Laboratoire de Physico-Chimie de l'Atmosphère

The Tropospheric Ozone Assessment Report (TOAR) is an activity of the International Global Atmospheric Chemistry Project. This paper is a component of the report, focusing on the present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation. Utilizing the TOAR surface ozone database, several figures present the global distribution and trends of daytime average ozone at 2702 non-urban monitoring sites, highlighting the regions and seasons of the world with the greatest ozone levels. Similarly, ozonesonde and commercial aircraft observations reveal ozone’s distribution throughout the depth of the free troposphere. Long-term surface observations are limited in their global spatial coverage, but data from remote locations indicate that ozone in the 21st century is greater than during the 1970s and 1980s. While some remote sites and many sites in the heavily polluted regions of East Asia show ozone increases since 2000, many others show decreases and there is no clear global pattern for surface ozone changes since 2000. Two new satellite products provide detailed views of ozone in the lower troposphere across East Asia and Europe, revealing the full spatial extent of the spring and summer ozone enhancements across eastern China that cannot be assessed from limited surface observations. Sufficient data are now available (ozonesondes, satellite, aircraft) across the tropics from South America eastwards to the western Pacific Ocean, to indicate a likely tropospheric column ozone increase since the 1990s. The 2014–2016 mean tropospheric ozone burden (TOB) between 60°N–60°S from five satellite products is 300 Tg ± 4%. While this agreement is excellent, the products differ in their quantification of TOB trends and further work is required to reconcile the differences. Satellites can now estimate ozone’s global long-wave radiative effect, but evaluation is difficult due to limited in situ observations where the radiative effect is greatest.

Abstract The final performance of a composite material depends strongly on the quality of the fibre-matrix interface. The interactions developed at the interface were studied using the acid-base or acceptor-donor concept. The surface characteristics of the carbon fibres and the epoxy matrix were studied using a tensiometric method and the inverse gas chromatography technique. Acid-base surface characters could be determined allowing the interactions at the interface to be described by a specific interaction parameter. It was shown that the shear strength of the interface, as measured by a fragmentation test, is strongly correlated to this specific interaction parameter, demonstrating the importance of acid-base interactions in the fibre-matrix adhesion.

A detailed and extended chemical mechanism describing tropospheric aqueous phase chemistry (147 species and 438 reactions) is presented here as Chemical Aqueous Phase Radical Mechanism (CAPRAM) 2.4 (MODAC mechanism). The mechanism based on the former version 2.3 [ Herrmann et al. , 2000 ] contains extended organic and transition metal chemistry and is formulated more explicitly based on a critical review of the literature. The aqueous chemistry has been coupled to the gas phase mechanism Regional Atmospheric Chemistry Modeling (RACM) [ Stockwell et al. , 1997 ], and phase exchange accounted for using the resistance model of Schwartz [1986] . A method for estimating mass accommodation coefficients (α) is described, which accounts for functional groups contained in a particular compound. A condensed version has also been developed to allow the use of CAPRAM 2.4 (MODAC mechanism) in higher‐scale models. Here the reproducibility of the concentration levels of selected target species (i.e., NO x , S(IV), H 2 O 2 , NO 3 , OH, O 3 , and H + ) within the limits of ± 5% was used as a goal for eliminating insignificant reactions from the complete CAPRAM 2.4 (MODAC mechanism). This has been done using a range of initial conditions chosen to represent different atmospheric scenarios, and this produces a robust and concise set of reactions. The most interesting results are obtained using atmospheric conditions typical for an urban scenario, and the effects introduced by updating the aqueous phase chemistry are highlighted, in particular, with regard to radicals, redox cycling of transition metal ions and organic compounds. Finally, the reduced scheme has been incorporated into a one‐dimensional (1‐D) marine cloud model to demonstrate the applicability of this mechanism.

Large impacts provide a mechanism for resurfacing planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peaks transition to peak rings. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Expedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust.

