Detection chain and electronic readout of the QUBIC instrument

The Q and U Bolometric Interferometer for Cosmology (QUBIC) Technical Demonstrator (TD) aiming to shows the feasibility of the combination of interferometry and bolometric detection. The electronic readout system is based on an array of 128 NbSi Transition Edge Sensors cooled at 350mK readout with 128 SQUIDs at 1K controlled and amplified by an Application Specific Integrated Circuit at 40K. This readout design allows a 128:1 Time Domain Multiplexing. We report the design and the performance of the detection chain in this paper. The technological demonstrator unwent a campaign of test in the lab. Evaluation of the QUBIC bolometers and readout electronics includes the measurement of I-V curves, time constant and the Noise Equivalent Power. Currently the mean Noise Equivalent Power is ~ 2 x 10⁻¹⁶ W/√Hz

Detection chain and electronic readout of the QUBIC instrument

The Q and U Bolometric Interferometer for Cosmology (QUBIC) Technical Demonstrator (TD) aiming to shows the feasibility of the combination of interferometry and bolometric detection. The electronic readout system is based on an array of 128 NbSi Transition Edge Sensors cooled at 350mK readout with 128 SQUIDs at 1K controlled and amplified by an Application Specific Integrated Circuit at 40K. This readout design allows a 128:1 Time Domain Multiplexing. We report the design and the performance of the detection chain in this paper. The technological demonstrator unwent a campaign of test in the lab. Evaluation of the QUBIC bolometers and readout electronics includes the measurement of I-V curves, time constant and the Noise Equivalent Power. Currently the mean Noise Equivalent Power is ~ 2 x 10⁻¹⁶ W/√Hz

Assessment of the reduction methods used to develop chemical schemes: building of a new chemical scheme for VOC oxidation suited to three-dimensional multiscale HO_x-NO_x-VOC chemistry simulations

International audienceThe objective of this work was to develop and assess an automatic procedure to generate reduced chemical schemes for the atmospheric photooxidation of volatile organic carbon (VOC) compounds. The procedure is based on (i) the development of a tool for writing the fully explicit schemes for VOC oxidation (see companion paper Aumont et al., 2005), (ii) the application of several commonly used reduction methods to the fully explicit scheme, and (iii) the assessment of resulting errors based on direct comparison between the reduced and full schemes. The reference scheme included seventy emitted VOCs chosen to be representative of both anthropogenic and biogenic emissions, and their atmospheric degradation chemistry required more than two million reactions among 350000 species. Three methods were applied to reduce the size of the reference chemical scheme: (i) use of operators, based on the redundancy of the reaction sequences involved in the VOC oxidation, (ii) grouping of primary species having similar reactivities into surrogate species and (iii) grouping of some secondary products into surrogate species. The number of species in the final reduced scheme is 147, this being small enough for practical inclusion in current three-dimensional models. Comparisons between the fully explicit and reduced schemes, carried out with a box model for several typical tropospheric conditions, showed that the reduced chemical scheme accurately predicts ozone concentrations and some other aspects of oxidant chemistry for both polluted and clean tropospheric conditions

Contribution of HONO sources to the NOx/HOx/O3 chemistry in the polluted boundary layer

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Modelling the evolution of organic carbon during its gas-phase tropospheric oxidation: development of an explicit model based on a self generating approach

International audienceOrganic compounds emitted in the atmosphere are oxidized in complex reaction sequences that produce a myriad of intermediates. Although the cumulative importance of these organic intermediates is widely acknowledged, there is still a critical lack of information concerning the detailed composition of the highly functionalized secondary organics in the gas and condensed phases. The evaluation of their impacts on pollution episodes, climate, and the tropospheric oxidizing capacity requires modelling tools that track the identity and reactivity of organic carbon in the various phases down to the ultimate oxidation products, CO and CO2. However, a fully detailed representation of the atmospheric transformations of organic compounds involves a very large number of intermediate species, far in excess of the number that can be reasonably written manually. This paper describes (1) the development of a data processing tool to generate the explicit gas-phase oxidation schemes of acyclic hydrocarbons and their oxidation products under tropospheric conditions and (2) the protocol used to select the reaction products and the rate constants. Results are presented using the fully explicit oxidation schemes generated for two test species: n-heptane and isoprene. Comparisons with well-established mechanisms were performed to evaluate these generated schemes. Some preliminary results describing the gradual change of organic carbon during the oxidation of a given parent compound are presented

Développement d'une chaîne automatique d'écriture de schémas chimiques explicites et réduits adaptés à l'étude de la pollution photooxydante aux différentes échelles

