrared observations. A hole in the CO
distribution coincides with the nucleus where most of the Halpha emission and
blue light are emitted. The kinematics are modelled in three different ways,
ranging from the purely geometrical to the most physical. This approach allows
us to constrain progressively the physical properties of the galaxy and
eventually to emerge with a reasonable fit to an analytical model of orbits in
a barred potential. Fitting an axisymmetric model shows that the non-circular
motions must be comparable in amplitude to the circular motions (120 km/s).
Fitting a model based on elliptical orbits allows us to identify with
confidence the single inner Lindblad resonance (ILR) of the large scale bar.
Finally, a model based on analytical solutions for the gas particle orbits in a
weakly barred potential constrained by the ILR radius reproduces the
observations well. The mass inflow rate is then estimated and discussed based
on the best fit model solution. The gravitational torques implied by this model
are able to efficiently funnel the gas inside the ILR down to 300 pc, although
another mechanism must take over to fuel the nuclear starburst inside 100 pc.Comment: accepted for publication in A&
Star formation main sequence and Kennicutt-Schmidt law within 12 strong galactic bars observed with IRAM-30m
ComunicaciĂłn de congreso, pĂłster virtual presentado en el European Astronomical Society Annual Meeting (formerly known as EWASS) 28 June â 2 July 202
Molecular Gas in NUclei of GAlaxies (NUGA) III. The warped LINER NGC3718
16 pages, 17 figures.-- Published in: A&A 442, 479-493 (2005), publisher version available at: http://dx.doi.org/10.1051/0004-6361:20041731.We present the first interferometric observations of CO(1â0) and CO(2â1) line emission from the warped LINER NGC 3718, obtained with the IRAM Plateau de Bure Interferometer (PdBI). This L1.9 galaxy has a prominent dust lane and on kiloparsec scales, a strongly warped atomic and molecular gas disk. The molecular gas is closely associated with the dust lane across the nucleus and its kinematic center is consistent with the millimeter continuum AGN. A comparison of our interferometric mosaic data, which fully cover the ~ 9 kpc
warped disk, with a previously obtained IRAM 30m single dish CO(1â0) map shows that the molecular gas distribution in the disk is heavily resolved by the PdBI map. On the nucleus the interferometric maps alone
contain less than one half of the single dish line flux, and the overall mosaic accounts for about a tenth of the total
molecular gas mass of ~ 2.4 Ă 108Mâ. After applying a short-spacing correction with the IRAM 30m data to recover the missing extended flux, we find in total six main source components within the dust lane: one associated with the nucleus, four symmetrically positioned on either side at galactocentric distances of about 1.3 kpc and 4.0 kpc from the center, and a sixth on the western side at ~ 3 kpc with only a very weak eastern counterpart. In the framework of a kinematic model using tilted rings, we interpret the five symmetric source components as locations of strong orbital crowding. We further find indications that the warp appears not only on kpc scales, but continues down to ~ 250 pc. Besides the sixth feature on the western side, the lower flux (a factor of ~ 2) of the eastern components compared to the western ones indicates an intrinsic large scale asymmetry in NGC 3718 that
cannot be explained by the warp. Indications for a small scale asymmetry are also seen in the central 600 pc. These
asymmetries might be evidence for a tidal interaction with a companion galaxy (large scales) and gas accretion onto the nucleus (small scales). Our study of NGC 3718 is part of the NUclei of GAlaxies (NUGA) project that aims at investigating the different processes of gas accretion onto Active Galactic Nuclei (AGN).The research presented in this paper has
been financially supported in part by the SFB 494. Stéphane Léon is partially supported by DGI Grant AYA 2002-03338
and Junta de AndalucĂa.Peer reviewe
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