An algorithm to detect non-background signals in greenhouse gas time series from European tall tower and mountain stations

We present a statistical framework to identify regional signals in station-based CO2 time series with minimal local influence. A curve-fitting function is first applied to the detrended time series to derive a harmonic describing the annual CO2 cycle. We then combine a polynomial fit to the data with a short-term residual filter to estimate the smoothed cycle and define a seasonally adjusted noise component, equal to 2 standard deviations of the smoothed cycle about the annual cycle. Spikes in the smoothed daily data which surpass this +/- 2 sigma threshold are classified as anomalies. Examining patterns of anomalous behavior across multiple sites allows us to quantify the impacts of synoptic-scale atmospheric transport events and better understand the regional carbon cycling implications of extreme seasonal occurrences such as droughts.Peer reviewe

Soil–atmosphere interaction in the overburden of a short-lived low and intermediate level nuclear waste (LLW/ILW) disposal facility

International audienceThe long-term safety of shallow disposal facility for short-lived low and intermediate level nuclear waste (LLW/ILW) relies on the performance of engineered barriers (caps and liners). Soil-atmosphere interaction may affect the capping material at shallow depths, due to changes of its coupled hydro-thermal-mechanical behavior under the effect of atmospheric conditions. This study aims to investigate the soil-atmosphere interaction at different time scales in the overburden of an LLW/ILW disposal facility, located in middle France. Actual meteorological data from Valencia El Saler station in Spain, including solar radiation, air temperature, latent heat, rainfall, and actual evaporation, at four different time scales (30 min, daily, weekly and monthly), were applied as the future climate conditions of the studied area based on climate analogues. A numerical approach combining a coupled hydro-thermal model and a soil-atmosphere interaction model was employed. Results show that the employment of meteorological data at a short time scale (30 min) can increase the simulation accuracy by capturing the rainfall events and accelerating the soil-atmosphere interactions. Furthermore, the effect of future climate conditions in the long-term (7 years) on soil hydro-thermal behavior was examined. This study allows a further detailed inspection of the climate’s role in the LLW/ILW storage system

Comparison of nitrous oxide (N₂O) analyzers for high-precision measurements of atmospheric mole fractions

International audienceOver the last few decades, in situ measurements of atmospheric N 2 O mole fractions have been performed using gas chromatographs (GCs) equipped with electron capture detectors. This technique, however, becomes very challenging when trying to detect the small variations of N 2 O as the detectors are highly nonlinear and the GCs at remote stations require a considerable amount of maintenance by qualified technicians to maintain good short-term and long-term re-peatability. With new robust optical spectrometers now available for N 2 O measurements, we aim to identify a robust and stable analyzer that can be integrated into atmospheric monitoring networks, such as the Integrated Carbon Observation System (ICOS). In this study, we present the most complete comparison of N 2 O analyzers, with seven analyzers that were developed and commercialized by five different companies. Each instrument was characterized during a time period of approximately 8 weeks. The test protocols included the characterization of the short-term and long-term repeatability, drift, temperature dependence, linearity and sensitivity to water vapor. During the test period, ambient air measurements were compared under field conditions at the Gif-sur-Yvette station. All of the analyzers showed a standard deviation better than 0.1 ppb for the 10 min averages. Some analyzers would benefit from improvements in temperature stability to reduce the instrument drift, which could then help in reducing the frequency of calibrations. For most instruments, the water vapor correction algorithms applied by companies are not sufficient for high-precision atmospheric measurements, which results in the need to dry the ambient air prior to analysis

The French ICOS ecosystems stations : an overview

National audienceThe terrestrial biosphere interacts strongly with the climate, providing both positive and negative feedbacks due to biogeophysical and biogeochemical processes. To understand and predict the evolution of the climate, it is critical to understand both the contribution of vegetation to the greenhouse gases (GHG) budget and the response of the terrestrial biosphere to the changing climate. The Integrated Carbon Observation System (ICOS), a new European monitoring network, offers a unique way of documenting and quantifying long term changes in the GHG balance of ecosystems. The ICOS research infrastructure includes atmospheric, ecosystem and marine station networks. The Ecosystem station network (ESN) of ICOS is based on a large number of monitoring stations that will be maintained for the next 20 years. The ESN uses a large set of standardised instruments to perform continuous and intensive measurements of meteorological and micrometeorological variables. A central part of this measurement set is the eddy covariance measurement, that allows a continuous monitoring of the flux exchanged between vegetation and atmosphere. All together these standardised observations allow a better understanding of the functioning of ecosystems in relation to climate and management practices. ICOS Ecosystems France, the French part of ESN is a cooperation of three research institutes: INRA, CNRS and ANDRA. ICOS Ecosystems France is extensive and includes eight observation stations ( 4 Class 1, 4 Class 2). In addition seven associated stations also contribute to the network. The network samples a wide range of ecosystems (forest, crop and grassland), of management practices and climates (from cold mountain climate to tropical humid in Guyana, including wet oceanic and dry Mediterranean climate). We will provide an overview of the stations and the measurement system (sensors and data flow). We will equally present the current status of the network, recent measurements and preliminary findings

A dedicated flask sampling strategy developed for Integrated Carbon Observation System (ICOS) stations based on CO2 and CO measurements and Stochastic Time-Inverted Lagrangian Transport (STILT) footprint modelling