Pour modéliser en 3D la pollution photooxydante, les schémas chimiques utilisés sont nécessairement réduits (environ 100 espèces). Ces réductions dépendent des milieux à modéliser. L objectif de ce travail est de développer une chaîne d écriture automatique de schémas explicites et réduits pour l étude de la pollution photooxydante aux différentes échelles. La méthode consiste à (1) développer un outil permettant l écriture automatique de schémas explicites d oxydation des COV depuis l initiation jusqu à leur oxydation totale en CO2 et H2O (2) écrire, à l aide de cet outil, un schéma de référence : pour 67 COV primaires représentatifs des émissions, il contient plus de 2 millions de réactions et 350 000 espèces et 3) évaluer en 1D, par rapport à cette référence, les biais liés aux réductions de schémas, sur des scénarios typiques de la troposphère. Le schéma final obtenu (150 espèces) reproduit la chimie de l ozone depuis les milieux pollués jusqu aux milieux éloignés des sources.Millions of compounds are involved in atmospheric chemistry. Chemical schemes must then be reduced (around 100 species) to model the photo-oxidant pollution using chemistry transport models (CTM). The reduction methods depend on the case under consideration. The goal of this work was to develop an automatic procedure allowing to write explicit and reduced chemical schemes suited to the study of photo-oxidant pollution at different scales. The method is based on (1) the development of an automatic tool dedicated to the writing of explicit schemes for VOC oxidation from the initiation to their total oxidation in CO2 et H2O (2) the writing of an explicit scheme for 67 primary VOC (350.000 species) and (2) the assessment, using box model simulations for several typical tropospheric conditions, of reduced schemes using the explicit scheme as a reference. The final reduced chemical scheme (150 species) is suitable to model the ozone and oxidant chemistry from polluted to remote conditions.PARIS12-CRETEIL BU Multidisc. (940282102) / SudocSudocFranceF

Impact of the subtropical mode water biogeochemical properties on primary production in the North Atlantic: New insights from an idealized model study.

International audienceAn idealized biophysical model of the North Atlantic was designed to investigate the setting and variability of the subtropical mode water (STMW) biogeochemical properties and its impact on surface primary production in the North Atlantic. The model solution first emphasizes that the exact timing of STMW formation versus the timing of the spring bloom is of primary importance for setting the STMW biogeochemical properties. The surface primary production reaches its maximum in March in the STMW formation region just before its subduction. Thus the spring bloom consumes nitrate at the surface before STMW subducts, and STMW leaves the upper layers depleted in nutrients and fueled in organic matter. This spring consumption explains the low nutrient content of STMW observed near its source region by J. B. Palter et al. (2005). Furthermore, the model suggests that STMW plays a key role in exporting dissolved organic matter (DOM) at subsurface. The spring bloom produces a significant amount of DOM sequestrated in the mode waters after its subduction. This large pool of DOM is then remineralized with time along the transit of STMW through the subtropical gyre. Consequently, the nutrient content of STMW increases as it moves away from its source region. Finally, the model shows also that STMW is very important in controlling primary production in the western boundary current (WBC) region. Indeed, STMW remains isolated from the surface along its trajectory within the subtropical gyre. It joins the mixed layer by obduction in the WBC region only. This nutrient-rich old STMW irrigates and fertilizes the euphotic zone primarily in the WBC and then spreads along the boundary between the two gyres by advection

Sources and Sinks of Isoprene in the Global Open Ocean: Simulated Patterns and Emissions to the Atmosphere

International audienceThe ocean is a source of isoprene to the atmosphere. Although their global estimates are relatively low compared with the terrestrial source, these emissions have an influence on atmospheric chemistry. The lack of knowledge about the sources and sinks of isoprene in the ocean has hitherto precluded a precise assessment of when and where these emissions might be significant. Here we use the general circulation and biogeochemistry model Nucleus for European Modelling of the Ocean, Pelagic Interaction Scheme for Carbon and Ecosystem Studies (NEMO-PISCES) to explore different parameterizations of the 3D oceanic sources and sinks of isoprene. In addition, we investigate a representation of the isoprene emission due to photoproduction in the sea surface microlayer. Our model estimates are complemented by a new data compilation of laboratory isoprene production rates and in situ isoprene concentrations. This study constitutes the first attempt to simulate isoprene in a global 3D ocean biogeochemical model. We find that sea surface temperature is an important driver modulating phytoplankton isoprene production and that light levels only play a secondary role at the scale of the global ocean. Furthermore, the use of a variable biochemical consumption rate improves the model-data comparison. We show the importance of isoprene production below the mixed layer and, as a consequence, demonstrate that models based on 2D surface satellite chlorophyll-a could miss up to 18.5% of oceanic isoprene emissions. The oceanic isoprene emissions to the atmosphere are estimated to 0.66 (0.43-0.82) Tg C yr −1 in the low range of previous estimates