Eddy-covariance with slow-response greenhouse gas analyser on tall towers: bridging atmospheric and ecosystem greenhouse gases networks

Greenhouse gases monitoring is important to ensure climate goals are being achieved. This study unveils the potential of using atmospheric tall towers in direct flux measurements, bridging the gap between atmospheric and ecosystem monitoring networks. The ICOS Cities (PAUL) project aims to monitor CO2 emissions in urban areas, where concentrated emissions make them key targets for climate change mitigation. This study explores synergy between ICOS atmospheric and ecosystem networks by utilizing slow-response analysers (~2 sec) on tall atmospheric towers for ecosystem studies using the Eddy Covariance method. A standard setup with an ultrasonic anemometer and an infrared (IR) fast-response CO2 analyser was installed and compared with measurements from an existing cavity ring down spectroscopy (CRDS) analyser measuring CO2, CO, and CH4. Deployed on the 100 m Saclay tower near Paris, covering a 43.9 km² 80 % footprint with heavy traffic roads, a nearby heating plant, and a forest, the setup addressed technical challenges and height-induced complexities. Corrections for flux attenuation by high frequency losses were limited to <20 % on average for all stabilities, around 11 % for unstable conditions. Wavelet-based eddy covariance allowed 18–34 % more data exploitation than standard EC enabling the analysis of non-stationary fluxes, particularly from a point source such was the case of a heating plant. The estimated storage term produced by atmospheric profiling measurements reported an expected increase at night, destocking during the first half of the day. Storage term represented at times more than half of the surface flux. Elevated mean fluxes for CO2 (10 μmolm−2s−1) and CH4 (200 nmolm−2s−1) were observed from the heating plant wind direction during December and January. Conversely, the forest direction exhibited the strongest sink among all wind directions, with −4 μmolm−2s−1 during July and August. These results demonstrate the feasibility and versatility of utilizing atmospheric towers for urban emission monitoring, offering valuable insights for emission monitoring strategies worldwide

Connaissance des émissions gazeuses dans les différentes filières de gestion des effluents porcins

Cet article résume les apports du programme "Porcherie verte" dans la connaissance et la maîtrise des émissions gazeuses intervenant lors des différentes phases de l'élevage porcin. Ces émissions comprennent des gaz à effet de serre, particulièrement le méthane (CH4) et le protoxyde d'azote (N2O), ainsi que l'ammoniac (NH3), nocif pour les animaux et pour l'Homme et qui a un impact sur l'environnement en termes d'acidification et d'eutrophisation. Les émissions de NH3 ont été modélisées pour le cas des bâtiments d'élevage sur caillebottis. Ces émissions peuvent être réduites en diminuant la teneur en protéines de l'aliment distribué aux animaux ou en renouvelant fréquemment le lisier dans les bâtiments. Le traitement biologique du lisier permet aussi de réduire ces émissions, surtout en l'absence de séparation de phases. Le brassage du lisier dans les fosses de stockage les favorise au contraire. Les émissions de NH3 varient fortement en fonction du substrat utilisé pour la litière et de son mode de conduite. Pendant le compostage, elles dépendent aussi fortement des caractéristiques initiales du substrat composté, mais aussi de la technique utilisée. Les émissions de N2O sont en général plus élevées avec de la litière que sur caillebotis, mais il y a de très fortes variations en fonction de son mode de conduite. Le compostage peut aussi conduire à des émissions de N2O, tout particulièrement s'il est pratiqué en couche mince. Lors du traitement biologique des lisiers, ces émissions sont assez faibles mais dépendent de la technique d'aération utilisée. Dans le sol, les émissions de N2O ne sont pas plus importantes après apports d'effluents animaux qu'après apports de fertilisants minéraux et restent difficiles à quantifier. Les émissions de CH4 sont plus faibles sur litière que sur caillebotis. Elles sont faibles également lors du compostage, sauf s'il est réalisé en couche mince. Le traitement biologique du lisier conduit à une forte réduction des émissions par rapport à un simple stockage. Les litières et le compostage ont une excellente image de marque auprès du grand public et sont souvent réputées avoir beaucoup moins d'impact sur l'environnement que le lisier. Nous avons pu montrer cependant qu'elles génèrent en général davantage de gaz à effet de serre, que ce soit de façon directe (émissions de N2O) ou indirecte (gaspillage de fertilisants azotés dont la synthèse est très "énergivore"), et ce d'autant plus que l'on cherche à rogner sur les coûts en augmentant la densité animale ou en diminuant la quantité de paille utilisée comme substrat de compostage. De même, le traitement biologique du lisier, qui semble à première vue avoir un impact favorable puisqu'il conduit à réduire les émissions de NH3 sans trop relarguer de N2O, a en fait un bilan environnemental très défavorable du fait qu'il est très "énergivore" aussi bien directement qu'indirectement (gaspillage de fertilisants). On a là un double transfert de pollution, du sol et de l'eau vers l'atmosphère d'une part, et de l'exploitation vers l'extérieur de l'exploitation d'autre part. (Résumé d'auteur