International audienceIn situ CO 2 and CO measurements from five Integrated Carbon Observation System (ICOS) atmosphere stations have been analysed together with footprint model runs from the regional Stochastic Time-Inverted Lagrangian Transport (STILT) model to develop a dedicated strategy for flask sampling with an automated sampler. Flask sampling in ICOS has three different purposes, namely (1) to provide an independent quality control for in situ observations, (2) to provide representative information on atmospheric components currently not monitored in situ at the stations, and (3) to collect samples for 14 CO 2 analysis that are significantly influenced by fossil fuel CO 2 (ffCO 2) emission areas. Based on the existing data and experimental results obtained at the Heidelberg pilot station with a prototype flask sam-pler, we suggest that single flask samples are collected regularly every third day around noon or in the afternoon from the highest level of a tower station. Air samples shall be collected over 1 h, with equal temporal weighting, to obtain a true hourly mean. At all stations studied, more than 50 % of flasks collected around midday will likely be sampled during low ambient variability (<0.5 parts per million (ppm) standard deviation of 1 min values). Based on a first application at the Hohenpeißenberg ICOS site, such flask data are principally suitable for detecting CO 2 concentration biases larger than 0.1 ppm with a 1σ confidence level between flask and in situ observations from only five flask comparisons. In order to have a maximum chance to also sample ffCO 2 emission areas, additional flasks are collected on all other days in the afternoon. To check if the ffCO 2 component will indeed be large in these samples, we use the continuous in situ CO observations. The CO deviation from an estimated background value is determined the day after each flask sampling, and depending on this offset, an automated decision is made as to whether a flask shall be retained for 14 CO 2 analysis. It turned out that, based on existing data, ffCO 2 events of more than 4-5 ppm that would allow ffCO 2 estimates with an uncertainty below 30 % were very rare at all stations studied, particularly in summer (only zero to five events per month Published by Copernicus Publications on behalf of the European Geosciences Union. 11162 I. Levin et al.: A dedicated flask sampling strategy developed for ICOS stations from May to August). During the other seasons, events could be collected more frequently. The strategy developed in this project is currently being implemented at the ICOS stations

Agriculture, sylviculture et gaz à effet de serre : observations du réseau Ecosystèmes-Fr de l’infrastructure ICOS

Agriculture, sylviculture et gaz à effet de serre : observations du réseau Ecosystèmes-Fr de l’infrastructure ICOS. Carbones atmosphériques naturels et anthropiques. Chaire Évolution du climat et de l'océan du Collège de Franc

The French ICOS ecosystem monitoring sites: an overview

The ICOS research infrastructure include atmospheric, ecosystem and marine station networks. The Ecosystem station network of ICOS (ESN) is based on a number of observation sites for monitoring and understanding the functioning of ecosystems and the exchange of energy and greenhouse gases between the ecosystems and the atmosphere in relation to climate and management. ESN use a large set of standardised instruments to perform continuous and intensive measurement of meteorological and micrometeorological variables. France is a founding member of the ICOS ERIC. The French part ICOS France is a cooperation of several research institutes: INRA, CNRS and ANDRA. The French ICOS ecosystem network is extensive and includes eight observation sites ( 4 Class 1, 4 class 2), in addition seven associated sites also contribute to the network. The network samples a wide range of ecosystems (forest, crop and grassland), of management and of climate (from cold mountain climate, to tropical humid in Guyana, and including wet oceanic and dry Mediterranean climate). A number of sites within the network have a long history of eddy flux measurements with some sites being continuously monitored since 1996 making them pioneer and good candidate for long term carbon cycle observation.We will provide an overview of the sites, and of the measurement system (sensor and data flow). We will then present the current status of the network, recent measurement and preliminary findings

Evaluation and optimization of ICOS atmosphere station data as part of the labeling process

The Integrated Carbon Observation System (ICOS) is a pan-European research infrastructure which provides harmonized and high-precision scientific data on the carbon cycle and the greenhouse gas budget. All stations have to undergo a rigorous assessment before being labeled, i.e., receiving approval to join the network. In this paper, we present the labeling process for the ICOS atmosphere network through the 23 stations that were labeled between November 2017 and November 2019. We describe the label-ing steps, as well as the quality controls, used to verify that the ICOS data (CO2, CH4, CO and meteorological measurements) attain the expected quality level defined within ICOS. To ensure the quality of the greenhouse gas data, three to four calibration gases and two target gases are measured: one target two to three times a day, the other gases twice a month. The data are verified on a weekly basis, and tests on the station sampling lines are performed twice a year. From these high-quality data, we conclude that regular calibrations of the CO2, CH4 and CO analyzers used here (twice a month) are important in particular for carbon monoxide (CO) due to the analyzer's variability and that reducing the number of calibration injections (from four to three) in a calibration sequence is possible, saving gas and extending the calibration gas lifespan. We also show that currently, the on-site water vapor correction test does not deliver quantitative results possibly due to environmental factors. Thus the use of a drying system is strongly recommended. Finally, the mandatory regular intake line tests are shown to be useful in detecting artifacts and leaks, as shown here via three different examples at the stations.Peer reviewe