Abstract. Due to the major role of the sun in heating the earth's surface, the atmospheric planetary boundary layer over land is inherently marked by a diurnal cycle. The afternoon transition, the period of the day that connects the daytime dry convective boundary layer to the night-time stable boundary layer, still has a number of unanswered scientific questions. This phase of the diurnal cycle is challenging from both modelling and observational perspectives: it is transitory, most of the forcings are small or null and the turbulence regime changes from fully convective, close to homogeneous and isotropic, toward a more heterogeneous and intermittent state. These issues motivated the BLLAST (Boundary-Layer Late Afternoon and Sunset Turbulence) field campaign that was conducted from 14 June to 8 July 2011 in southern France, in an area of complex and heterogeneous terrain. A wide range of instrumented platforms including full-size aircraft, remotely piloted aircraft systems, remote-sensing instruments, radiosoundings, tethered balloons, surface flux stations and various meteorological towers were deployed over different surface types. The boundary layer, from the earth's surface to the free troposphere, was probed during the entire day, with a focus and intense observation periods that were conducted from midday until sunset. The BLLAST field campaign also provided an opportunity to test innovative measurement systems, such as new miniaturized sensors, and a new technique for frequent radiosoundings of the low troposphere. Twelve fair weather days displaying various meteorological conditions were extensively documented during the field experiment. The boundary-layer growth varied from one day to another depending on many contributions including stability, advection, subsidence, the state of the previous day's residual layer, as well as local, meso- or synoptic scale conditions. Ground-based measurements combined with tethered-balloon and airborne observations captured the turbulence decay from the surface throughout the whole boundary layer and documented the evolution of the turbulence characteristic length scales during the transition period. Closely integrated with the field experiment, numerical studies are now underway with a complete hierarchy of models to support the data interpretation and improve the model representations.

: Tunable diode laser absorption spectroscopy (TDLAS), as a noninvasive spectroscopic method, permits high-resolution, high-sensitivity, fast, in situ absorption measurements of atomic and molecular species and narrow spectral features in gaseous, solid, and liquid phases. Advances in new diode laser sources and laser spectroscopic techniques generally have triggered an increasing application of TDLAS in various disciplines (for example, atmospheric environmental monitoring, chemical analysis, industrial process control, medical diagnostics and combustion monitoring, etc.) over the last four decades. This article reviews some important developments in TDLAS, from its basic principles as a spectroscopic tool to the demonstration of gas absorption measurements, emphasizing signal enhancement and noise reduction techniques developed for improving current TDLAS performance.

Abstract The surface energies, both the dispersive component, γ s d , and the specific component, γ s sp , of dry- and wet-pelletized carbon blacks, ranging from N110 to N990, were evaluated by inverse gas-solid chromatography at infinite dilution. The results indicate that the dispersive components of the surface energy of carbon blacks increase with increasing surface area. This dependence may essentially reflect an effect of microstructure on the surface energies, which can be confirmed by the relationship between the crystallographic parameters of crystallites and the graphitization of the carbon blacks. It was found that smaller crystallites characterized by a lower value of L c lead to higher surface energy, whereas graphitization of the carbon black points toward lower surface energy, perhaps resulting from the growth of the quasi-graphite structure. Surface area dependence of the specific component of the surface energy characterized by the specific energy of adsorption of a polar probe follows the same pattern as was observed for the dispersive component, i.e. , γ s d increases with surface area. This is believed to be related to the crystallographic structure and the surface chemistry. Studies on adsorption energies of the low-molecular-weight analogs of elastomers generally show that the interactions between carbon blacks and rubbers depend not only on filler surface energies but also on the structure of the elastomers. Due to their polar functional groups, NBR and SBR show a stronger interaction with blacks than unsaturated rubbers. Among the rubbers simulated, IIR would have the lowest interaction with the filler. A comparison of the surface energies of carbon blacks and silicas points toward a very high γ s d , for blacks which may show strong interaction with nonpolar- or low-polar polymers, while the very high S f value of the silicas, especially precipitated silicas, a measure of the relative polarity of their surface, is considered to be representative of strong particle-particle interaction, leading to the formation of a filler network.