Analysis of the potential of near-ground measurements of CO2 and CH4 in London, UK, for the monitoring of city-scale emissions using an atmospheric transport model

Carbon dioxide (CO2) and methane (CH4) mole fractions were measured at four near-ground sites located in and around London during the summer of 2012 with a view to investigating the potential of assimilating such measurements in an atmospheric inversion system for the monitoring of the CO2 and CH4 emissions in the London area. These data were analysed and compared with simulations using a modelling framework suited to building an inversion system: a 2 km horizontal resolution south of England configuration of the transport model CHIMERE driven by European Centre for Medium-Range Weather Forecasts (ECMWF) meteorological forcing, coupled to a 1 km horizontal resolution emission inventory (the UK National Atmospheric Emission Inventory). First comparisons reveal that local sources, which cannot be represented in the model at a 2 km resolution, have a large impact on measurements. We evaluate methods to filter out the impact of some of the other critical sources of discrepancies between the measurements and the model simulation except that of the errors in the emission inventory, which we attempt to isolate. Such a separation of the impact of errors in the emission inventory should make it easier to identify the corrections that should be applied to the inventory. Analysis is supported by observations from meteorological sites around the city and a 3-week period of atmospheric mixing layer height estimations from lidar measurements. The difficulties of modelling the mixing layer depth and thus CO2 and CH4 concentrations during the night, morning and late afternoon lead to focusing on the afternoon period for all further analyses. The discrepancies between observations and model simulations are high for both CO2 and CH4 (i.e. their root mean square (RMS) is between 8 and 12 parts per million (ppm) for CO2 and between 30 and 55 parts per billion (ppb) for CH4 at a given site). By analysing the gradients between the urban sites and a suburban or rural reference site, we are able to decrease the impact of uncertainties in the fluxes and transport outside the London area and in the model domain boundary conditions. We are thus able to better focus attention on the signature of London urban CO2 and CH4 emissions in the atmospheric CO2 and CH4 concentrations. This considerably improves the statistical agreement between the model and observations for CO2 (with model–data RMS discrepancies that are between 3 and 7 ppm) and to a lesser degree for CH4 (with model–data RMS discrepancies that are between 29 and 38 ppb). Between one of the urban sites and either the rural or suburban reference site, selecting the gradients during periods wherein the reference site is upwind of the urban site further decreases the statistics of the discrepancies in general, though not systematically. In a further attempt to focus on the signature of the city anthropogenic emission in the mole fraction measurements, we use a theoretical ratio of gradients of carbon monoxide (CO) to gradients of CO2 from fossil fuel emissions in the London area to diagnose observation-based fossil fuel CO2 gradients, and compare them with the fossil fuel CO2 gradients simulated with CHIMERE. This estimate increases the consistency between the model and the measurements when considering only one of the two urban sites, even though the two sites are relatively close to each other within the city. While this study evaluates and highlights the merit of different approaches for increasing the consistency between the mesoscale model and the near-ground data, and while it manages to decrease the random component of the analysed model–data discrepancies to an extent that should not be prohibitive to extracting the signal from the London urban emissions, large biases, the sign of which depends on the measurement sites, remain in the final model–data discrepancies. Such biases are likely related to local emissions to which the urban near-ground sites are highly sensitive. This questions our current ability to exploit urban near-ground data for the atmospheric inversion of city emissions based on models at spatial resolution coarser than 2 km. Several measurement and modelling concepts are discussed to overcome this challenge

Connaissance du devenir des éléments à risques dans les différentes filières de gestion des effluents porcins

Cet article résume les apports du programme "Porcherie verte" dans la connaissance et la maîtrise du devenir de l'azote, du phosphore et des éléments traces métalliques qui ont, à des titres divers, un impact sur l'environnement. La diminution de la teneur en protéines de l'aliment permet de réduire fortement les quantités d'azote excrétées par les animaux. Une part importante de l'azote est éliminée sous forme gazeuse lorsque les animaux sont placés sur litière ou lorsque le lisier est composté. L'importance de ces pertes d'azote peut cependant varier fortement selon les techniques utilisées et la nature des substrats. Le traitement biologique abat la majeure partie de l'azote et certains types de stations permettent de capter le reste dans des coproduits potentiellement exportables. La bonne valorisation agronomique des effluents nécessite de bien connaître leur valeur fertilisante azotée, ce que facilite l'approche typologique mise au point dans le cadre du programme. Un certain nombre de leviers alimentaires permettent de diminuer la fraction du phosphore alimentaire qui est excrétée dans les effluents: ajustement des apports alimentaires grâce à une meilleure connaissance des besoins des animaux, amélioration de la digestibilité du phosphore alimentaire par une meilleure connaissance de sa disponibilité dans les diverses matières premières ou via l'adjonction de phytase exogène. Les traitements biologiques avec séparation de phases permettent de capter le phosphore dans des coproduits potentiellement exportables et la valeur fertilisante phosphatée des effluents est en général très élevée et facile à prédire. Les éléments traces métalliques (cuivre et zinc) sont souvent ajoutés dans l'aliment à des concentrations dépassant largement les besoins stricts des animaux (pour éviter les carences) afin de bénéficier de leur effet protecteur vis-à-vis des pathologies digestives. La supplémentation par des éléments traces métalliques est utile pendant la phase de post-sevrage, mais pas au-delà et l'adjonction de phytase microbienne à l'aliment améliore la disponibilité du zinc pour l'animal. Les traitements biologiques avec séparation de phases permettent de capter le zinc et le cuivre dans des coproduits potentiellement exportables. Après épandage, les éléments traces métalliques sont peu mobiles dans le sol alors que les apports au sol excèdent en général largement les capacités d'exportation par les plantes, ce qui peut conduire à des situations de phytotoxicité à plus ou moins long terme. En fin de compte, la manière la plus simple et la plus économique de gérer les effluents d'élevage reste d'utiliser au mieux leur valeur fertilisante, ce qui s'obtient par un bon équilibre entre la quantité d'animaux produits et la capacité des sols à recevoir leurs effluents. En l'absence d'un tel équilibre, l'abattement de l'azote excédentaire par l'utilisation de litières ou par le compostage du lisier a un impact environnemental important alors même que ces solutions ne résolvent rien en termes de phosphore et d'éléments traces métalliques. Les traitements biologiques les plus sophistiqués permettent d'éliminer le phosphore et une partie des éléments traces métalliques dans des coproduits potentiellement exportables, mais ils ont un coût économique et écologique très élevé. (Résumé d'auteur

Diurnal, seasonal, and annual trends in atmospheric CO₂ at southwest London during 2000-2012:Wind sector analysis and comparison with Mace Head, Ireland

In-situ measurements of atmospheric CO have been made at Royal Holloway University of London (RHUL) in Egham (EGH), Surrey, UK from 2000 to 2012. The data were linked to the global scale using NOAA-calibrated gases. Measured CO varies on time scales that range from minutes to inter-annual and annual cycles. Seasonality and pollution episodes occur each year. Diurnal cycles vary with daylight and temperature, which influence the biological cycle of CO and the degree of vertical mixing. Anthropogenic emissions of CO dominate the variability during weekdays when transport cycles are greater than at weekends. Seasonal cycles are driven by temporal variations in biological activity and changes in combustion emissions. Maximum mole fractions (μmol/mol) (henceforth referred to by parts per million, ppm) occur in winter, with minima in late summer. The smallest seasonal amplitude observed, peak to trough, was 17.0ppm CO in 2003, whereas the largest amplitude observed was 27.1ppm CO in 2008.Meteorology can strongly modify the CO mole fractions at different time scales. Analysis of eight 45° wind sectors shows that the highest CO mole fractions were recorded from the E and SE sectors. Lowest mole fractions were observed for air masses from the S and SW. Back-trajectory and meteorological analyses of the data confirm that the dominant sources of CO are anthropogenic emissions from London and SE England. The largest annual rate of increase in the annual average of CO, 3.26ppmyr (

Country-scale greenhouse gas budgets using shipborne measurements: a case study for the UK and Ireland

We present a mass balance approach to estimate the seasonal and annual budgets of carbon dioxide (CO2) and methane (CH4) of the United Kingdom (excluding Scotland) and the Republic of Ireland from concentration measurements taken on a ferry along the east coast of the United Kingdom over a 3-year period (2015–2017). We estimate the annual emissions of CH4 to be 2.55±0.48 Tg, which is consistent with the combined 2.29 Tg reported to the United Nations Framework Convention on Climate Change by the individual countries. The net CO2 budget (i.e. including all anthropogenic and biogenic sources and sinks of CO2) is estimated at 881.0±125.8 Tg, with a net biogenic contribution of 458.7 Tg (taken as the difference between the estimated net emissions and the inventory value, which accounts for anthropogenic emissions only). The largest emissions for both gases were observed in a broad latitudinal band (52.5–54∘ N), which coincides with densely populated areas. The emissions of both gases were seasonal (maxima in winter and minima in summer), strongly correlated with natural gas usage and, to a lesser extent, also anti-correlated with mean air temperature. Methane emissions exhibited a statistically significant anti-correlation with air temperature at the seasonal timescale in the central region spanning 52.8–54.2∘ N, which hosts a relatively high density of waste treatment facilities. Methane emissions from landfills have been shown to sometimes increase with decreasing air temperature due to changes in the CH4-oxidising potential of the topsoil, and we speculate that the waste sector contributes significantly to the CH4 budget of this central region. This study brings independent verification of the emission budgets estimated using alternative products (e.g. mass balance budgets by aircraft measurements, inverse modelling, inventorying) and offers an opportunity to investigate the seasonality of these emissions, which is usually not possible