Abstract. In this paper we present the long term monitoring of ambient gaseous concentrations within the framework of the IDAF (IGAC-DEBITS-AFRICA) program. This study proposes for the first time an analysis of long-term inorganic gas concentrations (1998 to 2007) of SO2, NO2, HNO3, NH3 and O3, determined using passive samplers at seven remote sites in West and Central Africa. Sites are representative of several African ecosystems and are located along a transect from dry savannas-wet savannas-forests with sites at Banizoumbou (Niger), Katibougou and Agoufou (Mali), Djougou (Benin), Lamto (Cote d'Ivoire), Zoetele (Cameroon) and Bomassa (Congo). The strict control of measurement techniques as well as the validation and inter-comparison studies conducted with the IDAF passive samplers assure the quality and accuracy of the measurements. For each type of African ecosystem, the long term data series have been studied to document the levels of surface gaseous concentrations. The seasonal and interannual variability have also been analyzed as a function of emission source variations. We compared the measured West and Central African gas concentrations to results obtained in other parts of the world. Results show that the annual mean concentrations of NO2, NH3, HNO3 measured in dry savannas are higher than those measured in wet savannas and forests that have quite similar concentrations. Annual mean NO2 concentrations vary from 0.9±0.2 in forests to 2.4±0.4 ppb in the dry savannas, NH3 from 3.9±1.4 to 7.4±0.8 ppb and HNO3 from 0.2±0.1 to 0.5±0.2 ppb. Annual mean O3 and SO2 concentrations are lower for all ecosystems and range from 4.0±0.4 to 14.0±2.8 and from 0.3±0.1 to 1.0±0.2 ppb, respectively. A focus on the processes involved in gas emissions from dry savannas is presented in this work, providing explanations for the high concentrations of all gases measured at the three dry savannas sites. At these sites, seasonal concentrations of all gases are higher in the wet season. Conversely, concentrations are higher in the dry season in the wet savannas. In forested regions, we measure no significant difference between wet and dry seasons. This unique database of long term gases concentrations monitoring is available at: http://medias.obs-mip.fr/idaf/.

Abstract. West Africa and the adjacent oceanic regions are very important locations for studying dust properties and their influence on weather and climate. The SHADOW (study of SaHAran Dust Over West Africa) campaign is performing a multiscale and multilaboratory study of aerosol properties and dynamics using a set of in situ and remote sensing instruments at an observation site located at the IRD (Institute for Research and Development) in Mbour, Senegal (14° N, 17° W). In this paper, we present the results of lidar measurements performed during the first phase of SHADOW (study of SaHAran Dust Over West Africa) which occurred in March–April 2015. The multiwavelength Mie–Raman lidar acquired 3β + 2α + 1δ measurements during this period. This set of measurements has permitted particle-intensive properties, such as extinction and backscattering Ångström exponents (BAE) for 355/532 nm wavelengths' corresponding lidar ratios and depolarization ratio at 532 nm, to be determined. The mean values of dust lidar ratios during the observation period were about 53 sr at both 532 and 355 nm, which agrees with the values observed during the SAMUM-1 and SAMUM-2 campaigns held in Morocco and Cabo Verde in 2006 and 2008. The mean value of the particle depolarization ratio at 532 nm was 30 ± 4.5 %; however, during strong dust episodes this ratio increased to 35 ± 5 %, which is also in agreement with the results of the SAMUM campaigns. The backscattering Ångström exponent during the dust episodes decreased to ∼ −0.7, while the extinction Ångström exponent, though negative, was greater than −0.2. Low values of BAE can likely be explained by an increase in the imaginary part of the dust refractive index at 355 nm compared to 532 nm. The dust extinction and backscattering coefficients at multiple wavelengths were inverted to the particle microphysics using the regularization algorithm and the model of randomly oriented spheroids. The analysis performed has demonstrated that the spectral dependence of the imaginary part of the dust refractive index may significantly influence the inversion results and should be taken into account.

This paper describes the results of an experimental investigation of the turbulent boundary layer on a flat plate with zero pressure gradient, carried out at the Laboratoire de Mécanique de l'Atmosphère (I. M. F. Marseille). Transition to turbulent flow was obtained either by increasing the preturbulence upstream of the plate by means of a grid, or by a series of emery paper roughness elements beginning at the leading edge. The measurements were of the space-time double correlations, i.e. double velocity correlations with both spatial separation and time delay, from which isocorrelation lines for optimum delay can be drawn, and of the spectrum function, all for the longitudinal component of the velocity fluctuation.

Abstract Analogous to most new methods in science, photoacoustic spectroscopy (PAS) grew out of an advance in technology, in this case the dramatic improvement in novel light sources, modulators, and acoustic detectors, as well as signal recovery electronics, which in turn was made possible by the development of modern PAS techniques. PAS is a promising technique that can be used to analyze and characterize a broad variety of objects (gaseous, solid, and liquid samples). In the present review, the recent development of infrared PAS limited to the general area of gas-phase analysis techniques since 1990 is summarized, with special emphasis on the development of new or enhanced analytical methodologies based on the use of the photoacoustic (PA) effect to improve the sensitivity of PAS by enhancing signal or reducing noise levels, with regard to PA systems, applications, and conclusions. The applications of these novel PA methods are mainly concerned with molecular spectroscopic, industrial, atmospheric, environmental, chemical and biological, and medical and clinical analysis. New prospects and challenges in various application fields of PAS technique are described. Keywords: Photoacoustic spectroscopyanalysis techniquesapplicationsreview

Abstract Abstract Since the first demonstration in 1994, progress in the development of quantum cascade lasers (QCLs) has been breathtakingly rapid. Various techniques based upon novel QCLs have attracted much interest from researchers working in science and engineering disciplines (atmospheric environmental monitoring, chemical analysis, industrial process control, medical diagnostics, applications of life science, etc.) over the course of approximately the last two decades. Some background and recent advances in the development of QCLs are discussed together with a brief outline of a few representative atmospheric chemical species and their spectral features, as well as a short summary of terahertz-QCL. Among the various laser spectroscopic methods, the focus in this review is directed toward selected applications of QCL absorption spectroscopic techniques, which are commonly used to measure atmospheric trace gases, with particular emphasis on ground-based eddy covariance measurements, isotope measurements, and airborne-platform atmospheric measurements. Keywords: QCLlaser spectroscopyatmospheric chemistryapplications

From April 12 to 19, 1984, dust was collected by cascade impactor on Fuerteventura Island, 100 km from the Saharan coast. The samples were analyzed by X ray fluorescence spectrometry (elemental composition), by X ray diffraction (mineral constituents), and by scanning electron microscope (SEM) and energy dispersive X ray analyzer (EDXA) examination (shape, surface features, and mineralogy of particles), with the aim of determining the possible source areas of the dust. On the scale of dust clouds, another method allowed us to define the displacements of the dust: using remote sensing (METEOSAT II, National Oceanic and Atmospheric Administration (NOAA)) and computing trajectories for any starting or ending point at any time. These various methods gave complementary results and pointed out two successive episodes of dust with two different continental origins. The first originated from a nearby source in the Souss plain (southern Morocco) and was characterized by very fine quartz particles. The second drifted above more remote calcareous regions. This study allows us to show how different methods can be used to characterize dust and to find the source areas. The results suggest some general questions about the occurrence of coarse particles in the atmosphere and their role in the atmospheric deposition flux budget.

Abstract Inverse gas-solid chromatography, operated at infinite dilution, has been used to assess the surface energies of silicas, both fumed and precipitated. The dispersive components of the surface free energies of the silicas were calculated from the free energies of adsorption, corresponding to the —CH 2 — group, obtained from n -alkane adsorption. The specific components of the surface energies were evaluated separately by comparison of the free energies of adsorption of polar probes with those of n -alkanes, based on the surface areas covered by the probe molecules. The results indicate that while the dispersive components of silica surface energies is somewhat higher for the fumed silicas, the specific components are much higher for precipitated silicas, probably resulting from the higher silanol concentration on their surfaces. Moreover, the interaction able to take place between rubber matrix and the silicas are also estimated chromatographically from the adsorptions of low-molecular-weight analogs of elastomers. The free energies and enthalpies indicate that the interactions of functional groups with the fillers decrease in the order of nitrile, phenyl ring, double bond. The saturated rubber analogs show lower interactions with silicas. The lowest interactions of iso-alkanes imply poor interactions between butyl rubber and the fillers. As expected, the experimental data reflect an attenuation of polymer-silica interactions with decreasing content of functional groups and degree of unsaturation in NR, BR, SBR, and NBR.