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

Retrieval of atmospheric CH_4 vertical information from ground-based FTS near-infrared spectra

International audienceThe Total Carbon Column Observing Network (TCCON) column-averaged dry air mole fraction of CH 4 (X CH 4) measurements have been widely used to validate satellite observations and to estimate model simulations. The GGG2014 code is the standard TCCON retrieval software used in performing a profile scaling retrieval. In order to obtain several vertical pieces of information in addition to the total column, in this study, the SFIT4 retrieval code is applied to retrieve the CH 4 mole fraction vertical profile from the Fourier transform spectrometer (FTS) spectrum at six sites (Ny-Ålesund, Sodankylä, Bialystok, Bremen, Orléans and St Denis) during the time period of 2016-2017. The retrieval strategy of the CH 4 profile retrieval from ground-based FTS near-infrared (NIR) spectra using the SFIT4 code (SFIT4NIR) is investigated. The degree of freedom for signal (DOFS) of the SFIT4NIR retrieval is about 2.4, with two distinct pieces of information in the troposphere and in the stratosphere. The averaging kernel and error budget of the SFIT4NIR retrieval are presented. The data accuracy and precision of the SFIT4NIR retrievals, including the total column and two partial columns (in the troposphere and stratosphere), are estimated by TCCON standard retrievals, ground-based in situ measurements, Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) satellite observations, TCCON proxy data and AirCore and aircraft measurements. By comparison against TCCON standard retrievals, it is found that the retrieval uncertainty of SFIT4NIR X CH 4 is similar to that of TCCON standard retrievals with systematic uncertainty within 0.35 % and random uncertainty of about 0.5 %. The tropospheric and strato-spheric X CH 4 from SFIT4NIR retrievals are assessed by comparison with AirCore and aircraft measurements, and there is a 1.0 ± 0.3 % overestimation in the SFIT4NIR tropospheric X CH 4 and a 4.0 ± 2.0 % underestimation in the SFIT4NIR stratospheric X CH 4 , which are within the systematic uncertainties of SFIT4NIR-retrieved partial columns in the tropo-sphere and stratosphere respectively

Influences of hydroxyl radicals (OH) on top-down estimates of the global and regional methane budgets

The hydroxyl radical (OH), which is the dominant sink of methane (CH4), plays a key role in closing the global methane budget. Current top-down estimates of the global and regional CH4 budget using 3D models usually apply prescribed OH fields and attribute model–observation mismatches almost exclusively to CH4 emissions, leaving the uncertainties due to prescribed OH fields less quantified. Here, using a variational Bayesian inversion framework and the 3D chemical transport model LMDz, combined with 10 different OH fields derived from chemistry–climate models (Chemistry–Climate Model Initiative, or CCMI, experiment), we evaluate the influence of OH burden, spatial distribution, and temporal variations on the global and regional CH4 budget. The global tropospheric mean CH4-reaction-weighted [OH] ([OH]GM−CH4) ranges 10.3–16.3×105 molec cm−3 across 10 OH fields during the early 2000s, resulting in inversion-based global CH4 emissions between 518 and 757  Tg yr−1. The uncertainties in CH4 inversions induced by the different OH fields are similar to the CH4 emission range estimated by previous bottom-up syntheses and larger than the range reported by the top-down studies. The uncertainties in emissions induced by OH are largest over South America, corresponding to large inter-model differences of [OH] in this region. From the early to the late 2000s, the optimized CH4 emissions increased by 22±6  Tg yr−1 (17–30  Tg yr−1), of which ∼25  % (on average) offsets the 0.7  % (on average) increase in OH burden. If the CCMI models represent the OH trend properly over the 2000s, our results show that a higher increasing trend of CH4 emissions is needed to match the CH4 observations compared to the CH4 emission trend derived using constant OH. This study strengthens the importance of reaching a better representation of OH burden and of OH spatial and temporal distributions to reduce the uncertainties in the global and regional CH4 budgets