The mass-particle size distributions (MSDs) of Na, Al, Cd, and Pb were determined from 17, 1–5 day, high-volume cascade impactor samples collected throughout the Western Mediterranean atmosphere between 1980 and 1983. As expected, the mass median diameter (MMD) was the largest for Na, representative of sea-salt aerosol, with a median value of 5.9 μm. The median value for the MMD for Al, representative of mineral aerosol, was 2.8 μm. The smallest values of the MMD were found for pollution-derived elements, Cd and Pb: 0.7 μm. In most cases, the MSDs, for each of the elements, were log-normal. Total dry deposition velocities were calculated from the two-layer deposition model of Slinn and Slinn (1980) using three approaches: (i) by characterizing the distribution as a MMD, (ii) by considering the size distribution as directly given by the cascade impactor, (iii) by fitting the assumed log-normal distribution and dividing it into 100 successive intervals. The first approach appeared to give underestimates. The two other approaches yielded similar results for Cd and Pb, of the order of 0.05 cms−1. For these elements, however, more than 20% of the total dry deposition flux was due to particles with diameters of 7.2 μm or greater (collected by impactor stage 1). For Na and Al, the third approach yielded values at least one order of magnitude higher than when using the two others. This clearly underlines the major role played by large particles in controlling the dry deposition of sea-salt and mineral aerosol particles. Direct measurements of Al dry deposition, made in 1985–1986 on the northwestern coast of Corsica, agree best with the values predicted by the third approach (mean calculated and measured values of 1.8 and 3.0 cm s−1 respectively). Scanning electron microscopy examinations of samples confirm that mineral aerosol particles with diameters of 10 μm or greater dominate the dry deposition flux. Preliminary data indicate that for mineral aerosol particles, this flux is, on a yearly basis, about half of the wet deposition flux. However cascade impactor data are not adequate to retrieve true mass-particle size distribution in the size range which controls dry deposition (D > 7 μm), and this is shown to be the source for one order of magnitude uncertainties in dry deposition calculations.

Abstract. The ability of a Bayesian atmospheric inversion to quantify the Paris region's fossil fuel CO2 emissions on a monthly basis, based on a network of three surface stations operated for 1 year as part of the CO2-MEGAPARIS experiment (August 2010–July 2011), is analysed. Differences in hourly CO2 atmospheric mole fractions between the near-ground monitoring sites (CO2 gradients), located at the north-eastern and south-western edges of the urban area, are used to estimate the 6 h mean fossil fuel CO2 emission. The inversion relies on the CHIMERE transport model run at 2 km × 2 km horizontal resolution, on the spatial distribution of fossil fuel CO2 emissions in 2008 from a local inventory established at 1 km × 1 km horizontal resolution by the AIRPARIF air quality agency, and on the spatial distribution of the biogenic CO2 fluxes from the C-TESSEL land surface model. It corrects a prior estimate of the 6 h mean budgets of the fossil fuel CO2 emissions given by the AIRPARIF 2008 inventory. We found that a stringent selection of CO2 gradients is necessary for reliable inversion results, due to large modelling uncertainties. In particular, the most robust data selection analysed in this study uses only mid-afternoon gradients if wind speeds are larger than 3 m s−1 and if the modelled wind at the upwind site is within ±15° of the transect between downwind and upwind sites. This stringent data selection removes 92 % of the hourly observations. Even though this leaves few remaining data to constrain the emissions, the inversion system diagnoses that their assimilation significantly reduces the uncertainty in monthly emissions: by 9 % in November 2010 to 50 % in October 2010. The inverted monthly mean emissions correlate well with independent monthly mean air temperature. Furthermore, the inverted annual mean emission is consistent with the independent revision of the AIRPARIF inventory for the year 2010, which better corresponds to the measurement period than the 2008 inventory. Several tests of the inversion's sensitivity to prior emission estimates, to the assumed spatial distribution of the emissions, and to the atmospheric transport modelling demonstrate the robustness of the measurement constraint on inverted fossil fuel CO2 emissions. The results, however, show significant sensitivity to the description of the emissions' spatial distribution in the inversion system, demonstrating the need to rely on high-resolution local inventories such as that from AIRPARIF. Although the inversion constrains emissions through the assimilation of CO2 gradients, the results are hampered by the improperly modelled influence of remote CO2 fluxes when air masses originate from urbanised and industrialised areas north-east of Paris. The drastic data selection used in this study limits the ability to continuously monitor Paris fossil fuel CO2 emissions: the inversion results for specific months such as September or November 2010 are poorly constrained by too few CO2 measurements. The high sensitivity of the inverted emissions to the prior emissions' diurnal variations highlights the limitations induced by assimilating data only during the afternoon. Furthermore, even though the inversion improves the seasonal variation and the annual budget of the city's emissions, the assimilation of data during a limited number of suitable days does not necessarily yield robust estimates for individual months. These limitations could be overcome through a refinement of the data processing for a wider data selection, and through the expansion of the observation network.

Tunable diode laser absorption spectroscopy (TDLAS) based on a multipass cell (MPC) is a powerful analytical tool and is widely applied to air quality monitoring, industrial process control, and medical diagnostics. However, the conventional MPC as a core component in TDLAS devices has a large size, low utilization efficiency of the mirror surfaces, and tight optical alignment tolerances. In this paper, we design and fabricate a mini-MPC with an optical absorption path length of 4.2 m and dimensions of 4 × 4 × 6 cm3 (open cavity), which, to our best knowledge, is the current smallest MPC in terms of the same optical path length. The mini-MPC generates a seven-nonintersecting-circle dense spot pattern on two 25.4 mm spherical mirror surfaces, providing a high fill factor of 21 cm–2. A fiber-coupled collimator and an InGaAs photodetector are integrated into the mini-MPC via a high-resolution three-dimensional printed frame, hence removing the requirement of active optical alignment. Using a 1.65 μm distributed-feedback laser, the performance of this mini-MPC for methane detection was evaluated in terms of linearity, flow response time, stability, minimum detectable limit, and measurement precision. Continuous measurements of methane near a sewer and in the atmosphere were performed to demonstrate the stability and robustness of the highly integrated mini-MPC-based gas sensor. Our analysis shows that a methane minimum detectable limit of 117 ppbv is achieved, paving the way toward a sensitive, low-cost, and miniature trace gas sensor inherently suitable for large-scale deployment of distributed sensor networks and for handheld mobile devices.

In Drosophila larvae, growth and developmental timing are regulated by nutrition in a tightly coordinated fashion. The networks that couple these processes are far from understood. Here, we show that the intestine responds to nutrient availability by regulating production of a circulating lipoprotein-associated form of the signaling protein Hedgehog (Hh). Levels of circulating Hh tune the rates of growth and developmental timing in a coordinated fashion. Circulating Hh signals to the fat body to control larval growth. It regulates developmental timing by controlling ecdysteroid production in the prothoracic gland. Circulating Hh is especially important during starvation, when it is also required for mobilization of fat body triacylglycerol (TAG) stores. Thus, we demonstrate that Hh, previously known only for its local morphogenetic functions, also acts as a lipoprotein-associated endocrine hormone, coordinating the response of multiple tissues to nutrient availability.

The Chicxulub impact event generated a long-duration hydrothermal system suitable for microbial life.

This paper describes the results of further experimental investigation of the turbulent boundary layer with zero pressure gradient. Measurements of autocorrelation and of space-time double correlation have been made respectively with single hot-wires and with two hot-wires with the separation vector in any direction. Space-time correlations reach a maximum for some optimum delay. In the case of two points set on a line orthogonal to the plate, the optimum delay T i is not zero. In the general case it is equal to the corresponding delay T i , increased by compensating delay for translation with the mean flow. Taylor's hypothesis may be applied to the boundary layer at distances from the wall greater than 3% of the layer thickness. Space-time isocorrelation surfaces obtained with optimum delay have a large aspect ratio in the mean flow direction, even if they are relative to a point close to the wall (0·03δ); the correlations along the mean flow then retain high values on account of the large scale of the turbulence.